Where do the little AM guys hang out?

[K1JJ]

I was thinking of using coax because I'm more familiar with it. actually that's the only thing I've ever used.
Also, since my shack is in the basement, it would be easier to bring in coax down there. (I usually drill a hole thru the cement block foundation below the ground.)

If I just run a straight 57' dipole, it wouldn't be resonant at 75 meters, but the tuner should handle that. I'm assuming the coil dipole would be resonant if I tune the coils correctly, but I'm no expert on this, so I don't really know. I could probably use a balun with a straight dipole to transform the impedance, if I knew what it was at the feedpoint.
.

Hi Al,

The tuner will handle multi-band and low loss ONLY if you use openwire. Coax is good for one band only unless some other gimick is used on the antenna.

Unless the coils are adjusted to give you a good 50 ohm input to the dipole, the coax will have some loss. BIG loss on other bands - unacceptable. The antenna tuner will not affect the loss at all. It is there to keep your solid state rig happy, that's all.

You need to get the coils adjusted for one band using coax.

There are some gimmick antennas out there that will let ya run coax and a short antenna, but be aware some use power resistors to burn up power to provide a "fake" match.  

Post the URL of the antenna you want to buy/try and some of us will give you opinions before you proceed.

Still, consider using a simplke run of openwire with a tuner. No coils, little loss, ALL bands, efficient.  You are paying a huge price here to use coax for a MULTIBAND short antenna, OM.

T

[WA1GFZ]

Tom,
Why not just remote the linear and preamp in the building below the tower? Sounds like a pita to play with a long run of open wire line on 50 MHz. I got a good head ache standing next to  a low band ant at 50 watts
and it was only keyed to test the ant and repair it.
PVC insulation is lossy at 50 MHz. How about skin loss as the wire turns brown?? I would think teflon is the way to go. A twisted pair of say #12
would be around 100 ohms. But only good for 500 to 1000 volts.
Remember the 500 ft. roll of #12 twisted pair teflon your pal Craig and I split at Hostraders. ...

[K1JJ]

Tom,
Why not just remote the linear and preamp in the building below the tower? Sounds like a pita to play with a long run of open wire line on 50 MHz. I got a good head ache standing next to  a low band ant at 50 watts
and it was only keyed to test the ant and repair it.
PVC insulation is lossy at 50 MHz. How about skin loss as the wire turns brown?? I would think teflon is the way to go. A twisted pair of say #12
would be around 100 ohms. But only good for 500 to 1000 volts.
Remember the 500 ft. roll of #12 twisted pair teflon your pal Craig and I split at Hostraders. ...

Franz,

I did consider remoting the linear, but the problem is that I have 6M antennas on three towers. A central point in the shack is the only way to feed them all wid the linear.

I wud think that the field around the openwire wud be minimal due to the cancelation, assuming it's balanced. Plus, the openwire gets terminated outside the house with coax, and the house is shielded/grounded with aluminum siding.

Yes, that #12 Teflon was beautiful stuff. I actually ran out of it recently - used it in many projects.

OK of PVC insulation being lossy.  So why doesn't it heat up and burn in a microwave?  

I imagine the velocity factor of PVC insulated openwire is slower, so is it these circulating currents that causes the losses?  I will take your advice and go with bare wire.   K1FO uses open wire to connect his HUGE 450mhz? moonbounce Yagi  frame together. I shud axe him about it too.

T

[WA1GFZ]

remember you will also have resistive losses.
yup ax a spert and get the real dope.

I would think you have enough back ground noise to overcome 3 dB of cable loss on RX. All dat gain.

[W2VW]

Dave "The ApeMan" Axed:
"What is the construction of yer homie open wire?"
Good question. I haven't settled upon anything yet, still thinking.  
What do you think the maximum spacing can be between wires?  I figgered that 3" wud be the max before feedline radiation occured, but not sure.  The wider the easier to mount and keep apart. [/qoute]

I really don't have a clue as to max spacing for use with VHF. The references are few and far between unless one wants to deal with higher math. Ask the guru with the big signal.

Since I will have a good match in and out of the feedline, the SWR shud be good.  But, still, I was thinking of some heavy Home Depot wire. A friend seemed to think that insulated wire wud cause loss on openwire at that freq... what do you think?  Insulated wire is cheaper, esp the #10 spools of electrical wire.

