General alignment/process question

[Lkaskel]

Hi Everyone,
So I made a slight change to my process in that I added a bench radio (Ham) to assist with the overall results. The ham radio (AM, USB and LSB) is dead on (TX and RX) as verified by on air testing.
I am working on a Uniden Grant XL recapped, no mods and all functions work. The radio has been on for 24 hours. I first went through the PLL/Oscillator alignment . The last step is the TX offset I set the TX based on the reading from the antenna jack, single tone in LSB. When I switch to USB to verify the TX frequency its off by 68Hz. I tweak the USB coil (L58) to get it dead on. I then use the bench radio and TX on LSB and USB. LSB is crystal clear but USB is not so clear. I TX from the Grant and the bench radio receive is crystal clear on both LSB and USB.

The challenge is that if I adjust L58 for a clear receive it make the TX off. Because this radio has only 1 TX offset it does not have the capability of off-setting USB and LSB independantly. How do you correct this? How was this correct from the factory?

I am assuming that many radios have the same challenge. Because no one I know talks on 11 meter USB it never really crossed my mind.

Thanks!!

 

[nomadradio]

Doesn't make logical sense. If the transmit frequency lines up with the receive frequency on two modes, it should on USB as well.

More than once I have turned up the signal generator's output level to get both the monitor radio and the bench project lined up together on receive. If transmit frequency on the project radio is off frequency at all, you'll hear a beat note in its transmit audio.

But why it would flunk on USB only is not all that clear. That mode should behave like the other two, unless there's some kind of hookup crock on the mode selector.

73

 

[loosecannon]

if this radio has the trimmer cap instead of the variable inductor in the PLL section then you need to do USB first to trim the crystal and then do LSB and AM.
this may or may not be your problem but something led me to always do this way way back so far i can't remember what the issue was.

might be worth trying.

also, if you have a bench radio of known good calibration then dont worry about frequency when tuning the IF for the sidebands. Just go for the best sound in your bench radio.
LC

 

[nomadradio]

if this radio has the trimmer cap

Nope. This radio is the evolved Cobra 148GTL circuit board made after Cobra changed suppliers from Uniden in the Philippines to RCI in Malaysia. This model appeared just at the same time. Three trimmer inductors, one for each mode. I'd be wondering how much frequency change the slug in the USB coil can muster across its extremes. I would also gently rock the other two trimmer slugs while watching USB frequency to see that there isn't a crock in the switching diodes that select only one coil at a time. The other two inactive trimmers should have almost no effect when turned in USB mode. A trimmer coil that won't select is either bad or has a bad switching circuit in line with it. And if either of the other two slugs is active when you turn the slug, this confirms a select-circuit fault of some sort.

Found out where in Malaysia the RCI plant's located. A state (and its capital city) called "Melaka". Or "Malacca", depending on where you're from.

73

 

[AudioShockwav]

Found out where in Malaysia the RCI plant's located. A state (and its capital city) called "Melaka". Or "Malacca", depending on where you're from.

I had a picture of the assembly room at the Melaka plant that showed the half a dozen Asian girls that assembled these radios.
Not mass produced like everyone thinks of by any means, one small room with parts bins and soldering stations.
It was in a big facility, however the CB/export portion in that building was one single room.

I lost that picture and others with the last hard drive crash.
73
Jeff

 

[AudioShockwav]

Found this one.....
Part of the crew from 2015.

73
Jeff