SDR Dongle Panadapter on a CB?

500kpot said:

I wonder why bother with the 10.695 megahertz adapter?

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...then locked to your radio's RX. Otherwise common $15 dongles are adequate on their own. Direct sampling however has it's pitfalls. Without some bandpass in front of a budget SDR it's easily overwhelmed by BC MW, and 88-108MHz as well as nearby RF anything.

Hifi reception plus ssb, fm etc as well. I can see the point clearly now. I'll have to make one for myself and give it a try.

If you're familiar it's just Hi-Z in Low-Z out with good flat gain.

Then just fingering the offsets for your particular radio and configuring HDSDR or the like.

The circuit was super simple. I have the schematic or should I say a doodle on almost a cocktail napkin.

Good enough, thou, to make it.

148gtl for example TP1 @ 34.7xx MHz or the HR2510 @ TP304 around 38.6xx MHz (gate of Q305) may be the same for 2600 and Lincoln, don't have that handy atm...

kopcicle said:

148gtl for example TP1 @ 34.7xx MHz or the HR2510 @ TP304 around 38.6xx MHz (gate of Q305) may be the same for 2600 and Lincoln, don't have that handy atm...

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Right off the test points! Now I'm going to pop the cover of my 148 and check it out, thanks.

Shadetree Mechanic said:

Right off the test points! Now I'm going to pop the cover of my 148 and check it out, thanks.

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come to think of it it would have to be downstream of the mixer ...

An Airspy HF+ Discovery is a cheap but exceptional receiver; receives just about as good as any high price tag SDR transceiver on the market... sometimes even better. It has amazing dynamic range, harmonic rejection, preselectors and never gets overloaded in my usage.
One of those tucked under the hood of virtually any CB base station, along with an MFJ 1707B, a USB micro to USB B panel mount cord, some coax, a USB A to B cord to your PC and some minimal soldering would make a really cool CB FrankenPan system.
I have been dreaming of putting all such components inside a handsome base for a little while.
I honestly have no idea if anyone has done one like this all under the cover of a base rig..think I'll Google it now, as was suggested.
Edit: Thought I'd mention that I use a similar system, though all components are external and separate. I use a Stryker 955hpc, a DaveMade T/R relay, and Airspy HF+ Discovery. Works amazingly well.

EDIT 2: How about adding a Raspberry Pi within the innards of the base station and a panel mounted HDMI port on the rear! How awesome would that be? I mean, you could just buy an Icom 7300....but hey.

I think Kopcicle is right. Not at the the 34 megahertz for the 148 but the 7.8 megahertz IF. I'll have a try today as I made this circuit last night and played with it on my Cobra 29. There was some SSB skip last night which seemed to run North/South here on the west coast. It did sound real good thou.

Also, I found, that the 10.240 reference oscillator shows up when expanding the bandwidth. I might not be saying that correctly. To put it another way, if the center of the screen is 10.695 megahertz the bandwidth will be about 130 kilohertz total or up 70 kilohertz and 70 kilohertz down if you don't want to see the reference oscillator (and its not that clean as there are some other signals as well).

However, swapping the I/Q and setting 10.695 megahertz all the way to the right edge of the screen seemed to show the entire 40 channel band actually plus a bit more. It did require a bit of fiddling. I'm going to investigate a bit more today as last night my GF wanted to go out so that ended that for the evening.

On the 148 the connection at the 7.8 megahertz mixer which is at the emitter of TR15 right before it goes into L7. Or, I should say that where it seem to work best for me. Others may find better places to tap the IF.

There is an issue of seeing the 7.345 megahertz oscillator on the band scope (the same as the Cobra 29 10.240 megahertz oscillator) So I put a switch on R21 to shut off the 7.345 oscillator. Now the bandwidth is quite large at what appears to be about 1 megahertz. So I put channel 20 in the center and I get ~50 channels down and ~50 channels up. Pretty cool. I still need to do sensitivity tests but it appears to work and found some signals way below channel 1 which I think was some weak skip from Mexico as they were speaking Spanish and the signal came and went very quickly. I would have never found that without the "band scope" (I hope that is the correct term).

There seems to be 2 other signals and I'm not sure where they are coming from but its easy to eliminate them with fiddling of the configuration on the SDR software because they aren't that close to 7.8 megahertz.

I've also noticed the 148 is much cleaner and has a flatter IF response than the Cobra 29 if I'm reading the data correctly.

And now it has become quite apparent if the first RX IF is 10.695 megahertz and the PLL uses 10.240 megahertz as a reference it will limit the bandwidth unless one doesn't care about seeing it, but it makes my head explode and I want to jump through the window.

kopcicle said:

Without some bandpass in front of a budget SDR it's easily overwhelmed by BC MW, and 88-108MHz as well as nearby RF anything.

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Yes, I agree. I'm using a 125 megahertz HF upconverter into the rtl-sdr which I believe to have some degree of filtering. Perhaps the two signals I see on the "band scope" are actually real signals being received and not coming from the 148 - but there is no information on them just a carrier. I need to work on this a bit more and I really need to finish fixing my signal generator so I can get "down and dirty" with the IF and investigate more to understand what is really going on but clearly the adapter works as it should.


I wish everyone Happy Holidays and a Prosperous New Year.