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Author Topic: Combination Vertical Counterpoise and Dipole antenna  (Read 820 times)
WY7CHY
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Posts: 635




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« Reply #15 on: November 09, 2017, 11:32:25 AM »

KM1H; I'm not going to argue this with you. And definitely not going to debate it any further. Maybe YOU should re-read what w8ji wrote. A counterpoise is one or more conductors used to simulate/substitute for earth ground that isn't there. That's even according to w8ji website.

But if you want to call an elevated substitute earth ground system for a vertical antenna "Radials" instead of "Counterpoise"; I personally don't give a darn. Feel free.

NOW.... Back to our regularly scheduled program.

For the rest of the replies; I appreciate the input. I think we all know and agree what a vertical antenna with a single element (single bent "L-Shape" dipole) should do. And we all agree on what an elevated vertical should do with proper counterpoise elements for the bands on it. But I guess I'm going to have to experiment and see what happens when I combine the two.

BYU. When you say the model said by reducing and shortening as described, they didn't appear to make any significance difference; are you saying: BOTH the 80m SHOULD act as the dipole in an NVIS situation; AND the 40m/20m with multiple ground plane elements, SHOULD act as a traditional vertical antenna? e.g. lower takeoff angle, etc...

Thanks. Mike
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
KM1H
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Posts: 2435




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« Reply #16 on: November 09, 2017, 01:00:44 PM »

Quote
KM1H; I'm not going to argue this with you. And definitely not going to debate it any further. Maybe YOU should re-read what w8ji wrote. A counterpoise is one or more conductors used to simulate/substitute for earth ground that isn't there. That's even according to w8ji website.

You wont get anywhere with myself or others who fully understand the subject my cherry picking "sound bites" from that paper. Continue studying without a closed mind.

Quote
But if you want to call an elevated substitute earth ground system for a vertical antenna "Radials" instead of "Counterpoise"; I personally don't give a darn. Feel free.

Since I prefer established definitions/accuracy to personal sentiment I certainly will.
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WB6BYU
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Posts: 17038




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« Reply #17 on: November 09, 2017, 02:17:38 PM »

Quote from: WY7CHY

BYU. When you say the model said by reducing and shortening as described, they didn't appear to make any significance difference; are you saying: BOTH the 80m SHOULD act as the dipole in an NVIS situation; AND the 40m/20m with multiple ground plane elements, SHOULD act as a traditional vertical antenna? e.g. lower takeoff angle, etc...



The group of 7 radials should act as a single radial for 80m and 3 radials each for 20m and 40m,
just as one would expect.  Basically, most of the current flows in the wire(s) that are low impedance,
in this case, close to 1/4 wavelength long.
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KK4OBI
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Posts: 106




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« Reply #18 on: November 09, 2017, 03:12:08 PM »

Michael,

If you "tune" an elevated radial, the total length including vertical an will be a half-wavelength per band.

For 80M the vertical is about 65 feet... which is already a half-wave on 40M, and two half-waves on 20M. This an impossible situation.

There is only one possibility for both 20M and 40M with one vertical and two pairs of tuned radials.  This can be done by first starting with a 30M ground plane then lengthen two opposing radials to be about 1.4 times longer (40M) and shortening the other radials to be about 0.7 shorter (20M). Fine tuning is done by both length and angle of radials.

A multi-band vertical must avoid tuned radials.
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KK4OBI - the Old Band Instructor
Google: Bob Roberts Society Band
WB6BYU
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Posts: 17038




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« Reply #19 on: November 09, 2017, 03:40:21 PM »

Quote from: KK4OBI

A multi-band vertical must avoid tuned radials.



I suspect you are imagining a specific case, as in general this statement is not true.

A trap antenna such as a 4BTV or 14AVQ, for example, is often roof-mounted with
radials tuned for each band.  The same would be true with multiple parallel elements
(a quarter wave on each band), a single whip with a remote tuner, and any of a
number of other antennas that would be expected to cover multiple bands.  In such
cases, an elevated system of radials tuned to 1/4 wavelength for each band is often
one of the better solutions.


If you are assuming a single straight radiator of fixed length with no additional traps,
loading or matching, and want to make the system resonant on multiple bands, then,
yes, it would usually require radials that are not 1/4 wavelength (except perhaps on
one band), but the radials can still be "tuned", that is, adjusted for lowest SWR for
the combination on the radiator and the radials on each band.
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W1VT
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Posts: 2477




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« Reply #20 on: November 09, 2017, 03:45:35 PM »

I used a trap vertical with a pair of elevated radials on each band to work Hong Kong on 20 meters--one of the more difficult RF paths from Connecticut.

Zack W1VT
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WY7CHY
Member

Posts: 635




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« Reply #21 on: November 10, 2017, 11:27:47 AM »

BYU, u r correct. I am talking about a multi band trap, similar to a 4BTV.

So, you’re saying, that even if I only use one element for the 80m, the others will interact, and therefor, the 80m will NOT act as a tilted dipole? Thanks. Back to the drawing board. Lol. But that’s what makes this fun.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
WB6BYU
Member

Posts: 17038




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« Reply #22 on: November 10, 2017, 12:14:10 PM »

Quote from: WY7CHY

So, you’re saying, that even if I only use one element for the 80m, the others will interact, and therefor, the 80m will NOT act as a tilted dipole?



No, that's not what I'm saying.

The single 80m radial will act like an 80m radial, forming a bent dipole, and will provide some
80m NVIS coverage (but not as good in the direction opposite the direction of the wire.  The
other radials can basically be ignored in this case.

On 40m and 20m the other radials work exactly as you would expect radials to work for a
vertical antenna, and the 80m wire has little impact on the overall pattern.

So it works the way you were hoping it would.  Seems like a good approach to me.
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WY7CHY
Member

Posts: 635




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« Reply #23 on: November 10, 2017, 01:35:46 PM »

Ok. Gotcha. Sounds good. I'll have to give it a try. Of course, the weather here will be the determining factor.

Thanks for everything.

Mike
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
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