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

[Bob Camp]

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





On Oct 24, 2004, at 5:15 PM, Rbethman wrote:

> I agree!
>
> The use of "funny" feedlines and termination impedances makes for 
> interesting discussion "fodder".
>
> The diversity antenna requirements make this virtually impossible for 
> current use UNLESS you have massive real estate.  The space between 
> antennae being rather ridiculous.  Additionally it would require a 
> fairly large contigent of personnel to erect and maintain.
>
> I will be using this the same way I use all my HF receivers.  Simply 
> to receive the frequencies I use or monitor.
>
> The information received was gleaned from a prior employee of Northern 
> Radio.  All prints are indeed Northern Radio prints, and the cover is 
> DEFINITELY a Northern Radio Company cover, complete with Logo.
>
> Bob - N0DGN
>
> Bob Camp wrote:
>
>> Hi
>>
>> So we now have more than one radio running off of a weird impedance 
>> balanced line.
>>
>> Again with my favorite nagging question:
>>
>> What the heck kind of gear drove these inputs ?? There must be some 
>> sort of record out there !!
>>
>>     Take Care!
>>
>>         Bob Camp
>>         KB8TQ
>>
>>>
>>>      One item of note in the documentation.  The antenna input is 
>>> designed for 100 Ohm balanced line - in spite of the fact that it IS 
>>> an SO-239 connector.
>>
>
> -- 
> <                      Bob Bethman - N0DGN
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