The AM Forum

From previous thread in QSO section VJB wrote:


How much room do you have, both horizontally and vertically? If you have some room horizontally, an Inverted L of some sort might be the easiest. As far a pure vertical, top loading (or as close to the top as possible) is supposedly the most efficient. A top capacity hat is probably also in order. A T antenna may also work, since it is essentially a top loaded vertical.

But if you already have room for a 75 meter dipole, you can make that antenna work on 160.

What say?





http://www.amwindow.org/tech/htm/160smallants.htm

The longest path is barely 60 feet, and we ran a 40m dipole fed with open wire line that worked pretty well, on 40.

Running the 32V2.

The tuna let us squeeze 75m out of it, but 160 / 300-G was a no way.

Took it down for the summer and ready to put something aloft again.

Have room for a pole and ground radials up to about 40 feet max, and can guy but it has to all be temporary-looking.

Any possibility out of a wire wound pipe ? Great big coil of wire on a stick.

Wow! That's tight. Yes, a big coil will work. I used to have info on using a stretched slinky as a vertical radiator. Another approach would be a vertical with a big coil near the top, with a top capacity hat (you could make the guys act as the capacity hat) could work pretty well with 40 feet.

As always, the radials will make or break the system. I'd put the majority of the effort there.

Ergh, pretty much a Warren 160M mobile antenna that happens to be sitting on the ground.

With only 60' of space, I imagine there is building absorption everywhere (bad for verticals) plus the hope of putting down a 1/4 wave 160M radial field are nil. This alone will chop maybe 15db off your vertical signal. Not to mention the local high angle suck out for the close in guys.

I wud do this:  Put up a 60' flat top with the ends dropping down close to the ground, ala HUZ's 160M suggestion.  Feed it with open wire and use a good quality homebrew SERIES tuner to handle the low impedance. ( I assume the total flat top and side legs  equal 60' + 40' + 40' = 140' total = little more than 1/4 wave.

Use #8 wire from HomeDepot for the complete flat top and feeders.

If you build a strapping tuner to handle the low impedance current and the antenna is not too absorbed by buildings, my guess is you will be within 5db of a full size perfectly matched coax fed dipole that is completely flat, of the same height.  That's not too bad at all.

But with a 12 ohm input impedance or so, it is easy to give it all back via losses from thin wire and crappy tuners in this unique situation, so don't cheap out there.

***  If you use a center support for the flat top, you don't need feedline spacers! Just pull the openwire tight and keep it spread about 2' apart. This will cancel FB. I did this on 75M for a wire Yagi and it was fine.  Thus, you have a more transparant looking dipole for the neighbors, w/o spreaders.

T

Hello Friends,
The HUZ man had a very nice dipole that he made into a T and worked very well on 160M, but it sounds like your sqeezed for "horizontal space". Ya'll don't yell at me BUT CushCraft has a very nice 40 foot vertical for 160M........top loading.....capacity hat for $200.00. You can read any reports about the cushcraft on eHAM.com... I HAD the 30 foot Unihat which didn't mind close in objects and compared favorably on a wooded lot against a dipole 90 feet in the air. That was unfortunatley a $500.00 antenna not including the Phillystran wire and 4 ground mounted supports. I also had an "L" ant on this property and I "A-B-C'd" it against the Unihat and the Dipole. The real test would have been with a Ham over 500 miles away, I guess.
It sounds like you need to use the vertical space of your property to do 160M. An unshortened dipole for 75M can work on 160M with a big a## tuner.
I hope we hear you on 160 before the aerial planting season is over. For some of us that usually happens on the cold windy day in January...........hi

Fred

I have been stuck with a 60' flat top for years now, It works fairly well on 75, as most of you dont have any trouble hearing me, even running experimental pissweak low power. Like Tom said you need to have strapping feeders to minimize the feedline loss and get as much of the rf as you can up to the antenna instead of heating up the feedline.

I have experimented with this setup on 160. With 100w, people can hear me, but I'm pretty pissweak.  Running the 4x1 transmitter no one had any trouble hearing me, but the tuna was groaning from the heavy feedline current. I plan to do some experimenting this fall to come up with a better matching network and see how it plays out. Maybe a 1:4 or 1:6 UnUn or something of that nature. I will do more experimenting this fall and post he results here if I come up wih anything interesting.

                                                                          The Slab Bacon

Quit messing around with those ferrite thingies. Build a nice link coupled balanced tuner and be done with it. Copper tubing and a cap and you're ready.

But, but, its fun to watch the ferrite rings explode!! ;D ;D

Bang, lookie there!

Frank,
Check out measure's site. Build some strapping L networks to drive that low Z.
I would think a link tuner would have a problem driving a low Z. Maybe series tuned??.
I'm glad a number of hams have this problem because I'm in the same boat at the new place with 160 or so feet of span.  The lowfers do it so we should be able to make something strap.

Thats right!! I'll be wavin my hand in the breeze!!

Frank,
         I know that is idefinately doable. It is just a matter of finding out what works best and has the lowest loss. that is the fun of experimenting!! I had loads of fun blowing up baluns and tunas years ago! ;D ;D
 

The most efficient low frequency EMI test antenna I have ever seen is the parallel plate. two 10 foot long 2 feet wide metal plates 50 ohm drive on one end and a 50 ohm load on the other end. It can make a quite a near field

Never had a problem, just tap down on the coil or go series with the caps. The roller inductor approach seems far too complex for what you get - a tuner that STILL needs a balun. And running the balun on the input side doesn't help. Neither the current balance in the output conductors nor the voltage across the balun are any different when the balun is put at the input or
output of the tuner.

Go with the simple link design. It has 70 plus years successful use behind it.

Steve.
I use a BB transformer on th einput of my tuner. I have RF amp meters in each leg and there is a balance. Also the same current flows if I connect the Johnson Match box but the L network tuner has a lot more range. All in what your junk box produces. Step down with a link seems hard. fc

Different strokes. I just like the KISS approach.


Seventy years of success sez different.

As far as baluns and tuners, read the following.

http://eznec.com/misc/ibalun.txt


Here's what I'd do if I had Frank's setup.


 ______________  _______________
|______________  _______________|
               | |
               | |
               | |
               | |
               | |
               | |  Big A$$ Feeders
               | |  #8 or larger
               | |
               | |
               | |
               | |
               | |
          _____________
         |             | WX-proof box with
         |             | heavy-duty series
Coax to  |             | fed link coupled
station  |             | tuner (directly below center of antenna)
<------- _______________     

Steve,
1.How much spacing between conductors
2. How do you think it will work on higher bands?

I think Frank is using a 2-4 inch spacing. But spacing is not critical.

Don't see why is wouldn't work on the higher bands. At those frequencies, the length is closer to 'normal.'  :D

Hello
I built the K1JJ tuner and no regrets on this end for a cannot break or over heat tuner. I built last Winter.  And I was getting sick from the cancer growing inside of me!!!. There is info and pics somewhere on this forum.
Fred

Actually I'm using the crappy brown stuff (14 ga) I am planning to make up some home brew ladder line this winter somewhere #10 or 12. I feed it into a home brew 4:1 balun and a very short (about 6 or 8') run of coax to my big strapping homebrew single ended tuna. It has worked very well on 75 for some time now.

It works ok-fine on the uppa bands, but I seldom use it there as I have a small tribander on the top of the tower.
                                              The Slab Bacon

Frank:

Have you ever made an old buzzard and then went outside and checked for heating on the feedline? Might be interesting. Also, why a 4:1 balun? Seems the stepdown would only make the task on the tuner even greater (taking an already low impedance and making it even lower).

Just thinking out loud here.

Good thoughts. I have checked the balun for heating and it does not heat at all, but I have never checked the feedline. Hmmmm........................

