[Boatanchors] Receiver sensitivity

[w8au at sssnet.com]

At 12:13 PM 07/21/2004, William L Howard wrote:
>Using 1940s technology, how does one determine the sensitivity of a
>receiver?

Bill:

It's not much different than today, except simpler.  Back then there was no
test for "distortion," just "signal to noise" ratio.   And, the reference point
was typically 10 dB.

U need a sig gen (calibrated output, of course), the receiver, and an AC 
voltmeter,
preferably calibrated in dB.  Even a Simpson 260 VOM will do in a pinch.

The sig gen impedance (Z) should match the Receiver input Z, and the audio 
output
of the receiver should be terminated with a load resistor to match the 
output Z, say
500 ohms, or whatever.   (usually not 8 ohms in old days)

With RX on, (either AM or CW; you will get different readings from each 
mode) set
the output (with no signal input) for a reference value....  ("0" db?)

Inject RF from sig gen, until output goes up 10 dB.   Read uV from 
attenuator dial
on sig gen.  This is the sensitivity value. (for 10 dB S/N ratio)

This will probably change as you go higher in freq on the old sets.  It 
will get a bit
worse....

Perry    w8au