No, I didn't say the same thing.
I didn't say that it was required for the system to be resonant, and it
isn't. It is just trickier (sharper tuning) to tune any sort of
off-center feed to resonance if that is your objective. I (and others)
also said that you could use a matching network, either at the feedpoint
or in the shack, to feed the vertical against a counterpoise even if the
system wasn't resonant.
To be clear ... it is not necessary for the radials themselves to be
resonant for the antenna system to be resonant (you can adjust the
length of the vertical element to make it so), and it is not necessary
for the the antenna system to be resonant for it to work properly if you
are willing to use some sort of matching scheme to feed it.
Dave AB7E
Gary Schafer wrote:
> I said that "A vertical above your beam will not work. An elevated vertical
> must have resonant radials". At the end of your post you say the same thing.
>
> With a quarter wave vertical mounted on the mast above a tri band beam You
> would be very lucky if the beam provided a resonant radial system.
> While it is true that you can use a combination of matching networks to tune
> the combination and get it to work, it is not an easy task.
>
> I agree that neither the ground plane nor the vertical element need to be
> resonant in order to radiate. However getting power into a combination that
> does not present resonance requires matching networks in order to bring the
> feed impedance close enough to the feed line impedance in order to avoid
> large losses.
> Simply sticking a vertical on top of a mast above a beam is not going to do
> the job unless luck is with you.
>
> I tried doing this very thing several years ago. Played with it for a couple
> of weeks and never could get anything close to a match. Then one day I hung
> a quarter wave wire from the ground side of the feed at the vertical and got
> a decent input impedance.
>
> 73
> Gary K4FMX
>
>
>
>> -----Original Message-----
>> From: towertalk-bounces@contesting.com [mailto:towertalk-
>> bounces@contesting.com] On Behalf Of David Gilbert
>> Sent: Wednesday, October 21, 2009 11:39 PM
>> Cc: towertalk@contesting.com
>> Subject: Re: [TowerTalk] Ground mounting vs roof mounting verticals
>>
>>
>> That's not really true. Elevated radials don't have to be resonant for
>> an antenna to work well, or even be resonant.
>>
>> It is possible, for example, to have the COMBINATION of the vertical
>> element and the radials be resonant ... the feedpoint impedance will
>> just be higher than the classical 33 ohms. Think off-center fed
>> vertical dipole, except with a portion of the lower part of the "dipole"
>> splayed out. I've built antennas that way and I've modeled them with
>> EZNEC as well ... it works. Several hams have compensated for a
>> not-quite-quarter-wave vertical by making the elevated radials longer
>> than a quarter wave, and it works the other way as well (longer
>> vertical, shorter radials). Either way, tuning is a bit trickier than
>> if the vertical element and the radials were each a quarter wavelength,
>> though.
>>
>> And, of course, if the combination of the vertical element and the
>> radials is not resonant, it will still work fine if you use the proper
>> matching network to feed it.
>>
>> As far as feeding a vertical element against a yagi for a ground plane
>> .... well, that's pretty much a crap shoot and it would take a lot of
>> trimming of the vertical element if you want to make it resonant.
>>
>> 73,
>> Dave AB7E
>>
>>
>>
>>
>> Gary Schafer wrote:
>>
>>> An elevated vertical must have resonant radials.
>>>
>>> 73
>>> Gary K4FMX
>>>
>>>
>>>
>>>
>> _______________________________________________
>>
>>
>>
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>
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