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--- packet:transceivers_144pk [2025/07/08 09:21] – created g7taj
+++ packet:transceivers_144pk [2025/07/08 12:33] (current) – g7taj
@@ Line 2: / Line 2: @@
-A post by Nick G4TAI on the OARC forums about a boot sale find, turned into a few discussions about it as he was wondering how it worked and if it would be possible to change the frequencies. It was on the old 1980’s 144Mhz frequencies. A few discussions later and I agreed, for a few beer coins, to take it and see what I could find out as a little interesting project (I have always wanted to know how things work inside the box, from a young age).
+A post by Nick G4TAI on the OARC forums about a boot sale find, turned into a few discussions about it as he was wondering how it worked and if it would be possible to change the frequencies. It was on the old 1980’s 144Mhz frequencies. A few discussions later and I agreed, for a few beer coins, to take it and see what I could find out as a little interesting project (I always want to know how things work inside the box, even from a young age).
 The 144 PK is a 4 channel ~5w 2meter transceiver made specifically for packet. It has no speaker, no RX light, just a TX light and some adjustment pots and a 4 channel switch.
@@ Line 8: / Line 8: @@
 From the pictures Nick had posted online, it was already thought that an EPROM was at the heart of the controls. It had a few other chips on-board that were of interested.
-{{:packet:unit_front.jpg?400|}}
+{{:packet:unit_front.jpg?400|}}{{:packet:unit_back.jpg?400|}}
+{{:packet:front_1.webp |}} {{:packet:back.jpg?400|}}
@@ Line 18: / Line 19: @@
 The 4 channel switch is wired directly to some of the EPROM address lines, which Nick had already put to his multimeter.
-<switch state picture>
+{{:packet:switch_hl.jpg?400|}}
-Once in my hands ( a 400mile round trip back to my old QTH location, having just moved, which is coincidentally where Nick lives and I just happened to be there to visit family) and with all this information, it quickly lead me to work out that the binary counter driving the EPROM address lines and driving the synthesiser to setup the frequencies. What I didn’t know, is how.
+Once in my hands ( a 400mile round trip back to my old QTH location, having just moved, which is coincidentally where Nick lives and I just happened to be there to visit family) and with all this information, it quickly lead me to work out that it was the binary counter driving the EPROM address lines and driving the synthesiser to setup the frequencies. What I didn’t know, is how.
 I removed the EPROM and dumped it and noticed some very repeated patterns.
-<eprom.bin>
+{{ :packet:eprom.zip |}}
-The next phase was to trace out the digital circuit around the EPROM and these other chips to understand what was happening. This is where things started to get less straight forward.
+The next phase was to trace out the digital circuit around the EPROM and these other chips to understand what was happening. This is where things started to get less straight forward (this was a quick dump of tracing things. Most are surface mount and dont have any silkscreen identifiers).
-<<schematic>>
+{{:packet:schematic.png?400|}}
 Some points I noted about the circuit:
@@ Line 34: / Line 35: @@
   * The EPROM was clocked via the RC NOR gate oscillator
   * This oscillator could be stopped by D7 of the EPROM going HIGH
+  * D4 - D6 were used to send the DATA, CLOCK and ENABLE signals to the NJ88c22
   * The reset circuit was triggered each time the channel switch position was changed, which would start the counter again from zero
@@ Line 75: / Line 77: @@
 I modified my C program to account for the PTT line changes and found that on TX the frequencies were correct but at RX they were low. But they were all low by 21.4Mhz, which sounded very much like a standard IF frequency! So that answered that, phew!
 At this point, I was confident that I could change the data for a frequency I wanted.
 A quick modification to the C program made a new EPROM image and I was ready to test.
 On the bench, I plugged it into the dummy load and tested the channels according to what I had calculated from the EPROM image. They were all wrong :-?
@@ Line 99: / Line 103: @@
   * What is the audio path like for 3600 or 9600 ? I think it’s going to be restricted and may need some modification.
+<sub>//Some stupid mistakes and time wasting caused by me not being able to read or count properly have been omitted from this article for readability :-P//</sub>