MPD upgrade
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motgeradios
- Posts: 10
- Joined: Thu Apr 10, 2003 11:39 pm
MPD upgrade
I have a GE MPD standard radio and a GE MPD scan radio. What would I have to switch to put the scan front on the regular radio? The scan is a vhf, but the power amp board is damaged and the standard radio is a UHF. Possibly only the display screen and the board behind it work. Any help or success stories would be appreciated, thanks.
The good news and the easy part is that you can just put the good controller on the good rf section and program it as a MPD scan in the correct bandsplit, it will however warn you that the band split info and tracking data is wrong for the new bandsplit if the two bandsplits are different, just accept it and go on.
Now for the bad news and the tough part, the front/controller section from the scan radio will still have tracking values for the old radio rf section in it, if the 2 radios were from the same bandsplit then it is not a problem and should work without any major headaches but if the scan controller was from say an 800MHz or UHF radio and the good RF back section was from a VHF radio then you will need to go into the tracking menus and set all of the tracking values for the new RF section. This will require the use of at least a basic service monitor or something similar to set the following: Squelch opening point across the new radios freq range, High power, Low power and Modulation dac values all across the radios frequency range. The nice thing is that you can set your high and low power values to whatever you want.
As I said if the 2 radios were from the same frequency split then the tracking values, as I have found, will typically be close enough that minimal tracking changes if any will be required.
I have converted many VHF high splits to 220 Mhz and 800 radios to 902 - 928 MHz and had to do the tracking changes, however, it has been a while and I am very rusty on the proceedures.
Another thing you can do is read the tracking values from the basic controller section of the bad radio if the 2 frequency splits are different and write them down then put them into the new scan controller, of course you need to enter the values in manually in the MPD software tracking section but it is a lot easier than trial and error poking of the tracking values.
Mike
Now for the bad news and the tough part, the front/controller section from the scan radio will still have tracking values for the old radio rf section in it, if the 2 radios were from the same bandsplit then it is not a problem and should work without any major headaches but if the scan controller was from say an 800MHz or UHF radio and the good RF back section was from a VHF radio then you will need to go into the tracking menus and set all of the tracking values for the new RF section. This will require the use of at least a basic service monitor or something similar to set the following: Squelch opening point across the new radios freq range, High power, Low power and Modulation dac values all across the radios frequency range. The nice thing is that you can set your high and low power values to whatever you want.
As I said if the 2 radios were from the same frequency split then the tracking values, as I have found, will typically be close enough that minimal tracking changes if any will be required.
I have converted many VHF high splits to 220 Mhz and 800 radios to 902 - 928 MHz and had to do the tracking changes, however, it has been a while and I am very rusty on the proceedures.
Another thing you can do is read the tracking values from the basic controller section of the bad radio if the 2 frequency splits are different and write them down then put them into the new scan controller, of course you need to enter the values in manually in the MPD software tracking section but it is a lot easier than trial and error poking of the tracking values.
Mike
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willbartlett
- Administrator
- Posts: 85
- Joined: Wed Jan 23, 2002 8:00 pm
- Location: Boston, MA
It is pretty in depth. The first 2 parts were the easiest 1. Replace the power module with the same size mitsubishi 220 module. 2. Pull the 2 VHF helical bandpass filters and I replaced them with same size home made surface mount versions that unfortunately isn't well documented but basically it was a 5 element 2 section bandpass filter capacitively top coupled.
Now the hardest part is #3. cut the top off the VCO and again since the VCO PWB is not documented at all, this was and is hard to describe, but basically I drew the schematic of the VCO reverse eng. style from looking at the VCO pwb with the top cut off (using a dremel) and I then empirically chnaged 3 caps to get lock in the 220 band. Since the VCO for the MPD is not documented in any manuals it was very hard to describe and also out of 2 220 radios that I did the VCOs were both entirely different in the layout. This is exactly the same as what I found when converting 800 MHz MPDs to 900 ham, the VCO is not documented and the VCOs used varied in the board layout.
