[Milsurplus] Forest Service SPF radio detail

[Kenneth G. Gordon]

On 20 Nov 2020 at 1:59, Hubert Miller wrote:

> I was looking at WB6NVH's website pages on the Forest Service type SPF radio, and he gives the likely 
> output impedance of the transmitter as dealing with 100 ohm load. But - the SPF was intended to be
> used with either 1/2 wave endfed, or a Windom. I have just now looked at Windom antenna listings on
> the net, and I mean SINGLE-wire feed, not coax, but it seems every article is shy about giving the Z of
> the Windom antenna. I read that the original idea was to tap at guesstimated 600 ohm load. But I notice
> the commercial OCF antennas now offered have a 1:4 balun. I assume this is ohms ratio, not winding ratio?
> Otherwise the coax to antenna ratio would give 800 ohm antenna. If it's ohms ratio, then this assumes the
> antenna about 200 ohms. I don't know the exact impedance of an end fed 1/2 wave, and maybe no one
> else does either, but I assume around 1000 - 2000 ohm. So for the SPF article I mentioned above, I would
> instead state that the SPF is intended for antenna impedance of 600 to 2000 ohm. 
> What say?

One of my first antennas was an off-center-fed Windom, single-wire feed. My transmitter was 
a Heathkit DX-35, which loaded it just fine.

I suspect the impedance is 200 ohms, not 600, since as I recall it, the DX-35 wouldn't load 
into 600 ohms.

Ken W7EKB