[R-390] R-390A sensitivity measurements

[Cecil Acuff]

I've been contemplating a balun to go from the balanced input to the 
antenna/generator anyway.  Question is do I do a 2:1 or a 1:1.  Keep the 
radio at it's native 125 ohm nominal impedance or take it to around 50 ohms 
nominal which is what we are doing using current wisdom on the twinax 
connector to coax fabrication.

Cecil...
----- Original Message ----- 
From: <DJED1 at aol.com>
To: <ghayward at uoguelph.ca>; <r-390 at mailman.qth.net>
Sent: Wednesday, March 02, 2005 8:59 AM
Subject: Re: [R-390] R-390A sensitivity measurements


> What we old microwave guys are used to is having an impedance match 
> between
> components, so maximum power is transferred.   For newer equipment, we 
> almost
> always work in a 50 ohm system, and measure in dBm.   For older radios, 
> where
> the impedance is not 50 ohms, measurments were not so clearly defined. 
> This
> is true for the op-amp also, because its output impedance probably does 
> not
> match that of the receiver.   That's why I'm troubled by using resistors 
> to fudge
> the sensitivity measurement-it terminates the generator properly, by part 
> of
> the signal power is lost in the resistor.   I think we need a good 
> low-loss
> transformer to properly feed the R-390. Anyone have such a thing?
> Ed
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