another KB3AHE configuration

[WA1GFZ]

My cousin Joe has been trying to get on 160 but doesn't have the room for a full sized antenna. I talked him into trying Frank's antenna at double the size. His first report was the wires got too tangled in the tree branches so gave up. I thought it a couple days and suggester he rotate it 90 degrees so both wire runs hung vertical rather than horizontal.  He was able to get a total of 250 feet up hanging one run above the other. He ran open wire to his auto T tuner. (I'm bugging him to build a real tuner.) Anyway he JSed a balun and got on 80 but not 160. I wound him a big air core balun with 40 turns bifilar #12 teflon  on 4 inch pvc. I think it was around 68uh. now he tunes 160 through 6 meters. vswr a bit high on the high end of 160 so the balun may be a bit too much L. now I need to shame him into building a real balanced tuner to eliminate some losses. 

[Mike/W8BAC]

I did some searching through this site and I find many references to the KB3AHE short antenna configuration for a multiband antenna that includes 160 but I can't seem to find any building instructions or schematics. I think it might be worth publishing and posting in the articles section.

Mike

[W8IXY]

Just a couple of ideas....What about stringing up as many feet of wire , as straight as possible, in a "twisted, bent, inverted "L"", lay down as much wire or metal as he can for any kind of a ground system (a piece of metal screen, a garbage can, radials, old mattress springs(!), metal fence, an elevated couple of radials several inches (or more) above the earth, etc., and build a matching device at the feedpoint?  Its not really too much effort, and matching at the feedpoint eliminates much of the loss through a mismatched coax line.  If you can get the RF current flowing into that wire, and through some kind of ground system, it may be enough to allow some contacts---any port in a storm.  Put a feedline choke on the transmission line at the feedpoint to keep as much RF as possible in the intended radiator.

Happy New Year
73  Ted  W8IXY

[W1RKW]

I did some searching through this site and I find many references to the KB3AHE short antenna configuration for a multiband antenna that includes 160 but I can't seem to find any building instructions or schematics. I think it might be worth publishing and posting in the articles section.

Mike

Mike,
I think this is it:
http://amfone.net/Amforum/index.php?topic=12710.0
Someone please correct if I'm wrong.

Question regarding this Ant. What if one made it longer, closer to resonance on 160?

[Steve - WB3HUZ]

It should work better and tune more easily, especially on 160 meters. Karl, KD3CN is using one that is 90 feet long. Frank used 60 feet because that's all he could fit.

[Ed/KB1HYS]

So, why couldn't you add a 3rd leg folded back over the other two and add 1/3 more length to each end? (30ft out, 30ft back to center, 30ft back out 90 ft each side)? 

though still non-resonant wouldn't that give you an even better situation on 160?

[Steve - WB3HUZ]

You will gain something adding a third leg, but not as much as with the second leg. It's worth a try if you don't have much space.

[The Slab Bacon]

So, why couldn't you add a 3rd leg folded back over the other two and add 1/3 more length to each end? (30ft out, 30ft back to center, 30ft back out 90 ft each side)? 

though still non-resonant wouldn't that give you an even better situation on 160?

Becuz, ifn it aint broke, dont fix it! ! !  It just worked so well, that I decided to leave well enough alone!

[Mike/W8BAC]

Frank and All,

I barely have room for my 80 meter doublet to hang flat but I really want to get on 160. One end of the antenna crosses the street and is supported by my neighbors tree. I'm lucky to have such nice neighbors. I have been using a W7FG 80 - 10 doublet for 5 years now and love it. I picked up the 160 meter version and a Rohn 40' push up mast with plans to weave the ends into the shrubs. Not my idea of a great installation and it might disturb my friendly neighbor so plans have stalled until now.

If I make a folded dipole like this the antenna will hang flat like it is now (over my property) and with the new push up it will be 60 feet AGL with great ground conductivity. I wonder how much space would be ideal between the folds and how this would model Steve? Thanks for the help.

Mike

[K3ZS]

The antenna is not really a folded dipole as is usually defined in the antenna books, but that is not to say that it is not effective.   

[WA1GFZ]

I think HUZ posted simulations somewhere here. Check the link Bob  RKW posted.
I've also simulated it and looks ok. Adding the folded section raises the input Z making it easier to tune. You do need a good tuner to handle the low Z.

[KD3CN]

My antenna is a KB3AHE-style folded dipole, 90ft total length (180ft of wire).  Configured as an inverted V, top at 38ft, the ends at 9ft off the ground.   Feedline is about 75ft of 600ohm ladder line (W7FG).

My tuner is a double-L, like this:

              ______ L ________
             /                  |       \
coax-- 1:1 balun         C        feedline/Antenna
             \______ L ___|____/

Tuner values for 1:1:

Freq(mhz)   C(pF)    Each L(uH)
1.8               770        29.7
2.0               750        22.7
3.7               380        21.8
3.8               542        16.9
3.9               615        14.2
4.0               630        11.7

For 40 meters, the tuner capacitor is switched from the output to the input side of the inductors, as the load at the feedline is less than 50ohms.  Tuner values for 1:1:

7.1               159         4.5
7.2               155         4.9
7.3               130         5.5
7.4               120         5.5

My back yard space is about 50ft square, and this antenna and tuner have been working very well for me indeed!
73, Karl

[Ralph W3GL]

I guess you guys haven't been around long enough to recognize this configuration.

