[R-390] SP-600 - NRC Type 159 - Radio R-450/FRR-28

[Rbethman]

Perhaps the documentation makes more sense then.

The diversity antenna system recommends the use of rhombics BEFORE 
talking about others.

With what you've just written, that MAY be the reason.

Bob - N0DGN

Bob Camp wrote:

> Hi
>
> I have no doubt that the radios were deliberately designed for 100 or 
> 120 ohm feed. I also have ample evidence that they work perfectly well 
> when re-aligned for 50 ohm use. There is a ton of gear out there that 
> hooks to these radios when run with 50 ohm feed.  There is also a lot 
> of evidence of these radios being used in 50 ohm setups.
>
> Back to the original question - why go to all the trouble of designing 
> them for 100 or 120 ohms and then use them at 50 ohms?
>
> Most of the theory work on coax cables was done in the 1930's. The 
> relative merits of 50 and 75 ohm lines had been figured out before the 
> start of WW 2. The 50 ohm coax thing was not an invention that came up 
> some time in the mid 1950's after the radios were designed. The basic 
> impedance data on antennas dates back at least into the 1920's and in 
> some cases long before that. Again it's not something people 
> discovered in the mid 1950's.
>
> Obviously there are antennas like rhombics that you can match with a 
> 4:1 balun to 100 or 150 ohms and get a fairly good match. There are 
> also things like a full wave loop that are a better match to a 100 or 
> 150 ohm line. Obviously a number of radios were used with rombics.  I 
> have not seen a lot of data on full wave loops.
>
> Was the whole balanced input, high impedance input driven by some kind 
> of direction finding set? If so there must be data out there on them. 
> Was there a standard wire antenna that worked into a 100 or 120 ohm 
> impedance? Again there should be data on it.
>
> If 100 or 120 ohms was important enough to design all the radios for 
> that impedance there *should* be data to support the decision ....
>
>     Confused ....
>
>         Bob Camp
>         KB8TQ

<                      Bob Bethman - N0DGN
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