[TowerTalk] Another Ground Radial Question

[Jim Lux]

-----Original Message-----
>From: pfizenmayer <pfizenmayer2 at q.com>
>Sent: Mar 18, 2011 2:08 PM
>To: Kshaddrick <kshaddrick at jetup.net>, towertalk at contesting.com
>Subject: Re: [TowerTalk] Another Ground Radial Question
>
>
>>
>> Somewhere in the distant past I read that the radials of one antenna 
>> cannot overlap those of another. Is this really true? There are some folks 
>> who indicate that if the radials are insulated it shouldn't be a problem. 
>> My issue is I have an existing vertical installation within radial range 
>> of a new tower installation. I plan to shunt feed the tower and if I can't 
>> overlap the existing radials from the vertical antenna, that will leave 
>> quite a wide area with no radial coverage for the shunt fed antenna 
>> (basically from east through south to the west, the vertical sits in the 
>> south east and the house covers the rest).
>>
>> Kelley - W0RK
>> _______________________________________________
>
>
>Antenna Engineering Handbook by Jasik says -
>
>" Individual ground systems are required for each tower of a multielemnt 
>array . If the individual systems would overlap , the adjoining systems are 
>usually terminated in a common bus."
>
>Under fig 20-16 showing radial systems for a two element array - It goes on 
>to state " The adjoining systems  do not overlap but are terminated in a 
>common bus."
>
> E.A. LaPort's Radio Antenna Engineering shows the exact same situation .
>


A broadcast directional array would be a good example of something where you want the mutual coupling to be very stable, since that determines whether your nulls and lobes stay pointing the right directions at the right levels.

In the broadcast world, the 120 radial thing is popular (because you can build it by rule, as opposed to needing to do a performance proof, for one thing), and what Jasik and LaPort were essentially saying is that you don't buy anything by overlapping the ground fields, since they're bonded together at the overlap.


For hams, with different antennas serving different bands, or not being used simultaneously, I doubt it makes a lot of difference one way or another.