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

[Bob Camp]

Hi

So if this was all planned - are there any references to hooking up 
these radios to 120 ohm systems ? If they are out there I sure have not 
seen them.

	Take Care!

		Bob Camp
		KB8TQ




On Oct 25, 2004, at 10:32 AM, Rbethman wrote:

> 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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