[TowerTalk] Reflector in the back of shunt tower for 160m

[Ignacy Misztal]

I redid the simulations. WIth actual dimensions, the gain was 3 db
lossless, 2 db with 10 Ohm of extra resistance, and 1 db with 20 Ohm extra
resistance.

It took 3 hrs to make the reflector.I adjusted for resonance by feeding the
antenna with a wideband noise generator and receiving with beverages in the
back. The maximum F/B was only 6 db. Gain measurements were with KX3
located some 500 from the antenna; KX3 has a signal meter with a 0.1 db
resolution. The maximum gain was 1.7 db! Not perceptible and it did not
make any difference in the 160m contest.

Some of the loss is in a toroid coil made of type 2 material. It shows a 6
Ohm resistance. Perhaps can drop to 1 Ohm with air coils as used by Steve.

Ignacy NO9E



On Thu, Jan 27, 2022 at 12:19 PM VE6WZ_Steve <ve6wz at shaw.ca> wrote:

> Ignacy,
>
> I did notice that you were planning for elevated radials.
> Be aware that the gain and F/B of the array is very sensitive to parasitic
> loss.
> Ground loss will quickly diminish the current in the parasitic and the
> gain will crash.
> It’s easy to model this.  Just include a series resistance in the
> parasitic element and watch the gain and F/B drop.
>
> Field measuring the gain with on air tests can be difficult.  With only 3
> or 4 dB forward gain compared to the single vertical, it can be very hard
> to measure.  Even using RBN reports, QSB can easily mask this small change.
> However, 3 dB is, well…..3dB and it's like doubling your TX power.  For
> the really weak QSOs, when your signal is just bubbling around the noise,
> that 3dB can make the QSO.
>
> I recommend you read about my tuning method. It is not a trivial process
> to tune the parasitic to match the model.
>
> 73, de steve ve6wz
>
> On Jan 27, 2022, at 9:04 AM, Ignacy Misztal <no9e at arrl.net> wrote:
>
> Steve,
>
> Excellent work and sorry for missing it.
>
> I was thinking about a quick design. Elevated radials, not 100 ground
> ones. T coming from top of tower on ropes. Also 30m spacing so SWR
> changes less compared to the 20m and can be handled without extra matching
> by a tuner. If 4.5 db becomes 3 db it is still OK. If it drops to 1 db, not
> worth the effort. Perhaps I will experiment for the upcoming CQ 160 contest
> and report.
>
> Ignacy, NO9E
>
> On Thu, Jan 27, 2022 at 10:43 AM VE6WZ_Steve <ve6wz at shaw.ca> wrote:
>
>> Yes.
>> I wrote this paper about it. I talk about about modelling, design,
>> construction and about tuning the array:
>> https://drive.google.com/file/d/1eVklkZtlJW93JIJ9oDqbCyl-Jkik6YEX/view
>>
>> 73, de steve ve6wz
>>
>> On Jan 27, 2022, at 8:17 AM, Ignacy Misztal <no9e at arrl.net> wrote:
>>
>> I am trying to get some gain on 160m where currently I have a shunt fed
>> 100m tower. It works well but is not spectacular.
>>
>> I modeled a reflector some 100 ft away from the tower. Either as inv L
>> with
>> one elevated radial or T with two elevated counterpoises. EZNEC shows up
>> to
>> 4 dB gain as a reflector and up to 3 dB as a director. Is this realistic?
>> Has anybody done anything like that?
>>
>> Ignacy NO9E
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>