Regency Range Gain low modulation

[guitar_199]

Adding a little emphasis to Champos entry.......

All of this at the moment.... we are targeting the transmit carrier generation!

Oscillators 1 & 2 are shared with RCV & XMT.
At this point Oscillator 1 & 2 are working fine and from what we can tell are generating the correct mixed frequency.

The next thing we need for transmit is Oscillator 3/Mixer .... which is the 7.500 Mhz crystal oscillator and the mixer that should be giving us the 27 Mhz "CB range" carrier.

At this time it looks like .....
1) the 7.5 Mhz crystal oscillator is no "oscillating",
2) the mix is "not happening",
3) or.... BOTH.

With that... it looks like nothing is being sent to the Buffer or Final stages.... sometimes nothinhg....... but when it DOES....it is only causing very low output.

So we are focusing on transmit at the moment......

 

[Dmans]

EDIT:
I had to add this because I've never observed this before but I'm getting +14vdc before the 6.8k resistor, -16vdc after it and then +9vdc on the other side of the rf choke???

I just went back and re-read this thread. Champo's post (Above from #18) may be the culprit. The RF choke is supposed to keep RF out of the DC. If its bad, I would expect the result he reported above. A swap with another RF choke of the same or similar value may tell the tale.

73
David

 

[Champo]

I wanted to post an update now that I have some new tools in my arsenal. I acquired a Tektronix 2236 oscilloscope and it has proven to be helpful. I was able to confirm several things that I observed with the VNA.

The internal frequency counter on the scope is extremely helpful and is close if not on. I used the scope to adjust all of the slugs to their maximum. I confirmed the 19.70378 signal is coming to V11 from the first 2 sets of crystals. I also confirmed the 7.5 MHz crystal reads 7.25 just like the VNA. Also just like the VNA, pulling the 7.5 MHz crystal out of the radio will still give you the 7.25 MHz signal and....get this....you can adjust the frequency and height of the sine wave with the slug for the crystal while the crystal is completely removed. I'm not sure how that's possible but that's the case. I tried 2 different crystals with the same result.

Lastly I confirmed that if you key the radio with the scope probe on the output of the final slug adjustment you get a 26.9526 frequency which is exactly the .250ish low from the 7.5 MHz crystal. I was on channel 20 - 27.205 at the time. You get this whether the crystal is in or out.

Any insight or guidance on any of this would be greatly appreciated. Thank you.

 

[Champo]

I wanted to update my update. The radio is now keying 1 watt on channel 20 at 27.206.45. Apparently the 7.5 MHz crystal is only activated when the mic is keyed and that 7.25 value is some transient signal of some sort.