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Cobra 29LX Changed Again
- Thread starter CbRadiosPRONTO
- Start date
The FM models are now available; both, the Classic as well as the Chrome. (As of March 1)
Hey now, this is cool. I've been working on writing code to use different pll's in the Cobra 29 with an arduino. I'm really interested in learning more about the pll in the new style 29. I'm not to good with RF electronics but programming Im very comfortable with.
Does anyone know where I can get more information on this new style?
Thanks
Does anyone know where I can get more information on this new style?
Thanks
The PLL in the 29 radios has always been the "ROM" type. The actual binary divide-by-N codes are stored in a ROM. The binary code coming out of the channel selector is only the ROM address, not the binary divisor value. The VCO feeds directly into the PLL chip, no down conversion is needed. The ROM has two separate stored divisors for each channel, one for receive and one for transmit. The PLL jumps frequency by 455 kHz between transmit and receive.
Have you encountered Lou Franklin's "PLL Handbook"? Best explanations of this kind of PLL ever published.
73
Have you encountered Lou Franklin's "PLL Handbook"? Best explanations of this kind of PLL ever published.
73
Well, let me know if you want a radio. Maybe we’ll all learn something if you’re going to post some type of results here.
Hopefully some of the smarter members here can figure out the channel mod. It would be great if I could solder one of my expo kits on the back side of the vco board. That way I could take my Lincoln 2 out of the mobile for the hot Oklahoma summer.
The PLL in this latest generation of Cobra 29LX and the new 29 AM/FM models are serial programmed, this particular PLL outputs the VCO frequencies direct.
Here are FCC submittal pictures for the new AM/FM Cobra 29 radios out now. This also uses the same PLL/VCO daughterboard as what the 2nd Gen 29LX now uses.
On Page 11, shows what is under the soldered down metal lid of the PLL/VCO daughterboard, a Beken BK4802P, which is a repurposed FM/ASK chip.
These images pulled from the FCC submittal PDF listed above.
One of my ideas for this is a Microcontroller (like Arduino) that intercepts the PLL Data, does fancy math stuff to the data ( +or - 450 kc for upper/lower bands of channels, -5 kc to get Zero's or +10kc to get "A" channels), then pushes the modified data to the PLL.
Any time there is a change in PLL chip used, the data would have to be reprogrammed to match the new chip. So, a Uniden 980SSB uses one PLL, where a President Madison (new mobile) uses another, these C29 AM/FM radios use a 3rd.
I do not think there is any way to get between the PLL and internal VCO, I believe it is an internal connection to the chip itself.
But, I may still have another way! Think Outside The Box!
Here are FCC submittal pictures for the new AM/FM Cobra 29 radios out now. This also uses the same PLL/VCO daughterboard as what the 2nd Gen 29LX now uses.
On Page 11, shows what is under the soldered down metal lid of the PLL/VCO daughterboard, a Beken BK4802P, which is a repurposed FM/ASK chip.
These images pulled from the FCC submittal PDF listed above.
One of my ideas for this is a Microcontroller (like Arduino) that intercepts the PLL Data, does fancy math stuff to the data ( +or - 450 kc for upper/lower bands of channels, -5 kc to get Zero's or +10kc to get "A" channels), then pushes the modified data to the PLL.
Any time there is a change in PLL chip used, the data would have to be reprogrammed to match the new chip. So, a Uniden 980SSB uses one PLL, where a President Madison (new mobile) uses another, these C29 AM/FM radios use a 3rd.
I do not think there is any way to get between the PLL and internal VCO, I believe it is an internal connection to the chip itself.
But, I may still have another way! Think Outside The Box!
Thank you for the info. Yes, I have a copy of the PLL data book by Franklin and I am familiar with the ROM based type PLL and the shift to generate the 455.
In this case i can't see how it would be fruitful to put an arduino in between the channel selector and pll.
We were thinking of a full pll swap. I think the issue would be the channel selector not being compatible with a different pll so that would be where the arduino comes into play.
This all started from my buddy wanting to turn the fake frequency counter into a real frequency counter on his LX.
I bought a used LX from ebay and when I told my wife she didn't have a cow but took it to a whole new level where I thought she was about to give birth to a cow. But I didn't really care. I hope the radio will be here soon.
In this case i can't see how it would be fruitful to put an arduino in between the channel selector and pll.
We were thinking of a full pll swap. I think the issue would be the channel selector not being compatible with a different pll so that would be where the arduino comes into play.
This all started from my buddy wanting to turn the fake frequency counter into a real frequency counter on his LX.
I bought a used LX from ebay and when I told my wife she didn't have a cow but took it to a whole new level where I thought she was about to give birth to a cow. But I didn't really care. I hope the radio will be here soon.
The original 23ch Cobra 29A is still alive and well because of quality parts and good workmanship. Part of that longevity is also credited to the far lower amount of hacks preformed back then. The occasional crystal swapping for extra channels was about the only mod done. The prolific number of clipping diodes, audio hacks, final substitutions etc. that now exists came along much later in the 40ch era. As you know, quality has decreased substantially over the years. Grandfather 29A is truly saddened to what has happened to all his offspring.
I have a few of the 23ch 29’s, and one 29GTL and one first model 29LTD (no classic etc). They all work very well. I am not really an AM only type, so I got rid of the rest I had so they would be used at least. Overall, I would have to agree with Sunbulls.