Mike
Now the hardest part is #3. cut the top off the VCO and again since the VCO PWB is not documented at all, this was and is hard to describe, but basically I drew the schematic of the VCO reverse eng. style from looking at the VCO pwb with the top cut off (using a dremel) and I then empirically chnaged 3 caps to get lock in the 220 band. Since the VCO for the MPD is not documented in any manuals it was very hard to describe and also out of 2 220 radios that I did the VCOs were both entirely different in the layout. This is exactly the same as what I found when converting 800 MHz MPDs to 900 ham, the VCO is not documented and the VCOs used varied in the board layout.
Mike
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willbartlett
- Administrator
- Posts: 85
- Joined: Wed Jan 23, 2002 8:00 pm
- Location: Boston, MA
Well, This is interesting. I took out both the front end filters, and by just changing out the ferrite cores with some random #4 steel hardware, I was able to get -3 to -4.2db from 189-227 mhz. Not quite the -2db I had at 146 mhz before I started, I'll try some brass cores tomorrow., see if I can eak a few more db out of them.
As for the VCO, if you had a scan of the hand drawn schematic, I'd love to get a look at it, even just for reference. I hope all mine have similar vco's. They're almost sequential in serial number, all from the same source.
I was able to open the case of the VCO by heating the bottom edge of the lip of the top cover, one side at a time with a 75 watt iron and sliding a razor plade in and gently seperating it away. DO ONE SIDE AT A TIME. vco needs to be removed from the board first, and place it in a loose vise, the whole vco gets too hot to touch.
Also, do you have a source for the amp. I'll look up the part with rf parts, see where I get
As for the VCO, if you had a scan of the hand drawn schematic, I'd love to get a look at it, even just for reference. I hope all mine have similar vco's. They're almost sequential in serial number, all from the same source.
I was able to open the case of the VCO by heating the bottom edge of the lip of the top cover, one side at a time with a 75 watt iron and sliding a razor plade in and gently seperating it away. DO ONE SIDE AT A TIME. vco needs to be removed from the board first, and place it in a loose vise, the whole vco gets too hot to touch.
Also, do you have a source for the amp. I'll look up the part with rf parts, see where I get
Will,
I found more notes yesterday so I edited this on thursday july 24. 2003 I corrected the type of power module used and added more in depth info.
On the 2nd one that I moved to 220 I did use brass slugs on the VCO and the VCOs both went to 220 fine but I couldn't quite get the brass to tune on the preselectors and that's why I used the pseudo home brew bandpass filters. I actually used the same preselector PWB and same coils but removed the tuning slugs if any and replaced all of the caps in the preselector and then I used a combination of brass and or ferrite slugs to get the new filter aligned most of my coils in the preselectors don't have any tuning slugs. The first radio converted was a very old MPD and that may have been why it was a dog. I also wrote a small program to calculate the new hex values for 220 frequencies.
Some more parts changes that I found yesterday:
On the main RF boards rear side I replaced R113 with a 100 K ohm chip resistor to speed up the lock time when going from tx to rx. On the transmitter low pass filter I removed capacitor C223 and Changed Capacitors C222 and C224 to 3.9 pf chip caps. On the 1/4 wave line isolating the rx port from the tx port I changed capacitors C212 and C219 to 18 pf chip caps.
The receiver bandpass filters, FL301 and FL302 are harder to describe as they do not have any component locators so I will have to do a drawing of the circuit boards bottom and show what caps I changed to get to 220 Mhz, unless you can achive good sensitivity by using brass tuning slugs in the coils which may work.
Updated programming on july 24 2003:
To make programming easy I set the radio up initially as a ~ 136 to 152 MHz or whatever the low split VHF radio is, you must set it up as a low split VHF to get the proper VCO switches on the receive side otherwise it is a major hardware mod to get it to work. I initially programmed all transmit frequencies to 170.000 Mhz, use CTRL-E to make the software take the 170.000 value. BTW 170.000 is the highest that the software will allow using CTRL-E if the radio is set as a low split, 136 to 15X., VHF radio so this isn't some magic number.
For receive frequencies I entered the desired 220 Mhz frequency minus 90 MHz and used CTRL-E to make the software take it and I also entered in the alpha tags, channel guard tones scan lists, all required zones and channels, everything since once you do the hexediting you will not be able to make changes from the MPD software, and then I ran my little program to calculate the new HEX values for the 220 MHz transmit frequencies that replaced the original ones for the 170 MHz TX placeholder values.
