[ARC5] Receiver sensitivity

[Scott Robinson]

Folks,

In wood German table radios, I have a very interesting exception:

The usual German radio circuit uses an ECH81 (triode-hexode) converter 
with separate oscillator. The Grundig model 4040, unique as far as I 
know, uses a dual triode mixer. Neither circuit uses an RF amp. I should 
go measure its noise floor, some day.

Now, about receiver noise measurement: I follow the usual commercial 
method. What you do is feed in 30% 400 Hz modulated RF and turn the RF 
level down until the output audio is 10 dB more with the modulation 
turned on than with it off. You do NOT turn the carrier off! If your 
receiver has noticeable hum, you might want to high pass the audio at 
200 Hz or so.

Measured this way, good SW receivers (My SX-28A and R-390A, for 
instance) achieve 2-3 microvolts generally.

I'll also suggest a test to do with any such receiver: connect an 
ohmmeter from antenna to ground and run the bandswitch through all the 
bands. This finds the band whose antenna coil primary got zapped by a 
lightning storm before you waste time wondering why one band is so deaf. 
Don't ask me why I know this...

Peace, good listening, and fond remembering of times when teh SWBC bands 
had all sorts of good stuff to hear.

/scott