I have a Philly 148 GTL, modded with a LesComm board and Freq counter in my truck. When the truck is running or idiling, the radio freq drifts BAD. I suspected that it was the LesComm board, so I checked to see if it was mounted tightly and it was. I also checked all connecters on the board, and the crystal for tightness, and everything checks ok. Anybody have any ideas on how to fix this?
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148 GTL Drifting Help
- Thread starter BoogieDown
- Start date
I would take it back to the tech that did the work for you and have him check it out. If he can't get it right then you need to find a better tech. If you got out your golden screwdriver and did the work yourself then your kinda stuck.
I do know that some of these Expo, Viagra, and Less Comm kits can and do drift alittle. This is usually in the mobile during winter weather in the colder parts of the country.
I do know that some of these Expo, Viagra, and Less Comm kits can and do drift alittle. This is usually in the mobile during winter weather in the colder parts of the country.
This is the cold time of year - right? Even the favored 148 will get drifty when temps change. A change of 15f temp can cause a 148 to shift 50-60 cycles or more. The best thing to do is to keep the temp in your radio room as stable as you can. Summer temps will cause a shift/drift in the other direction too.
If it is used for the mobile; then other measures are in order. Having the clarifier unlocked is one; as temps change you can slide right along with the change. Do the standard clarifier mod that does only ~700hz slide either way. A clarifier with 5khz slide or more is going to be too sensitive to keep centered on the desired station and even a bit worse when temps aren't favorable. Turn your heater on and make the inside of the vehicle toasty; that will surely help too.
Keeping the voltage feed at a constant 13.8v to the radio is another. Not a large change but the radio is a bit more stable at the nominal recommended operating voltage.
You might also try tying these coils together (L22, L23, & L59) with the crystal next to them. As you can see from the picture L22 is already tied to it. Just solder a bridge wire to L22 from L23 and from L22 to L59. It helps some; but not much.
Even the adder IC chip of the LesComm board can be influenced by temps. You just added another variable to this situation. LesComm may have some tips for you to follow too if you send them an email and just ask . . . $.02 cents . . .
If it is used for the mobile; then other measures are in order. Having the clarifier unlocked is one; as temps change you can slide right along with the change. Do the standard clarifier mod that does only ~700hz slide either way. A clarifier with 5khz slide or more is going to be too sensitive to keep centered on the desired station and even a bit worse when temps aren't favorable. Turn your heater on and make the inside of the vehicle toasty; that will surely help too.
Keeping the voltage feed at a constant 13.8v to the radio is another. Not a large change but the radio is a bit more stable at the nominal recommended operating voltage.
You might also try tying these coils together (L22, L23, & L59) with the crystal next to them. As you can see from the picture L22 is already tied to it. Just solder a bridge wire to L22 from L23 and from L22 to L59. It helps some; but not much.
Even the adder IC chip of the LesComm board can be influenced by temps. You just added another variable to this situation. LesComm may have some tips for you to follow too if you send them an email and just ask . . . $.02 cents . . .
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Good Stuff, Thanx guys. I don't dare let the tech who installed it back inside my radio. I'll find another tech.
RatsoW8
Supporting Member, W9WDX ARC Member - WD8T
Motorola use to stick 100 ohm 1/2 watt resistors on the side of the crystals when their 2-Way radios were crystal controlled. Put 12 volts across the resistor and it was their low budged version of a crystal oven.
The Philly 148 is not known for frequency drift and is noted for good SSB stability unlike the China ones. Frequency drift in these radios is usually related to voltage drift on the 8 volts line. However, this radio has another frequency board installed. It probably has crystal oscillators on the board. Hopefully it has its own on board voltage regulator or is powered by a regulated source in the radio. I would look here first.