Batboard

I have recently acquired a VHF GP360 which is the European equivalent of the HT1250. The GP360 was manufactured in April 2001 (749TBG****) and has firmware version R03.01.22 and CP 4.3

Using an external antenna, the GP360 works very well and has excellent sensitivity.

Using a set top helical, I am getting processor noise on weaker signals. I can monitor the interference using a separate AM receiver. The interference appears to be greatest around the LCD of the GP360.

I researched the archives and found mention of processor noise on HT1250's made around 1999. The solution was a firmware update, a better antenna and some mods around the antenna matching circuit.

I am already using an ex-GP300 VHF antenna which works very well on other radios.

Any thoughts on whether the internal VHF interference is firmware related? I've searched the internet and can find no comments. My initial thought was poor screening?

I have had similar "processor noise" issues with radios made by other manufacturers - I tested 4 identical UHF sets , 2 of which were new , and manufactured over a 4 year period, and they all generated 5-8dB of wideband hash between 430-440MHz completely blocking out weak signals when using the set top antenna - but worked OK using an external antenna.

The Moto GP360 is receiving weak signals OK but there is processor noise on the weak signal. Is a firmware update going to remove this noise?? Or do all VHF HT1250/GP360's have processor noise on weaker signals.

Thanks

Seems to be a common ailment on the older Waris radios. I had some 1250's made in 2000 that did that, they all ended up going to the depot under flat rate, they came back completely rebuilt with new boards, new chassis and new front covers. Well worth it under the price schedule at the time to get basically new radios. This was in 2007. I noted on the work order "noise on RX" and this is what they did to address it, replace the entire radio from top to bottom.

It's also common in MT2000/MTS2000 radios made in 1997-2000. I've got an MT2000 VHF A7 made in 1997 that is exhibiting these same symptoms.

If I press down hard with both thumbs on the front of the radio just below the center of the 6 buttons, the internal interference disappears!!!!!!

Any idea what pressing down in that spot is doing? Something loose? Poor earthing of screening? Any fix?

Pressing down on other positions on the front of the radio such as near the top also removes most of the noise - but the spot just below the 6 front keys seems to be the best spot.

The noise is also slightly desensing the RX causing the squelch not to open on a very weak signal - until you press down on the front.

I would now say that the micro processor noise is NOT 100% removed but is 95% removed when I press down. Using an external antenna results in 100% clean signal.

Any thoughts on what I should do next to fix the noise?

Long and short of it: The antenna matching circuit was/is no good causing very bad RX sensitivity and pickup of Up noise.

You could change out the surface mount components in the antenna matching to the latest values.

Thanks Will - but why does pressing down on the front case just below the 6 front keys remove the noise? Could it just be a poor grounding issue? I looked in the service manual and there appears to be what looks like a grounding contact point "behind" the 6 keys?? There also looks to be a grounding point near the top of the radio. Is poor grounding ever an issue?

RX sensitivity is also very good using an external antenna - although maybe the antenna matching circuit works OK with a 50 ohm match but an end fed helical probably has a much higher impedance.

Is the antenna matching circuit issue a design fault or component failure?

"Is the antenna matching circuit issue a design fault or component failure?"

I would say it is a serious blunder...

Any views on whether my noise issue is just a grounding problem?

I checked out SRN1290 which applies to radios with serial numbers/manufacturing dates from ***TYW*** to ***TZR***. My radio's serial number / manufacturing date is ***TBG*** (April 2001) so it was made a couple of years after the RX noise issue was identified.