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Any mods for the new Cobra 29 Classic am/fm yet
- Thread starter n0zna-1
- Start date
Shadetree Mechanic
Delaware Base Station 808
For a better sounding fm, 5khz deviation is alot better than 2.5khz narrowband deviation. You will need an fm deviation meter to properly adjust it.
It's better left alone. If you want better audio stay on AM. FM will never sound as good for transmit audio in my opinion & it's all Carrier & no Forward Swing so you will Not get the audio Punch. It's just the nature of the beast for FM. It's easy to over deviate on FM & sound like POOP!
Speaking of deviation, any idea where you can find a cheap deviation meter, cheap as in good enough for cb but not good enough for NASA?
I am working on designing a replacement CPU board that talks directly to the BK4802 chip they used for this series of radios. I found the "secret sauce" code to translate frequency to PLL codes, and am working on the code to read the Delta Tune pot (which does go to the original CPU board), to add/subtract Delta Tune calculations to the calculated center frequencies. My idea is to have it stepped in 5kc jumps in VFO mode, to hit the Zero's, but in Channel mode, it would have a "look up table" for the original Channel to Frequency codes, and add in the offset for bands to make it match a Galaxy style radio.
I had thought of using an onboard Si5351 (more code examples) but that would need to be hard LPF'ed to "kill" the harmonics generated from the square wave signals from the outputs. Of the which I did incorporate into this version of the boards being designed.
I need to work up a Dual 7 Segment LED driver in the board hardware and software, to talk to the existing LED display, or a 128x64 OLED display to replace the original dual 7 segment LED in the radio. Maybe a 128x32 OLED to replace the meter (if using the original LED Display), would need to "read" the existing meter voltages, for S-Meter and Power output, SWR calibration and reading??
Like a Johnny Cash Cadillac, "One piece at a time, and it didn't cost me a Dime"
I had thought of using an onboard Si5351 (more code examples) but that would need to be hard LPF'ed to "kill" the harmonics generated from the square wave signals from the outputs. Of the which I did incorporate into this version of the boards being designed.
I need to work up a Dual 7 Segment LED driver in the board hardware and software, to talk to the existing LED display, or a 128x64 OLED display to replace the original dual 7 segment LED in the radio. Maybe a 128x32 OLED to replace the meter (if using the original LED Display), would need to "read" the existing meter voltages, for S-Meter and Power output, SWR calibration and reading??
Like a Johnny Cash Cadillac, "One piece at a time, and it didn't cost me a Dime"
There is going to be a lot of crappy over deviated sounding radios created by the screwdriver crowd.
As SS said just leave it alone and enjoy having a new "mode" now.
Not in this case. They have made it too hard for your average golden screw driver type. People will just get an export radio like they have been doing for the last 30 years.
The FM transmit audio is going into the BK4802 chip, which is actually an FM 2 way transceiver chip, in this case, only being used in the TX mode, for the Cobra 29 FM radios TX (direct frequency) and RX (offset by +10.695, High Side injection into the 1st mixer). The RX functions of the chip itself are locked out and not used.
As to an FM Deviation meter, I found a quad-op-amp schematic that can be calibrated and used for FM deviation measurement.
This has a meter and O'scope outputs. I have this meter board design started in EagleCAD.
As to an FM Deviation meter, I found a quad-op-amp schematic that can be calibrated and used for FM deviation measurement.
This has a meter and O'scope outputs. I have this meter board design started in EagleCAD.