I recently purchased a UHF maxtrac and was able to program some 70cm ham frequencies into the radio, but I seem to be having VCO locking problems when the transmit frequencies are below 443MHz. I was googling around for an answer to this and found a site which suggested that I tweak the VCO coil in a turn to remedy this. The problem is that the site wasn't too specific on which coil to adjust. There are two coils in the PLL can, one is shielded, and the other is a low inductance unshielded coil filled with wax.( If I were to make a guess, the one filled with wax is probably the VCO coil, but I don't really like guessing on things like this). I understand that this is no substitute for having a manual, but the manual probably won't cover any adjustments necessary to get the radio to transmit ion the low end of the ham band.
My question boils down to this: What has anyone done to UHF Maxtracs to get them to transmit in the low end of 440-450 MHz relliably?
BTW: The same link also mentions to remove the Al slugs in the RX preselector coils. This sounds pretty drastic to me.
Steve
WA6ZFT
UHF maxtrac (449-470MHz) and the PLL
Moderator: Queue Moderator
Hello:
EEgads, Don't make any hardware changes to your radio !
What you have to do is " Realighn " your radio
for operation in that area first!
In the Section covering the " Logic Board " replacement
area, you will find ( Most of the time ) the 440 ~ 449 Mhz
range has NOT been alighned at all.
Most have just the default settings, and as such the radio
will not work well at the lower range.
So, go to the Logic Board Replacement window, be prepared
to go through a number of steps as they MUST be done in
order, and you will come accross the area where the output
Power, DEV settings will have to be set correctly. This is done
from the 440 Mhz settings all the way through the 470 Mhz
area.
Once that is done, go back and see how the radio responds
( but you will have to use the correct Software ) and then
if the operation is still erratic, then you can perhaps make
some physical adjustments to the VCO.
But, one does need a Service Monitor if you want to have
this done properly.
In the days when Maxtracs and Radius Mobiles were super
popular, we came accross just 100's of radios that were
hacked by Hams, and the majority of the time, all the radio
needed was a Slight realighnment of the Radio.
If you perghaps want to operate below 440 mhz, Yes, you may
have to make some hardware changes.
Monty
EEgads, Don't make any hardware changes to your radio !
What you have to do is " Realighn " your radio
for operation in that area first!
In the Section covering the " Logic Board " replacement
area, you will find ( Most of the time ) the 440 ~ 449 Mhz
range has NOT been alighned at all.
Most have just the default settings, and as such the radio
will not work well at the lower range.
So, go to the Logic Board Replacement window, be prepared
to go through a number of steps as they MUST be done in
order, and you will come accross the area where the output
Power, DEV settings will have to be set correctly. This is done
from the 440 Mhz settings all the way through the 470 Mhz
area.
Once that is done, go back and see how the radio responds
( but you will have to use the correct Software ) and then
if the operation is still erratic, then you can perhaps make
some physical adjustments to the VCO.
But, one does need a Service Monitor if you want to have
this done properly.
In the days when Maxtracs and Radius Mobiles were super
popular, we came accross just 100's of radios that were
hacked by Hams, and the majority of the time, all the radio
needed was a Slight realighnment of the Radio.
If you perghaps want to operate below 440 mhz, Yes, you may
have to make some hardware changes.
Monty
Need help on a Program Cable or (/\/\) Rib Box ?
Contact me anytime/All availible / Free Support Info !
mail to: MSisco9939@aol.com
PLease avoid PM's whenever possible. Box gets too full.
Contact me anytime/All availible / Free Support Info !
mail to: MSisco9939@aol.com
PLease avoid PM's whenever possible. Box gets too full.
Typically, the VCO coils in a Maxtrac do not have wax in them. Both coils look identical and are shielded. The TX VCO is located closest to the middle of the board. The RX VCO is more towards to right top corner of the board.
It is true that these radios often are not aligned for the ham band in the service screens. But these service screen adjustments only affect power and deviation for that section of the band. They do not affect synthesizer locking.
Nand.
It is true that these radios often are not aligned for the ham band in the service screens. But these service screen adjustments only affect power and deviation for that section of the band. They do not affect synthesizer locking.
Nand.
UHF Maxtrac VCOsomem
Thanks Monty,
I do have a service monitor so I will investigate the aligning of the radio using the RSS software first. Failng that, the second poster indicated there were RX and TX vco coils. Whould you happen to know of the top of your head what the reference designators (L?) are for the RX and TX VCO coils in the UHF maxtrac?
BTW: If you are the person I'm thinking you are we have met on and off over the past 25 years at the Santee swapmeet and other places.
Steve
WA6ZFT
I do have a service monitor so I will investigate the aligning of the radio using the RSS software first. Failng that, the second poster indicated there were RX and TX vco coils. Whould you happen to know of the top of your head what the reference designators (L?) are for the RX and TX VCO coils in the UHF maxtrac?
BTW: If you are the person I'm thinking you are we have met on and off over the past 25 years at the Santee swapmeet and other places.
Steve
WA6ZFT
UHF VCO layout.
The previous info as to VCO coil location is for the VHF version. Above is the layout for the UHF Maxtrac.
Nand.
