High Power GTX-900 mobiles?

[train_radio_guy]

Is anyone familiar with the high power GTX-900 mobiles? Specifically the LTR Version (M11WRD4CU1_N), and the Privacy Plus Version (M11WRD4CB1_N). According to the following links:

LTR Mobile:
http://www.condord.com/lmr/motorola/MOT ... nglish.pdf

Privacy Plus Mobile:
http://www.tridon.com/tridon/images/pdf/gtx.pdf

M made two flavors for the LTR & Privacy Plus markets

- a 10-12 watt standard version, M11WGD4CU1_N for LTR & M11WGD4CB1_N for P.P., both of which are commonly sold on eBay, &

- a 20-30 watt a high power version, M11WRD4CU1_N for LTR & M11WRD4CB1_N for P.P., which seem to be rather rare.

Even though the RF output between the standard & high power version doesn't seem to amount to very much, I'm sure the added 'kick' would be very desirable to those with a serious interest in this band. This is especially true when folks like TPL are getting $ 1k for their basic 900 MHz power amplifier. With the revived interest in 900 MHz for hams, the high power GTX-900s would definitely fetch a bit more, than the standard 10-12 watt version.

If anyone has had their hands on one of these high power GTXs, I'm curious about their experience with it. Does it readily tune the 900 MHz ham band, like its lower power brother?

Thanks,


- trg,

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"When it's my time to pass on to the hereafter, I would like to go like my grandfather did - peacefully in his sleep, rather than the passengers of his car - kicking & screaming!"

- Bill Cheek (God Bless)

[kcbooboo]

I would expect that the only difference is an extra transistor amplifier in the power amp circuit. That's what they do on 15/30w MaxTracs and Spectras. A similar "blue brick" is used as the PA in all of these radios, and they just follow that with a 6dB grounded-base power amp to get more juice.

You can probably realize just as much signal improvement with a better (i.e. more gain) antenna and a short run of low-loss coax.

Bob M.

[Tom in D.C.]

I compensate for the low power with a Larsen 12db gain beam and a SHORT
length of 9913, but it would still be great to have the additional HP running
from the radio itself and THEN getting the gain!

One other difference I've found between the LTR and PP M11 radios is that on
one (I forget which) you can hide the trunking channel so the "1A" indicator
never shows.

This info is great to have and I'll be keeping my eyes peeled for an "R" model,
but since apparently none of us has ever seen one maybe the low power radio
was the only type actually made.

[kcbooboo]

I saw one for sale on eBay sometime during 2005, so they WERE made. Maybe no one has a need to sell any just yet.

I found a way to eliminate the last trunking mode on a Spectra but haven't tried it on a GTX yet.

Bob M.

[train_radio_guy]

I managed to pick up two high-power LTR GTX-900s, in a lot sale from yet another sacrificial lamb of Nextel. Apparently Nextel bought the local 900 MHz SMR system, and shut it down 30 days later. One of the major users of the system was a rather large trucking company, now forced to 'upgrade' their trucks to UHF.

Consequently, they were liquidating all of their 900 MHz assets. It was a mixed bag of GTXs & Kenwoods. I figured the two high-power LTR GTX-900s were worth the effort, since they appeared to be such a rare find. It's very interesting that there's no prior mention of this subject on batlabs. Maybe it's one that just slipped through the proverbial cracks in the floor.

Anyway, keep an eye out for the 'R' versions.

trg,

[jackhackett]

I've seen a couple of the high power ones, and yes, they basically just add a transistor output stage. They appeared to work much better than the low power ones, which have a tendency to cook PA modules if you just look at them the wrong way.

[train_radio_guy]

So the standard or low power version tends to cook the final amplifiers? This isn't by chance when used in a repeater or full-duty cycle application?

I've seen many radios used as part of a repeater, however the finals went south when usual precautions weren't taken (i.e. reduced power, constant & adequate forced-air cooling, etc..).

Strapping radios together as a repeater is fine for a temporary setup, but experience has proven that there are better, more permanent & reliable solutions.

- trg,

[kcbooboo]

My GTX mobile radio gets hot when I use it as a base station to talk on a repeater, so it's less than 50% duty cycle. If I talk more than 20 minutes, I can not keep my hand on the chassis. It must get to over 140F. Hasn't hurt it yet, but who knows how long it will continue to operate that way.

The GTX is a bit more intelligent about heat and power control in general, so I'd think it would cut back if things got out of hand.

Bob M.

[jackhackett]

So the standard or low power version tends to cook the final amplifiers? This isn't by chance when used in a repeater or full-duty cycle application?
- trg, 8)

No, the one's I've had to deal with are mainly in hotel shuttle buses, we only service a relatively small number of them, but I've had to replace the PA modules in a lot of them, much higher failure rate than I would expect.

[kcbooboo]

What do you use to unsolder the PA heatsink from the bottom of the circuit board? I just obtained a heat gun and I'm hoping that will have enough power to melt the solder.

Bob M.

[train_radio_guy]

I replaced a few blown PA's over the years, and typically we used a decent wattage de-soldering station. In a pinch you could probably use a 100-watt Weller soldering gun with decent de-soldering wick (Chemwick).

Be careful not to get things too hot, or you could damage adjacent components, or even rip traces off the PCBs. Removing PAs is not always an easy task, since the heat sink tends to wick your heat away, before the solder liquefies.

Patience, technique, practice are the secrets to success, when working on electronics. Experience is the best teacher in the end.

- trg,

[jackhackett]

What do you use to unsolder the PA heatsink from the bottom of the circuit board? I just obtained a heat gun and I'm hoping that will have enough power to melt the solder.

Bob M.

I've got this big old heavy duty iron, I'd guess it's about 300Watts, looks similar to this, except older (wooden handle, cloth covered cord). That tip is about an inch wide.
http://americanbeautytools.com/images/products/3178.jpg

As was mentioned in another thread, I don't solder the heatsink when I put the new one in, there's enough contact for it to work just by bolting it down.