The reason that I chose a 4:1 came after much experimentation and testing: I wound / built many different 1:1 designs (that is really what I was looking for) and swept them from 10 ohms to 500 ohms and 1.5 - 15Mhz. I found that most of the 1:1's for kind of flakey as you got away from their 50 ohm characteristic impedence. They did not stay 1:1, and added a noticable amount of reactive component of their own when you started getting away from 50 ohms. (I knew that my antenna was nowhere near that impedence)

I twisted up several different 4:1 designs and found that they worked much better. They seemed to give a much more accurate inpedence match, and added less/no reactive component of their own. The 4:1's gave a real accurate 4:1 ratio no matter what the input or output impedance was. Keeping in mind that I had to still run a short (about 6') piece of coass to get from the balun to the tuna, I have always felt that if you have to sin and run a high SWR through coass, it is always better to sin in the direction of a low impedence.

Keeping in mind that coass is nothing more than a capacitor, the capacitive reactance loss is going to be a lot less in a low voltage high current situation I did what I did and it worked. I rolled up a strapping 4:1 with heavy wire and tons of ferrite and I lived happily afta.

All seemed well and good till I tried to use it on 160 with the big rig last year. Something kept changing and I constantly had to keep retuning the tuna. The coass amd pl259s were getting very hot, so I knew that the current in the short coass was very high. I also blew out a 10A rf ammeter while doing the initial testing. I will figger this thing out in time and post the results here.
                                                             The Slab Bacon

Interesting. It's all about working and if the 4:1 works better, you go it. Can't argue with your signal.

One MORE thing (I keep thinking of things), do you notice having to retune with it's raining or snowing. From what I've read (and from some observations during use) the impedance and loss of the brown crap ladder line can change when wet (in some cases drastically). Going with some strapping open wire line will remove this potential problem. 

Sincer were talking odd antenna setups.  this is what I've got.

Two Tall Pines, about 65 ft to my wire.  They are only 50 or so feet apart, straddling the house. 

I have an 80 meter dipole which drops the ends quite far.  I think I could get a 160 m dipole up with some creative zigging around some other trees.  Feed point would still be up around 65 ft or so.

The problem is, I am limited for feedline.  I can't run ladder line directly to the shack/tuner, so what I have now is coax to the attic, a coax choke feeding cheap brown TV twinlead.   

Whats a better way to transition from the coax to ladder line in the attic with a shack in the basement??

For even less path loss across the line, don't use spacers at all, but pull the open line tight and keep it 2' apart for 75M. Air spaced open line, caw mawn. You need a strong center support and a bridal at both ends to pull it off, put it is bullet-proof in the hi hi FB bad WX, OM.

T

         "a better way to transition from the coax to ladder line in the attic with a shack in the basement??"

Sounds like a job for the










 


                                                                                                       G5RV

Frank find yourself some Johnson spreaders and you will be set for life. My 1983 #10 feeders spaced 4 inches with johnson spreaders still in good shape. I did tighten the tie wires once or twice. I'm lucky to have collected enough over the years to make another line for the new place. It never warms up and takes a lot of wet ice to mess it up....but QRO takes care of that.

Is the attic accessible? If so, put your tuner there.

This sounds like a nice Vertical.

Well, there ya go, thinking again.stop thinking, it could be dangerous!!

Actually I have found the crappy brown stuff to be pretty stable in my situation. Dont forget that I am still running it way below its characteristic impedence. Ice will cause a slight change in tuning, if there is a large build up. But rain doesnt seem to have much effect on it.

One of the other problems with fat copper feeders that everyone seems to overlook is the weight. If your feeders are too heavy, you must have some kind of center support or use a car engine block as a bob weight to keep the antenna pulled tight and flat. this can create other engineering issues to consider.

Ed, You might try using a STRAPPING 4:1 balun if your tuna can handle the current. This will keep the coass from radiating and keep the operating impedence of the coass low to minimize losses from capacitive reactance. (just my thought)

                                                          The Slab Bacon

My center fed 80m zepp is fed with the brown crap...I made a 1/2 wave tuned feeder,
then tap off it to the shack with more of the stuff...
that goes to a Johnson KW Mbox...
In in install, with just a drop of rain I am retuning the Mbox....
In the winter, with ice/snow it gets even worse.
I contructed HB  open wire, can't wait for a dry weekend to install it!
For 160m, I bought a ALpha Delta 40/160m  1/4 wave sloper...it was crap...
Next I took the coil, made a 2nd one to match it...
Then configured it as a 1/2 wave 2 band dipole...
This works ok, but this fall, it goes further out in the yard, higher up and fed with
HB open wire.. rather than coax.
This will go to a HB tuner (like a Johnson KW mbox) already installed
in the back yard in a wx proof enclosure!
This will give me 160 & 40m with good bw...
It will be broad side E-W and at 70 feet!

73 steve 8tow

While I am still thinking about this stuff, (here i go thinking again) there are a few things to look out for when using short antennas on lower bands. You can be very surprized how well they can work if EVERYTHING else in the system is optomized to work together. A shortened antenna is ALWAYS a compromise, but sometimes you gotta do what you gotta do. A compromised antenna is still much better than none at all! Dave, the apeman, has been running short antennas for years and puts out a strapping signal.

The first thing to do is MINIMIZE ALL LOSSES, make sure that all of your RF is going to the antenna. Heat=loss!! Anything that is getting warm or hot is creating loss, your RF is making heat and NOT getting to the antenna.

Use a strapping tuna, one that can handle the feeder current and not get warm. Mine is homebrew with 2 large bread slicers and a rollie duck from a broadcast transmitter. (it is as large as an R-390) It never even gets tepid under mormal operating condx.

If you must use baluns, find or build ones that dont heat up under heavy feedline current. Or If you dont like baluns, build a STRAPING balanced tuna.

RF ammeters in the feedline TO THE ANTENNA are really good indicators of how well things are working. TUNE FOR MAX FEEDER CURRENT.

Do not rely only on an swr meter between the tuna and the transmitta to tell you what is happening!! It doesnt tell the whole story.

Your tuna sometimes offers too many choices for a "good match". Especially if you are using a roller.  You really need something like an MFJ antenna analizer (or something better) to find the right combination of L and C for the best match. Tune for max resistive and min reactive load on the analizer. Any setting other than that is usually wasting power trying to heat up the tuna (or something else).

Look at your Feeder current (if possible) while tuning. Sometimes a setting with less than a perfect match will produce more current in the feeders. this is the setting you really want to use if you run into this scenario.

Use balanced line feeders if at all possible, they dont know what swr is, or care. If possible make your own using the heaviest wire you can, at least #12 or heavier.

If you must use coass for a feeder on a non resonant antenna, it will always work better with a short antenna than a long one. If you must sin with a high swr and coass feeders, keep the impedence as low as possible to minimize the loss from the capacitice reactance of the coass.

I have been using a 60' flat top on 75m for a long tome now and no one seems to have any trouble hearing me, even running lower power.

Sometimes you gotta do what you gotta do!! ;)

                                                         The Slab Bacon

Good point about the tuners and loss. Most commercial tuners are of the T variety. They can give you an low SWR at more than one setting. But only one will be the lowest loss setting. That one is almost always occurs when the LEAST amount of inductance is used. You can see all of this in action at the URL below - a great Java T tuner simulation!

http://fermi.la.asu.edu/w9cf/tuner/tuner.html

My Tuner uses a pair of 5 KW broadcash inductors to avoid loss. There is a fairly wide range of adjustment but if I run the L too low the 10 KV caps flash over.

but can it tune up some eggplant?? or does it burn the eggplant when it flashes ova??

Frank,
Just got the word pickled egg plant will be on the menu Friday night.