Here again, the references that I found said to purposely use feedline with a surge impedance different than the load. I don't know why.

For spreaders I was thinking of getting 3/8" Lexan rod at Industrial Safety in West Hartford. I plan to use as few as possible on the run over the ground since it will be very tight and tensioned between wooden poles.

I use plexiglass stock whacked up with a combination plywood blade equipped circular saw. 2 part epoxy holds the wire in place.

BTW, I'm building up a large 40' X 40'  H-frame to hold the four 48' boom 6M Yagis. Rotated by a prop pitch and sproket/chain using a large swing gate on the side of the tower.  Coupled wid the openwire low loss, I'm hoping for the best.

I'd want to see if that gets AFU during weather. The feedline will be very long in terms of wavelength. Might want a better mousetrap.

I'm not satisfied wid the triple stack config - good for F2 only and the new config will be 180 degree swichable (top/bottom) to produce high angles for E skip, but still have all in phase to handle horizon stuff.

Use an elevation rotor for yer new stack and save on phasing/switching crap maybe?

[K1JJ]

Yes, Dave, the open wire will not be "environmentally stable".  The WX OM will have an effect I wud think. Well, I gots two other 6M beams fed wid hardline to use when it gets wet out there.

As for an elevation control....  That wud be a nightmare to implement in the real whirl off the side of a tower. The H frame already is 40' X 40' and the whole mess with antennas will probably close in on 300 pounds.

I don't do moonbounce nor am interested cuz they use digital computers to tell you a contact was made. Too weak for CW and ssb...  Big thrill, huh?

I'd be better off just switching a 6' piece of coax in and out for 180/0 degrees.

BTW, can you get on 6M?  I worked Rich KB2AM in Yonkers last night. He was +20, big signal even using a PW TX.  I had the 33el array facing him by chance, tied off with rope.

Boy, these emoticons are getting more violent - great for the Enquirer forum, don't ya think?


 :gib:

T

[W2VW]

BTW, can you get on 6M?  I worked Rich KB2AM in Yonkers last night. He was +20, big signal even using a PW TX.  I had the 33el array facing him by chance, tied off with rope.



T

Yup, I can get on six w/ about 10 Watts of AM. No sideband gear for that band. Maybe this weekend. I just need to figure out the tuner settings. Sat or Sun afternoon works.

[W1GFH]

Please don't BUY a wire antenna (Van Gordon, etc). Hiram Percy Maxim will spin in his grave. Hams were meant to build and erect their own antennas, preferably in sub-zero weather, out of spit and baling wire.

Peruse this fine article at....

http://www.qsl.net/wb1gfh/antenna.html

And don't underestimate Radio Shack TV Twinlead...

http://www.eham.net/reviews/detail/1750

[/url]

[w3jn]

I used Radio Shack twinlead for a quick/dirty antenner I put  up when I moved back from overseas.  Handled my Junkston Valiant just fine with no apparent heating.  I'd be leery of shoving any more power than that thru it though.

Long as you're gonna do it, though, do it right with decent open wire.

73 John

[WD8BIL]

preferably in sub-zero weather, out of spit and baling wire.

Great advise Elmer Frank !!!

I've used 17ga. electric fence wire in a pinch.
1/2 mile for $13.00 at Tractor Supply !!!

[W1UJR]

I recently got a Heathkit DX-40 on the air, but I'm not sure where there are other low power, screen-modulated rigs on the air.
I know there must be some, but all I hear AM-wise, are the big boys with their maximum legal limit plate-modulated transmitters.
Nothing against them, but I would feel intimidated trying to keep up with them in nets or rountables.

I heard there is a DX-60 net, but I think it moved to early Sunday morning somewhere, and I'm usually not able to get on the air then.

Any of those peanut whistles like mine on the air regularly, and if so, where and when might they be?

Thanks,
Al, NE2D

Al,

Give me a call or email whenever you would like to arrange a sked.
Always happy to escape the QRM maddness and have a nice moderate power QSO.

Old buzzard station here is 1940s vintage Collins 75A1 and 32V.

bruce@atlanticmotorcar.com
www.brucehowes.com

[W1UJR]

Tom, et al.,

Now that I think of it, how about a revival of the PW Net?

I was not living in New England at the time, but I understand that you were instrumental in getting the guys to build up PW rigs?

