I found a comment in google groups about changing the crystal in the
Cobra 148 GTL radio

http://groups.google.com/group/rec.r...719754 5990ad

Plase, I apreciate too much a respose to this questions:

1.- In the comment say:

"...For every 0.150 Mhz increase in freq of this Crystal you will get a
450Khz increase in operating freq..."

QUESTION: What is the minimum operating frecuency that I can reach
changing the X3 crystal ? 25Mhz, 20Mhz, 15 Mhz, 10Mhz, 7Mhz.

2.- About "...retune the Mixer coil..." how I can do that? (an url may
be usefull to read about that)

3.- About "...retune the Mixer coil..." is realated with the voice look
or 10khz steps ? what will be the bad functioning in the radio if I can
not retune de mixer coil.

Thanks a lot

Att.
Diego.

In article .com, "Diego
Cueva" wrote:

1.- In the comment say:

"...For every 0.150 Mhz increase in freq of this Crystal you will get a
450Khz increase in operating freq..."

QUESTION: What is the minimum operating frecuency that I can reach
changing the X3 crystal ? 25Mhz, 20Mhz, 15 Mhz, 10Mhz, 7Mhz.

2.- About "...retune the Mixer coil..." how I can do that? (an url may
be usefull to read about that)

3.- About "...retune the Mixer coil..." is realated with the voice look
or 10khz steps ? what will be the bad functioning in the radio if I can
not retune de mixer coil.

Diego-

I am not familiar with that radio but have modified others to work in the
Ten Meter Ham Band.

The various tuned circuits in the radio have a limited adjustment range,
probably around 25 to 30 MHz at most. Beyond that, you would need to
replace or rewind coils and/or change tuning capacitors for each circuit
affected.

1. The X3 crystal is mixed with other signals to achieve the operating
frequency. If you change its frequency far enough, other harmonics
(Fundamental, 5th, 7th) may be selected. In addition, the mixing process
has both sum and difference products present. Moving the frequency far
enough, the wrong product could be selected. Either case might produce an
unexpected operating frequency.

2. The mixer coil probably has a ferrite core that you can adjust with
the appropriate plastic tool. DO NOT use a metal tool. This could easily
crack the core, causing it to dig into the coil form as you attempt to
turn it.

3. The mixer coil should not be related to the voice or 10 KHz steps.
However it might result in a different step size or opposite sideband if
adjusted for the wrong product as in (1) above. For small frequency
changes such as converting to the Ten Meter Band, not being tuned would
probably result in low output on transmit and poor sensitivity on receive.

73,
Fred, K4DII