The tuner can't do egg plant but handles the 4CX3000A FBOM

Frank,
        I wish I could be there! But unfortunately due to family obligations I cant be that far away for that long. I can taste it from here!!

Always remember, you can tune a piano, you can tune a radio,
but you cant tuna fish!! ;D ;D ;D

                                                   The Slab Bacon

The best reason for using a BalUn in the input side of the "tuner" has little to do with balancing the system. It's much cheaper and easier to construct a BalUn to work from a 50 Ohm generator to resistive 50 ohm load rather than the very wide range of sources and loads found at the feeder end. The BalUn can now be constructed using leftover coax.
Almost every single antenna coupling scheme seen today has 70 plus years of successful use.

Dave:

Ref: Baluns on input side of tuner being better.

Not according to W7EL. Read his stuff here.

http://eznec.com/misc/ibalun.txt

My tuner had a 1:2 BB transformer on the input with 2 caps on the output having both rotors connected to ground. The secondary of transformer has a CT also grounded. The two rotors help balance things and the tuner seems to work better.
The feeder currents are balanced and the cores stay nice and cool. (6- 2 inch red iron 3 beside 3) Winding is 5 turns quadfilar #14 teflon. Two windings in parallel for primary and secondary is 2 in series. The caps are a pair of 300 pf cardwell 10 KV units (they are in series CT at ground) I also have a 50 PF padder from BC610 for 160M.
The inductors are 22UH each. I done a lot of testing and it seems to work fine and no better or worse than the KW matchbox. BB iron core transformers work better at low Z and that is why they belong on the input. They also don't like high voltage because wire breaks down and some materials conduct. High numbers of turns introduce leakage L loses. High Z needs lots of turns. So I can't agree with the article
fully. It is true with the effects but you have to look at the way the part wants to work. been my choice of tuner for 23 years way before Measures discovered it around '91. I came up with it in about '81 and built it when I came back to CT and collected the parts.

Consider the extremes. The givens in some of those formula go out the door. I'd like to see Frank Witt's homework on that subject. I'm not associated with anyone in the BalUn business.

I don't remember Measures claiming anything about discovering that tuna. He did however put the idea out for experimenters to make something useful. Needs no toaster wire. Similar tuner network is in pre-war ARL book.

That was exactly what I found while experimenting with 1:1 baluns. They were all OK when they operated at their characteristic impedence at both ends. But when you strayed away from the characteristic impedence they ALL got pretty squirrely. I found that the 4:1's were much more forgiving.
                                                                   The Slab Bacon

Frank,
You have the same problem on 75 that I will have on 160 at the new place. I wonder if you could share the schematic of your tuner configuration and feed line length? This will give me an idea of component values I need. I don't think BB transformers like a lot of reactance but work well in a resistive transfer. I have a 250 foot spool of #8. I'm not sure if #8 will fit in the slot of Johnson spreaders but #10
will.  tnx, gfz

Frank,
        I am at work and dont have it here, but I have a scanned in drawing of my antenna system. Send me ur email and I'll send it to you.

The tuna is a nothing fancy, just srtappingly large. It is your basic "T" type with 2 large breadslicers and a rollie duck out of a broadcast transmitter. (edgewound thick ribbon coil)
I have a 6' piece of RG-8 coass coming out of the back of the tuna and going to the home made 4:1 balun on the back wall of the house. (too much metal in that area to run ladder line all the way to the tuna) The balun is ur basic center tapped coil 4:1 from any arrl handbook except it is uses 10 T-120 (or maybe 130) cores stacked like a pair of binoclears (5+5) and wound with large silver teflon stranded wire wound through the cores and not around them.

The ant is 120' of wire folded back on itself spaced at 10 or 11" to make for its 60' overall length. It resembles a 40m folded dipole, but doesnt make a complete loop. I have a second dogbone insulator above the feedpoint. (fed at the bottom) Sort of like 2 U's laying on their sides.

The feedline is the 14ga crappy brown stuff, random length, I guess somewhere around 50-60'.

The antenna was an experiment that worked so well that i just left it up and have been using it ever since. I only have about 65' of horizintal space to put up any kind of wire antenna, so you gotta do what you gotta do. As I said before a compromised antenna
is still far better than none at all! Make up for the difference with "antennas by Eimac"

                                                                   The Slab Bacon
                                                     



 

Wow my feed line may be 10 or so feet longer but the antenna length will be about 150 to 160 feet depending on which branch I catch on the trees. The feed line will come in the knee wall of the basement so just need to install some strapping feed throughs. Too bad you can't locate the tuner outside to eliminate the balun. Sounds like motor control would be cool. sounds like you could really improve the antenna but you do get out well. I wonder if you ever tried hanging vertical conductors at the end? Also how tricky is it to tune? It must be pretty sharp.

http://www.arraysolutions.com/Products/bushcommantennas.htm

Here is an idea but use an antenna tuner and eliminate the dummy load
Three conductors rather than two

I've looked at those BushComm antennas before. Interesting stuff. What I can't quite tell is if the three wires in the flattop are all tied together, just making it a "fat" dipole, or if some sort of folding back or snaking of the wires are done to increase length. Some company in the NE area (IIRC) make such an antenna. It was discussed here on the forum a while back.

W3R might want to try this,

(http://www.iol.ie/~bravo/images/LowBands/VertDip.jpg)


More info at http://www.iol.ie/~bravo/low_band_antennae.htm

Some ideas here too.

http://www.kn4lf.com/kn4lf2.htm

Where's the full size graphic of that?  Found it.
I need typeface for the hard-of-seeing.
Center support is possible yes, but yow, 60 feet is a lot of lumber. 
Remember this has to be or at least look temporary.
Tnx

Any thoughts on this one?

(http://www.iol.ie/~bravo/images/LowBands/Loopgif.gif)

Steve,
Look close the fold back to the load is the center of the three and all three tied at the ends. So the high current section is two conductors in parallel on the outside.
The feed line is terminated to the outside 2. Look at the configuration with the balun at the ground using open wire line.  fc

The one you posted is a receive antenna. A push-up, guyed mast is temporary.

Frank, that is plenty. Should not be too hard to feed on 160 at all. Run the model. Just has plenty of SWR on the feeder. No big deal. More copper = more signal.

Yea, what he said!!

I ran some simulations on tuners driving low Z loads and it is interesting how one could have a nice match but 4 to 6 dB of loss. Frank You said you had a tee but what is it 2 Caps and one inductor? how are the caps connected. I would like to dump your values in and see how it compares to others I have tried. We know your's works so I could find the antenna Z that sets the loss lowest then use that load to try other configurations. I found the balanced/balanced tuner didn't need much L to convert 50 ohms to 25 ohms. Reconfigurating it turned it into a high pass network.
The only way I could use l valuse greater than 2 uh each was to step 50 ohms up to 450 then use the network to get back down. Not pratical.This makes me think the transformer on the output side works when the antenna Z is low. Then what happens when you go to higher bands?? 


A dual differential cap in the output like the johnson match box gave it a very wide tuning range. But the value has to be much higher than used in the matchbox.

Frank,
         It is 2 caps and 1 inductor. the 2 caps are in series from the inpoot to the outpoot, with the inductor from the junction point of the 2 caps to ground. Your basic simple as it comes "T" tuna.

I have used it on 80, 40, and 20. I have never found a situation that it would not give a good matchup, and have never needed to add any parallel capacitance across the outpoot.
 
                                                  The Slab Bacon

Hi Frank,

This is what I would suggest for a small 160M antenna. It is modeled on the antenna that I used to used on my 1750 M Beacon in the early 1990's - It really got out with a 1 Watt input power transmitter. That antenna was 30 Feet high and had a 40 FT diameter Top Hat which was made of a loop of hardline suspended by several large Pine Trees. It looked wierd but worked very well. I call it WLW. This is a mini version.

See you at Hosstraders!