And I think Rick ETP had a hand in designing the famous “cakepan” TX?

What do you guys think of having a Saturday/Sunday afternoon New England PW Net?

Here's my copy -->>

[ne2d]

I was thinking of using coax because I'm more familiar with it. actually that's the only thing I've ever used.
Also, since my shack is in the basement, it would be easier to bring in coax down there. (I usually drill a hole thru the cement block foundation below the ground.)

If I just run a straight 57' dipole, it wouldn't be resonant at 75 meters, but the tuner should handle that. I'm assuming the coil dipole would be resonant if I tune the coils correctly, but I'm no expert on this, so I don't really know. I could probably use a balun with a straight dipole to transform the impedance, if I knew what it was at the feedpoint.
.

Hi Al,

The tuner will handle multi-band and low loss ONLY if you use openwire. Coax is good for one band only unless some other gimick is used on the antenna.

Unless the coils are adjusted to give you a good 50 ohm input to the dipole, the coax will have some loss. BIG loss on other bands - unacceptable. The antenna tuner will not affect the loss at all. It is there to keep your solid state rig happy, that's all.

You need to get the coils adjusted for one band using coax.

There are some gimmick antennas out there that will let ya run coax and a short antenna, but be aware some use power resistors to burn up power to provide a "fake" match.  

Post the URL of the antenna you want to buy/try and some of us will give you opinions before you proceed.

Still, consider using a simplke run of openwire with a tuner. No coils, little loss, ALL bands, efficient.  You are paying a huge price here to use coax for a MULTIBAND short antenna, OM.

T

Ok, I'm getting convinced to build an antenna, rather than buying one. I do like to do homebrew projects if they're not too complicated or time-comsuming.
(I'm also a beer homebrewer, and have built most of my own brewing equipment.)

I'm considering either a 60 foot inverted vee, or a 57 foot longwire, or end-fed Zepp, or something like that.
I have a few questions: First, what does 450 ohm balanced feedline look like? Is it the stuff that's about 3 inches wide, or is it only less than an inch? Second, will 300 ohm tv twinlead work almost as good?
Third, according to some stuff I found on-line, an 80 meter dipole that is only about 60 feet long will have a resistance of about 8 ohms and a capacitive reactance of around 2000 ohms. Will that work if connected directly to balanced feedline, with a tuner at the other end? I only have a cheapy MFJ "Econotuner", and I'm not sure what the range of impedances are that it can match.

Another idea that I came up with (which may be dumb), is using a 66 foot piece of wire running along the top of the house for one end, and using the tie point of the radials on my vertical for the other end of a "1/4 wave sideways vertical", or "horizontal vee" (the 80 meter radial is the other leg). I might even be able to use coax if it is resonant at 80 or 75.
This might have a very weird radiation pattern though.

Any thoughts?

[W1UJR]

Loop antenna OM, works great!
Run it right around the house.

See -->> http://brucehowes.com/zig_zag.htm
and
-->> http://brucehowes.com/loop_antenna.htm

73 Bruce W1UJR

[ne2d]

A loop is sounding pretty gud.
If I run it around the house, not including the garage, it would come out to almost exactly the 132 feet needed for a half-wave loop on 75 meters.
(35' + 30' + 35' + 30' plus a few inches for standoffs and stuff like that.)

I can probably only get it up around 20 feet at the highest point, but maybe it will still work reasonably ok.

[K1JJ]

A loop is sounding pretty gud.
If I run it around the house, not including the garage, it would come out to almost exactly the 132 feet needed for a half-wave loop on 75 meters.
(35' + 30' + 35' + 30' plus a few inches for standoffs and stuff like that.)

I can probably only get it up around 20 feet at the highest point, but maybe it will still work reasonably ok.

Hi Al,

Usually, a loop is a full wave loop. In the case of 75M it would be about  65' per side or 260' total.  The one you described is suited for 40M.  I must model it, but I think the input impedance on 75M would be very low -like 10 ohms?  if closed at the opposite diamond.  Lossy.

BUT, if you leave the top of the diamond open, not connected together, you have a dipole that is in the form of a square. It will "work"  OK, though some cancellation will take place.

I use full wave loops here for 2el quads that stand straight up and work great, but are 260' each.

But here's what I would do....  Take a 130' dipole fed with openwire. Run the legs around the yard any way you can, while keeping the legs as straight and away from each other as possible.

