Batboard

Hello all,
I just recapped one of two UHF Spectras for a friend, and I believe it's a 450-482 radio... It, however, is a little bit off frequency, I believe. Using the service menu on the radio (A5 head), I went to look at the test frequencies, and saw 450.025, 466.025, and 481.975 (or something like that.) So, listening on 450.025 on another radio, I keyed the Spectra, and heard nothing on the other radio! Went up to 450.050 on the other radio, and there was the Spectra's signal. So I thought to myself, "Oh, well, it's off frequency!"
So, I figured, "OK, this is what the REF OSC adjustment is for, right? It was set at 73, so I wrote down the value and began adjusting. With the adjustment at 0, it was breaking squelch on the second radio, but the audio was still a bit off-frequency. Is there a physical adjustment to shift this, or some other way to get it on frequency?
And I think I also need to add some conductive ink to the VCO stripline, too... We'll see once we get this issue solved, and the radio programmed up with some of our own stuff.
Any ideas?

maxkelley_kc2spy wrote:Hello all,
I just recapped one of two UHF Spectras for a friend, and I believe it's a 450-482 radio... It, however, is a little bit off frequency, I believe. Using the service menu on the radio (A5 head), I went to look at the test frequencies, and saw 450.025, 466.025, and 481.975 (or something like that.) So, listening on 450.025 on another radio, I keyed the Spectra, and heard nothing on the other radio! Went up to 450.050 on the other radio, and there was the Spectra's signal. So I thought to myself, "Oh, well, it's off frequency!"
So, I figured, "OK, this is what the REF OSC adjustment is for, right? It was set at 73, so I wrote down the value and began adjusting. With the adjustment at 0, it was breaking squelch on the second radio, but the audio was still a bit off-frequency. Is there a physical adjustment to shift this, or some other way to get it on frequency?
And I think I also need to add some conductive ink to the VCO stripline, too... We'll see once we get this issue solved, and the radio programmed up with some of our own stuff.
Any ideas?

Unless you have the needed service equipment like a frequency counter to measure the TX carrier, I wouldn't
go playing with any settings. You can mess up the operation of the radio in short order not knowing what
your doing or where the radio is going.

Are you sure the other radio is not off frequency or both of them?

Jim

Seems to me I've had trouble using the front panel test freqs for alignment. They didn't land where they were supposed to.

Watch the display when you key, the test freqs are different for transmit and receive, tx is 25khz off from the rx, higher or lower depending on the channel, but you'll see it change on the display.

jackhackett wrote:Watch the display when you key, the test freqs are different for transmit and receive, tx is 25khz off from the rx, higher or lower depending on the channel, but you'll see it change on the display.

OK, now that makes the results I was getting make sense

Jim202 wrote:Unless you have the needed service equipment like a frequency counter to measure the TX carrier, I wouldn't
go playing with any settings. You can mess up the operation of the radio in short order not knowing what
your doing or where the radio is going.

Are you sure the other radio is not off frequency or both of them?

Jim

Yeah, I do need to get my hands on a frequency counter... I figured I'd be able to get it adjusted just enough to get it roughly back on 450.025, by listening for the distortion in the audio, etc. Better than 25khz off! Yet, now I know that the 25khz shift is intentional

I doubt you are going to find an accurate enough frequency counter outside of a lab environment. You need a service monitor to accurately align that radio and set deviation, etc.

It ended up being my lack of knowledge about the transmit offset on the test channels, rather than anything wrong with the radio itself! Thanks for the insight, however!

maxkelley_kc2spy wrote:It ended up being my lack of knowledge about the transmit offset on the test channels, rather than anything wrong with the radio itself! Thanks for the insight, however!

The display shows the transmit frequency when the radio is keyed in the test mode(s)....