MIDLAND CB MODEL 79-265 MOBILE EXTRA CHANNELS/CLARIFER MODS

[500kpot]

Well now you've got me thinking about mixers and now may have to run some experiments. Sound like a fun way to pass a few more days before school
starts again.

As for my Cobra 29, and I appreciate your Expo100 A+ advice, the mod on trasmission1 looks really cool and I think I'm going to give that a whirl.

Best Wishes
500kpot

 

[NZ8N]

The transmission1.net posting is basically an updated Expo 100 A+ kit. They are programming the si5351 to do the same thing as the Expo, but with -5kc etc.. offsets. I would leave L22 intact (it is a tuned circuit at 15 MHz), and instead, lift the leg of C94 coming from pin 10 of the PLL (5.12 out), and inject the signal from the si5351 to the lifted leg of C94.

 

[500kpot]

Hello again Mr. NZ8N,

Yes, Sir. I think I got what your getting at. Please correct me if I'm wrong. Are you saying to run the Si5351 at ~5 megahertz and let L22 triple that to ~15 megahertz, meanwhile add the VCO to the ~15 megahertz then obtain funnies based on the tripling action of L22?

Best,

500Kpot

 

[nomadradio]

The 15.36 MHz that mixes with the radio's VCO is fixed in the original circuit, since the 5.12 MHz square wave from the chip is the 10.24 MHz crystal frequency divided by two. The PLL is effectively "locked" to this 15.36.

The PLL will "follow" this 15.36 frequency, whether it's fixed or if it changes. Subbing a VFO for the fixed 5.12 MHz will cause the radio's PLL to follow that VFO wherever it goes.

Until the PLL's tuning voltage reaches its upper or lower limit.

73

 

[500kpot]

The PLL is effectively "locked" to this 15.36.

I was under the impression the PLL measures the VCO frequency output and makes sure the ncode from the channel selector, or internal ROM in this case, is the same as the VCO ouput. Like the rx ncode for channel 1 is 91 and the PLL measures the VCO and uses a DC voltage to adjust the VCO to .91 megahertz and then mixes the VCO frequency with the 15.36 megahertz which is then applied to FET 1 to mix the incoming signal of 26.965 megahertz to obtain 10.695 megahertz then subtracted from the reference oscillator of 10.240 megahertz to get 455 kilohertz.

I think this correct for rx anyway but I could be wrong. It certainly wouldn't be the first time and I'm sure not the last LOL.

Subbing a VFO for the fixed 5.12 MHz will cause the radio's PLL to follow that VFO wherever it goes.

I am also under the impression the transmission1 post uses the Si5351 as a straight oscillator with frequency output of 14.91, 15.35, and 15.81 megahertz - a digitally enhanced Lescom board. By enhanced I mean the 5 and 10 kilohertz switch. If this is the way it is done I would assume the VCO will never limit out because its still using the stock ncodes from the channel selector.

I can't verify this method of operation until I see the code. I have requested from the author of the post on transmission1. So far, I haven't received any reply.

Which raises another question that I will hunt down the answer for is why can't the PLL and VCO be removed from operation, a simple oscillator at 15.36 megahertz built, then use the Si5351 to generate a false VCO frequency, and then mix that false VCO output with the 15.36 megahertz. I can't see why this won't work but I'm eager to mock it up and see what happens. I also think for maximum frequency range a 10.695 megahertz transmit oscillator would need to be fashioned up and it appears youtube poster "TT" has already accomplished this and looks simple to make.


Thank you for your post nomadradio and as always I appreciate any information or input. And many thanks to NZ8N for valued information and helping me understand the methodology of the Cobra 29 PLL.

Best Wishes,

500kpot

 

[hpssb]

I can't verify this method of operation until I see the code. I have requested from the author of the post on transmission1. So far, I haven't received any reply.

Mentioned this tonight to them on t1, they said no request has been received by email, priv msg, or in the t1 forum.

Cant help with the technical stuff on method of operation it's way over my level, can pass you on their direct email address in a pm if you like.

They did a similar mod in my 3900 ssb radio to cure the drifting and its still working great 6 months later.

 

[500kpot]

Thats odd. I'll have to try again. However, I have found a great deal of information about the Si5351 since I made the initial request.

