Dave
So where is the optimum place to place the ferrites for this antenna if you
have a problem like Alan described?
Does the near field extend roughly to half the stacking distance of that
antenna (i.e. 6 feet or so), making that the best place for the ferrites?
Does a mostly vertical coax passing through the near field of a horizontally
polarized antenna (i.e. an antenna side mounted to a tower) need ferrites?
Do you need to decouple ALL of the rest of your coaxes and control lines at the
lower near field edge of that antenna (or at some other point)? I have heard
that argument (decouple everything) made to improve performance of inverted L
antennas on 160 meters located near a tower.
73, Mike, W3IP
On Saturday, October 31, 2020, 10:04:48 AM EDT, David Olean
<[email protected]> wrote:
Hello Alan
That was my antenna design. It has a teflon coax 1/2 wave balun that
kills RF on the shield side of the coax, but there is not much you can
do about near field energy getting picked up by the outside of the coax
due to radiation. It is best to tape the coax down snugly along the
boom and masting etc. Still, it does not hurt to add more RF chokes to
any antenna! It is pretty easy for RF energy to get impressed on the
outside of the coax in any typical installation. The balun at the
antenna only keeps the energy from the coax center conductor from going
to the outside of the coax at the feedpoint.
The way I check for decoupling effectiveness is to match the antenna
really well, and then run your hand along the outside of the feedline
near the feed. While looking at the screen of a network analyzer, you
can see little perturbations in the return loss 20 or 30 dB down if
there is RF leaking to the outside of the feedline. This is a
qualitative test and you can estimate the bandwidth of the decoupling
network. You will see larger return loss change amounts away from the
resonant frequency of the decoupling element. This won't apply to
ferrites, as they can be broadband, but with a quarter wave choke, or
similar, you can definitely see the effect.
73
Dave K1WHS
On 10/31/2020 5:39 AM, N3ALN wrote:
> Hum, I was getting this HI CUR error only with my Directive Systems 6 Meter
> antenna (DS50-5) that has a 1:1 SWR I hope they know antenna design? Maybe
> not? The toroids fixed my issue. I just love how some of the forum or so
> judgmental, it is a only a freaking hobby, chill.
>
>
>
> --
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