Trouble adjusting M1225 deviation.

[cracked]

I'm looking for some help adjusting the deviation on a M1225 mobile. Following the instructions in the (Version 4) RSS, I injected a 1 kHz tone at 800mV RMS into the BNC port of the (Motorola) programming cable and it produced a deviation of only 3.3 KHz with the deviation soft pot turned to maximum. The RSS tells me I should be setting the deviation between 4.5 to 4.7 KHz. Am I doing something wrong here?

[HumHead]

Forgive the obvious question, but is the channel you are tuning on set for wide or narrow-band operation? It sounds like you may be working on a narrow channel. Also, is the X-Pand companding enabled?

[cracked]

The single personality I have programed is set for wide band (25 kHz) and X-Pand is disabled. When the radio is read for service, only 460.200 Mhz is used for the deviation adjustment. Is there some way to change the channel spacing used for the deviation adjustment?

[jackhackett]

What's it do with a mic on it? Give it the ol' "fiiiiiiiiiiiive" test.

[cracked]

The deviation* is nearly 7 kHz when the soft pot is set to maximum (31) and about right (4.8 kHz) at 23. This is of course on the programmed personality (447 MHz), not on the 460.200 used during the adjustment.

* "Measured" using the as-close-to-1 kHz-as-possible-feedback-into-microphone test.

[jackhackett]

I figured as much, I'm always suspicious of those 'inject so many milliviolts' tests, sometimes it's better to just give it a real-world test.

[Al]

I've seen the same problem using revision 4 of the 1225 RSS. I believe the software presets the unit you're testing to 12.5 khz parameters and doesn't allow resetting to 25/30 khz parameters. I just set deviation to 2.4-2.45 khz and after exitting the RSS double check with a service monitor on a 25/30 khz programmed personality for 7-800 hz PL deviation and 4.6-4.7 khz voice deviation. Unless there's something I've not seen in the help files, it's a software bug.

[Rayjk110]

Sort of OT, but, I've noticed that when using the black Radius Mics with these, they produce a horrid over-deviated, "sounds-like-you're-pinching-your-nose" type audio.

[Will]

I figured as much, I'm always suspicious of those 'inject so many milliviolts' tests, sometimes it's better to just give it a real-world test.

Agreed... "real-world test" with the mic.

The spec is 180 mV audio at 1KHz into the mic jack. There should only be a coupling cap in the 'box' on the programming cable between the BNC jack and the mic input.

The TX modulation should start to limit at 80 to 100 mV mic input, so run the audio input up from 60 to 180 mV and watch the mod on a scope looking for symetrical clipping/limiting.

[cracked]

Indeed, the problem is the version 4 software. I adjusted the deviation as if it were narrow band, and then a "real world" test showed 4.5 kHz. I guess that'll do.

[Bat2way]

Just curious, but why do all the hook-ups for the tone injection thing when you could just test it with speech, adjust, check again and be done with it in a couple of minutes?

[cracked]

Just curious, but why do all the hook-ups for the tone injection thing when you could just test it with speech, adjust, check again and be done with it in a couple of minutes?

Because there's a certain inaccuracy and non-repeatability involved with just yelling into the mic. I have three M1225 mobiles, any of which can and may be put into service as the exicter in my repeater, so I'd like to be sure they're all adjusted the same.