Batboard

I have a UHF Maratrac T74XTA7TA7BK did the mods to the .OVL file for ham band, and RX is find, TX is almost nothing. In the TX Align the power is (at 455mhz) fine, just not in the 440-450 range.

It seems like the problem with the M400 that is mentioned on the site elsewhere. Does anyone know a way around this? Seems like it may be as simple as a TX inhibit but hard to say since I don't have a manual handy (not sure if I have a UHF)

Also the radio I think had a 8 channel head on it, and I switched it to the advanced and still only has 8 modes shown in the radio settings. Can't figure out how to get the rest.


Sandy

As for the TX power, nothing you can do short of hacking and chopping in the PA and then it still won't do full power output across the ham band. I had one UHF like that, below 450 it dropped off to nothing in a couple Mhz, it went from 100w at 450 to zero at 448! Shocking but true.

I had another one that would put out about 50w down to 445 and then died off beyond that. It's just the limits of the PA, nothing else.

The VHF Maratrac on the other hand is much more broadbanded, it will do 144-174 with nearly full power across the entire spread, i went through a couple of them and it would drop slightly to around 90-95 at the bottom of the ham band but that was it.

If you went from a clamshell to an advanced head you have to set it to an advanced head in the RSS, then you have to add the modes with the mode utility. When your in the mode editing i think it's F8, shown on the bottom of the screen, for the mode utility and you just select add mode and then execute.

I just finally said the heck with it and went to X9000's, full power across the band and with a little tuning excellent performance on the ham band. My X9000 UHF just came back from an alignment at Brinkley Electronics, .12uv sensitivity in the ham band, it was as bad as 7uv in the ham band, so they definitely need to be realigned even with the ones that have the preamp!

Did you measure the control voltage at the different TX points?
That should give an indication of 1, the uP not sending the correct voltage to the control stage 0 volts, or 2, the control voltage is 10 volts or more indicating the power amp is not liking the lower frequencies.

There may be some differences in the firmware in the M400 vs. the Maratrac. I do not know for sure.

Thanks for the reply's.

I spent the afternoon looking for the missing box with the manuals for the radio, no luck yet. Will that was my plan to see if infact the firmware is killing the drive or if it just is not capable of that freq. If a firmware problem that is probabally easy to 'jimmy' to force it to make work. I just need to get the schematic before I blow it up I wonder were the roll off is taking place (2mhz drops to zero is pretty steep), my guess is in the pre-driver (or what ever the official term is).

I have a VHF working at 100+ watts in the ham band and was looking at doing the same with the UHF, well that plan is a scratch without more work...

Sandy

If you crack the Maratrac nut let us know. I think the PA simply is not widebanded enough to allow much use beyond the specified band.

It might just be a matter of changing components, but i don't have a service manual either for the Maratrac. I could understand if they designed it somehow for a cutoff below 450, but it might just be a coincidence in that the parts they used don't work beyond that point since some produce more power than others in the ham band.

The VHF on the other hand just isn't picky whatsoever.

And yes, it might still be a firmware or software issue but i don't think so since i have put the latest 5.05 firmware in both VHF and UHF radios anyway. And if it was firmware or software causing it then how do you account for each radio acting differently as for power output on the ham band.

Are you sure it's a Maratrac and not an M400?

I recently programmed a UHF Maratrac down in the 440's. I haven't put it on the meter yet, but I can work a 444 machine about 35 air miles (my guestimate, I know it is 65 miles on the road for sure) without a problem using a 1/4 wave magmount. I didn't have to do anything with the radio except plug in the frequencies in the software. The ham machine is on the same tower as their med repeater, and I get an equal copy out of each of them.

kb0nly wrote:If you crack the Maratrac nut let us know. I think the PA simply is not widebanded enough to allow much use beyond the specified band.

It might just be a matter of changing components, but i don't have a service manual either for the Maratrac. I could understand if they designed it somehow for a cutoff below 450, but it might just be a coincidence in that the parts they used don't work beyond that point since some produce more power than others in the ham band.

