The AM Forum

Hello out there in radio land.
I changed out my 450 ohm window line and 3/8 wave VEE (192 feet ant/125 feet feed) For a store-bought "True Ladder Line"
600 ohm ladder and 240 feet antenna. One continous wire that transisitons from ladder to antenna.
No matter how I connect my ammeters into the circuit, they no longer read RF current. They obviously are passing RF through but not indicating. They were 5 amp peak. They used to read 3 amps on the old system with 300 watts carrier.
I have read other postings about increasing the range. I wonder if I should pursue repairing. How can I check that the meter movements are still good?
I can't believe the changes I made to the antenna system would be that dramatic!
Although I have received a couple of emails on my Hotmail account asking what I am using for an antenna. I was on the air with this new ant. Thanksgiving eve with W1UX and K4KYV. Apparently there was some big change, that I'm unaware of without my ammeters.

Fred

Hook it up to a variac, short out the circuit with the meter in series with the load (short)  and slowly bring up the variac. You need a clamp on amp meter to verify how much current is flowing in the circuit. Or you could hook it up to a 100 watt light bulb in series with the meter, the meter should read about one amp.

It also works on DC if they are thermocouple type. Definitely put something in series with the meter to limit current to the full scale value. The wires inside are usually very thin.

Fire them up with a AA dry cell.  Not a whole lot of poop, will show a couple amps or so.

Dennis

From my experience, if the thermocouple is blown, the meter will show up as an open circuit.

The only other possibility I can think of would be if there is a shunt across the thermocouple to increase its range.

I blew two 0-5 amp thermocouple meters before I discovered that running the Gates into an unloaded L-network produces too much circulating current for the thermocouple.  One time, it was an antenna relay malfunction; the second time it was operator error, forgetting to switch the antenna back in line after it had been disconnected during a T-storm.

I just shorted out the terminals to the dead meter and left it in line.

I'm wondering how you came to the conclusion that the stuff is junk, and why it might have caused Fred's ammeters to burn out (if they did).

Don, the meters still have continuity. RF is passing through, but no meter readings.

Hi John,
I was wondering the same thing. Brian, I get a sense that you really hate this stuff. No issues here with QRM from the surrounding area affecting the RX.
It's just a bunch of wire constructed as the familiar 600 ohm ladder line and at the feed point this wire turns into an antenna. What a simple idea and without the worry of bad connections. It's pretty well constructed....time will tell with our Winter WX in Pa.
The antenna made a helluva improvement in my TX and RX signal. I have been very disappointed in the 450 ohm window line and dipole since we moved here. THere's more people cursing at the window line because of it's shortcommings.
The ammeters are a mystery. I won't know until I do more troubleshooting and disassemble them. They may now be at a voltage point, maybe there 's more than 5 amps going out to the antenna system, dunno.

I'll be delving into their demise later today...SAT...No money left to go any where. Black Fri took care of that!!

Fred

I guess the main thing I don't like about the stuff is the fact that it uses # 16 wire.

Perhaps at 120 volts its good for 10 amps but how much loss does it have particualy at ten meters?

It's #16 26 strand wire. Light weight and nice to work with.

Discovery time: Brian may be onto something with impedance. The meters work fine. I dissected them and the thermocouple is good and connecting a AAA batt across the meters, they indicate a flow of current. So Pandora's box has been opened.
What I have is the familiar Simpson RF ammeter 5A full scale. Model 135R I do not have any idea of the specs for these.
But I'm still sticking by my story for the True Ladder Line
MY MFJ buddy now says that with the questionable 600 ohm ladder/antenna that I have is nearly 1:1 SWR and the Xs is 2. I may not know all of the antenna magic terms, but past experience shows me that single digit Xs is a good thing. It's series reactance??? Could be inductive capacitive? Dunno The manual for the MFJ 259 is not clear either.

Fred

So Brian, I assume you purchased just the ladder line and not the entire package?
And soldered/connected to your existing dipole of what ever wire you're using?

