Can anybody tell me what board is in the Cobra 142 GTL? Is it the same as the 2000 and many of the export radios out there?
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
-
Retevis is giving away Radios for the New Year and Every Member is Eligible. Click Here to see the details!
Cobra circuit boards
- Thread starter Still Runner
- Start date
Pretty sure the circuit-board number is PC-385.
It's similar to but different from the Cobra 2000GTL and 148GTL as well as the Uniden Madison. Those three radios split the receiver's signal path into two "conversions". The intermediate frequency for SSB is 7.8 MHz. This makes it a single-conversion radio in SSB. AM mode converts the 7.8 MHz down to 455 kHz. That's where the term "dual conversion" comes from. stepping down the frequency of the receiver signal twice from the original channel frequency.
This permits using a crystal filter for sideband that's fairly narrow. Pretty sure it's 4 kHz. This would not be wide enough for AM.
The 455 kHz path the AM receive signal follows is wider, to let both sidebands and the carrier pass through. Typical width is 8 kHz.
The Cobra 142 and Uniden Washington have a receiver that is single conversion for AM and SSB both. Since a single crystal filter has to be wide enough for AM it's a bit too wide for sideband. Some folks will complain that it's too narrow for AM and too wide for SSB.
Bottom line is that the simpler receiver layout was cheaper to build. Dual-conversion models were priced higher when they were introduced. I'm not convinced the penalty in receiver performance is all that big a deal.
Trust your ears. If you don't like the way a radio's receiver audio sounds, stay away from that model.
73
It's similar to but different from the Cobra 2000GTL and 148GTL as well as the Uniden Madison. Those three radios split the receiver's signal path into two "conversions". The intermediate frequency for SSB is 7.8 MHz. This makes it a single-conversion radio in SSB. AM mode converts the 7.8 MHz down to 455 kHz. That's where the term "dual conversion" comes from. stepping down the frequency of the receiver signal twice from the original channel frequency.
This permits using a crystal filter for sideband that's fairly narrow. Pretty sure it's 4 kHz. This would not be wide enough for AM.
The 455 kHz path the AM receive signal follows is wider, to let both sidebands and the carrier pass through. Typical width is 8 kHz.
The Cobra 142 and Uniden Washington have a receiver that is single conversion for AM and SSB both. Since a single crystal filter has to be wide enough for AM it's a bit too wide for sideband. Some folks will complain that it's too narrow for AM and too wide for SSB.
Bottom line is that the simpler receiver layout was cheaper to build. Dual-conversion models were priced higher when they were introduced. I'm not convinced the penalty in receiver performance is all that big a deal.
Trust your ears. If you don't like the way a radio's receiver audio sounds, stay away from that model.
73
Umm.
Why?
Lots of talent here to contribute in an open thread. Plenty of folks here familiar with this kind of radio.
73
Why?
Lots of talent here to contribute in an open thread. Plenty of folks here familiar with this kind of radio.
73
Okay basically what I'm asking is there are so many people that are modifying and bastardizing these old classic radios adding extra channels channel mods vfos echo boards and all that stuff and I'm seeing a lot of YouTube videos where people say I got x number of parts radios that I'm taking apart to make good radios and what I'm wondering is if I can take a 10 m radio board and put it in a Cobra 142 or a Cobra 2000 and save a classic radio chassis and modernize it by doing that?
As for pulling out the main circuit board from a 40-channel SSB CB and replacing it with something else? This will be a mechanical challenge. Holes in the heat sink won't line up. Circuit-board mounting hole tabs will have to be fabricated. Pretty sure the mount holes for a Uniden 40-channel board won't line up with the mount holes on a typical RCI-made 10-meter radio. More fabrication.
Knew a guy who customized 1970s base CB cabinets by installing a Cobra 148GTL into DAK or Tram cabinets. Said he wouldn't put a RCI-made radio into one. Said the shrill receiver audio and higher noise level hurt his ears. Was an artillery officer in 'Nam. Said his hearing was never the same after the last tour. Said the sound of the Uniden-made circuit boards was just better.
So just what is the objective, all in all? To use a radio in a classic cabinet on the 10-meter ham band?
Not all 10-meter radios are created equal. Some of them are more broad banded than others.
And the tendency for the frequency to drift makes operating sideband less satisfying.
I think I would start with a clear objective and take it from there.
73
Knew a guy who customized 1970s base CB cabinets by installing a Cobra 148GTL into DAK or Tram cabinets. Said he wouldn't put a RCI-made radio into one. Said the shrill receiver audio and higher noise level hurt his ears. Was an artillery officer in 'Nam. Said his hearing was never the same after the last tour. Said the sound of the Uniden-made circuit boards was just better.
So just what is the objective, all in all? To use a radio in a classic cabinet on the 10-meter ham band?
Not all 10-meter radios are created equal. Some of them are more broad banded than others.
And the tendency for the frequency to drift makes operating sideband less satisfying.
I think I would start with a clear objective and take it from there.
73
Well that is my objective to save and resurrect one of these old classic chassis with say bored out of a superstar or general Lee or something and have all the modern 10 m capability but it's not necessary from what you're saying it sounds like I could do it with a 148 board and just go that route but then you don't have the extra channels and all that stuff either
I just figured it's a way to save an old classic radio chassis from the scrap pile and have a modern updated radio
The 148 was built and sold for the better part of 40 years. Came from a long list of different vendors and factories.
They are not all created equal.
If you care about sideband, the "updated" radios may be a disappointment.
And if AM alone is your thing, go for it! The AM/FM-only "10-meter" radios may suit you better than an old sideband CB that has age-related issues.
73
They are not all created equal.
If you care about sideband, the "updated" radios may be a disappointment.
And if AM alone is your thing, go for it! The AM/FM-only "10-meter" radios may suit you better than an old sideband CB that has age-related issues.
73
