The holy grail for FM performance testing, which includes adjacent channel
rejection measurements, is EIA/TIA-603. I believe revision C is the latest.
Unfortunately, you'll have to pay to get a copy of that document unless you
can scrounge one up.
To summarize how the test is done (and I'm doing this from memory, so
someone please verify/correct me).
1. You need a way to sum the output of the two sig gens together such that
they are properly isolated from each other, and done in such a way that the
amplitudes can be calculated accurately at the output of the summing device.
2. You start out by measuring the 12 dB SINAD of the receiver with only the
on-channel signal generator active (standard SINAD test, 3 kHz deviation, 1
kHz tone, typically measured at the speaker terminals after
deemphasis/filtering/etc.). Simple enough.
3. Increase the RF level of the on-channel generator 3 dB higher than the
12 dB SINAD sensitivity value you found in step 2. This will push the
measured SINAD up higher than 12 dB obviously, that's what's supposed to
happen.
4. While still generating the on-channel signal, now also generate a signal
on the adjacent channel, modulated by a 400 Hz tone at 3 kHz deviation.
5. Increase the level of the adjacent-channel signal until you degrade the
SINAD reading of the on-channel signal back down to 12 dB (remember, it was
something greater than 12 dB, because you had increased the RF level by +3
dB before you started introducing adjacent-channel dinterference).
6. The difference (in dB) between the offending signal and the 12 dB SINAD
sensitivity measured in step 2 is the adjacent channel rejection ratio.
So, for example, if the 12 dB SINAD sensitivity was measured at -117 dBm in
step 2 without any interference, and you were back down to 12 dB SINAD in
step 5 when you had the interfering signal cranked up to -30 dBm, the
adjacent channel selectivity would be 87 dB.
--- Jeff WN3A
> -----Original Message-----
> From: Repeater-Builder@yahoogroups.com
> [mailto:repeater-buil...@yahoogroups.com] On Behalf Of tahrens301
> Sent: Saturday, July 24, 2010 10:27 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: [Repeater-Builder] Repeater receiver testing
>
>
>
> I have this lowband Micor receiver
> that I want to test for adjacent channel
> rejection.
>
> I have two calibrated signal generators
> and a calibrated spectrum analyzer if
> I need it.
>
> How can i measure the rejection of the
> off channel signal?
>
> Thanks,
>
> Tim
>
>
>
>
>