Mike WU2D

Frank,
I'll throw it into my simulation some day next week and see what happens.
Egg plant was pretty FBOM and my buddy Gary gave me 2 jars to bring home.

2 JARS!! AND YOU DIDNT EVEN SEND ANY DOWN THIS WAY!!

with 2 jars aorund, you better be careful that you dont throw the eggplant into the simulator ;D ;D

Frank,
I would have if I knew a way to get it delivered. I had to bug out at 7:30 Friday night.
I think most of the gang was out eating.
Bought some antenna rope and a pair of fixed vac caps 75 pf lots a volts.

Frank,
I simulated your tuner and found a good match at a number of combinations but only a tight range put maximum power / current into the feed line. The more I look at tuners the more I'm convinced of the need to monitor tuner output current at the feed line. I don't see any other way of knowing if the tuner is in the best position to transfer power to the antenna.

Frank,
        I have said that for years. An swr meter between the tuna and the transmitter doesnt tell the whole story. It only tells you if ur keeping the transmitter happy or not.

With a roller inductor tuna you have too many possible choices, and not all of them work in your favor. An RF ammeter in the feedline WILL tell the whole story. Many times a setting that shows some rize in the swr to the transmitter gives a lot more current into the feeders. Unfortunately, I smoked my last one playing with my short antenna on 160 with the 4X1 transmitter.

Many times the old way is still the best way. Ah, yes, what's old is new again!

                                                                The Slab Bacon

2 cents...

The best method I've found to adjust the adjust C - L - C tuners is to start with the capacitors at full mesh and look for a vswr dip with the  inductor. Only reduce C values enough to get a match. This normally yields max antenna current.

Jay 

I read online an article about tuning a T tuner for maximum efficiency (don't remember the website).   The main point was to have both caps fully meshed and tune for minimum SWR with the inductor first.  Then go back and forth with the inductor and the input capacitor for the best SWR, leaving the output cap fully meshed if possible.   I managed to tune my 135 ft doublet and about 160 feet of ladder line on all bands except 80M with the output cap fully meshed to 1:1 SWR.  I am using an external DX Engineering balun on the output.   I suppose the lower impedance of the antenna matched with an almost 1/4 length of the feedline on 80M is the reason for not being able to do it on 80M.

Jay,
that makes sense. My balanced antenna tuner has a pair of variable inductors in l networks with a wide range of adjustment. I need to connect the rf amp meters back into the line. I find the caps will flash if I run the series L too low.
 I'm thinking of building a pair of high voltage current transformers. This way the output could be rectified and monitored at the operating position.

Roger the current transformers. At LF I use a single wire primary through the ferrite torroid core with 50 or 100 turns as the secondary and terminate that in 50 ohms so the reflected resistance into the pass through single turn wire is low. If you had one of these on each leg of the open wire you could run the two outputs to a dual trace scope and have a real look at things. Once happy with the tuner adjustments replace the scope with a couple diodes, resistors and meters.

Jay   

Yup,
I figure a 1 inch ID core with a plastic spacer inside to hold the feed line in the center of the core. Also a couple layers of teflon tubing on the feed line. 50 ohm load would also be a good interface to a monitor scope or spectrum analyzer. 50 ohm attenuator pads if required. Also 50 ohm coax could work.  A center tapped winding would also work as a SWR monitor if you wanted to be crazy about measuring things. This would work cool in Frank's set up since the balun is outside.

Hey, if somebody has a chance, could they draw a quick diagram of the link-coupled tuner? I dont know if its just a matter of not enough caffeine in the blood yet, but I'm having difficulty visualizing it!

Thanks,
Jason kf6pqt

I think the tom vu tuner is on this site somewhere ansl check out rick measures turer. frank is using a t tuner 2- 500 pf variable caps in series with a variable inductor to ground connected at the junction between the two caps.
The T tuner has a heck of an adjustment range but it is a hipass network so does not help much in reducing harmonics. The t might be easier to use with a low Z load.

A schematic is found in the article below.

http://www.amwindow.org/tech/htm/160smallants.htm

Awesome, thanks! Something tells me there was a direct link that I missed.  :P

Caffeine's a hell of a drug!

-Jason kf6pqt

If that tuner config won't work (may not for some very low-Z loads), try this config.

(http://www.amwindow.org/misc/gif/SeriesTuner.gif)
http://www.amwindow.org/misc/gif/SeriesTuner.gif

This is a configuration I need to throw into the simulator..

I posted previously...


Found the link. Called the Cobra, caw mawn!

http://www.k1jek.com/

MMM Good and it keeps you and the XYL warm under the covers.

Mike

I simulated the balanced/balanced tuner with series tuned caps into 10 ohms. It worked pretty well. Then I added another cap across the input 1500 pf variable.
this really raised the Q of the tuner. A higher Q may reduce noise so need to look at it some more.
Every configuration I have tried so far seems to work about the same as long as the correct LC ratio is hit. The Hi pass T network will not help harmonic rejection. A T with 2 inductors and 1 cap seems to do a better job as a low pass filter.
I've only worked with resistive loads so things may change with reactance but suspect it may only modify the L/C ratios
A low Q network has the advantage of wide bandwidth but a high Q might help under poor conditions.
I will try to put the link coupled tuner in and see how it plays.
The Balanced/balanced with a dual differential cap has some interesting results.
I have one from a KW match box and might consider making a custom with 350 pf per section just to see what it will do.
Glad to share switcher cad files if anyone wants to play. You will also have to download switcher cad (freeware)

Interesting. Need to check out Switcher CAD.


Although you don't want to have the Q go too high. The circulating currents get up there and loss is incurred.

http://www.linear.com/index.jsp

go here and down load it Steve. Pretty easy to use.

Frank:

If your seaside antenna was 180 feet long and about 60 feet high, the Z at the feedpoint at 1.9 MHz would be 31 -J586 Ohms. At the end of about 75 feet of 600 Ohm open wire made with #14 wire, the Z would be 19 +J96 Ohms. Not too bad. If you go with about 74 feet of 450 Ohm open wire line (same #14 wire),  you would get 14 +J0, no reactance! A Z step up of 4 gets you 56 Ohms. Might not even need a tuner.

Steve,
We had some high winds Friday night that pulled a lot of leaves off the trees. I  have my eyes on a tree branch that is close to the top of the shorter tree almost 70 feet up. Now if I can get a clean shot at it from the street under the  primary power run. The high side is all low voltage so it will be an easy shot up higher plus the 30 or so foot increase in elevation. I'm planning on #10 spaced 4 inches which is around 400 ohms. Also have some old glazed 6 inch spreaders so could press them into service. The feeder length should be 60 to 70 feet. I've run a number of simulations at 10 ohms on 160 meters and find I don't need a lot of L. This is good because I have a matched pair of strapping 12 uh variable inductors. The lot is 60 by 175 feet so not sure if I can get 180 feet without some hanging vertical. The end of the house is near the middle of the lot so it will depend on the branch I
 hit. TNX for the information higher Z. gfz

OK Fine  ???
Thanks for planting a thought in my shorted out mind......GFZ
Now that the leaves have come down, it might be time to smoke over the situation in the back yard. There are some nice tall pines back there..........approx 500 feet from the house.

Fred

Another modeloing program shows the feedpoint impedance to be around 18 Ohms resisitive, with 500-600 Ohms of capacitive reactance. Adjust feedline length and Z accordingly.

