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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

<blockquote data-quote="nomadradio" data-source="post: 763481" data-attributes="member: 22">Pretty sure the circuit-board number is PC-385.It&#039;s similar to but different from the Cobra 2000GTL and 148GTL as well as the Uniden Madison. Those three radios split the receiver&#039;s signal path into two &quot;conversions&quot;. 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&#039;s where the term &quot;dual conversion&quot; 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&#039;s fairly narrow. Pretty sure it&#039;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&#039;s a bit too wide for sideband. Some folks will complain that it&#039;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&#039;m not convinced the penalty in receiver performance is all that big a deal.Trust your ears. If you don&#039;t like the way a radio&#039;s receiver audio sounds, stay away from that model.73</blockquote>

[QUOTE="nomadradio, post: 763481, member: 22"] 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 [/QUOTE]

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