900 MHz Quantar with low/no deviation

[n6mef]

I have a 900 MHz Quantar which was working and producing acceptable performance. But I had not run through the alignment procedure so I figured I should. I went through the alignment procedure screens, including: UHSO, Power, TX Deviation, and Reference Modulation Compensation. On all screens, I opened the HELP button on each screen and followed the instructions exactly. Only very minor tweaks were needed. Everything seemed to work fine and the SAVE actions were all accepted.

In particular on TX Deviation, the frequency one value was off by 0.05 and the frequency two value was off by 0.01. That's probably of no consequence and within the margin of error for my service monitor (IFR 2948B), but I entered the observed values anyway and saved as per the instructions. FWIW, the values were 4.20 and 4.33.

After resetting, the thing puts out next to no deviation - only 170-180Hz. Going back to the TX Deviation alignment screen, I see that the values I entered are still there. But now what?

I tried setting them really low (min is 1.82 so I chose 1.9), thinking that this would tell the system to deviate more. That didn't change anything. I tried setting them to 6. Still no change. I set them back to the values above. Still no change. I've powered off and back on the unit. I've pulled the SCM and Wireline cards and put them back in. Still no change.

The thing keys up fine and puts out the specified carrier power, but the deviation is just next to nothing. I'm certain that the problem is on the transmit side because when I command the external controller to speak (quantar is in Base mode), it keys up the Quantar transmitter but I hear no audio. I've talked to a couple of other folks with Quantars and they've never seen this. We're all stumped.

Is there a way to tell the SCM to reset the alignment data to factory defaults, or to otherwise tell it to start over? Any other suggestions?

Michael
N6MEF

[d119]

Program the station into it's normal bandsplit (commercial 900MHz. Pick a 938MHz frequency and opposing -39MHz receive frequency).

Align the station.

Program it back into the ham band.

Report back.

[KI4M]

I concur with D119 above on where to start first. I have had several Quantar Data stations I maintain completely lose TX deviation for no reason. Most of these just quit on their own and the RNC showed low #'s of messages passed for a week for no reason. In those situations I have changed probably 3-4 SCM's and 1 exciter. I found that adjusting the TX deviation in the alignment screen did absolutely nothing. When trying to do a Mod Comp there was no waveform present on the service monitor at all as well. If you have another exciter you might try swapping it out to see if that helps. If not try another SCM.

[n6mef]

That did nothing. It still only puts out 170 Hz of deviation.

[escomm]

Bad SCM imho

[d119]

Bad SCM imho

Agreed. If it won't align in it's native band, either the SCM or exciter have gone out, with the SCM being the likely culprit.

I've experienced SCM's die on reprogramming in the past.

[KI4M]

Do you have access to another SCM or exciter? If not do you have access to another Quantar/Quantro station, regardless of operating, band to test the SCM in? I just hate for you to purchase a SCM and it be an exciter or other way around. I would lean towards an SCM like the two other gents stated.

[xmo]

When you programmed the station to a commercial frequency - did it align and deviate properly on that frequency before you put it back on the ham frequency?

[n6mef]

Nope. Same 170 Hz deviation in the commercial band.
I just heard from another person that this same thing happened to him last weekend with a UHF system. I also heard from a reseller that they have had similar problems with other Quantars. Now I'm reticent to even touch the thing. If I put another SCM in and realign, it may break that one too.

[KI4M]

Nope. Same 170 Hz deviation in the commercial band.
I just heard from another person that this same thing happened to him last weekend with a UHF system. I also heard from a reseller that they have had similar problems with other Quantars. Now I'm reticent to even touch the thing. If I put another SCM in and realign, it may break that one too.

I maintain hundreds of Quantars in service and out of them are my listed failures over the past ~ 5 years. I would not hesitate a bit to try a SCM or exciter. Just observe ESD safe handling procedures and you will be just fine.