Poor performance Motorola VHF handheld?

Hi Guys,

I have a VHF repeater setup on the farm (155MHz) and use a mix of 25W mobile radios and Motorola GP339 handheld 5W radios. The performance of the Motorola radios is abysmal - I can get a maximum of about 3/4 mile line of sight out of them to the repeater. The mobiles in the car get at least 10 miles when operating @ 5W.

I think the problem is a configuration issue but its got me stuffed how to fix. Anyone have any experience in programming Motorola handhelds?

I have a suspicion it is related to the CTCSS / PL tone setup. In the Codeplug for the handheld each channel is configured for Encode/Decode type of “PL” In the radio’s “personality” configuration the RX mode is set to Tone Squelch. I note the choices in the personality config file include:

-PL/DPL + Tone Squelch
-Tone Squelch
-PL/DPL Squelch
-Carrier Squelch

I can’t quite figure out what the difference is between PL and Tone in this context - I thought PL was just Motorola’s name for CTCSS?

<technical stuff>

The repeater is configured for a 12.5Khz analog channel with a CTCSS tone of 141.3Hz. Outputting around 10W EIRP and the coverage predictions in the software match the real world performance very closely when used with the mobiles. In other words - this is not a coverage problem or a performance issue with the repeater itself - it is working properly.

I tested the 8x handhelds on a RF test set - they are outputting around 5.3W each and the receiver mutes are opening at around -120dBm so seem to be operating normally. I do note that users have complained when operating the radios in Simplex mode that they have very poor range - less than 1/4 mile in some circumstances which makes no sense unless there is a configuration issue. I first thought it was just operator error but now not so sure…

OK - bit more testing today shows the problem is with a couple of the radios only and these are the ones that the guys who are complaining had! These 2 are deaf as a post compared to the others - the performance on the remaining portables is about what I expected - coverage to at least 5 miles no problem.

All the portables have the same codeplug (program) so there is no difference between them. The RF performance as measured on the RF test set for the faulty radios is identical to the others. I’ve swapped antennas around and that made no difference.


You sure they’re the same?

If the radios on the bench are the same, and the good and bad radios have had their antennas swapped then this makes no sense.

Is the issue they cannot hear the repeater, or the repeater cannot hear them? I can’t think of anything that would produce the issue if the tests say they are identical?

Yep - that’s why I am scratching my head too! Positive they are the same, I only have the one codeplug and did all 8 radios at the same time. I put all 8 radios onto a calibrated test set and confirmed that they were all within a very narrow window of power output and receiver sensitivity. The dodgy radio was in the middle of that range so nothing obvious. When it reaches its limit of operation (less than a mile) it fails to open the repeater AND it fails to open the squelch when another radio opens the repeater.

I can only think that there is a problem with then internal CTCSS generation of the radio - maybe its only just generating enough subtone to open the repeater at close range - remember PL is enabled in both paths of the link so that might explain why its failing in both directions. Dunno… all I have as a working theory right now!

CTCSS level usually works better than audio, so if the RF is sufficient to open the squelch, AND the tone is present, all usually works. What happens at the repeater, does the access light come on when there is RF present, but the transmitter not power up? If the poor radio doesn’t open the system, then every radio won’t hear it. Poor RX and TX suggest that the antenna on the radio is poor, but you’ve swapped these I think you said - so I’m mystified. How about of you program just the iffy radio with no CTCSS at all, and see if it can then hear but not transmit?