Doesn't this suggest that there is a role here for cut and try? Take a
set of clip leads to the base of the tower and experiment?
73, Pete N4ZR
The World Contest Station Database, at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at
reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000 and
arcluster.reversebeacon.net, port 7000
On 6/20/2012 3:45 PM, Herb Schoenbohm wrote:
> Tom,
>
> This is not encouraging news for those of us with towers already ground
> and are either shunt fed or cage fed. Even though they are not
> resonate, although top loaded and approaching resonance, it seems that
> even with some elaborate decoupling arrangements, and I hope I am wrong,
> not to much can be gained by even trying to get them "detuned". This is
> crucial for me to know, and I would assume many others that have
> Beverage terminations or feed points 100 feet away,
>
> Thanks for the warning as this summer I was going to install a HV relay
> on the shunt cage to ground....but as you point out it may not help as
> the grounded shunt or cage fed tower is already a noise source for close
> proximity RX antennas.
>
>
>
>
> On 6/20/2012 2:09 PM, Tom W8JI wrote:
>> There are two potential problems with this. As general rules:
>>
>> 1.) Grounding any antenna which is dependent on a ground system to be
>> resonant will maximize reradiation.
>>
>> 2.) Resonant elevated radials, even without an antenna connected, are
>> resonant and re-radiate.
>>
>> 3.) Things that are not resonant can still re-radiate.
>>
>> To minimize coupling from a resonant radial, the radial has to be
>> disconnected from ground and from other radials.
>>
>> Different systems can be different, and in some cases re-radiation can
>> actually cause a null that reduces noise, but the general rule is
>> self-resonant antennas with a ground (Marconi), or nearly self-resonant
>> antennas when grounded, should be floated. Other antennas can be terminated
>> in an inductor, capacitor, or opened, depending on the system.
>>
>> My 220 ft insulated tower, in the center of a four square, is "opened" by
>> shorting a specific length of coax to the "L" matching network. It has much
>> more radiation when open or grounded. radiation is minimal when detuned by a
>> proper impedance.
>>
>> 73 Tom
>>
>>
>>
>>
> _______________________________________________
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>
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