08-24-2020, 05:16 PM
Hi Folks,
I'm resurrecting this thread, since the frequency counter module I had been using seems to have led me astray! In my recent thread in "Other Radios" I'm working on a more modern digital set. I'd used one of the modules a while ago, to follow the procedures in the service manual. For communications receivers, I'm picky about frequency calibration to the "last digit" level - this probably says a lot about my OCD nature....
Anyway, After completing alignment, I found the radio slightly "off" tune, which could be corrected by using its fine control. We're talking a few hundred Hz here, and the offset was similar on all frequencies. That led me to check the BFO oscillators for LSB ad USB. Both were off by the same amount with respect to a tuned carrier. Verified by a good instrument, this pointed the finger directly at the cheap counter. It also explained why it looked as if the 18 MHz crystal in the PLL would not trim properly.
It is likely not a problem for many applications, but beware the accuracy delivered by these units if you plan to use them for precision work.
Cheers
Ed
I'm resurrecting this thread, since the frequency counter module I had been using seems to have led me astray! In my recent thread in "Other Radios" I'm working on a more modern digital set. I'd used one of the modules a while ago, to follow the procedures in the service manual. For communications receivers, I'm picky about frequency calibration to the "last digit" level - this probably says a lot about my OCD nature....
Anyway, After completing alignment, I found the radio slightly "off" tune, which could be corrected by using its fine control. We're talking a few hundred Hz here, and the offset was similar on all frequencies. That led me to check the BFO oscillators for LSB ad USB. Both were off by the same amount with respect to a tuned carrier. Verified by a good instrument, this pointed the finger directly at the cheap counter. It also explained why it looked as if the 18 MHz crystal in the PLL would not trim properly.
It is likely not a problem for many applications, but beware the accuracy delivered by these units if you plan to use them for precision work.
Cheers
Ed
I don't hold with furniture that talks.