You axed about making open wire....  what I use to do was go to Home Depot and pick up a 500' roll of stranded, black, #12 insulated wire in the electrical dept.   Then buy a few 10' pieces of PVC 3/4" gray electrical rod. Cut the rod into 5" pieces and drill small holes in each end for the wire.

Stretch the wire out in two lengths. Feed the spacers on and distribute them every 3' along the new openwire line.  Strech the openwire TIGHT and then tie the spacers on using 6" long #14 solid copper wire pieces.

Use the same #12 wire for the 130'flat top of the dipole. Solder the dipole/feedline connections.


Use a small 10" loop of #12 wire thru the end insulators to attach to dark plastic/daycron/nylon or whatever  rope to support the ends.

You can use these same PVC 3/4" pieces for your center and end insulators. This system is rated 10kw+ assuming your ant tuner is too.

Cost about  $20 for the wire and $3 for the pvc tubing....

Your MFJ antenna tuner will work FB with the system as described.

If you put up this antenna as described, even at 20' high,  you will be shocked at the improved performance over that short vertical on 75M. QSO's will be easy and you will be hearing the locals like a champ, caw mawn. You might even run in Tom Vu or the Mucas Member.  
Does this all make sense?

T

[ne2d]

Yeah, I was just reading some articles about loops. One said you could use them as half-wave antennas, but all the rest said they had to be full-wave.
The idea you have sounds good, but again, because of very limited things to string to, and keeping the XYL happy, I want to keep it attached to the house at all points. I think it might be possible to put up a 260 foot loop, but I would have to zig-zag it in a few places, I'm not sure.

I could put up a 130' dipole, and run half of it along the back of the house, with the center raised up from part of the roof, but the ends would have to be wrapped around the sides of the house.

Also, what about an end-fed antenna like a Zepp? I couldn't run it straight, but I could run a half-wave around the house. I'm not sure how well that would work or what direction it would radiate in.

[WA1GFZ]

Joe PJP uses the the fiber glass rods Home Depot sell as driveway markers. I think they are about $3 each and are about 4 feet long
which will make about a dozen 4 inch spacers.
I like solid copper wire myself I used #10 with old johnson spreaders
in 1983 and tighten the tie wires now and then.  fc

[K1JJ]

Yes, I agree, Frank, 3/8" dia plexiglass or Lexan spacer rods wud be better. Maybe clear stuff for Al since he wants stealth. I've used PVC for years - just a habit, but don't use openwire anymore here since 1988.

Anyway, Al.....  The best configuration is to have a flat, straight dipole as high as possible. Even shorter is better to keep it high and straight. If you run it close and down and around the side of the house you will get absorbtion, RFI in the house, pattern distortion  - mostly from the metal house infrastructure - close to the ground losses too. Wiring, plumbing as we discussed before.

But since you are now talking about open wire, the whirl has opened up for you. You can tolerate a low input impedance with open wire and eat the small losses.

It's really a judgement call based upon how LOW the longer legs will be, but from what you've described about the mangled legs of a full sized dipole installation there, my intuition tells me that if you put a short 57' straight dipole above the roof of the house like you described before, it might be your best bet. It wud be a bomb on 40M almost full sized and straight. On 75M it wud be down only a db at most IF you use quality #12 openwire and your tuner stays cool with a high impedance feed. A 1/4 wave long feeedline would probably be best on 75M to do this. (60' or so)  Tho, any feedline length will probably be FB with that tuner, OM.

Tom, K1JJ

[K1JJ]

Al,

I thought of an idea to improve upon the last post's antenna...

Put up your open wire fed 57' long flat dipole above the roof on short masts as you intended.  Make it flat as possible.

Make each leg an additional ~20'  (or whatever you can fit in) and pull the remainder out as far as your property will allow, to the ground. Even if these addtional legs are nearly straight down, that's OK.  Both legs must be equal lengths to stay balanced, of course.

This will create  "end loading" and bring your input impedance up from 8 ohms to maybe 30 ohms on 75M. This will be much better for matching and lower losses.

This will aproximate a 95' long dipole, electrically.  You will have most of your current portion up high and flat where you want it on 75M.

