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Author Topic: hygain av 18vs  (Read 5678 times)
W3TEZ
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Posts: 32




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« on: April 03, 2010, 08:45:34 AM »

i have major antenna restrictions where i live here in buffalo ny. i was looking at the hygain av 18vs because it was about the same size as the antron 99 i plan on taking down off my roof that i plan to replace with the hygain 18vs. now i have heard of a few people removing the loading coil for the bands and just attaching the stub directly and letting an antenna tuner do the work. i am just curious how good this will work.
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N3LCW
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« Reply #1 on: April 03, 2010, 09:22:32 AM »

It works very well.  I ground mounted my av18vs in between trees for cover, attached the SGC-239 auto tuner at the base, and used 2 counterpoise wires 35ft long laying on the ground.
The antenna loads up and works great 10-40M.

Andrew
N3LCW
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WX7G
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« Reply #2 on: April 03, 2010, 09:24:02 AM »

If you use an autotuner at the base it should work well on 40-10 meters.

Tuned at the shack through a length of coax you will have additional transmission line loss. You'll have to balance convenience against performance.
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KA1YUW
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« Reply #3 on: April 06, 2010, 06:16:38 PM »

if you want to work on 80 meters make sure your radials are about 67 ' long and the more the better.
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WB6BYU
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« Reply #4 on: April 07, 2010, 12:55:55 PM »

Any sort of vertical radiator of the same height would work about as well.
If you are going to use a remote autotuner right at the feedpoint to the
antenna, you can get by without the coil.  (You still need an effective
ground system, however.)  If your tuner is in the shack at the other end
of a long piece of coax, the losses may be rather high on some bands.
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WX7G
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« Reply #5 on: April 07, 2010, 08:15:13 PM »

Roof mounted you will need two resonant radials per band to have any decoupling of the feedline shield.

Ground mounted a dozen or more radials 20' long will do the job.
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KA1YUW
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« Reply #6 on: April 08, 2010, 06:03:59 PM »

I used this vertical for many years ground mounted with 67' radials so I could operate on 80-10 meters and had 50 of them. WX7G is wrong about the 20 foot length. It would be ok if you only operated on 20-10 meters with a 20' length but will not work on the lower bands. On the roof mounted he was correct. I plan to build a 23' vertical this year something like the av18vs and operated it 160-10 just like the old Gotham vertical I use to use also. If you use an antenna tuner make sure you mount it right next the the antenna to replace the coil. If you plan only to work 20-10 you can add 1/4 stubs for the other bands and make the main part of the antenna 1/4 wave for 10. Then you won't need any antenna tuner. I have done this before and works great.you can use wire for the stubs. And WX7G I suggest that you go to HRO or AES and pick up the ARRL Antenna hand book and read up on the chapter on ground mounted verticals. I think you just might learn something so the next time you can give the correct answer to someone else who needs help!
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WX7G
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« Reply #7 on: April 08, 2010, 07:32:02 PM »

Ground mounted the radials can be any length. In general a length equal to the antenna height offers maximum performance for a given amount of wire when less than one to two dozen radials are used.

Configured as a ground plane antenna it does require two or more resonant radials per band.
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KA1YUW
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« Reply #8 on: April 09, 2010, 04:33:05 PM »

WX7G you are very wrong! A multiband vertical ground mounted you use 1/4 wave length radial of the lowest freq. and the more the better.
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N3LCW
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Posts: 149




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« Reply #9 on: April 09, 2010, 05:47:02 PM »

No, WX7G is not wrong.  I've also read about and studied the models that show losses with ground mounted verticals are minimized when using a modest number of radials as long as the radiating vertical itself.  Adding longer numerous radials will certainly help but it is a matter of the law of diminishing returns.  You can prove this for yourself using an antenna analyzer and watching the ground losses lower as you add 8-16 short radials.

I did an experiment last year with my av18vs.  I ground mounted it using only an 8ft ground rod at the base for ground.  I matched it on 40M using the supplied base coil and made many contacts, stateside and DX, with excellent signal reports.  The 2:1 SWR was the whole 40M band which told me there are ground losses.  I added a second 8ft ground rod at the base with the same results and less bandwidth (ground losses lower).  I then added two 33ft radial wires (since I had the room), retuned the coil, and still had excellent results with even more reduced bandwidth (lower losses still).  I consistently made DX contacts on all modes on 40M with this antenna hidden between trees.  Of course a vertical with 120 full size radials will squeeze every last bit of efficiency out of the signal but that should not be the driving factor for limited space operations.