I saved this codeplug in the MPD software and then opened the MPD codeplug up using a hexeditor and looked for the hex value 6122 which are easy to find as they proceed the alphnumeric tags for the desired channel that you are editing, the actual channel alpha numerics can be seen in the right side of the hex editor software. I was looking for the same repeating numbers, HEX 6122 which are the initial placeholder values for 170.000 Mhz transmit frequency.
When you finish editing the codeplug the MPD conventional software will display the actual transmit frequency and the 220 receive frequency minus 90 MHz, IE the rx frequency should display somewhere down in the 132 to 135 Mhz range, do not move down to the frequecny entry area of the MPD software other wise the program will complain and not let you out until you enter in a valid frequency for the radios range.
I'll have to dig up the basic program that calculates the new 220 hex values, it is in QB45 (quick basic) but should be compilable in any version of basic. There were some other notes I need to find about what VHF bandsplit to set the radio up in etc. I'll dig these up and edit this post or post an update when I find them but this should get you started. Otherwise you can send me your desired 220 tx frequencies and i can send you the corresponding hex values for them.
The correct power module is a M68707L mitsubishi, 9.6 volts module capable of 7 watts, I set mine to 3 watts and as I remember it is a direct drop in and only required setting power along with deviation and squelch opening tracking values in the mpd tracking menu.
If you have the MPD software I can e-mail you a codeplug for a systems radio with one zone and several channels in it with 220 test frequencies to help align the VCO. You can read this codeplug with the MPD software to see the actual 220 frequencies but don't move down to the frequency entry area otherwise it will complain that these freq's are out of the radios range.
In the mean time you can check 220 receive if you dont have the tx side edited by going into the MPD conventional software and entering in the desired 220 frequency minus 90 MHz by using CTRL-E, this will help you get the receive VCO on frequency and also test RX sensitivity. It's best to do one section at a time, IE Rx first then go on to the TX work.
Mike
I found more notes yesterday so I edited this on thursday july 24. 2003 I corrected the type of power module used and added more in depth info.
On the 2nd one that I moved to 220 I did use brass slugs on the VCO and the VCOs both went to 220 fine but I couldn't quite get the brass to tune on the preselectors and that's why I used the pseudo home brew bandpass filters. I actually used the same preselector PWB and same coils but removed the tuning slugs if any and replaced all of the caps in the preselector and then I used a combination of brass and or ferrite slugs to get the new filter aligned most of my coils in the preselectors don't have any tuning slugs. The first radio converted was a very old MPD and that may have been why it was a dog. I also wrote a small program to calculate the new hex values for 220 frequencies.
Some more parts changes that I found yesterday:
On the main RF boards rear side I replaced R113 with a 100 K ohm chip resistor to speed up the lock time when going from tx to rx. On the transmitter low pass filter I removed capacitor C223 and Changed Capacitors C222 and C224 to 3.9 pf chip caps. On the 1/4 wave line isolating the rx port from the tx port I changed capacitors C212 and C219 to 18 pf chip caps.
The receiver bandpass filters, FL301 and FL302 are harder to describe as they do not have any component locators so I will have to do a drawing of the circuit boards bottom and show what caps I changed to get to 220 Mhz, unless you can achive good sensitivity by using brass tuning slugs in the coils which may work.
Updated programming on july 24 2003:
To make programming easy I set the radio up initially as a ~ 136 to 152 MHz or whatever the low split VHF radio is, you must set it up as a low split VHF to get the proper VCO switches on the receive side otherwise it is a major hardware mod to get it to work. I initially programmed all transmit frequencies to 170.000 Mhz, use CTRL-E to make the software take the 170.000 value. BTW 170.000 is the highest that the software will allow using CTRL-E if the radio is set as a low split, 136 to 15X., VHF radio so this isn't some magic number.
For receive frequencies I entered the desired 220 Mhz frequency minus 90 MHz and used CTRL-E to make the software take it and I also entered in the alpha tags, channel guard tones scan lists, all required zones and channels, everything since once you do the hexediting you will not be able to make changes from the MPD software, and then I ran my little program to calculate the new HEX values for the 220 MHz transmit frequencies that replaced the original ones for the 170 MHz TX placeholder values.
