Convert CB to 10

[Dovebar1]

Hi,

I have a Cobra 140 GTL that is similar to the Cobra 142 GTL which is the base version of the
140.

I would like to convert it to operate only on 10 Meters. Originally it uses a 11.1125 Mhz Crystal
and a tripler circuit to raise it to 33.3375 Mhz .
At channel 1 it mixes with 1.43Mhz to bring it to
34.7675 Mhz. This mixes with 7.8025 Mhz to
bring it to 26.965 Mhz.

I purchased a crystal for 11.555 Mhz which when the same math is done should bring channel 1 about 28.2925 Mhz.
I also purchased a copy of the Sam's for this model.

It turns out in the alignment it reads that the tripler output has be tuned for max output
with scope at test point 16 but that tp does not have a white test point coming out the component side, the manual reads that the tp
Is monitored at output of L18 which connects directly to TR 19 mixer thru the circuit board trace.

So either go thru this finding the trace point
solder a wire for the scope probe and the circuit ground or as an alternative use or make a expander 160 circuit like cbc international made.
My question is has anyone on the forum worked with this radio and has any information on this
exact alignment and how to best go about it.

Any help will be highly appreciated.

Thank you, Jim.

 

[prcguy]

An 11.5575MHz crystal would put you at 28.300 for ch 1. Its easy to pad crystals down slightly in frequency but not up.

Hi,

I have a Cobra 140 GTL that is similar to the Cobra 142 GTL which is the base version of the
140.

I would like to convert it to operate only on 10 Meters. Originally it uses a 11.1125 Mhz Crystal
and a tripler circuit to raise it to 33.3375 Mhz .
At channel 1 it mixes with 1.43Mhz to bring it to
34.7675 Mhz. This mixes with 7.8025 Mhz to
bring it to 26.965 Mhz.

I purchased a crystal for 11.555 Mhz which when the same math is done should bring channel 1 about 28.2925 Mhz.
I also purchased a copy of the Sam's for this model.

It turns out in the alignment it reads that the tripler output has be tuned for max output
with scope at test point 16 but that tp does not have a white test point coming out the component side, the manual reads that the tp
Is monitored at output of L18 which connects directly to TR 19 mixer thru the circuit board trace.

So either go thru this finding the trace point
solder a wire for the scope probe and the circuit ground or as an alternative use or make a expander 160 circuit like cbc international made.
My question is has anyone on the forum worked with this radio and has any information on this
exact alignment and how to best go about it.

Any help will be highly appreciated.

Thank you, Jim.

 

[Dovebar1]

An 11.5575MHz crystal would put you at 28.300 for ch 1. Its easy to pad crystals down slightly in frequency but not up.

 

[Dovebar1]

Thanks for that but just looking for info on
this alignment procedure on this exact model.