I am interested in having a peek at the code though. I'm curious to know if the programmer who wrote the software created a lescom emulation. I almost have to think so due to the fact of where the output of the Si5351 is interfaced to the radio and the band selection has the same frequency range as a lescom Corbra 29 funnies kit.

Ill have to go back and request again and I thank you for bringing this to my attention and also the feedback on your radio.

Best Wishes
500kpot

 

[NZ8N]

Lescomm got his idea from an Expo 100 A+, that being the original "funny channel" kit for a Cobra 29 type radio. He also copied the S kit for his 25 kit.
Speaking of, the S kit idea is a bad idea from the start. They want you to bypass the 10.695 filter, which opens it up for a whole lot of bleedover. Receive the Superbowl on every channel, anyone?

 

[500kpot]

They want you to bypass the 10.695 filter, which opens it up for a whole lot of bleedover. Receive the Superbowl on every channel, anyone?

That doesn't sound too good at all.

And some of those Lescomm products are quite expensive. Even scratched off part numbers from I.C.s. Thats just silly.

 

[nomadradio]

Les is jealous of the details of his design. Gotta figure he spent money to perfect and produce it.

I never gave away source code for the prior-generation embedded stuff we sold over the years. The source file for the Mark 4 synthesizer we sold was 1100 lines long. In PIC assembler, mind you.

Anyone actively selling a VFO solution using the Arduino and Si5351 seems to be keeping their cards close to the vest as well. One outfit will sell you the executable binary along with a way to upload it into the Arduino nano board. But they don't let loose the source code used to produce the firmware image. For that matter they use some sort of copy protection key in the thing.

I'm still learning to use the OLED displays with the nano. Haven't decided what I'll do with source code once we have a version that fits our needs. If it works with a Tram and Browning, that's all I need.

73

 

[TM86]

Les is jealous of the details of his design. Gotta figure he spent money to perfect and produce it.

I never gave away source code for the prior-generation embedded stuff we sold over the years. The source file for the Mark 4 synthesizer we sold was 1100 lines long. In PIC assembler, mind you.

Anyone actively selling a VFO solution using the Arduino and Si5351 seems to be keeping their cards close to the vest as well. One outfit will sell you the executable binary along with a way to upload it into the Arduino nano board. But they don't let loose the source code used to produce the firmware image. For that matter they use some sort of copy protection key in the thing.

I'm still learning to use the OLED displays with the nano. Haven't decided what I'll do with source code once we have a version that fits our needs. If it works with a Tram and Browning, that's all I need.

73

I found interfacing with OLED modules to be pretty easy, if you use existing libraries and fonts. Getting the size and placement of your display elements can be a bit tedious, but once you get it it seems easy enough.

Also, I don't think it would be that difficult to develop VFO based on the Arduino and Si5351 pair, since there's plenty of examples out there from the ham world. If I can ever be bothered to do one I'd throw the source code out there. Not like it would destroy my business. (HOA rules, no home businesses!) It's just a matter of time before someone does it anyways.

 

[nomadradio]

The hardware is pretty much tinkertoys. An analog buffer for the output will be needed for some radios, but apparently not for the Cobra 148-type boards.

Finally got this batch of OLED displays to run the Adafruit demo. Turns out if you disregard the "address 78 or 7B" printed on the display board's screen print it works a lot better. Turns out to run at the default address for the AF demo.

Next to try the encoder library.

Progress, inch by inch.

 

[Retro CB Guy]

The 15.36 MHz that mixes with the radio's VCO is fixed in the original circuit, since the 5.12 MHz square wave from the chip is the 10.24 MHz crystal frequency divided by two. The PLL is effectively "locked" to this 15.36.

The PLL will "follow" this 15.36 frequency, whether it's fixed or if it changes. Subbing a VFO for the fixed 5.12 MHz will cause the radio's PLL to follow that VFO wherever it goes.

Until the PLL's tuning voltage reaches its upper or lower limit.

73

Actually I brought some of these over recently, but time elapsed and we didn't get to them, thanks for input Chris!

73's

 

[Retro CB Guy]

So also I could just have Nomad put in the DDS setup that was discussed here but not sure I want to go that route. I do know someone in UK was selling this very radio with upper channels above 40 in it but I didn't buy it as I have 4 of them alredy LOL.

73's Retro