[TowerTalk] How to mod a 40m 4-square for 10m use?

[Lux, Jim]

On 1/22/22 6:53 PM, Michael Tope wrote:
> Mike,
>
> This presentation goes into excruciating detail on how to make all the 
> necessary design calculation to setup and optimize the Comtek style 
> hybrid in a 4 square array: 
> https://www.kkn.net/dayton2011/Demystifying%20the%20hybrid%20coupler-vers-FOR%20k3lr.pdf
>
> The presentation focuses on an 80 meter design, but there should be no 
> reason you can't change the frequency to 28 MHz and re-run the 
> calculations to scale it for 10 meters. Without diving into the 
> details of the design, the extent to which stray reactance in the 
> layout and frequency dependent component limitations compromise 
> performance at 28 MHz is not clear to me. It sounds like a fun 
> experiment. 


This is really useful..

And with cheap VNAs, dialing it in (if needed.. it's critical for nulls, 
not so much for forward gain) would be easier.


What I've done for these things where you have frequency dependent 
networks is run NEC from a python script that generates NEC input files 
for each frequency. Then, another python script extracts the numbers of 
interest from the output file(s).

In fact, you can run multiple different models in the same NEC run - XQ 
card runs the model, then a bunch of new LD and NT, then XQ again.  As 
long as the *geometry* is the same, it's pretty fast (because the hard 
part is computing all the couplings between the segments in the physical 
antenna).  A change in frequency changes the interaction matrix.

And it lends itself to parallelization on a cluster, if you have access 
to one.

If someone wants copies of my codes, let me know, and I can send them to 
you.