My point is this:  let us NOT discourage people from trying a ground mounted vertical by letting them believe the only way they will achieve good results will be using an extensive radial system.  That simply is not the case.  

Install the antenna where you can, attach the autotuner, give the autotuner the required counterpoise it requires, and enjoy operating!

Andrew
N3LCW
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AD6KA
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« Reply #10 on: April 13, 2010, 06:25:30 PM »

KA1YUW
"A multiband vertical ground mounted you use 1/4 wave length radial of the lowest freq. and the more the better."

Cutting a ground mounted radial to 1/4 longest wavelength is meaningless, and a waste of time spent measuring. Those radials are capacitively coupled to the earth so in no way can they **ever** be resonant.

But if you have a CHOICE or LIMITATION, it's much better to have many more shorter radials than a few long ones. By far the highest ground losses will be close to the base of the antenna, no matter what frequency you're operating on. So it's best to have that close in area covered with as many radials as possible.

There is a MUST READ article in a recent QST about the
gain in efficiency of ground verticals in regard to number and length of radials. You'll also be surprised about the gain in efficiency of raising those radials 3-4 feet off the ground.
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WX7G
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« Reply #11 on: July 12, 2010, 12:06:24 PM »

WX7G you are very wrong! A multiband vertical ground mounted you use 1/4 wave length radial of the lowest freq. and the more the better.

There isn't a set radial length that is optimum for a ground mounted vertical. Quarter wavelength radials are to be avoided unless you are installing 4 or more wavelengths of radial wire. This is 16 quarter wavelength radials. In his paper Radiation Resistance Variation with Radial System Design (Rudy Severns), the author points out the extra losses due to resonances in 1/4 wavelength radials. This is illustrated in Figure 10.

Rudy covers the 1/4 wavelength radial issue again in his power point presentation HF Vertical Antenna Ground Systems where he gives an example where cutting the 1/4 wavelength radials shorter increases gain by 4 dB.

His paper Radial System Design And Efficiency in HF Verticals, Figures 5 and 6, shows how long radials should be for maximum gain given a set amount of wire. For example, for a 1/8 or 1/4 wavelength vertical with 4 wavelengths or less of radial wire the optimum radial length is 1/8 wavelength. Given 8 or 16 wavelengths of radial wire the optimum radial length is 1/4 wavelength.

I have a vertical that is 1/4 wavelength tall on 14 MHz and 1/8 wavelength on 7 MHz. The 64, 20' radials amount to 9 wavelengths on 7 MHz and 18 wavelengths on 14 MHz. 20' radials just about maximize the gain on both frequencies given 1300' of radial wire.
« Last Edit: July 13, 2010, 09:35:37 AM by DAVE CUTHBERT » Logged
N4UM
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Posts: 472




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« Reply #12 on: July 12, 2010, 04:17:01 PM »

KA1YUW:

Wise Chinese saying... "Engage brain before putting mouth in gear." Roll Eyes
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WX7G
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« Reply #13 on: July 12, 2010, 08:34:42 PM »

I took additional measurements of my test vertical and I stand by my advice to make the radials as long as the antenna is tall. If one wants a more conservative rule-of-thumb use this one: Make the radials 1/8 wavelength at the lowest frequency of interest.

My test antenna consists of an 8' to 20' vertical with 64 20' radials. These radials are 0.07 wavelength on 3.5 MHz, 0.14 wavelength on 7 MHz and 0.28 wavelength of 14 MHz. The measured ground loss resistance is approximately 10 ohms on 3.5 MHz and 15 ohms on 7 MHz.

The N6LF papers do not include data on short verticals such as this. This is where, other than my data, there is a gap in our knowledge. I might as well make a project out of this and perform more detailed experiments along with more simulations and publish the results.The bottom line here is that a good ground system can be built using relatively short radials; 1/8 wavelength or less. Hams who do not have the room for 1/4 wavelength radials can rest assured that they can obtain good performance with an abbreviated radial field.

Radial Installation: The biodegradable plastic lawn staples from DX Engineering (100 for $16) are great for holding radials into a lawn. I place one every 6'. Soak the lawn first so they will push into the ground without breaking. 200 staples took care of 1300' of wire. Have an extral bag of staples on hand to add as radials pull loose due to walking on the lawn. 

« Last Edit: July 13, 2010, 09:38:00 AM by DAVE CUTHBERT » Logged
WW5AA
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Posts: 2086




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« Reply #14 on: July 13, 2010, 06:03:19 AM »

W7XG wins here...ground mounted antenna radials are not resonant at any frequency...the longer the better.
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