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Author Topic: Modified 20M Ground mounted MFJ Hamtenna  (Read 7721 times)
K1WJ
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Posts: 458




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« on: February 08, 2012, 08:46:53 AM »

Presently have a 20m MFJ Hamtenna (20m hamstick design) ground mounted 2ft above the ground, with single 1/4 wave counterpoise also 2 ft off the ground held up by tripod on insulator side. Works decent - many stateside contacts - Japan & others. Live in Arizona HOA.

Wondering if anyone has tried:

Using a MFJ 1600T mast extender at 4.5ft plus lower section of 10m hamstick then on top a 102in whip.

This would give me a more true size 20m 1/4 wave vertical - total length would be 16-17 ft.

Moving soon and looking to make a more efficient 20m antenna - anyone try this? I think may be interesting to try.

73 K1WJ David
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WX7G
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« Reply #1 on: February 08, 2012, 09:16:36 AM »

Your idea will work. You might also add three more radials and a 1:1 feedline balun to make it a true ground plane.
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K1WJ
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Posts: 458




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« Reply #2 on: February 08, 2012, 02:08:21 PM »

WX7G - Thanks for reply.

Yeah I have a coax balun on my present set up.

In a few months - I will give this a shot.

Understand about 4 radials v.s. 1, I have now.

Maybe someone out there has done this exact set up. Chime in.

73 K1WJ David - SUNNY AZ Cool
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KF6ABU
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Posts: 351




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« Reply #3 on: February 08, 2012, 06:33:11 PM »

that hamstick will not accept a very large diameter "stinger" in the top of it. Anything approaching 102 inches of width that will fit in that hamstick will just bend right over.

I have done something similiar though. 15ft or so of 1" EMT conduit as my mast, a typical cb whip mirror mount to the top of that mast, a 60 inch 3/8 threaded mast extension from dx engineering and a 102" cb whip at the top. I insulated the antenna mounting bracket from the conduit, and added 4 symetrical 20m radials to the bolts on the mirror mount going out at 45 degrees or so.

Worked ok as far as low verticals go.
« Last Edit: February 08, 2012, 06:39:36 PM by KF6ABU » Logged
KF6ABU
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Posts: 351




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« Reply #4 on: February 08, 2012, 06:41:15 PM »

also, you can’t just add length to a hamstick and expect it to resonate on other bands due to its new length.
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K1WJ
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Posts: 458




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« Reply #5 on: February 09, 2012, 07:02:52 AM »

I would be surprised if it bent over - a 102in whip is 4ft+-longer.

I figured a 102in whip + lwr section of 10M hamstick & 4ft extender mast would be correct for 20m.

Because I know the whip for the 10m hamstick is 4-4.5ft - therefore the bottom section should be the other half of the 10m 1/4 wave.

So 8ft + 4ft + 4ft = 1/4 wave for 20M - 73 K1WJ David Roll Eyes
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WX7G
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« Reply #6 on: February 09, 2012, 07:54:56 AM »

The 10 meter hamstick has almost no loading inductance. In fact it is about 1/2 uH.

Using NEC we see that to resonate your proposed antenna of a 4' mast plus a 10 meter Hamstick plus a whip requires a 93" whip. A bit of trimming of your 102" whip and your plan will be a success.

Another way to go is to mount the 10 meter hamstick on a 9' mast extension. The Hustler mast extensions (6' + 3') work great for this. 3/8" couplers are used to spice the mast sections together. DX Engineering stocks the Hustler components. Or simply mount the 102" mast on top of an 8' mast extension (6' + 2').
« Last Edit: February 09, 2012, 08:00:50 AM by WX7G » Logged
KB4QAA
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« Reply #7 on: February 10, 2012, 03:03:54 PM »

Best performance gain for the least cost and effort would be to add as many radials as possible.
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WB6BYU
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« Reply #8 on: February 10, 2012, 04:46:59 PM »

Quote from: WX7G
...
Using NEC we see that to resonate your proposed antenna of a 4' mast plus a 10 meter Hamstick plus a whip requires a 93" whip. A bit of trimming of your 102" whip and your plan will be a success.
...


Or install it as described and add a capacitor in series with the feedpoint to correct for it being
a bit too long.  It is easier to adjust the capacitor than to vary the length of the whip.  The longer
length will slightly improve the SWR.
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K1WJ
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Posts: 458




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« Reply #9 on: February 11, 2012, 08:45:21 AM »

Thanks for the input.

I like the fact that it should show as long on swr adjustment.

I'll just cut whip short as required to get around 1.5:1.

Having the right tool to cut the whip makes it easy to deal with.

Going to move soon so looking forward to changing antenna system a little.

You can see present set up on QRZ.com - K1WJ 73 Cool
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W7KB
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Posts: 57




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« Reply #10 on: February 12, 2012, 07:19:10 AM »

David:I am also in an HOA restricted community.What has worked well for me is a MFJ-1979 16.9' telescopic whip antenna.I have this very sturdy,stout whip antenna mounted on a mirror mount antenna bracket clamped to a  a 8' PVC pipe placed inside a metal tripod.The feedpoint is about 7' above ground and the two attached resonant radials are about 5' above ground @ 180 degs.apart.The vertical radiator and radials are measured for a full 1/4 wavelength for each band 10-20 meters.I consistently get great signal reports using it for either stateside or DX qso's including 5/9 reports into China,East Malaysia,Australia,New Zealand,Europe,Africa and elsewhere.This simple antenna just flat out works,and works fantastic.73..Dennis W7KB.
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K1WJ
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Posts: 458




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« Reply #11 on: February 13, 2012, 06:46:54 AM »

Thanks W7KB -

Does the telescopic whip stay where you put it? It seems like it would move over time.

I would like to have something around 1/4 wave on 20m - that would be great, & low profile.

I will have my new house in Laveen AZ around mid March - let the games begin......CQ - CQ - CQ........73 K1WJ David
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W7KB
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Posts: 57




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« Reply #12 on: February 13, 2012, 07:27:44 AM »

K1WJ:Yes,this antenna will stay as measured.You know how well the winds blow here in Arizona,so I have not tried using it above 15-20 mph wind speeds.This isn't like a telescopic antenna on a smaller transistor radio,it has tight tolerances in it's sections and at $59.95 the price is right,too.W7KB
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K1WJ
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Posts: 458




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« Reply #13 on: February 13, 2012, 11:35:26 AM »

Thanks, sounds good - I'll invest $60 & see how it goes. 73 K1WJ
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AE5QB
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Posts: 269




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« Reply #14 on: February 14, 2012, 03:09:40 AM »

The MFJ 16.5' stainless steel whip works pretty well.  Here is an example of an implementation by my friend Dave KD5FX.  He has some pictures of his backyard ground mount installation.  I have mounted a similar setup on top of my school for the School Club Roundup except I mounted it on a 5 foot tripod with the tripod sitting on top of a vent hood.  This puts the base of the antenna about 7' above the roof which is 30' up.  I have the radials sloping down to 4' and tuned to the middle of the 20 meter band.  I run it into an LDG tuner and it seems to be working fairly well.  I need to add a balun and would prefer a remote tuner but does work.  I have not done nearly enough testing to be specific so all I can say now is it does get out.

http://www.kd5fx.com/FXportable/fx_portable_antenna.htm

If money is not an object, the buddipole system is a great portable rig.  Or for less money the buddistick.  But these are not designed for permanent installation.  On the other hand there are a large number of verticals out there designed for this very setup.  The S9 31' will get you on 40 and up for a couple of hundred bucks including the ground radial plate and radials. 
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