I have a UHF GM300 438-470 MHz. I have checked out the archive which has helped answer a number of likely problems/issues which are listed below:
- Radio was 5KHz off freq. Understand that this is likely due to poor contacts on the RF/logic inter-board connectors. Ref Oscillator Warp was originally set to 119. Needed to adjust to 167 to get radio onto freq. Probably need to clean pins on interboard connectors.
- Volume cannot be turned down to a low level . More or less at "room level" at switch on point although can turn up volume so that its very loud. Is no "zero volume" likely to be due to "dirty contacts" on RF/logic board? Or is it possible that the radio has been set so that volume cannot be turned down to zero?
- Adjusting squelch level : I understand that the squelch adjustment is via a board pot not in software. The pot is marked "sq" so that it should be easy to find . I have not yet opened up the GM300 - is the squelch pot on the top or bottom board ? Any hints on opening up the radio will be appreciated ? I understand that you need to release the front panel not just the side screws?
- TX power :originally radio was putting out about 2W. Set at 46 in service menu . Increased power to 5w by setting at 57 in service menu. Did not try to get more power in case due to "dirty contacts" problem? Would you normally expect to get 25W at , say , 63, in alignment ( halve way between min/max level) or should you get 25W at original setting of 46?
- Internal speaker: short pins 15 and 16 on accessory connector
- External speaker : connect to pins 1 (-ve) and 16 (+ve)
- Scan mode : short mic hook to GND
- front end alignment : I used the "shift key" trick to program the radio down to 433MHz. Sensitivity is OK but around 3/4dB down on 438-470MHz. Is it possible to realign the front end of the GM300. Is this done in software or manually? Is tweaking the front end a good idea or should I leave well alone !!
Thanks,
Martin
GM300 UHF - a few questions
Moderator: Queue Moderator
Pulling the RF board and cleaning the connector pins witn Craig Pro Gold Cleaner, no substit, is step one.
Volume control has a chip resistor in the ground end so the volume does not go to minimum, you can jump the resistor if you wish. It is on the Vol/Mic jack board.
Ref Osc Warp should be 100 to 120, first try cleaning the interconnect pins and check for any debries arround the feed thru caps on the connetor plate. If that does not cure the problem, change the feedthru plate. Also look for stuff on the circuit boards, that could cause leakage that upsets the voltage(s) that set the frequency, deviation, ect.
Volume control has a chip resistor in the ground end so the volume does not go to minimum, you can jump the resistor if you wish. It is on the Vol/Mic jack board.
Ref Osc Warp should be 100 to 120, first try cleaning the interconnect pins and check for any debries arround the feed thru caps on the connetor plate. If that does not cure the problem, change the feedthru plate. Also look for stuff on the circuit boards, that could cause leakage that upsets the voltage(s) that set the frequency, deviation, ect.
Probably right about the dirty pins between the boards.
As for the volume problem, check to see that the bottom of the volume pot hasn't been lifted from ground. That will make the radio REAL loud and not adjustable. This is often done inadvertantly while trying to ground the hook line internally to keep the radio scanning without concern for the mic being on hook or not. This wiring is all inside the front panel.
You're right about the speaker wiring too.
The other stuff I'll leave to the real experts. I haven't yet had any trouble with my GM300s.
As for the volume problem, check to see that the bottom of the volume pot hasn't been lifted from ground. That will make the radio REAL loud and not adjustable. This is often done inadvertantly while trying to ground the hook line internally to keep the radio scanning without concern for the mic being on hook or not. This wiring is all inside the front panel.
You're right about the speaker wiring too.
The other stuff I'll leave to the real experts. I haven't yet had any trouble with my GM300s.
Chris,
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Hamming 31 years
http://www.wa2zdy.com
Wesley Chapel, Pasco County, Florida
Snow? What's that?!
The human race is proof that Darwin was wrong.
-
jackhackett
- Posts: 1518
- Joined: Tue Jun 10, 2003 8:52 am
The feedthru pins in the older radios go bad. If the part # on the pins is 6480535B01 replace it with part # 2804637J01. Th numbers are marked on them. If you do have the second number already, just clean the pins, but if it's the first one it's 100% guarranteed to be bad and cleaning them will at most make it work for a very short time before it craps out again.
The warp range Will gave you should be about right, most run right about 103 from what I've seen.
And remember.. never adjust the oscillator coil in one of these, you'll throw off the temperature compensation.
The warp range Will gave you should be about right, most run right about 103 from what I've seen.
And remember.. never adjust the oscillator coil in one of these, you'll throw off the temperature compensation.
On MaxTracs and Radiuses (very similar to GM300), the output power for 25 or 45 watts usually happens at a power setting around 80. The recommended power is 20 or 40 watts depending on X34 or X44 model number.