73,

Tom, K1JJ

[ne2d]

I was thinking about doing something like extending the ends after reading that the dipole should be at least .35 wavelenths long for a good match and effeciency and all that stuff.
What I had in mind was extending the ends 15 to 20 feet horizontally along the house in a 90 degree angle from the main part of the antenna, but it sounds like maybe I should go straight down instead. Or doesn't it matter?

[Steve - WB3HUZ]

It doesn’t matter if you drop the ends down vertically to extend the length. Yes, technically, it does matter since your antenna is closer to the ground, but the gains you get in increased feedpoint resistance (and the attendant lower losses in the feedline and tuner) more than offset this.

Tom is right in that you should try to get your antenna as high and flat as possible. But an extremely short antenna that is flat is not likely to work as well as on that is at or near the proper length, even if it is not flat.

We can talk about this ad nauseum. And you will get tons of opinions (some even conflicting). The info gathering is good, but bottom line is at some point you will need to decide on something and build it. Build it, test it, get reports, modify it, test it get reports, try something different, test it get reports .... In other words, the likelihood of you getting the optimum antenna setup for YOUR situation on the first try is pretty low.

[ne2d]

yeah, I figured I'd have to do some experimenting.
I don't expect it to ever be perfect, but as long as I can get out a pretty decent signal to most of the states, I'll be happy.

[W2VW]

It doesn’t matter if you drop the ends down vertically to extend the length. Yes, technically, it does matter since your antenna is closer to the ground, but the gains you get in increased feedpoint resistance (and the attendant lower losses in the feedline and tuner) more than offset this.

Tom is right in that you should try to get your antenna as high and flat as possible. But an extremely short antenna that is flat is not likely to work as well as on that is at or near the proper length, even if it is not flat.

We can talk about this ad nauseum. And you will get tons of opinions (some even conflicting). The info gathering is good, but bottom line is at some point you will need to decide on something and build it. Build it, test it, get reports, modify it, test it get reports, try something different, test it get reports .... In other words, the likelihood of you getting the optimum antenna setup for YOUR situation on the first try is pretty low.

FWIW, I used to have a 160 dipole here which had the ends folded all over the property to make it resonant so it could be directly coax fed. I now have a dipole up which is straight, fed with heavy balanced line and way too short for 160 (about .25 wl) They both work. The new dipole works on every band. The higher bands have a pattern but that seems to be working to my advantage. The full length dipole caused a crapload of interference issues in the neighborhood and my own home. Ground fault interruptors used to pop, crazy stuff. It was most likely not electrically balanced. Present short dipole does not seem to have interference issues. The full length dipole was completely useless anywhere other than 160. Point is there are many ways to get a signal out even with our limited real estate. The idea is to get something useful in the air that will give you good service with little grief.  
It looks like you are trying to do the same thing there but on a little better than half scale so you can get on 75. You are going to find out that you will land up having to fabricate some parts of the system. If you do go with a short center fed dipole then it will require feeders with low resistive loss and a tuner of much greater quality than the junk which is usually available commercially. Out of all commercial ham radio accessories, antenna tuners have got to have the most examples of total crap designs than anything else.
My vote is for the longest fully balanced center fed dipole fed with heavy open wire line that you can get in the air. The maximum current point will be the feedpoint on the lowest band so maximum radiation will be at the center. If you can get a little extra height advantage at the center then do that. You might want to add even amounts of wire to each end. Droop it down or fold it sideways. Try to keep the whole thing a mirror image about the feedpoint. Maybe try it without the extra ends first to establish RFI issues. You will find the tuner quite touchy on the lowest band. It may take quite a while to find the proper tuner settings with a low impedance meduim reactance load. One note of caution: The physical ends of your antenna will have dangerous Voltage while transmitting. Even 100 Watts will give you enough Voltage to catch a tree on fire. Keep the very ends away from stuff except that neighbor's cat that pisses under your porch.
    Getting on the air from a small lot is not out of the question. It's better to be on with only 5 cylinders then not on at all.
All the stuff you will learn from this can be used someday when you hit the lottery and buy a big lot.

[ne2d]

I was doing some calculations, and I think I might be able to put up a full half-wave inverted vee for 75 meters, which would be around 120 feet long. (Each leg=60 feet). I can maybe get about 66 feet across the long side of the house/garage, and then I would just have to put the remaining 27 feet  on each end along the other sides of the house. If I run them diagonally down, they should make it.