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Frequency Checkpoints...

On a Cobra 25, there are just two - well more if you're curious.,..

[ATTACH=full]45283[/ATTACH]

TP3 is the main one - that one not only is the PLL/VCO out to grab the channel - it also is how much signal you have from the VCO to work with. So you use TP3 to determine the 1St IF Mixer frequency, and the QUALITY of it - on a scope P-2-P.
- the IF is between 16 to 17MHz - and starting at channel 1 - 16.27x - BUT IN TX it's 16.72x
That difference is that 455kHz shift - you'll see it all on TP3
The "x" is relative, it can bounce between 3 to 2 to as high a 5.
In TX, to "center" you adjust your 10.240 X! - with TX on TP4 (your 27MHz) R46 and R47 in TX section
10.240 is adjusted thru VC1 or if none, choose value used at C111 to trim it up higher or lower to get it closer, can't always hit the exact - but unless you have VC1 (a variable cap) there's not much you can do. Except plug in values until you can get its' last digit to 4 5 or 6 - at TP4 that would be 27.184 to 27.186 - you're ok.
[ATTACH=full]45285[/ATTACH]

Check your connections, look for your soldering and make sure no shorts.

<blockquote data-quote="Handy Andy" data-source="post: 765493" data-attributes="member: 52309">Frequency Checkpoints...On a Cobra 25, there are just two - well more if you&#039;re curious.,..[ATTACH=full]45283[/ATTACH]TP3 is the main one - that one not only is the PLL/VCO out to grab the channel - it also is how much signal you have from the VCO to work with. So you use TP3 to determine the 1St IF Mixer frequency, and the QUALITY of it - on a scope P-2-P.<ul>
<li data-xf-list-type="ul">- the IF is between 16 to 17MHz - and starting at channel 1 - 16.27x - BUT IN TX it&#039;s 16.72x</li>
<li data-xf-list-type="ul">That difference is that 455kHz shift - you&#039;ll see it all on TP3</li>
<li data-xf-list-type="ul">The &quot;x&quot; is relative, it can bounce between 3 to 2 to as high a 5.</li>
<li data-xf-list-type="ul">In TX, to &quot;center&quot; you adjust your 10.240 X! - with TX on TP4 (your 27MHz) R46 and R47 in TX section</li>
<li data-xf-list-type="ul">10.240 is adjusted thru VC1 or if none, choose value used at C111 to trim it up higher or lower to get it closer, can&#039;t always hit the exact - but unless you have VC1 (a variable cap) there&#039;s not much you can do. Except plug in values until you can get its&#039; last digit to 4 5 or 6 - at TP4&nbsp; that would be 27.184 to 27.186 - you&#039;re ok.</li>
</ul>
[ATTACH=full]45285[/ATTACH]Check your connections, look for your soldering and make sure no shorts.</blockquote>

[QUOTE="Handy Andy, post: 765493, member: 52309"] Frequency Checkpoints... On a Cobra 25, there are just two - well more if you're curious.,.. [CENTER][ATTACH=full]45283[/ATTACH][/CENTER] TP3 is the main one - that one not only is the PLL/VCO out to grab the channel - it also is how much signal you have from the VCO to work with. So you use TP3 to determine the 1St IF Mixer frequency, and the QUALITY of it - on a scope P-2-P. [LIST] [*]- the IF is between 16 to 17MHz - and starting at channel 1 - 16.27x - BUT IN TX it's 16.72x [*]That difference is that 455kHz shift - you'll see it all on TP3 [*]The "x" is relative, it can bounce between 3 to 2 to as high a 5. [*]In TX, to "center" you adjust your 10.240 X! - with TX on TP4 (your 27MHz) R46 and R47 in TX section [*]10.240 is adjusted thru VC1 or if none, choose value used at C111 to trim it up higher or lower to get it closer, can't always hit the exact - but unless you have VC1 (a variable cap) there's not much you can do. Except plug in values until you can get its' last digit to 4 5 or 6 - at TP4 that would be 27.184 to 27.186 - you're ok. [/LIST] [CENTER][ATTACH=full]45285[/ATTACH][/CENTER] Check your connections, look for your soldering and make sure no shorts. [/QUOTE]

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