Fred

We cannot reach the finish line if we don't recognize feedline impedance transformation in balanced feed doublet installations and what happens at the shack end with varying lengths and impedances of feedline.
[/DEU voice OFF]

Typical doublet/openwire line installations are VERY forgiving in terms of imbalance.

You can easily destroy an R.F. ammeter movement without opening the shunt. Ask me how I know.

Look for a reading on twice or half the frequency if you suspect being at a voltage node.

For Brian and anyone else who has either elected to dislike W7FG ladder line (more on that in a moment) or simply desires a different Z and/or heavier gauge wire, you can easily make your own with schedule 80 1/4 inch PVC pipe, the wire of your choice, and UV resistant cable ties.  In a lot of places the regular schedule 40 PVC holds up for years outside but sched. 80 may be better in the sunbelt. 

With a bandsaw or fine tooth wood saw you take a fist of 10 foot sections and saw off a wad of spacers at the spacing of your choice.  Repeat until you have enough spacers.   Take your two wires  you are using for the feed and poke a cable tie end through one of the spacers.  At the other end loop the emerging cable tie around one of the wires and poke it back through the pvc spacer where it came out.  It will grab and hold the wire at the end of the spacer.  When the cable tie end comes out the other end loop it around wire number two and stick the tie through the little plastic click stop ratchet and pull it tight so it holds the second wire to its end of the spacer.  Clip off the excess cable tie.  You can do this in much less time than it took me to write it.  Photo showing short example below.

Now that the dislike for ladder line has once again been established and a method for rolling one's own has been given, perhaps we can move on to Fred's problem.

73

Rob
K5UJ

Credit for the hb ladder line trick is something I can't take, as much as I'd like to; that goes to George, K9TRQ.  I didn't even make the sample -- that was done by WB9DNZ (I did snap the photo though).

p.s.  The spacers used in the W7FG line are simply black plastic pipe of the type used for lawn in-ground sprinkling systems.  You can find it for sale at Lowe's in the section devoted to lawn irrigation DIY supplies.  The quarter inch pvc and cable ties are extremely light weight.  That trick actually works better with heavier gauge wire, so go wild, use no. 10 or 12  :D

I wish I had something small enough to be able to shove the power through 8 ga.  This 4/0 gauge 100 foot ladder line span is getting HEAVY, specially when the wind blows :)


8 gauge is what feeds the driver amp into the pumphouse.  8 gauge heliax, that is :)

--Shane

The glass and ceramic is going to turn the assy. into a very heavy monster that will come down when tested by MaNature. I did all this with No. 8 solid and the ceramics in my JN days, early 90's.wow! It hurt to fix it.
So W7FG shudda used solid copper? 600 ohm ladder (6 inch spacing) was the mainstay for many Ham ops. And some prefer even wider spacing from my Googling around.
I have gotten over not seeing the ammeters move, I shudda taken a field strength reading with the old system and then compare what I have up now. I was depending on the meters....oh well, more on air testing with folks who remember passed QSO's on the other Ant system.
I posted earlier that the meters are good. The impedance changed dramatically that they barely indicate now. I would have to get my wife to PTT and I watch for any movement.

Fred

Ok then, this thread must be done. What more could be said without being redundant??  I'll bet there must be someone who has something to say?

There must be a way to determine when a thread is dead?

Wait a minute, I have more to say but your going to have to wait till tomorrow ;D ;D

put your meter in series with a 100  watt bulb an it should measure about 1 amp when the bulb is lit.You can test it at 60 Hz.. You cant't test 600 ohm line unless it is terminated in 600 ohms not an antenna.

bull pucky

not to hijack this thread or anything but since we are talking about the maligned ladder line, which I have been happily using for five or six years, I finally got around to conducting some field strength measurements late this afternoon.  I found a clear freq. at 3700 and tx 20 watt carrier into the horiz. dipole at 50 feet with the flashbox tuned to 50 j0 then I walked around outside with a cheap diode driven meter box connected to a telescoping antenna 30 or 36 inches long.  out in the yard under the dipole I adjusted the meter to read almost zero with the antenna vertical. Horizontal and parallel to the dipole I get a tiny meter reading.  With it vertical I walked around.  I walked up to the balanced feeders.  No meter movement until the antenna is 12 inches away from the feeders then it starts to move up.   more signal on the meter when the whip is parallel to the feed and 12 inches away, not surprising since it is now in line with the fields. 

