Quantar SINAD and pre-selector alignment

[chrismec]

Hi all, been diving into Quantar's lately and been noticing on the two UHF radios we have that the SINAD will not get near 12dB when the radio is at full volume, even at power levels as high as -80dB. BUT, if I drop the volume down one notch the distortion level drops and I can get the 12dB at around -110dB. Being new to quantar's I performed the pre-selector alignment but this only seemed to make it worse. I tried with the calculated freq values as noted in the procedure first, then the actual frequency, same result. In the end I just adjusted the pre-selector by ear. Do any of you all have any insight you would care to share? Thank you!

[kb4mdz]

Just off the top of my head, I don't know that SINAD is defined at full volume; I'll look into it.

But that makes sense; every time I've run a SINAD test, I just set to volume control to a 'comfortable' level, maybe mid-range. And I'm not surprised by your results either, as audio chains in such simple radios as LMR (as opposed to your stereo) would distort at the maximum volume.

Remember, SINAD is Signal+Noise+Distortion, over Noise + Distortion. Bump up the volume control to max, you'll be introducing distortion other than that which is inherent to the audio chain, making your SINAD value useless.

What's your final RX level, in dBm or uV?

[MotoFAN]

Check papers for proper volume level. Most of SM describe that voltage Vrms you must set before measure SINAD, for e.g. 5 Volts peak to peak @ 8 Ohm load.

Also, you must have some adapter to measure SINAD - 2 caps and load (speaker emulation). The same scheme is published in many service manuals, including Motorola and Kenwood. Do you have it or just connected service monitor instead of speaker? If YES, it's wrong!

Also, -110 dBm @ SINAD 12 dB definitely is not nominal sensitivity. You must get something like -118 as minimum. But -119..120 is nominal.

Anyway, read Quantar manual and RSS help to ensure that you're precisely following the procedure.

[chrismec]

The adapter I am using to measure is a Motorola 3082059x01 (Amp 558461-1) and an Aeroflex 3550. The moto procedure states to set the volume to full. In the end, after the pre-selector alignments by ear alone on two UHF radios, 12dB sinad came in at -113dB on one radio and -122 on another. The second radio only came in after restoring air conditioning to the building! Before that its best was also -113.

[motorola_otaku]

The preselector in VHF/UHF stations is just a simple bandpass filter. It's much easier to tune on a spectrum analyzer with a tracking generator, which your 3550 should have. I've never had a problem getting one right on the nuts with >2dB insertion loss.

[jry]

the last place you want to check SINAD is at full volume.

Just about guaranteed to have distortion on the audio so the SINAD will be off as well.

Usually mid to lower audio levels provide the lowest distortion in the audio amp and a more accurate SINAD measurement.

[Karl NVW]

SINAD is measured at the rated audio output listed on the radio specification sheet, NOT wide open. And it's the last step in receiver alignment, after everything else has been peaked up correctly.