Re: Topband: Inverted J antennas?

[Grant Saviers <grants2@pacbell.net>]

For a portable helix loaded 160m vertical, I measured 1 and 2 127ft 
radials at 3.5ft and 6.5ft above ground (average or worse) and found a 
significant difference in the resonance R.
1 radial 3.5ft 50 ohms
1 radial @ 6.5ft 33 ohms
2 radials @ 6.5ft 28 ohms

Which quantified the change in ground loss for this situation.  The 
perfect ground R was about 11 ohms for this vertical design.  More 
radials higher will further reduce ground loss.
Two radials at 10ft or higher for a decent height (>70ft) T or L will 
work pretty well and only be a couple db or so down from the recommended 
8+ much higher.  N6LF has the plots on his website.
NEC2 models verticals with elevated radials pretty well, and can compute 
the theoretical R over perfect ground.  Then with the radials you can 
afford or fit the antenna can be modeled and the efficiency compared.
Grant KZ1W

On 1/12/2021 10:48, sawyered@earthlink.net wrote:
> Mike,  All ¼ wave verticals have the same elevation angles.  The question is
> what is the feedpoint efficiency which is dominated by the ground.  That
> ground is a combination of your soil characteristics and the radial field
> design.  In my opinion, 2 elevated radials about 5 ft above the ground is a
> poor ground system for good performance.  Elevated 160M radials really need
> to be more like 20 – 25 ft above the ground to be efficient.  Otherwise, my
> experience has been you are way better off putting a lot of them on the
> ground vs a few in the air – below 10 ft.
>
>   
>
> One thing to try is take a Z + R reading at the actual feedpoint as it is
> now and add 2 more radials.  If the R drops by more than 0.5 Ohm, then keep
> adding.
>
>   
>
> I started with an R of about 24 Ohms with 4 radials on the ground and got it
> down to 12 Ohms by adding radials.  I have 44.  I could not see any
> difference with the last 4 so I stopped.  I have 2 T top verticals in phase
> and they are 260 ft apart.  And the same result occurred on both.  That is
> highly a function of my rocky (Granite) soil here.
>
>   
>
> 73
>
>   
>
> Ed  N1UR
>
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