The squelch pot is on the RF board, which is on top for MaxTracs and Radiuses (and probably GM300s). The pot is marked SQ. There could be one or two other pots on the board; on MaxTracs and Radiuses it's near the front panel but _not_ the one closest to the front panel.
There's nothing to align in the receiver, unless someone has messed with the front end to make the radio perform better below 438 MHz. I recall that brass screws are often inserted into the coils to lower the frequency band of the radio. You should get the receiver to open squelch (with a PL/DPL signal) around 0.15 microvolts (about -124 dBm).
Bob M.
The squelch pot is on the RF board, which is on top for MaxTracs and Radiuses (and probably GM300s). The pot is marked SQ. There could be one or two other pots on the board; on MaxTracs and Radiuses it's near the front panel but _not_ the one closest to the front panel.
There's nothing to align in the receiver, unless someone has messed with the front end to make the radio perform better below 438 MHz. I recall that brass screws are often inserted into the coils to lower the frequency band of the radio. You should get the receiver to open squelch (with a PL/DPL signal) around 0.15 microvolts (about -124 dBm).
Bob M.
Picky, picky. Sorry, I should have left off "brass". I never use them myself anyway.
The squelch pot is R60 and it's just to the left (looking at it with the front panel closest to you) of the 14-pin connector that feeds the logic board. There are three pots on the RF board; don't touch the other two (one very close to the front panel, one just to the rear of the 14-pin connector) as they control modulation of the VCO.
Bob M.
The squelch pot is R60 and it's just to the left (looking at it with the front panel closest to you) of the 14-pin connector that feeds the logic board. There are three pots on the RF board; don't touch the other two (one very close to the front panel, one just to the rear of the 14-pin connector) as they control modulation of the VCO.
Bob M.
Thanks for all the feedback.
Max-trac - I noticed that it was 5KHz off freq after programming the radio onto a particular freq and then checking it on my frequency counter when stations sounded way off freq on receive. I don't think its a software problem. Also when I checked out the TX power etc , the radio defaults to a test freq of 452MHz and this was also 5 KHz off freq. Using the Ref Osc Warp bought it back onto freq but I think I will need to clean/replace interboard links rather than attempt to "offset" voltage changes due to dirty contacts. Also it looks like any vibration causes radio to go back off freq!
Front end alignment :I did not check the "board replacement" functions in software , but is there any band pass filter alignment you can do using software which can help to tune up my GM300 which is programmed 5MHz out of band ( ie 433 MHz on a 438-470MHz radio)
Thanks
Martin
Max-trac - I noticed that it was 5KHz off freq after programming the radio onto a particular freq and then checking it on my frequency counter when stations sounded way off freq on receive. I don't think its a software problem. Also when I checked out the TX power etc , the radio defaults to a test freq of 452MHz and this was also 5 KHz off freq. Using the Ref Osc Warp bought it back onto freq but I think I will need to clean/replace interboard links rather than attempt to "offset" voltage changes due to dirty contacts. Also it looks like any vibration causes radio to go back off freq!
Front end alignment :I did not check the "board replacement" functions in software , but is there any band pass filter alignment you can do using software which can help to tune up my GM300 which is programmed 5MHz out of band ( ie 433 MHz on a 438-470MHz radio)
Thanks
Martin
There's no such alignment of the receiver or transmitter in the MaxTrac or Radius RSS, so I'll assume the GM300 is the same. There are several different band splits, one would cover 403-430 or so. If yours isn't the right split, perhaps someone else on the BBS has one they might swap with yours. Other than that, I think you're just about stuck with whatever sensitivity you get that far out of the band.
All the radios I've encountered, that use RSS, allow you to set things like the deviation (voice and tone), output power, squelch, and frequency warp. An actual RF alignment is not done these days - the radios are fairly wide-band to begin with, and some could even be electronically tuned, so anything you attempt would likely make the radio work worse than it already does. In a nutshell, it's not something that anyone should even think of trying to do.
Bob M.
All the radios I've encountered, that use RSS, allow you to set things like the deviation (voice and tone), output power, squelch, and frequency warp. An actual RF alignment is not done these days - the radios are fairly wide-band to begin with, and some could even be electronically tuned, so anything you attempt would likely make the radio work worse than it already does. In a nutshell, it's not something that anyone should even think of trying to do.
Bob M.
Re. GM300 front end filter alignment in software?
- as well as the GM300 , I also have a GM350 . The GM350 is all software aligned which includes not only squelch, TX power etc but also front end filters. I have not actually tried to do any alignment on the GM350 as the freq I am using the radio on is in-band (and exceptionally sensitive - the best front end out of 11 other models of low band radios - only wish it was a 128 rather than 4 channel rig!!)