No significant reading with the meter unit and antenna along side one of my steel dipole support masts.  Over at the 65 foot 80 meter vertical significant presence of RF on that antenna but nothing on the 160 m. inverted L wire co-located with it and hanging down about 3 feet out from the 80 m. vertical.   Perhaps it is de-tuned by the feedpoint L network tuner for 1.885 MHz. 

I'd say not getting any field strength reading until the 3 foot whip is inside 12 inches from the ladderline is pretty good.

Rob
K5UJ

Back to topic.
The RF ammeters are at a current node of zero.
Both of them.
You have a well balanced feed line/antenna combo.
heh, heh.

Not sure that #14 wire over the 16 ga W7FG will improve things, because it seems to me you have an inadvertent P-N junction somewhere in the system acting as a mixer.  If you can't tune out the BC t-rash using the tooner, it's most likely intermodulation products you're seeing.   Can't be the fault of the feedline unless it's broken somewhere and semi-conducting, acting like a mixer.

It's gotta be coming from SOMEWHERE.  It's not an image.  It's not intermodulation.  Then what is it?  That's my point - something OUTSIDE is acting as a mixer and creating trash up to 10 meters.  No way the feedline alone is responsible for it, unless it's acting like a mixer.

I also fail to see a way that the feedline alone - whatever the impedance - can change the resonance of the antenna.  I am betting you have a break in the feedline or antenna somewhere and it's acting like a Zepp.  All my of experiences with W7FG have been great, but if you think this causing your antenna problems, by all means change it.

yeah Terry,
It seems we go around in circles and the antenna gurus we have on the forum have left the building. So much chatter about the plusses of ammeters and here we sit befuddled.
Brian, it sounds like the antenna you're describing has or had a self resonance of 1.6mc  instead of the desired 3.6mc with the 600ohm ladder line?
Let's try to forget who made it. I had to change the taps on my tuner with the new system and I'm getting great reports now. More operating time and various band condx will prove out what is happening here. I wish I did field strength measurements before and after.
 
And Jack your theory almost makes sense about the meters being at a 0 current point? I'll have to do some testing on other freqs and bands to see what the results are. I may have started a thread with half baked info....dunno.

I have performed the tests posted here and the meters are fine. I don't have any thing to substitute to prove any theories out.


FRED

The surge impedance of the open wire won't significantly change the resonant frequency of the antenna/feeder system.  The only effect it will have will be on the SWR of the resonant feedline.  The total length of one feeder plus one leg of the antenna is what determines the resonant frequency of a balanced open-wire fed dipole.

The surge impedance of two-conductor open wire line can be calculated from the formulae and charts found in any ARRL handbook from the 30's to the present.  It is a function of wire spacing and wire size, with perhaps a very small influence from the dielectric materials used.

For a multi-band tuned feeder system, 600Ω is an optimum compromise, since the load impedance may vary from 50Ω or less to several thousand ohms depending on the band in use and whether the feedline is working into a high voltage point or a high current point.  On the fundamental half-wave frequency and odd harmonics, a dipole fed at the midpoint will be fed at a low impedance.  On even harmonic frequencies, it will be working into a very high impedance point.  With an end fed Zepp, OTOH, the feeders will always be working into a high impedance since the end of the antenna wire is always a high voltage/Hi-Z point.

