[TowerTalk] VHF/UHF Transmitting Chokes

[Jim Brown]

On 3/7/2020 11:47 AM, Richard (Rick) Karlquist wrote:
> A logical question to ask would be:
> 
> As an alternative, would it be sufficient to simply
> bond the shield of the coax to the boom, such that
> there is a free-space 1/4 wavelength of coax
> between the driven element and the point of bonding
> to the boom?

I haven't looked at that.

> Also, it is surprising to see #31 cores at 50 MHz,
> as opposed to #43 or #61, as Fair-Rite recommends.

#61 is a much higher Q part, and both parts tolerances and winding 
tolerances come into play. I looked into Fair-Rite published data for 1, 
2, and 3 turns of #31 and #43 parts, and #31 looked the best on 6M.
> 
> I notice that the 6 inch diameter 2 turn loops
> have a free space electrical length of exactly
> 1 radian at 50 MHz.  Is that just a coincidence,
> or is that in some sense optimum?  

It's a coincidence. I looked at Fair-Rite's data, noted above, wound 
some chokes and measured, and liked what I saw.

Harold Wheeler
> coined the term "radianlength" and noted that
> it seems to be magic length where systems transition
> from lumped element to distributed elements, etc.
> 
> Keep up the good work.

Thanks for all the comments. That 6M antenna is now in the air, and the 
chokes are clearly working -- when I turn away from noise sources, they 
are GONE!

73, Jim