R2001C RF internal wattmeter calibration

[cahighwayman22]

Hello.

Anyone familiar with the calibration procedure for calibrating the internal wattmeter on the R2001A/B/C SM's? The book doesn't anything about a calibrating procedure. There are two pots on the RF wattmeter board (labeled R122 "GAIN" and R143 "OFFSET").

The wattmeter reads fine on UHF, but is about 25W low on VHF.

-Thank you

-Trevor

[DJP126]

Your problem is not likely just a cal problem. We used the gain and offset adjustments to balance the DC voltages between a 10X gain in wattage (we commonly used 5W and 50W RF in). The different reading accuracy between UHF & VHF is USUALLY caused by a bad impedance between the frequencies. Most likely you are looking for a component that is causing a linearity problem. Main possibilities are AT2, K101, CR111, R106 (selected value could be wrong), CR105 or one of the chip caps in the circuitry in those areas.

[cahighwayman22]

I did find CR110 and CR111 to be bad. Motorola only shows there part number for those diodes. My father had me replace them with 1N5711 diodes.

It did make a little difference, but the VHF side is still low.

BTW, are those relays still available? Cause if that's bad (Or AT2) then I may be SOL.

Thank you

-Trevor

[cahighwayman22]

I fixed the problem. The S101 reed coil was bad, and so was CR105. I replaced both from a spare RF module that had one good coil (the other coil was burned to bits, which makes me think someone applied too much RF for too long).

The A B C models sure are fragile when it comes to applying RF into the I/O port. I wouldn't even apply 100W for more than 5 seconds every hour. Lol

This must be why the D series has the power attenuator at the RF I/O port before the relays.

-Trevor