400-600Ω is optimum for physical reasons.  It is extremely difficult to construct two-conductor open wire line at Zο much lower than 400Ω.  Either the wire size is very large, the spacing is extremely close, or both.  You  might be surprised at how little it changes the impedance of a given pair of wires to go from 2" spacing to 6" spacing.  To go very far above 600Ω requires very wide spacing to the point that the feedline becomes unwieldy, or else conductor size becomes so small that the resistive losses will be excessive.  I  don't think it matters at all what the surge impedance of a tuned feedline is if it is built to any of the practical dimensions in terms of wire size and spacing.   If you are planning to run the open wire as a  non-resonant (flat) line, then surge impedance is of utmost importance.

To build open wire line much below 400Ω, you need to go to 4-wire or higher.  4-wire line is constructed in rectangular fashion, with the conductors at opposite corners of the rectangle tied together.  Six-wire line can be constructed as a cage, with every other wire strapped together at each end so that a cross-sectional view would resemble a Star of David.

Somewhere round here I have an article that gives formulae for calculating the impedance of multi-wire line, but I haven't been able to find it.  I recall something like 16-conductor line to reach an impedance below 100Ω.  The biggest problem with multi wire >2 conductors is finding or constructing the spacers.  

For homebrew two-wire line, I would prefer fibreglass rods over plastic pipe for spacers.  Critters like bugs and small spiders have a habit of taking up residence inside the hollow tubing, and likely causing rf losses.  PVC itself is not much better as a dielectric than old fashioned wax impregnated wooden dowel rods like they used in the 30's.  A good and cheap source for solid fibreglass rods is electric fence posts sold at farmers supply stores.  Just wear gloves when cutting and filing the stuff to avoid very painful microscopic glass splinters in your fingers.

Open wire line can also be constructed in coax form, like the 4-wire line described above but with all 4 conductors strapped together, and a 5th wire suspended in the middle to serve as the central  conductor.  I believe WSM used or still uses that configuration for the transmission line to feed their Blaw-Knox diamond tower.

As far is the spurious intermod products from broadcast frequencies, make sure that all wire connections make firm contact.  Sometimes a defective insulator or even a branch or leaf in contact with the feeder or antenna wire can cause problems. Absolutely the worst case of intermod (and TVI) I ever had was when I built the end-fed Zepp in Houston and unthinkingly used zinc-plated steel wire to tie the copper conductors to the ends of the  spreaders.  It worked great until after the first rain, when the dissimilar metals corroded and formed a diode rectifier at the end of every spreader on the feedline.  I took it down and replaced the steel wire with small gauge copper and the problem was gone.

It's #16 G 26 strand wire.
My configuration for the antenna is 125 feet of feedline and 240 feet antenna.
70 foot high VEE ends 40 feet high
Maybe these numbers help with what is happening in radio land.

Fred

Roughly a resonant doublet on 160. Your feedline is slightly longer than a 1/4 wavelength when velocity factor is applied and is transforming the low impedance at the feedpoint to a very high impedance at the antenna coupler. The ammeters won't budge. Many "tuners" wouldn't tune this config at all. Try it on 80. Those ammeters will read like you are in series with a cantenna.

EDIT. They won't read much on 80 either. Duh.

So what does the surge impedance of the parallel conductor open wire line have to do with it?


Assuming approximately a half wave radiator,  that will happen only if the impedance of the transmission line approaches the impedance at the mid point of a half wave dipole, usually about 70 ohms in a real world installation.  Anything as high as 390 ohms will be a resonant feedline and the feeder length will add to the dipole leg length to determine the resonant frequency.  The added length is strictly a function of the length of resonant wire, even in the case of coax running at high SWR.  One factor that may make a difference is velocity factor.  Solid 300-ohm ribbon and even that crap with the rectangular holes punched in the ribbon will have a higher velocity factor than true open wire line, and will  lower the resonant frequency.  But real open wire line with two wires spaced together with plastic spreaders every 6" to several feet, will be minimally affected by the insulation over the wire or the spreader material and display a 97% wavelength velocity factor, even if it is el-cheapo stranded #16 wire with PVC tubing for spreaders.

