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Author Topic: 40 meter wire yagi at 30ft....worth it?  (Read 11441 times)
W6TGE
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Posts: 154




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« Reply #15 on: June 25, 2009, 07:07:41 PM »

Thank you Jerry.

"You should use a 1/4 wave section. For 20 meters that's 11.5 ft of RG11."

I am a little surprised as 11.5 Feet seems short for 20M 1/4 wave.
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K4SAV
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Posts: 1837




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« Reply #16 on: June 25, 2009, 08:57:12 PM »

1 wavelength  at 14.4 MHz = 69.76 ft.   (69.76/4) x .66 = 11.51 ft
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K4SAV
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Posts: 1837




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« Reply #17 on: June 25, 2009, 08:59:43 PM »

Darn typo.  Try again:

1 wavelength  at 14.1 MHz = 69.76 ft.   (69.76/4) x .66 = 11.51 ft
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W6TGE
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Posts: 154




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« Reply #18 on: June 26, 2009, 12:00:59 PM »

OK, so on 28.4 I get

34.65 X 1/4 X 0.66 - aan RG11 section of 5.72 Feet?
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W6TGE
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Posts: 154




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« Reply #19 on: June 26, 2009, 12:05:18 PM »

...also isn't the RG11 VF 0.75? You show 0.66, or am I missing something here. Can you imagine an 11DB antenna on 10M when it is open?
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K4SAV
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Posts: 1837




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« Reply #20 on: June 26, 2009, 01:42:08 PM »

RG11A (Belden 8261) velocity factor = 0.66
RG11 Foam (Belden 8213) velocity factor = 0.78

RG-59B (Belden 8263) velocity factor = 0.66
RG-59 Foam (Belden 8212) velocity factor = 0.78

It's only 11 dB gain in the direction it's pointed.  In other directions it will be lower gain than a dipole.

Jerry, K4SAV
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W6TGE
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Posts: 154




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« Reply #21 on: June 26, 2009, 07:11:48 PM »

OK...I am going to put my R5 6' off the ground and see how that works. Perhaps I can use it for the "bad" directions!
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AJ8T
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Posts: 2




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« Reply #22 on: July 19, 2009, 07:26:53 AM »

There's a correction in the August 2009 QST to his article in the July issue.  

See "Feedback" in QST or on the ARRL web page:

http://remote.arrl.org/qst/feedback/2009/08/

"In “A High Gain Single Wire Beam” [Jul 2009, pp 38-39], the author notes that the inductor should be in series with the center conductor of the coax, not across the coax. The resonant frequency, that at which the SWR is lowest, may need to be adjusted by adding or subtracting turns from the coil. In his case, on 20 meters, the coil only needed about 8 turns rather than 26 turns. If the inductor is in parallel, the antenna will work, but the SWR will likely be about 3 to 1."

The original looked wrong to me too.

73

AJ8T
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W4VR
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« Reply #23 on: July 19, 2009, 01:31:03 PM »

I had a 3-el 40 mtr wire yagi at 30 feet for many years in the 1970's.  I lived in VA and used to chat almost every evening with stations in CA.  I also had a dipole to compare with and the difference was very significant on both transmit and receive.  That should work well for you.  Try it and find out for yourself!  I still use wire yagi's on 40 but they are up a higher than 30 feet. I have a 2-el beaming east and a 3-el beaming west, all using pine trees for supports.
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WB5VBB
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Posts: 19




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« Reply #24 on: July 21, 2009, 10:49:56 PM »

I built one using 20 and 44 with 13 feet of 600 ohm ladder line. I fed it with 80 feet of 600 ohm ladder line with hopes of making it multiband. SWR not great on 20 would like to change frequency of operation.  I think I could use the built in tuner with it.  Looks like maybe even on 160.  Should I change measurements back to closer what is in article instead of 20 and 44.

I have a antenna analyzer and I can sen you my file if you have a aim 4170.

Thanks
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WB5VBB
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Posts: 19




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« Reply #25 on: July 21, 2009, 10:53:15 PM »

I almost forgot my antenna is about 55 feet up.
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WB5VBB
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Posts: 19




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« Reply #26 on: July 21, 2009, 10:57:22 PM »

I had written the author of the QST article and for single band operation using the inductors, should have one in each lead.
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KA3HIE
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Posts: 9




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« Reply #27 on: July 26, 2009, 10:34:45 AM »

Wonder how one of these(wire beam) would work on 6m, say 50.100.

In order to complement a beam, could face ne/sw maybe to pick up a weak eu signal otherwise unheard.  I realize this is likely double hop Es and not F2 prop.


Could get it at least 50 feet or so.  
Jerry, any measurement advice using the rg11??

thanks, rob
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K4SAV
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Posts: 1837




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« Reply #28 on: August 02, 2009, 04:52:07 PM »

In reference to the HGSWB from July QST by AL7KK, I just received a note from AI2S forwarded from AL7KK with information generated by N6RY that said the currents in the stubs are not equal and so the calculations listed in QST which are based on simulations are off.  He is indeed correct.  Unfortunately I also made that same mistake when I modeled it.

EZNEC transmission lines are mathematical models.  They do not radiate, and any current forced in one of the wires is immediately returned out that wire's return line.  That is not the way this stub works, so you can't model it with a transmission line.  Those vertical stubs do radiate a little due to unequal currents in the pairs, but the second stub mostly cancels out the first one, so if they are both vertical the result is no significant radiation.

To prove that, I modeled the antenna using wires for the stubs and eliminated all transmission line models.  The 20 meter antenna (without inductors) at 35 feet resonated on 13.8 MHz with a feedpoint impedance of 193 ohms.  Big difference from the transmission line model which made the antenna resonate at 15.2 MHz (without the inductors).

AL7KK's suggestion was to remove the inductors and add a 4 to 1 balun, and cut 6 inches off the stubs for the 20 meter version, and scale that for the other bands.  In my model I had to remove 10 inches, if 450 ohm line was used.

Since my alternate model suggested earlier is also in error due to the same modeling error, rather than fix that error I will offer what I think is a better suggestion (which I should have included the first time but didn't).   The gain claim of the HGSWB is slightly inflated due to modeling over a Mininec ground and not including attenuation loss of the ladderline stubs (amounts to about 0.9 dB).  He also calculated the gain over the best ground available except for salt water.  If you take that into consideration and compare antennas on a equal footing, then the HGSWB has less than 0.5 db more gain than an Extended Double Zepp.  That includes the loss due to a matching section line for the EDZ.  The EDZ is significantly smaller and less complex.  The radiated patterns are virtually identical.

Jerry, K4SAV
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