Steve,
How would you simulate that load across the output of the tuner? A 18 ohm resistor with a 600 ohm Xc in parallel?
I was trying to determine the load on the home qth antenna and seems to be an inductor across the load. It is a 125 foot on a leg Vee with about 70 feet of feed line.
Adding this reactive component required a lot more C in the tuner to get a match.
This is exactly what happened. When the dipole broke I lost about 50 feet of feedline and the tuner wanted more C. Also went from a dipole to a vee.
Dave Ape Man shared some tuner ideas at hostraders.  The nice thing is I won't need a lot of L so I can build another strapping tuner and use heavy wire to reduce losses.
fc

That's the impedance at the antenna feedpoint, not the output of the tuner. The resistive component will be lower at the end of 60-100 feet of open wire. The reactive component will be changed in value and may be even be inductive, depending on the line length and Z. Use the feedline calculator posted today  in another thread to determine the load at the end of your feedline/output of the tuner.

Yes, you can simulate the impedance as an 18 Ohm resistor in parallel with a capacitor of 500 Ohms reactance at the frequency of interest (I used 1.9 MHz).

TNX will do

Check this out. What are realistic Q values for tuner inductor and capacitors though?
http://fermi.la.asu.edu/w9cf/tuner/tuner.html

Z at the end of 70 feet of 600 Ohm ladder line calculates at 11.86 + J80.65.

A good coil would have a Q above 100, maybe more like 200.

That tuner simulator is for a unbalanced T.

Yup on the unbalanced T. Most hamateurs use those into a BalUn. Watch the loss with reactance... yikes.

Anybody ever try a 1/2 wave delta loop on 160 with the center of the top open with an insulator in the middle. This would alow me to put up a full 250 feet of wire.
I would be on a 30 degree tilt all up about 70 feet. 60 feet across the top with an insulator in the middle sides would be 95 feet and fed at the bottom with open wire line.   

Frank,

What it sounds like you would have is a 160M dipole with the ends configured in a "rhombus" and kinda laying on it's side.  The antenna take-off angle would be the average height of the array.  No a good scenario pattern-wise.

I would definately opt for your original plan of putting up a flat top fed with #8 or #10 open wire (I would instead use coax due to the ~50 ohm match - keep it simple)  and the ends dropped down for whatever you needed to fill it out to 1/2 wave.  Can't beat a flat dipole.  Any other config close to the ground in terms of wavelength is a compromise, OM.

T

Sounds more or less like a 160 meter halo. Don't see how it would be much, if any better than a dipole.

only that it would have 1/2 wave length of wire in the air and tilted 30 degrees on the side of a hill facing west.

The quad or delta or even rhombus to some degree works FB when used as a full wave, but as a 1/2 wave broken at the opposite junction you are into the leg cancellation zone. Picture it like a severly angled 1/2 wave inverted vee.

Try to get that flat 160M dipole using dropped loading ends into the same place on the hillside for better performance, OM.

T

OK just putting too much thought into it.

I've been thinking about this and can't grasp the concept. I know that the circuit impedance can be converted from series to parallel but I keep picturing what a change in the J portion does. No J and all that is left is radiation resistance and a little (in practical terms) resistance from copper loss. Lots of J and the power will not transfer unless the J is overcome. That looks like a series circuit to me. I did find one online reference which agrees with this for a model of less than a resonant half wave ant. The reactance model then changes with the J in parallel up to a full wave where it flips to series again. Calling all professors.

I think I was smoking dope when I wrote that. It should be R in series with the cap. It can be converted to the parallel equivalent by


R_par = R_s² + X_s²/R_s

X_par = R_s² + X_s²/X_s

OK. I feel better now.

Hey, for the tuner design in the amwindow tech page... Do I really, really need to run 3/8" tubing for the main coil? Sad that its the most painfully expensive part these days! I have a 4kv ef johnson varable cap as big as my thigh that I picked up at a swap for cheap, but the thought of shelling out for all that copper makes me cringe.

I'm not going to be running a "New England Kilowatt," just a pair of 811a's.  ;)

Thanks,
Jason kf6pqt

This tuner?
http://amfone.net/ECSound/K1JJ13.htm

As the power handling capability is defined by the diameter of the tubing/wire used in the main coil, I think you could get away with some #4 ga. solid copper coated steel.  Bet Apex would have a hunk.

Nah, this one:

http://www.amwindow.org/tech/htm/160smallants.htm

;)  The same, but with pictures...

I have a question about this antenna tuner.  Two things need to happen.  You need to add inductance to the 'short' antenna, and you need to match the impedance of the resulting tuned antenna to 50 Ohms of the transmitter/transmission line. So I would think that both the primary and secondary of the tuner coils need taps.  Is this right.

The cap on the antenna coil is clearly for in-band fine tuning (or for shortening the antenna for higher frequency bands).

I think for a 'New England AM KiloWatt', 1/2" or larger copper pipe should be used on the antenna side, particularily if the antenna is quite a bit less than 80M.

73, AB1GX

Only one thing needs to happen - the SYSTEM (that's the antenna and the feedline) need be brought to resonance. That's it. Whether it's a capacitive or inductive situation will depend on the complex impedance at the end of the feedline and that is determined by feedline length.

The cap on the antenna side of the link is varied to bring the system into resonance. You could use fixed caps and roller inductors to do the same thing, although this would be a more difficult mechanical problem with a link topology.

The matching to 50 Ohms does not require taps on the transmitter side of link (although it could be done this way). The transformation ratio is easily varied by the taps on the antenna side (look at it as an autotransformer) and by varying the coefficient of coupling between the antenna and transmitter sides of the link (either through physically varying their relative positions as in a swinging link, or by putting a cap in series with the transmit side link).

Half inch copper pipe is probably overkill for anything under 1 kW into the tuner, but if you already have it on hand, it should make for a high efficiency tuner.

Steve Thanks!

I'm using a 80 meter dipole antenna for 160 meters, and I added a large inductor at the feed point to resonate the antenna.  There's an air variable cap across this inductor for tuning down the 160 meter band.

Obviously, the output is balanced, but I really like you autotransformer approach.  I think I'll try attaching the transmission line coax ground to the center of the inductor and attach the unbalanced feed to a tap for impedance matching.

Now, if I want to measure antenna current does it make sense to put a current sensing loop around a center tap wire but in the direction away from the autotransformer taps.  That way the feed current is not sensed and the voltage near the loop is low (as opposed to where the inductor attaches to the antenna).

73

There are actual antenna tuners using the design you describe. Other than the lack of magnetic isolation provided by the link, the electrical action is identical. Go for it!

So, I have a coax-fed 75m inverted V that is a near-perfect 50-ohm match at 3870. Yeah, I'm that good. ;)
-jk.

So, after gathering the parts and supplies that I need for this tuner, (50-foot coil of 1/4" tube, yowtch, $39!!) and a 100ft roll of new 450-ohm line, its hit me...

If I want to keep using this antenna on 3870, with the new feed an tuner, I had better alter the length, right? Lengthen it, to get away from 3870 so that I can use the tuner to effectively bring it BACK to 3870?

Or am I overthinkin' this?

Thanks,
Jason kf6pqt

Yep, you're overthinking it....

Actually overlooking something.....

The antenna is STILL going to be resonant at the same frequency it was with coax feed......

The feedline won't change that....


You MAY want to lenghten the antenna anyway though....

If you intend 160 meter operation.... get all the length you can on the dipole....

If you're restricted....
try to get at least long enough to cover the 80 meter band.... ( 130 feet + ...overall length)


You'll be ok either way.... don't sweat it...

I am at just under 130', 124' as I recall, as the vee is a tad shorter than the regular dipole.

So this sort of tuner isnt the sort that will care about about loading up an exact 1/4 and 1/2 wave of the input frequency? I understand this to be a problem with other tuner types.

I'm just hoping to get 160/75/40m functionality out of the one 75m antenna, with the emphasis only on slightly improving the efficiency on 75 by getting away from coax feed. 160 and 40 will just be a big bonus!

Thanks,
Jason kf6pqt

You might want to add some extra wire to the ends of the antenna legs if you have room to "droop down" these in a dangling fashion.