Air is 1 any other material is lower than 1

Hi Fred,
   I originaly had 130 ft of 16G copper wire up with 450 ohm Solid conductor line. This was a factory made antenna given to me. It was made by Van Gorden.  Called the ALL BANDER.  It tuned wonderfull on every band of my KW matchbox. I had a BIG signal on all bands. 2 years in the AZ Sun made the ladder line turn white.
  I replaced the 450 ohm line with 600ohm True ladder line.  I ordered 200 Ft.  I used 85 for my feed.  Ran it up the house and over, then up to the antenna.

I had a HUGE increase on 40 meters.  About the same on 75.  I lost 20 meters.. Cant tune it below 2 to 1.  10 and 15 tune great.  I worked the world on 10 just last week.

I have checked the balance and I to cannot get an RF ammeter to read.  I only have one.  I ended up using light bulbs and they where the same brightness when tuned flat.  My old meter might be bad... I have not checked it.

I wanted to list out the lengths for 600 ohm line from Tip of antenna to end of open wire line for this antenna config. This info is listed in several books. I had Bill orrs on my desk:

L is the flat top measurement. 
S is the ladder line length.

L + S should equal one of FOUR measurements.

110 ft
133 ft
177 ft
212 ft


I think this is where people are having trouble.  Your antenna is the correct length.  Mine is not and Brians is not.  The book explains that if you dont have one of these four lengths, The antenna will have trouble tuning on some bands.

Clark

Brian,  YOU GOT F*&^(*.   

I just counted mine.. 26 Strands. 16AWG.   Oil resistant, 600 volts.


Clark

Yeah.. I agree.  I had 450 ohm line.. It tuned FLAT on every band, mid cap on my KW matchbox.

With 130 ft of line and 85 to 90 ft of this 600 ohm line, I just measured resonance at 3.990.  The 450 ohm line measured 3.600.


Clark

My 130 foot long center fed dipole is fed with around 90' of ladder line.  When I put up my new dipoles last summer I re-read the business about the "magic ladderline length" i.e. an odd multiple of 1/8 wave at the lowest frequency for the antenna and attempted to follow that just for the heck of it.  I never paid it much attention in the past figuring the tuner would deal with whatever length I used.  I decided there must be something to it because the matchbox tunes the dipole like a dream on 80 40 and 20.  I have not tried it any higher because I have a separate smaller dipole for the high bands, but I did the same thing with it re the length of the line, and the matchbox tunes it on all bands 10 to 20 including 12 and 17. 

Brian it sounds like you got a bad deal on that ladder line.  I guess it is too late to get a refund.   I ordered 200' last summer and got the right wire, the 26 strand no. 16.  My hunch is that the new guy who took over the business after W7FG went sk probably didn't know what he was doing at first and used the wrong wire until someone set him straight.  Just a theory; doesn't make it any better.  You never know until you try--I'd call them up and explain what you got for your money and see if they'll offer some kind of credit, or refund or something.  You have nothing to loose.

Rob

Thanks for showing the cheap-o ladder line. I had no idea such cheezy line was being touted as full bore product.

Number of strands is irrelevant, except in flexibility.

Stranded wire is available in many different strand/lay configurations.

For #16 that can be anywhere from 7 conductors to about 445 conductors.

The nominal OD of the conductor will be anywhere from 0.0508" to 0.0670"

Could also be noted that some strand/lay configurations of #18 wire, will be larger in diameter than some strand/lay configurations of #16 wire.

And then, if we're talking about tinned, plated  (sucha as copper clad steel) then there's another whole set of parameters that gets thrown in.


If you can tell you didn't get #16 wire, just by looking at it.... your doing pretty darn well.
Most people would have to mic the strands.

However, since it's advertised as "16 guage 26 strand..."  you may well find it easy to get your money back INCLUDING any shipping costs, as the product was definately misrepresented.


I don't see though, how it would be possible for the impedance of the line to be over 1000 ohms .. it would take more than a 0.01" change in wire diameter to make that kind of difference!

or the load Z and the right length of feeder that transforms the input Z higher. This is why you have to terminate the line to test it.
I suggest you plug in your numbers to the HUZ provided transmission line site and see what happens.

