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Obie
Posted on Friday, January 25, 2002 - 3:28 am:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

Something I have wondered for a long time, I hear time and time again that the uPD2824 cannot be easily modified.. I even read a popular early 80's CB book written by Lou Franklin (and read on his website) that the only way to modify the PPL on these radios is to inject an external oscillator between pin 10 and the mixer to change the 15 mhz signal.
I have 2 radios that are supposed to be 'un-modify-able' using a replacment for the 10.240 reference XTAL.
They are Cobra 146GTL's with the uPD2824 (same as a Realistic TRC-451).
About 5 years ago I decided to modify these and replaced the 10.2417 reference xtal with a 9.9417 and can easily drop below (to 26.485 to 26.915) and I also had them cut to go above 27.405 but I forget (without pulling the cover) what XTAL freq. I used. This afternoon I talked to a fellow on 27.585 LSB from my shack in Phoenix, AZ to Raligh, NC for 45 minutes till the conditions went bad. Last night I talked to several people in Illinois on 27.650 AM.
I had read the information before (that the PPL would NOT allow you to shift frequencies by changing the ref. XTAL) but I figured if the clarifier could add some capacitance offset and shift the freq a little bit I didn't see why I couldn't change the reference frequency and arrive at the freq I wanted.... and I did! Sometimes something will work best when you are told you CAN'T do it! LOL
Am I the only one that is running a modified 2824 PPL using XTAL exchange method? It works great on AM and SSB.
Just curious.
-Obie
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Tech181
Posted on Saturday, January 26, 2002 - 12:06 am:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

Obie,

Changing the XTAL will give you 26.485 - 26.915, but what are you going to do when you wanna talk on the regular 40, or above that? Change crystals in and out all the time?

Steve
Tech181
Tech181@copperelectronics.com
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Obie
Posted on Saturday, January 26, 2002 - 4:51 am:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

181,
Yes... in a way, but I simply use a couple of switches and built a small PC board with the XTALS on it and placed a small trimmer cap across each to 'fine tune' when I installed them. I used diodes to switch 'em to avoid long runs with the wires.
I had a gutted out SBE Console V that I rebuilt using a TRC-451 that had a smacked up face I put the board in the SBE and used all the switches (the SBE has a GANG of toggles on the front!) that used to control the stuff I don't need or want like Channel 9, Scan, PA, etc. I kept the ANL, NB, RF/SWR, power switch.. ect. and simply used those wired into my 'new' radio.
It's really a pretty nice set, the SBE even had a 'modulator' pc board built in that I used, it works really well with my Turner +3 compression Mike.
I even converted it to be able to go to FM but could never find anyone to talk to other than my own mobile!! LOL
See ya later,
Phil

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