I have however tuned up the front end of other LMR radios in software - this usually involves tuning the band pass filters in software on 3 test freqs(low,mid,high) - the radio will then use a "line of best fit" technique to automatically align the radio's front end filters on any other freq in band. I have previously been able to "pull" the filters to provide excellent sensitivity upto about 10MHz out of band.
I suspect that the GM300 does not have the capability to align the front end filters by using software, unlike the later GM350 . Howver , there is the facility to do something in software when you go into the "board replacement" section in the service menu. Does anybody know what the alignment options are when you go through the board replacement procedure?
Thanks
Martin
- as well as the GM300 , I also have a GM350 . The GM350 is all software aligned which includes not only squelch, TX power etc but also front end filters. I have not actually tried to do any alignment on the GM350 as the freq I am using the radio on is in-band (and exceptionally sensitive - the best front end out of 11 other models of low band radios - only wish it was a 128 rather than 4 channel rig!!)
I have however tuned up the front end of other LMR radios in software - this usually involves tuning the band pass filters in software on 3 test freqs(low,mid,high) - the radio will then use a "line of best fit" technique to automatically align the radio's front end filters on any other freq in band. I have previously been able to "pull" the filters to provide excellent sensitivity upto about 10MHz out of band.
I suspect that the GM300 does not have the capability to align the front end filters by using software, unlike the later GM350 . Howver , there is the facility to do something in software when you go into the "board replacement" section in the service menu. Does anybody know what the alignment options are when you go through the board replacement procedure?
Thanks
Martin
The MaxTrac/Radius board replacement procedure, and I'll assume it's similar for the GM300, has you enter the crystal data (found on little stickers on and near the reference oscillator crystal), a measurement of the 9.6v supply, frequency warp, voice deviation, tpl/dpl deviation, and output power, not necessarily in this order (I'm going from memory here). The PA replacement procedure has you go through power output settings at 16 frequencies across the operating range of the radio. I think the deviation adjustments are also done at these same 16 frequencies. Many of the settings would be about 2/3rds of the way across the scale, i.e. 14/20, 80/120, 11/16 depending on how you look at it. The frequency warp should be reasonably close to the center, i.e. 101/200 or so. You'll need a good wattmeter, a dummy load, a frequency counter, a deviation meter, an audio oscillator, and a digital multi-meter, or the equivalent in a service monitor. Of course, several hand tools to take the covers off, and appropriate RF and audio jumpers and adapters as needed.
According to the GM300 and MaxTrac service manuals, the two radios are fairly similar in design and even share some parts in common. The MaxTrac is a bit more squared-off; the GM300 is a bit more rounded. The MaxTrac has a separate two-wire speaker cable; the GM300 runs the speaker signal through the same cables that feed the control head. There's filtering on the pins that feed the control head and interconnect the RF and logic boards; the MaxTrac just uses unfiltered connectors. Other than these slight differences, they're like brother and sister, born of the same parents several years apart.
However, I've never had one in my hands nor worked on a GM300, so I suppose it is possible that it does some things I'm not aware of. I have worked on GTX 900 MHz mobile and portable radios - the alignment for those radios is very similar to the MaxTracs.
Bob M.
According to the GM300 and MaxTrac service manuals, the two radios are fairly similar in design and even share some parts in common. The MaxTrac is a bit more squared-off; the GM300 is a bit more rounded. The MaxTrac has a separate two-wire speaker cable; the GM300 runs the speaker signal through the same cables that feed the control head. There's filtering on the pins that feed the control head and interconnect the RF and logic boards; the MaxTrac just uses unfiltered connectors. Other than these slight differences, they're like brother and sister, born of the same parents several years apart.
However, I've never had one in my hands nor worked on a GM300, so I suppose it is possible that it does some things I'm not aware of. I have worked on GTX 900 MHz mobile and portable radios - the alignment for those radios is very similar to the MaxTracs.
Bob M.
Last edited by kcbooboo on Fri Oct 01, 2004 2:46 am, edited 1 time in total.
" There's no such alignment of the receiver or transmitter in the MaxTrac or Radius RSS, so I'll assume the GM300 is the same. "
kcbooboo is correct, there is NO receiver RF front end alignment
on the GM300, M120 and Maxtracs/Radius mobiles.
The only "alingnment" that affects the receiver is the Refference Oscilator Crystal Compensation Alignment. The is done in the RSS, Service section and requires test equipment.
kcbooboo is correct, there is NO receiver RF front end alignment
on the GM300, M120 and Maxtracs/Radius mobiles.
The only "alingnment" that affects the receiver is the Refference Oscilator Crystal Compensation Alignment. The is done in the RSS, Service section and requires test equipment.