Hi Dick,
I have 15 Beverage wires, 5 of which traverse within 50 feet of the main XMIT
shunt fed tower, and 3 of the wires are only 30 feet from one of the parasitic
160m elements.
(my JA, West, North, EU 45deg, and EU21deg wires)
I have the ability to do RX comparison tests of the noise level on each wire
with the parasitic elements or the tower “tuned” or not.
The noise floor rises noticeably by about 2 or 3 dB on those closest wires when
the parasitics are tuned. I use the Flex waterfall and spectrum display to
measure the noise increase and it is very obvious between tuned or de-tuned.
When the tower is “tuned” into shunt-fed mode, the noise will increase on two
of the closer wires but by a much smaller amount.
The question from many will be “well how do you know the noise is not still
somewhat elevated even when the elements are de-tuned?”
On all 5 of these wires, they are ONE of a broadside pair, and the other wire
in the pair is 400’ away. I have the ability with a relay switch box at each
phased feedpoint to isolate a single wire and therefore compare background
noise levels. In ALL cases, when the nearby radiators are de-tuned, the noise
level is identical to the other wire in the pair 400’ away.
Regarding shunt-fed tower de-tuning. I had spent a lot of time implementing a
complex de-tune circuit for my tower, but some years ago I realized that my
tower is no where near resonance on 160m without the shunt-feed in circuit.
Now, my "de-tuning” method is simply using a relay to disconnect the gamma wire
from the matching network on receive.
Of course my parasitic elements are most certainly resonant so those can be
simply lifted off ground with a relay to de-tune, but then they become resonant
on 80m!! Therefore, I now have a capacitor in series to ground which tunes
them somewhere around 2.8 mHz or so (I measured it but cant remember), and a
relay shorts this out to ground when they are “in-circuit” for TX.
73, de steve ve6wz
> On Jul 29, 2021, at 1:15 AM, RVZ via TowerTalk <towertalk@contesting.com>
> wrote:
>
> Hi Guys,
>
> I realize "the farther the better", but please advise the minimum recommended
> distance for a 460' Beverage mounted 7' above ground from a 130' high
> self-supporting steel Tower with a 2-element 40m. Yagi top mounted? Note:
> the Beverage won't be facing towards the tower. Is the Beverage likely to
> receive noise from the Tower with a separation of 100'? Thanks & 73, Dick-
> K9OMRLVZ@aol.com
>
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