B&W sold (still does so far as I know) several versions of this antenna and a lot of commercial HF service (not broadcast) stations that jump around in frequency (IE more than an octave) use it as an easy way to achieve fairly good results.  I think one of the Japanese plastic radio manufactures also sells a version.

To make it more or less flat over the useful range, you place a 50 ohm non-inductive resister rated for at least half the RF output power in place of the insulator there in the top section.    

This configuration was/is known as the "T2FD"...

Not your most efficient sky wire but works where needed...

EDIT:   I miss spoke in calling for a "50 Ohm" non-inductive resister on this antenna, that should
           read 600 Ohm.  Also, this is a rather good wide band receiving antenna and if I recall
           correctly, the original published write-up stated it was meant to be installed as a sloper...

[KD3CN]

No terminating resistor on mine.  I don't like extra things in my antenna system that only make heat. 
Works very well.
Karl

[KD3CN]

Efficiency-wise, I guess I should make more comments.
The double-L balanced antenna tuner puts the balun on the INPUT side of the tuner, on the lowest impedance part of the circuit.  Reduced heating of ferrite cores, and lower power loss.  Better yet, use a air-wound coax balun.

Check out Rich Measure's balanced tuner webpage.

73, Karl

[W2XR]

Efficiency-wise, I guess I should make more comments.
The double-L balanced antenna tuner puts the balun on the INPUT side of the tuner, on the lowest impedance part of the circuit.  Reduced heating of ferrite cores, and lower power loss.  Better yet, use a air-wound coax balun.

Check out Rich Measure's balanced tuner webpage.

73, Karl

Hi Karl,

I also use a homebrew balanced-L antenna tuner. It works very well for me and can probably handle 10 KW PEP (as a guess!!!). It allows me to tune my 126' dipole fed with 600 ohm open wire feeders anywhere from 160 to 10 meters with a unity VSWR.

When I first built this unit, I used a coaxial balun at the input. As I recall, I used about 20-25 turns of RG-213 on a 4" OD PVC form.

After a few months, I changed over to a 50 ohm, 1:1 ferrite balun rated at 5KW CW and built by Array Solutions of Texas. What little remaining RF I had in the shack was completely gone with this balun, and I do not notice any percepible heating (i.e. insertion loss) over room ambient with this very well made/high power handling capability device when running the AM legal limit. I would recommend it to anyone, and I would use it in place of a coaxial balun in any case.

Just my thoughts and personal experience. Your mileage my vary.

73,

Bruce

[KD3CN]

That's interesting Bruce.  I need to improve my tuner from breadboard/clipleads to something permanent, and was on the fence with the balun.  I guess I'll try a ferrite unit to save save space.  Thanks for the info!!!

For others interested in this balanced tuner design, you can buy a very good tuner from Palstar:
http://www.palstar.com/bt1500a.php

or, you can home-brew a unit, tailored to your antenna system:
http://www.somis.org/bbat.html

Personally, I really like this tuner, it only has two controls to diddle, and anything more gets too complicated for me!

73, Karl

[W2XR]

That's interesting Bruce.  I need to improve my tuner from breadboard/clipleads to something permanent, and was on the fence with the balun.  I guess I'll try a ferrite unit to save save space.  Thanks for the info!!!

For others interested in this balanced tuner design, you can buy a very good tuner from Palstar:
http://www.palstar.com/bt1500a.php

or, you can home-brew a unit, tailored to your antenna system:
http://www.somis.org/bbat.html

Personally, I really like this tuner, it only has two controls to diddle, and anything more gets too complicated for me!

73, Karl

Yes, my version also is based upon the Rich Measures design that appeared a number of years ago in QST.

I used a pair of turns counters salvaged from a Gates BC-1G AM BC rig in mine for easy QSY using a log chart/spreadsheet for frequency selection; one turns counter for the two mechanically-synchronized large E.F. Johnson roller inductors, and one for the 1000 pf @ 14 KV vacuum variable normally at the output of the network. I built the whole thing on a roughly 30" x 24" piece of MDF, so as to maintain the highest possible Q; a metallic housing or structure would degrade the Q of the roller inductors unless the housing was inordinately large. It truly works fine business, and also provides additional harmonic suppression for the output of my transmitter.

73,

Bruce

[KD3CN]

FB Bruce,

I will only use one turns-counter, for the inductors.  I have a 4.5KV 1000pF breadslicer for the capacitor.

For others considering building the tuner, you can pad the capacitor you have with a fixed-vacuum or doorknob cap to put you in tuning range.  To avoid heating effects it's best to stick with vacuum and air caps.  Looking at the Palstar tuner can give you layout ideas.

I've used this design in a plywood box, and clip-leaded together on top of a wooden shelf.  It's an FB tuner!

The ubiquitous link-coupled tuner is a mainstay, but this tuner should also be considered by the new builder!

73, Karl

[WA1GFZ]

I designed my fugly tuner in '82 when I lived in lA. and built it in '83 when I moved back East a few years before Rick invented it. I called it a dual L network fed 180 degrees out of phase. I had a 1:2 BB transformer then a coax  balun. both worked fine. Latest antenna wanted a 1:1 ratio on 160 so tried the coax balun.
I use a pair of large 22 uh inductors and a pair of 300 pf 10 kv cardwells. My Q is a bit high on 160 and could use more L.