If you can give up 160M: Some AM ops have successfully employed an EDZ antenna for 80-10M using 44' per side making it 88' in total length - a very compact size that has the advantage of getting ALL your WIRE IN THE CLEAR. Check out K6ESE's Mar Vista shack pix for the antenna setup: http://www.k6ese.com/Mar_Vista_Shack.htm

And....I hope you are changing out that coass for balanced line.  Never mind, I see you are. ;D

I believe you're refering to FEEDLINE length there.... NOT antenna length....

With any tuner, matcher whatever you choose to call it....
IF you run into trouble obtaining the match you desire....

Trimming or adding FEEDLINE will usually do the trick....

Trimming the feedline is usually easier, but changing the length of the antenna will too. You have to look at the wire in the air, the feedline and the tuner as the antenna SYSTEM. The entire system must be brought to resonance for it to accept power and work. Changing any of the physical parameters of the system will have an effect.

Ohhhkay... I think I gots it now.

Joe, I actually went in to HRO today... believe it or not, they actually had the best deal running on a 100ft roll of 450 ohm, 18ga solid ladder line, even cheaper than MFJ!

Making my own out of bare 14ga and home-made spreaders would have been cool and oldbuzzardly and all, but would have co$t a lot more when you add the copper+time together.

Trevor's kite-pole sounds great, but I'm wondering about a plain 'ol painters pole from home despot...

"In the clear" will never describe my antenna, until I move!  I did buy one of those combination lopper/saw on-a-pole thingys from Harbor freight, should allow my to get one end of the antenna ten feet higher in the Mulberry tree from hell...

Thanks,
Jason kf6pqt

Sounds like you did good. As others have said, don't overthink the deal. Antenna challenges build character. And if the neighbors see you fooling with coils of copper tubing, just tell them you're making a still.

Noooo! Then they'll be pestering me non-stop... "Is ready yet? No? How 'bout now? Are you sure? Well, how 'bout now, maybe?

Jason,

Chat up your local electricians: they routinely deal with scrap lengths of wire, often in larger diameters, and will likely sell it to you for the scrap price.

HTH.

Bill

No you may not be overthinking this!  First you need to recognize the term 'antenna tuner' doesn't necessarily mean antenna tuner (making the antenna resonate).

If the antenna tuner is actually an antenna tuner and is located at the feed point of the antenna, you are correct in that the length of the antenna may need to change if you just add inductance from that expensive copper tubing you bought.  But you can also add capactance to keep your 'perfect' dipole in tune.  In fact, with this approach any length of wire can be brought into resonance (but the impedance may be too high or low to be useable).  This is the best performing placement of an antenna tuner, but it's also a pain to climb up 50' to tune the damn thing and adjust VSWR.  How do I know?  I fell out of the tree.

Next, you can move the antenna tuner to the ground by using ladder line from the feed point to the tuner.  This also works well because you're still mainly tuning the antenna which is now the combo of the transmission line and dipole.

And finally there's the antenna tuner in the shack which is just a glorified VSWR adjuster and doesn't tune anything.


Another choice is to go with a vertical 1/4 wave.  Now the tuner is on the ground!  This is the approach the US Navy has been using for the last 50 years (even though big dipoles can be installed on most ships).

Steve's input was key to my getting a handle on this antenna tuner jazz.

Au contraire my friend. The tuner performs the same function, no matter where it is located. And yes it does tune, just as one tunes their transmitter by adjusting the tune and load controls. In each case, the system is being brought to resonance - be it the feedline and wire in the air as part of the antenna system, or the tube and the output network in the transmitter.

Suggest you get a copy of the book Reflections by Walt Maxwell. All this antenna, feedline, impedance, tuning, resonance stuff is very clearly explained. I've read the book twice and learned new things each time. I'll probably read it again, since my brain can only absorb so much, and I've probably forgotten what I learned the first time around. :)

What!!!  Say it isn't so. :o
When the antenna tuner is connected to the output of the transmitter, and it's output is connected to the transmission line (of non trivial length), I claim (as I previously learned from your posts) that the antenna tuner can only (I repeat only) adjust VSWR!!!  Yes the LCs in the antenna tuner are tuned, but so are the LCs in the transmitter.  The antenna (it's resonance) is 100% uneffected by any knob twisting at the antenna tuner (actually in this configuration the antenna tuner should be called a transmatch).

All this is much clearer if you just sketch the equivalent circuit.

 

Look at it this way - The transmission line is nothing more than an impedance transformer when there is anything other than a perfect match at the far end (i.e. flat line). So there is a Z at the feedpoint of the antenna (R +/- jX). Let's call this Impedance A. That impedance is transformed to some other impedance at the other end of the feedline. Let's call this Impedance B. The exact impedance is dependent on the length of the line. So, if you place a tuner right at the antenna (the wires in the air) feedpoint, it will have to deal with Impedance A. If you place the tuner at the end of the feedline, it will have to deal with Impedance B. Either way, it's dealing with impedance. There is no difference. Sure the impedances will be different (higher or lower resistive component and inductive or capacitive reactance at varying amounts), but both are complex impedances and the tuner will deal with each in the exact same way.

The only reason to be concerned with the length of the feedline is if Impedance B is one that cannot be properly dealt with by the tuner (doesn't have enough capacitance, inductance or some combination thereof). So, changing the feedline length to a point were Impedance B is better dealt with by the tuner is a good option.

Go to the URL below and play around with the feedline length to see for yourself.


http://fermi.la.asu.edu/w9cf/tran/index.html

Steve,

I know exactly what you're suggesting, but... It's well known that losses from this type of transmission line impedance transformation are almost always excessive in multi-frequency applications.  It's bad enought to put a fan on the tuner, but having a red hot coax is over the limit. ;)  Things are much better with 600 Ohm ladder line, but at 1.5KW the losses are still around a few hundred Watts.

Just to avoid terrible losses - using that calculator applet, I'd have to install my dipole at least 80 ft in the air (at 40 or 50 feet the resistance of my antenna is way too low for reasonable efficiently at 75 and 160 meters).

I don't think there is any way to come close to the efficiency of a tuner at the base of a vertical antenna.

Does anyone know what '51W Fred' uses? (other than a 2KW linear)

tom

It's well known where? Losses with open-wire line are minimal. Here's an extreme example using the W9CF calculator.

Freq: 1.9 MHz
Feedline: 600 Ohm Ladder
Length: 100 feet
Input Resistance (that at the antenna feedpoint): 10
Input Reactance: -500 (these two numbers are about what a short dipole, like only 120 feet long, will yield on 160 meters)
Z at end of the feedline (in the shack): 11.95 +j373.11
Load SWR: 92.16 (pretty extreme)
Input SWR: 74.43

Now let's look at the losses.

Match Loss dB/100 ft: 0.02 (this is the loss of the feedline when SWR is 1:1, perfect match, you can see ladder line is rather low loss at this freq).

Total Loss (additional loss due to the mismatch/SWR): 1.64 dB (yes this amounts to several hundred watts if you are running 1500 watts into the feedline) but no one is going to notice a 1.64 dB drop in your signal. And this is a extreme case. Generally, the loss is well less than 1 dB (e.g. a slightly longer antenna and a 70 foot feedline yielded only 0.5 dB loss).

 In an absolute sense, you are correct. You can't beat a tuner right at the antenna feedpoint. But in practical application, it makes little or no difference where the tuner is located. And it's a heck of a lot simpler with the tuner in the shack. ;D

Unless you want to use an exceedingly short antenna on 160 meters, losses will be a fraction of a dB with the right feedline. What sort of antenna are you proposing?

Steve,

First, thanks - great discussion.  I had planned to use a dipole that's 40 meters long for 160 meter operation.

