Galaxy 88 Alignment

[Herbert Lindsey]

I get to the part where you check R151 for 10.2965 and get nothing. I’ve checked all the components from the X4 crystal to R151 and everything looks good. At the crystal one side has 10.29680 and the other side is like 29.something. Help! AM carrier offset....L26

 

[nomadradio]

This is not an easy signal to measure. We use a receiver calibrated to WWV and "tune it in" to set the carrier on this kind of radio. That way we don't have to connect a probe to the circuit.

And that's part of the problem. The tip of a probe will also act as if it were a capacitor connected to ground on one side. This tends to change the frequency of a crystal if you tap directly into the oscillator circuit to make a measurement.

The instructions posted for this at cb tricks are messed up. Don't try to hook anything up to "R102". The test point at R151 is right for all 3 modes, but you need to use a "times 10" or "X10" or "ten-to-one" type 'scope probe to feed the counter's input jack. This reduces that pesky probe-tip capacitor a lot. Just one problem. The counter input has to be REALLY sensitive to give you a steady reading this way.

All that hassle is why we stopped using a counter to make that adjustment.

You don't need to key the mike to get a reading in sideband modes. You'll have to key the mike to get this reading on AM.

73

 

[groundwire]

I use my scope as a preamp for the frequency counter to read those pesky low level signals.

 

[nomadradio]

My favorite feature of the Tektronix 465. The "Channel B output" jack. Stayed patched into my counter's input jack.

Haven't had a 'scope since those days that provided that function.

73

 

[Herbert Lindsey]

And I thought I was doing it right for once. My scope is an old BK Precision and my signal generator is one of those new cheap digital ones. The radio came out good except AM mode sounds a little low after I put the limiter back in. It’s been a learning experience but now I’m hooked.