UHF MCX1000 Alignment

[w4rez]

I've got one of these things that I'm trying to use on the amateur 70 cm band. It programmed up and the VCO locks just fine on 70 cm but it was pretty deaf.

Unfortunately I have little in the way of test equipment, and only have access to service manual for the VHF version of the radio. What I do have is a PC-based Windfreak SynthUSBII signal generator and a VOM.

The service manual calls for a Motorola RF probe and adapter that I do not have, so what I did was this:

1. Connect VOM across speaker leads.
2. Inject weak signal into radio (This signal generator doesn't have uV or dB signal level settings, so I can't provide them).
3. Adjust L5 for maximum AC voltage reading on VOM.
4. Adjust L707-L709 for minimum AC voltage reading on VOM.

All of my channels are within 5 MHz of each other, and adjusting L704-L706 had no effect so I'm going to presume that the radio is only using the "high" front end.

The radio can definitely hear better than it could before, but it's Rx sensitivity is pretty poor compared to my GM300 and GE Monogram that I use on this band.

I'm probably doing something wrong, aside from the obvious problem of not having the proper test equipment.

Can somebody offer up a better way to tune this thing using what I have available?

[d119]

Realistically, since you don't have the correct test equipment (which I would say in this application is OK) - I'd set the receiver for something mid-point across the spread you are working with, run the signal generator into it, get it noisy and tune the front end for max quieting, reducing the input signal as required until you reach saturation.

Then check sensitivity at either end of the 5MHz and make sure it's reasonable.

Is adjusting the front end isn't doing anything, something is wrong...

[Will]

Use a pad on the antenna to match the receiver's input to 50 ohms. you may have to loosely couple the signal to get down into the noise and adjust for best signal to noise.

MCX1000 AKA Canadian Syntor. Worked on lots of them when I worked for Motorola.