If you are using 600 ohm line (say 12 awg spaced 6 inches which is 586 ohms) to feed a center fed antenna then depending on the FREQUENCY you measure it at you can see an impedance anywhere from 70-5000 ohms at the transmitter end of the line!   If you are using 300 ohm line the impedance seen at the transmitter end drops to 75 -1200 ohms - depending on the frequency you measure it at.

This is a function of the transmission line making an impedance transformation (based on the electrical length of the line - which is frequency dependant) of the impedance seen at the antenna feed point.

The simplest example of this is a quarter wave stub. At the fundamental frequency (the one that determined the length) a dead short on that stub will appear as an open (and vice versa). At the second harmonic of that fundamental frequency, this same line is now a half wave long and will show a short when shorted and an open when open.  So this same line, terminated the same way, will have an impedance varying from zero (short) to infinity (open) based on frequency.
 
This same transformation occurs regardless of the termination impedance. So if you have a simple dipole at around 72 ohms or so at the feed point, the transmission line will transform this impedance to something else, unless you are feeding it with an exact electrical half-wave long feeder.  This means that (almost) any multiband antenna that does not use some type of matching system at the Antenna Feed Point will see widely varying impedance based on frequency. The combination of antenna feed point impedance change (due to being on a different frequency than it was cut for) and the feed line transformation (due to varing frequency changing the electrical length) results in the impedance range we see at the transmitter end of the feed line.

The smith chart was created to simplify the calculations for feedline impedance based on electrical length (it can do a lot more too!) Down load a Smith Chart Simulation and run scenarios and you can see this effect quiet clearly. If your a book person, there is a good smith chart chapter in Practical Microwaves by Laverghetta with simple examples you can work for your self.

This is also covered quiet well in some of the older handbooks that deal with balanced line with much more detail.

attached is a chart from Bill Orrs Radio Handbook, 15th ed. This shows the effect on the impedance at the transmitter end for a multiband antenna with feeder and element lengths vs frequency.

The chart is for 300 ohm line, but the ratios are true for 600, just the impedance values change due to the higher Zo.

Ok, if we look at a case where your transmission line is an  odd multiple of quarter wavelengths (simplest case) the input impedance is given by

Zin = Zo^2 / Zload  where Zo is the characteristic impedance of the line, and Zload is the load as provided by the antenna.  So if your antenna impedance is  72 ohms where your Feed line is also an odd multiple of quarter wavelenght the input impedance becomes:

(600^2) / 72 = 5000 ohms.  So if you have a half wave dipole (72ohms) fed with 600 ohm line that is 3/4ths wavelength long (or any odd 1/4 wave multiple) you will see 5000 ohms at the end of the feeder in the shack.

If you know both the real and imaginary values you can calculate the impeadance at the transmission end for any length of line.  The formula for that is:

Zin = Zo ((ZL+jZotan(betaL)/(Zo+jZLtan(betaL))   (sorry I can't do symbols here)
Where Zo = characteristic impeadance of the line
         ZL = load inpedance
      Beta = 2PI / wavelength (in the transmission line used NOT free space this is called the wave number)
and L = length of line between the Load and the point you are calculating to.

The only time a transmission line will ever measure as it's characteristic impedance (Zo) is when it is terminated in a purely resistive value equal to Zo.


Also, all these equations assume a zero-loss or lossless transmission line. It's a handy assumption that doesn't effect accuracy too badly but makes the calculations much simpler (my calculus is sooooo rusty).

DATS what I has.
Brian you musta gotten the discounted model or the economy version.....geesh
 The length of the antenna part of the system must be the key.
Do you have the real estate to expand your antenna length? It's too short for 160M or is there no interest in 160?

Fred

YEah..  I have spent hours and hours on this subject this week.  It seems that its important to get the Top and the feedline set in the octaves of the ham bands.  This way, The tuner wont have to match over 1200 ohms. When this is done,  All bands will tune.