I saved this codeplug in the MPD software and then opened the MPD codeplug up using a hexeditor and looked for the hex value 6122 which are easy to find as they proceed the alphnumeric tags for the desired channel that you are editing, the actual channel alpha numerics can be seen in the right side of the hex editor software. I was looking for the same repeating numbers, HEX 6122 which are the initial placeholder values for 170.000 Mhz transmit frequency.
When you finish editing the codeplug the MPD conventional software will display the actual transmit frequency and the 220 receive frequency minus 90 MHz, IE the rx frequency should display somewhere down in the 132 to 135 Mhz range, do not move down to the frequecny entry area of the MPD software other wise the program will complain and not let you out until you enter in a valid frequency for the radios range.
I'll have to dig up the basic program that calculates the new 220 hex values, it is in QB45 (quick basic) but should be compilable in any version of basic. There were some other notes I need to find about what VHF bandsplit to set the radio up in etc. I'll dig these up and edit this post or post an update when I find them but this should get you started. Otherwise you can send me your desired 220 tx frequencies and i can send you the corresponding hex values for them.
The correct power module is a M68707L mitsubishi, 9.6 volts module capable of 7 watts, I set mine to 3 watts and as I remember it is a direct drop in and only required setting power along with deviation and squelch opening tracking values in the mpd tracking menu.
If you have the MPD software I can e-mail you a codeplug for a systems radio with one zone and several channels in it with 220 test frequencies to help align the VCO. You can read this codeplug with the MPD software to see the actual 220 frequencies but don't move down to the frequency entry area otherwise it will complain that these freq's are out of the radios range.
In the mean time you can check 220 receive if you dont have the tx side edited by going into the MPD conventional software and entering in the desired 220 frequency minus 90 MHz by using CTRL-E, this will help you get the receive VCO on frequency and also test RX sensitivity. It's best to do one section at a time, IE Rx first then go on to the TX work.
Mike
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willbartlett
- Administrator
- Posts: 85
- Joined: Wed Jan 23, 2002 8:00 pm
- Location: Boston, MA
Wow
Hi Mike, I haven't checked in in a few weeks. I was able to track the PA down, seems to be kind of rare. As for the hex editing of the transmit frequencies, I can probably handle that, I figured oit that the lsb is on the left side of the 4 digit frequency value in the codeplug, with the MSB on the right, and each step is 7.5 khz or something like that, easy to calculate. I don't remember the specifics of what I discovered, but I'll get back into it in a week or so, work and home improvements have been full bore as of lately.
It's a good thing I have a couple of MPD's with sequential serial numbers. As I was in the process of trying to open the VCO using the big iron, I inadvertently heated the board up to flow temp. and managed to displace a bunch of components on the smaller of the two boards. I'll open another one up (carefully) and rebuild it. If I can't, I think I paid like $25 for each radio, it's just frustrating to bung up a radio by mistake.....
In any case, I was able to get the sensitivity to a reasonable level, maybe 2.5-3db loss at 225 as opposed to the original 1.75-2.25 db loss in the original configuration. I f you dod find the notes on specific values, I'll likely try it on another radio. I could always just do up a filter in eagleware too.....
Thanks for all the info, I'll definitely take a stab at this in a week or so when I get a breather....
tnx, Will
It's a good thing I have a couple of MPD's with sequential serial numbers. As I was in the process of trying to open the VCO using the big iron, I inadvertently heated the board up to flow temp. and managed to displace a bunch of components on the smaller of the two boards. I'll open another one up (carefully) and rebuild it. If I can't, I think I paid like $25 for each radio, it's just frustrating to bung up a radio by mistake.....
In any case, I was able to get the sensitivity to a reasonable level, maybe 2.5-3db loss at 225 as opposed to the original 1.75-2.25 db loss in the original configuration. I f you dod find the notes on specific values, I'll likely try it on another radio. I could always just do up a filter in eagleware too.....
Thanks for all the info, I'll definitely take a stab at this in a week or so when I get a breather....
tnx, Will