I used coax for my calculations which yielded much, much worse results (3x worse).  Not everyone can string 600 Ohm ladder line through their home and walls. 

What's worrying is that the current in the transmission line peaks in one physical location along the line.  Even 14 gauge copper ladder line will not support the 100+ Amps at a single position that we see in the calculator's plot.  That's several hundred Watts being dissipated in a couple of feet.  Clearly for KW+ operation requires 10 or 12 gauge copper!

Assuming ladder line, ff I combine the insertion loss of the antenna tuner (which gets HOT) of about 1.5 dB with the 1.5 dB from the transmission line impedance converter, I see 3 dB of loss.  That means my 90% efficient 1.5KW rig which I worked so had to build has the effective power of a 750W transmitter.

And -3dB may not seem like not much is lost.  In absolute terms that's right, but there's a noise floor in signal reception and the higher the noise floor, the more important 3 dB is.

Since I'm tired of falling out of trees, I think I'm gonna go for a 50' vertical antenna with the tuner at the base. Burying radials is much lower risk!

Tom

Good discussion indeed. Yes, coax is a no go for sure. A 130 foot long antenna feed with open-wire line will work. I've done it. So have others, some putting out very good signals on 160 meters. It's not easy though. Open wire line with #12 or larger conductors is needed and a strapping tuner. Whether this is more it less work than a vertical and a bunch of radials (probably at least 30 to keep the losses down) is up to the individual. If you go the vertical route, take a look at the losses involved with a short radiator and the associated ground losses.

Have fun!

coax on a short antenna with high VSWR is a waste of time.

One feedline type that gets overlooked may come in handy for this type of application...

I use 2 runs of RG8-U coax, (#9 awg solid center) as 'balanced line'....


The two braids are connected at the shack end, and to ground.

The two center conductors go directly to the link-coupled (k1jj type) tuner.


Now... It works... the impedance was measured at 115ohms

I have not done ANY efficiency calculations, or measurements...

I just see it as an easy way to run a balanced line through the attic to the back of the house....

The braids tied together to ground reduced the noise (computers, etc.) by at least 15-20db (2+ 'S-units on reciever).



The only other "test" I did... was to sling the 2 pcs of coax about 20 feet apart in the middle of the run... There was NO difference in the measured vswr...
To me, that only means that the lines probably stayed balanced, unaffected by their proximity to each other and other objects.


As I said, no idea if I'm losing scads of power or not...
Might be worth looking into....

Thoughts?

thats cool, I never seen that done b4.....how did it work?

Works fine,

As I said, I have no idea how much loss there is....

I found the idea on a corntester site a few years ago.


There's about 110' of the double coax, and 75 ish feet of 450 ohm 16 guage up to the ant.

Would have gone all the way with the coax....but that stuff is HEAVY!!

I guess its time to throw my $.02 in the mix. Due to having a postage stamp sized yard, I have been forced to run a short, non resonant antenna for many years now, and no one seems to have any problem hearing me. (unless I'm running piss-weak low power)

I am running 100w in the early evenings, and full legal limit in the later nights when the going gets rough. I am using a 60' long center fed flat top, fed with 14ga crappy brown stuff. It works just fine from 80m all the way up to 10. I can even get it to work reasonably on 160. It puts out a very good signal on 80 and 40, and is tollerable on 160. I have no other choice, its either use a short skyhook or buy another home.
Since verticals suck for close in work due to the low angle takeoff angle, a flat top was the only choice.

The tuna and all of the other accessories were optimized for the short antenna / high feedline current scenario, and it was an interesting learning experience. The tuna is strapping and HB and engineered to hamdle the high current WITHOUT HEATING UP!.  Remember that anything that is getting hot is dissapating power. The biggest priority is simply to get absloutely as much of the transmitter's output as you can to the antenna. Minimize your I-R losses as much as possible and it will work.

Putting the tuna at the antenna's feedpoint would be ideal, BUT, lets face it it is really not practical. The small amount of loss in the balanced line really makes it pretty much a moot point. Why bother!!
It simply has to just make the complex impedance at the end of the feedline look appealing to the transmitter. Thats it- game, set, and match!!

Letz face it .5-1db is a pretty neglible amount of loss, no one is going to see that on the receiving end. Just not worth the bother to worry about. Sometimes you hit the "point of diminishing return" and its really not worth pulling your hair out to improve things any further. Also sometimes it is just easier to accept the fact that something works instead of wasting your brain trying to figger out how it works.

                                                       The Slab Bacon 

double coax will force a balance but feedline loss comes in two flavors. Dielectric and resistive. The idea of a shielded line is a big help snaking it through the house and #9 wire is pretty good but a high VSWR will drive up dielectric losses. Still "race what you brung."

Yes that's quite true about dielectric losses, especially since (assuming the tuner, is at the radio point) you are having some radiation from the feedline, due to the antenna system being non resonant .  Since the the center conductors are being used for the feedline, the braid has now become a part of your dielelctric losses.  I would assume that this affects radiation efficiency for the system.  I've read about using twin coaxes for a balanced feedline.  Years ago (remember people, I corntest too), it was sort of flavor of the month for contesting.  You don't hear as much about it anymore.   I think the losses, and that fact that the feedline is so heavy have a lot to do with that.  The company I work for uses twin coax assemblies (some are as long as 350 feet), made out of RG-59 for transmission lines from ultrasonic transducers, to the readouts.  That stuff is clunky enough as it is, much less making it out of RG-8.

Antennas are always interesting to me.  Due to my being challenged for space, I've done a fair amount of expirimenting with short, non-resonant antennas.

73,
Ellen - AF9J 

there is really no substitute for a really good skyhook,BUT.......

Sometimes you just gotta do what you gotta do! A short non resonant antenna is still better than no antenna at all. The fun of it all is getting it to work well. thats the challenge!


Long runs of coax at high swrs (high impedance mismatch) are too lossy. The capacitive reactance just acts like a sponge and soaks up all of the power. If you have to sin with high swr and coax i have found that a low impedance situation (low voltage / high current) is definately less lossy as long as the I-R losses dont eat you up. I have a SHORT run of coax (about 8') between my tuna and the balun at my back wall. That coax runs at an outrageous swr, but the losses are pretty minimal because it is running at a low impedance. The rest of the feeders are balanced line.

Use balenced line whenever and wherever you can and you will never regret it, especially if you want multi band operation with 1 antenna!

                                                       The Slab Bacon 

Frank, your antenna system is not non-resonant.

Steve, you can repeat this on every hammy site until blue in the face. The average ham thinks resonance is necessary. Frank is only stating it the way I see everywhere. The antenna is non resonant but the system is. Maybe your approach will stick in a few minds. BTW coax heads, a full wave antenna is resonant and will show quite a bit of magic SWR when fed with cow-axe. 

If the ends of the top and bottom lengths are tied together, I would call it a linear-loaded antenna.  I think that RF sees it as a 160 foot dipole with wierd cross-coupling on each wing.

I did something a little similar with 160 feet of that 450 ohm brown twin lead stuff.  But I made it into a 40 foot per side square loop.  Where the ends came together, I connected the left top to one side of the feedline and the right bottom to the other side of the feedline.  I did not tie the opposite corners together.  So it was like 320 feet of wire coiled into a 2-turn open loop (a solenoid), and center fed.

My thinking on this was that the current of the two wires would be in-phase this way, while with the doubled-back linear loading, the current is out of phase.  And it did work on 160, as well as anything I tried.  However, it needed to be vertical - when it was horizontal, it put a big fat null straight up where all the local signals were coming from, but it heard static from a thousand miles away just fine.

Some day I want to try this arrangement with the loop size self-resonant at the operating frequency.