I am going to have to lower my Antenna and measure the feedline out. Once I know that, I can refer to the chart and add or cut until its right.

The big screw up for me happened when I read Lou McCoys book. He states, The feedline and top length does not matter.. String it up and use the most wire you can. 


C

Lew McCoy made other big mistakes beside this one.

So whats best?   There seems to be a line deviding people on this..


Throw up long wires, Run open wire down, Make your own tuner that will tune ANYthing. 

Cut the flat top and feeder so it is in the octaves of the ham band with the goal of not going on 1200 ohms on any band.


People really seem to be devided on this..  I have  a KW matchbox so I cant adjust the coil.  I require an antenna that works with this tuner.. that means 1200 ohms or less.  Others just keep modifying the tuner so what ever antenna they have, Tunes.  If you do this, Are you inducing loss?

C

There's no one size fits all solution. you put up the best antenna system you can for your situation and adapt.  A dipole cut for the lowest frequency of interest and fed with ladder line works well as a multiband antenna. A fan dipole off off coax also works well.  The much maligned trap dipole fed with coax also works.  Of these three options, the only one that should require a tuner would be the ladder line fed antenna, unless your rig uses a link coupled balanced output tank. (P-P triodes).
A well designed robust tuner will have minimal loss, but some guys don't like having the extra controls of a tuner in the shack, so the go for the simpler options.  Some folks go with a resonant coax fed dipole for each band of interest and just use a switch in the shack no tuning.

the simple truth is nearly any conductive thing can be made into an antenna (trees, gutters, downspouts, wires lying right on the ground, etc. have all been used with success). The rest of the system is up to the wants or needs of the designer.  The "Best" antenna is a beast that has a different face for every station/operator.  You have to ask yourself what are the most important parameters for you at your station?   All band use?  Directivity and Gain? effciency? Compact size for a small lot?  DX (low takeoff angle) use? Local QSO's?   Once you identify the requirements that are imporant to you, and figure out which are the most important (you can't have your cake and eat it too!) you can design an antenna system.

In the end if you are happy with how it work, it is a good antenna!

If that is true, then adding length to my Feeder is not going to help.

C

Since you can't change the coil, why don't you change the spacing on a section of your feedline.  That would act as an impedance xformer, allowing your KW box to see a different impedance.

Might be a PITA, but could actually get you on the band thats hard to tune now...?  Go from 6 inches to 4 inches for 20-40 feet or so....  You could even play with the location of the xformer to get different impedances AT the tuna.

Add in enough length of existing line, and you'll get something similiar, but I think changing the spacing, AND KEEPING IT IN BALANCE would do you quite well.

--Shane

what a major pain. But you know what?   That is a hell of a suggestion..  I bet if I cut that space down, It would work..

C

I got led astray (maybe not the best way of putting it) by an article on horizontal loops in QST around 2002.  One of the things it advised was to just make the balanced feed any length and let the tuner deal with it.   I had a tuner with the range needed to make my feed work okay so I thought that was good sage advice. 

Then on AM, I found that on some frequencies I had a lot of sustained current in the tuner or a lot of voltage at the end of the antenna  feedline (or maybe it's both?) and things were not very good with a 300 w. carrier.   

Some of this advice on antennas and feedline and tuners may work for SSB and CW but not for AM.  I think that may be part of the problem--the HF technical material in the ham literature for the past 30+ years has been written with low duty cycle in mind?  I'm sure the author of the article I read never operated AM, or he didn't mention it if he did. 

Anyway I got rid of the tuner with its toy inductors and put in the KW matchbox.   Now the range was less so I did the thing with making the feedlines an odd multiple of 1/8 w. on the lowest frequency.   On 3.6 MHz (what my dipole was cut for) that turned out to be around 97 feet (3/8 w.).  I fudged some and it is really more like 91 or 92 but it's close enough.  The MB tunes it no problem.   So I advise trying to get the feed 1/8, 3/8, 5/8...wavelength.   In my case 92 feet was longer than I needed so I had to loop it out over the back yard in a wider loop to get it to fit.  The length matters to the matchbox but handles my level of AM power so well that I don't mind adjusting the feed length. 

