[Elecraft] Receiver impedance?

[Wes]

About 40 years ago I was a Responsible Engineer for the Phoenix Missile 
Receiver/Transmitter Unit (RTU). This was a monopulse radar and my unit fed ~30 
MHz i-f signals to the following Electronics Unit (EU) which did the signal 
processing.  The EU test position had a Collins 51S-1 receiver in it just to 
measure the output levels of the RTU.  As usual there was always finger pointing 
when specs weren't met.  As a referee a PhD was brought in to analyze the 
interface of the two units.  At one point he focused on the input match of the 
51S-1 and since I was the RF guy, I was asked to measure it.  The numbers are 
fuzzy but suffice it to say, he wasn't happy and asked me to fix it.  I gathered 
up some General Radio airline stuff and built a double-stubbed tuner and got it 
to about 40 dB return loss.

He came back about an hour later with two pages of equations, written in 
mouse-type that almost required a magnifier to read, and happily announced that 
his "quick analysis" showed that the error would be some (unmemorable) fraction 
of a dB.  Everyone was happy.

I never had the heart to tell him that the minute the AGC activated, all bets 
were off.

So the answer to the question is, it depends.

Wes  N7WS


On 5/25/2022 11:18 AM, Walter Underwood wrote:
> Thanks. I’ll make a wild generalization that transceivers are generally designed for the receiver portion to be 50 Ω.
>
> Anybody have an idea about SWL receivers?
>
> wunder
> K6WRU
> Walter Underwood
> CM87wj
> http://observer.wunderwood.org/ (my blog)
>