Hi Jeff, Thanks for the info..... any idea about the complexity of the 'summing' device? Can I do with a resistor combo, then perhaps sub some from the actual generators' output?
Tim --- In Repeater-Builder@yahoogroups.com, "Jeff DePolo" <j...@...> wrote: > > > 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 > > > > > > > > > > >