You can of course build a tuner to tune any Z at the end of the feedline, but if you have a far out Z that the MB won't handle it might be better to work on the feed length because your loss may be high otherwise, in a big tuner with high current on the coil(s).   

Rob

Putting a switchable section of feed line in the shack is not that hard. There are some guys on the list that do it to enable them to tune the band that gives them trouble.  I think the easiest way is that once you determine how much line you need to add, (often just 1/8th WL of the freq in question) simply put some bannana jacks on the ends and plug it into/out of the system as needed. 
If you want old-buzzardly, you could use a beefy knife switch araingment.

Either way would work FB.

The line transfomer using different feedline spacing does work, look up using shorted stubs as impedance transformers.  I think switching in a few feet of the original feedline is simpler.

Clark and others,
I'm thinking that the ops of the past were just happy to get a signal out. THey did not have the sophisticated gadgets we have now to see the shortcommings of improper lengths of feedlines or antenna lines and the impedances and reactance, etc.
Throw it up and tune it up.
Today we're going for the most we can get to be channel masters....yeah!!!

Fred

Clark,

To test this theory, try throwing 20-30 feet of windowline or something else in line with it.  Then you'd just have to make a support to keep the additional line from flexing or waving in the breeze and coming up on a gutter or downspout.  If it works, change the ladderline your using to have the transformer in it.  If it doesn't, throw the windowline in the garage above the car, and you've lost nothing.


--Shane

Fred,

I coined a term on an amplifiers mailing list once, dealing with this:

"MFJ, making engineers out of idiots"

What with the 259 and it's variants, actually learning the math behind the theory is a thing of the past!

--Shane (tongue in cheek)

Interesting Rob. I ran into issues with my 250 foot center-fed after building my new open-wire feedline, which I had cut to a convenient length of 90 feet. It tuned easily on all bands, except for the upper portion of 160 meters, where it got very nasty with lots of interesting arcing and spitting. I examined the "magic feedline formula" that you have indicated above, and found that all the touchy tuning issues ceased when I used an odd multiple of 1/8 wavelength for my feedline length. This meant using either 63 feet or 189 feet, plus or minus 10 feet or so. I did the looping feedline thing you described above for several months with excellent results, but it was physically awkward and brought jokes from my daughter-in-law about the long "hamster ladder" in the trees. So, I eventually used about 70 feet and it has been very happy with that length for 160-75-60 and 40 meters. I found that 80 feet to 100 feet induced the unhappy tuning issues on the top end of 160 meters. I have no background in antenna theory what-so-ever, but I would agree with you that the "lowest frequency to be used 1/8 wave-odd-multiple-magic-open-wire-feedline length" design does seem to work. Now, if I could just remember where I put my RF ammeters last fall, I could re-check the system for balance...

Rob W1AEX

The ops of yesterday looked for rated final plate current and probably a certain depth to the dip. That along with lack of heated parts would indicate max power transfer pretty close to what todays dips use. 

Being one, I used a florescent tube hung under the wire of my flat top.  I also used the two neon bulbs across the feedline. 

Rob Thanks, but here's something I completely forgot, just to show you I am no antenna brainiac either:  I never thought to take into account the 95% velocity factor of ladder line in working out my 3/8 wave feedline length.   I wrote that 3/8 comes out to around 97 feet and I shorted it by fudging it, but when I figure in the VF it works out to being 92 feet and change.  I'd like to say I had it all figured out and nailed it but it was nothing other than dumb luck.

Rob

Ok.. Ok...  This weekend, I will add 10ft of line to the feeder, Restring it and rehang it.  I will report back.. 


I agree about the days past.. Hook it up and tune it.. The Champ and the king could careless and will match the line.. Heck, 20meters does work. But when I see that SWR meter showing 2.5 to 1 on 1, I just cant except that.. LOL


Clark