The wires Frank has in the air are nothing more than a 120 foot long "full-sized" dipole folded in half. It's just a way to fit 120 feet of wire into a 60 foot space. I don't know if the set of wires he has in the air are resonant on 75 meters but they are resonent somewhere. From the reading I've done, this sort of antenna will resonate at about 0.6 or 0.7 times the "normal" resonant frequency for the antenna length. In Frank's case, the antenna is 60 feet from end to end. A single-wire dipole of this length would resonate at around 7.8 MHz, so Frank's wires would probably resonate in the 4.7 to 5.5 range. But a grid dipper would tell the real story.

But all the above really doesn't matter, just as it really doesn't matter for any set of wires feed with open-wire line and a tuner (except in the case where the open-wire line is used as a flat line). My point is that the SYSTEM, thatis the wires in the air, the feedline and the tuner ARE resonant. The system would not take power and radiate if it weren't.

Actually this very true, just everybody doesnt see it that way. Any length of antenna is resonant on any frequency. it is just NOT a 1/2 wave / 50 ohm match. Any length is wire is some wierd fraction of a wavelength, if it is not a 1/2 wave  / 50 ohm match it just doesnt work with coax and plastic ricebox radios. You must use a tuna (transmatch if you must) to make it work. With balanced line feeders, SWR is no longer any real issue, you just have to have something to make the complex impedance that appears at the end of the feedline look like something that the transmitter wants to pump a little rf into.

Always remember that ladda line is your friend. If you are using balanced feeders on a balanced antenner and a good strapping tuna, you can just about always make it work.

I'm not saying that piss poor antenner is always the answer. there is no substitute for a good well designed and installed antenna. BUT...........................sometimes you just gotta do what you gotta do. Some of us just dont have the physical room for a real antenna. I just cant afford to move the QtH at this time. So in the true spirit of ham radio, I experimented until I found something that would work.

Bill, my antenna is 60' in length. Just like steve said, it is 120' of wire folded back on itself, but not forming a complete loop. The spreaders (spacers) are 12" and it is up about 33' off of the ground. It sure works a hell of a lot better than on antenna at all.

Always remember: you can tune a transmitter, you can tune an antenner,
but you cant tune a fish!!    ;D ;D

                                                                        the Slab Bacon

Frank,

You know what they say about how Bumblebees can't fly, and your sky hook just keeps buzzing around in my brain. ???

The next time I'm at Timonium, I'm going to bring some sand and concrete to the party. If you can find forty feet of flagpole, I'll be glad to help dig the hole: we'll get you a 120-foot span from back to front - and my head will stop trying to explode every time I think of your antenna.  ;)

73, Bill

Frank you silly goose!  You misquoted REO Speedwagon:

"You can tune a piano, but you can't tuna fish!" ;)  When I was expirimenting with what I call loopy dipoles (dipoles with each leg configured in a loop - pretty good on the hihg bands, lousy on the low bands) at the present QTH, I always used balanced line (although it was speaker wire, which can get pretty lossy above 40m [I had a short run, so it wasn't much of an issue]).  Because as people mentioned, it's the system that counts.  Remember, unless you have a balun right at the antenna itself, the further off of resonance you are, the more your feedline will radiate, hence, becoming a part of the (radiating) antenna.  Dielectric losses determine how much field strength this feedline radiation will have.  Since wire/twinlead type balanced lines have relatively low dielectric losses, they will radiate decently.  Hence the reason why balanced feed (and I don't mean twin coaxes) antennas such as the Zepp, original G5RV, and the original Windom, make decent multiband antennas.  You'll have a screwy radiation pattern, due to the feedline radiating, but you will radiate more RF, than a coax fed, non-resonant antenna.

Coax feeds as we well know, will not radiate well, due to dielectric losses.  In some cases, the heating from these losses, can be enough to melt the dielectric at high RF voltage points, if you're running enough power.  As a result, coax fed antennas make lousy multiband/non-resonant antennas, unless you use traps, capacitive coupling, etc., AND a balun to keep that "evil" feedline radiation from occurring.  A coax fed antenna that tries to bypass the above provisos, with mediocre results, is the modern G5RV.  As I mentioned before, the original G5RV was an OK balanced feed antenna.  But, when internal tuners on radios like the TS-430 & 440 became the rage in the 80s, they encountered a little problem: the limited impedance range of these tuners couldn't deal too well with the complex impedances presented when using wire antennas for multiple bands.  It was noticed that by removing some of the balanced/ladder line feed from a G5RV, and replacing it with coax (sorry, I don't remember what the length is, I'm not a big fan of G5RVs), you could put the system impedance into a range that the internal tuner could handle, in effect making the G5RV an "all band" antenna.  Unfortunately adding the section of coax, turned the G5RV into not much more than an air cooled dummy load on some bands, due to feedline radiation in the coax, soaking up RF, in dielectric losses.  On some bands like 17m, a hamstick will radiate better than a modern G5RV.  In another group I belong to, another ham mentioned how during Field Day, the G5RV they were using on 40m with 100W was netting them no QSOs, while the 40m dipole he threw together in 15 minutes, was working like gangbusters.  In some cases (if your coax section is made from wimpy coax, or you're running serious power), system SWR conditions can be enough to melt the dielectric in the coax section of a G5RV.

Nope, the only advantage that coax has over balanced line is that it's physically  sturdier, and isn't affected much (impedancewise) by nearby metallic objects.

73,
Ellen - AF9J

Bill,
      You dont have to worry about my antenner. It works just fine the way that it is. No one ever has any problem hearing me on 75m, even at a 100w power level. and even on 160 I usualy GET the same signal reports as I GIVE, which isnt too shabby for a 60' long antenna.
I have configgered the whole station for high angle rag chewing and am also heard quite well out into the midwest. I was talking with Skip, K7YOO last night with no problems. the only change that I plan for the antenner system is to make some new homebrew #12 or 10 ladda line feeders to help minimize the I-R losses a little better on 160. If it aint broke, dont fix it. Sometimes you just gotta accept the fact that something works instead of tearing your brain out trying to figger out why it workz.


Ellen,
         I am very familiar with that quote, I just figgered that the other references would be a little more apprepo here. I love that quote too! As far as feeding a balanced antenna goes, if it is not operating on the the frequency that it was cut for (1/2 wave) no one will ever convince me that coass is any better than ladda line. Coass is fine for feeding an unbalanced antenner (ground plane, vertical etc) but for a flat top antenner operating on any other than its 1/2 wave frequency ladda line kicks butt and takes names. As long as you keep your ladda line balanced it wont radiate because it is balanced. I was given a demonstration many years ago by the Derb that made me a believer.  When he was living at his mothers house in Columbia, Md. he had a small cheap P.O.S. b&w television ( with rabbit ears) sitting on a shelf in his radio room. His ladda line from the transmitter went up the wall not more than a few inches from the television. With the TV on and the transmitta fired off at full strap he didnt even put a line on the tv screen. That demonstration made a believer out of me!! I saw it with my own eyes.

Feeding an antenner with balanced line is the only REAL answer for multiband operation. Yea you can put up a fan dipole or lossy ass traps, but why botha if you dont have to!!
I feed my "non resonant" antenner with ladda line (14ga crappy brown stuff) and have used it from 160 all the way up to 10m without any "rf in the shack" problems. None at all!
Coass is fine for an unbalanced antenna operating on its resonant frequency, but anywhere else it getz lossy. Keeping the outer shield from becoming "hot" with rf can be a real challenge once the coax gets more than 1/4 wavelength in length.  Trust me it works, anyone who has ever worked me agrees that I put out a pretty good signal for using a compromised antenner. It is the end result of quite a bit of experimenting. If you feed it with ladda line, do everything possible to get as much of the rf as you can to the antenna (minimize I-R losses) and find a way to match its complex impedance to the transmitta, it will play!! Trust me on this one.

                                                                       the Slab Bacon