Hi Lawrence,

you are very correct in guessing that receiver testing is done at VERY
low amplitudes of the test signals. Normally your RF generator is a very
heavy piece of equipment (both shielding-wise and price-wise) because it
has to be able to do +20 dBm (100 milliwatt) and also -130 dBm (less
than a picowatt) out of the same assembly.

Also there are different methods for determining the quality of
reception. This is easy for a receiver with an audio output: you listen
to the speaker or connect a SINAD meter to the signal.
For a cellphone it also works somewhat this way - you reduce the TX
power and at some amplitude the unit will not receive any more...
A digital receiver for Time standard signals sometimes has a lot longer
observation and acquisition periods - not so easy. And also your
"natural" RF signal should be blocked effectively, or your results are
worth less than zilch...

Hope this helps - more info available if not....

Greets

Jochen Feldhaar DH6FAZ

Lawrence Lile schrieb:
>
> How do people go about testing sensitivity of radio recievers?  I've got a
> batch of clocks that recieve a time code over WWV, and some of them "seem"
> to be less sensitive than others.  Some nights I'll see 5 out of 5 lock onto
> the WWV signal, other nights only 1 out of 5.  I don't have any calibrated,
> predictable way of saying "Yes, this reciever is sensitive enough".  Niether
> me nor my supplier has a good way to do this.
>
> I am imagining a transmitter, suitably armored in a really good faraday cage
> to prevent problems with the FCC, that I can turn way, way down in a
> measurable way, and test whether the reciever modules can pick up the
> signal.  I think this would be quite difficult to build.  A transmitter that
> fakes a WWV signal and transmits 100 mW would be trivial to build, but how
> about one that only transmits 0.01 microwatt?  I could see building the
> transmitter in a separate can, moving the 100mW signal through a coax to an
> attenuator, then through another coax into another can holding my product.
>
> What is actually a reasonable level of power that a reciever in the US might
> get from a transimtter in Colorado?  It must be vanishingly small.
>
> Hmmmm.....
>
> -- Lawrence Lile
> Sr. Project Engineer
> Salton inc. Toastmaster Div.
> 573-446-5661 Voice
> 573-446-5676 Fax
>
> --
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