The VHF on the other hand just isn't picky whatsoever.

And yes, it might still be a firmware or software issue but i don't think so since i have put the latest 5.05 firmware in both VHF and UHF radios anyway. And if it was firmware or software causing it then how do you account for each radio acting differently as for power output on the ham band.

Are you sure it's a Maratrac and not an M400?

The case is definitly badged as a Maratrac, but no idea how to tell if the guts were messed with. For the PA section it should work fine at a bit lower freqs, at the high end is typically were you would see the roll out (if not done on purpose that is).

For some radios doing different power you are right, I thought about that and about the only thing I could think of is different version of the drivers, different power calibrations, etc. None of which sound as good as your reason. What I'm going to do (when I get another free space of time) is to program it from 450 on down and see what happens. If firmware issue I would guess it is a hard drop of TX power at some point, but more then likely the driver has a steep filter on it and that might just be the problem, and my guess is that this is on the predriver somewhere.

Still need that manual which I have not hand anymore chance to look for. For an RF engineer probabally would spot it in a second

Hookanladder - Get it on a watt meter! It may be putting out a couple of watts, or watch the amps it draws on TX, my maratrac UHF only move the amp meter a bit (maybe less then an amp on TX). If you are up in the TX power you should see in to the ~20's.

The good thing is that even with almost no power out, with an HT monitoring the signal is stable and clean, so I don't think any problem with the PLL or any of that jazz.

Sandy

Just a couple more comments... A few more pennies if you will.

That's another thing i was going to mention, put it on a wattmeter and an ammeter to see what the radio is drawing on transmit. Of the ones i have played around with one would pull significantly higher amperage in the ham band while producing around 50w, and the ones not producing much if any power would be way below average. So it seems that if it does transmit on the ham band its not as efficient as it is in the intended split.

Also, you mentioned monitoring it and having a good clean signal with nearly no power out. A couple things can be deduced from that bit of info. That means that the VCO is locking and the RF board has power going out to the PA, which further rules out a firmware or software issue, if it was one of the two it would either not lock or not allow transmit at all i would think.

As an experiment, try disconnecting the rf board output to the PA and connect the output of the RF board to a wattmeter/dummy load. I would have to dig up my Maxtrac info on what the RF board (exciter) output is, since the Maratrac shares these parts in common with the Maxtrac. But i suspect if you have a sensitive enough wattmeter you will then see the output into a dummy load.

I scavenged the coax off a 800Mhz radio, Maxtrac, to get the connector that plugs into the rf board, and the end that is normally soldered to the PA has a BNC installed. I don't have any Maxtrac's here now otherwise i would take a UHF and measure the rf board output to give you a number to compare to. I know its mentioned in the service manual also, just have to find it.

A Maratrac is just a Maxtrac logic board and rf board with a custom interface board for the control heads and a 100w PA strapped to its butt.
I replaced a faulty rf board in a VHF Maratrac with the rf board from a Maxtrac of the same split.

Remember with the PA disconnected, the control voltage will go way high and the uP will sense overvoltage and shutdown the TX. This is part of the Maxtrac logic boards.

When testing, as was mentioned, monitor the RF output, and dc current drawn, AND the control voltage. This will tell you more. At some point the control voltage will go way high and then drop off to nothing when the uP senses the TX control voltage going too high.

The problem with M400 not transmititting any or very low power in amateur band is that the alignement points have been set to 0 on the 4 points that corospond to 440 - 450. If you have the RSS software do the F2 service menu then F6 for board replacemnt. Now select F4, RF PA/exciter power control and finally F5 to align the 16 points for power output. The first 4 are the ones we are interested in. They corospond to the 440-450 amatuer band. Align these as you would the others and the power out should be fine. Typical values for these points are 80 - 90. Good luck!

N0FAZ

Before you go too crazy attempting to re-aligning the radio, I would check and see if the VCO is locked. I took 450-470 Maratracs up to 482 with no problem with full power. The radio still worked at the mid 450 channels, but not much below.