white noise fix for RCI 29xx radios ??

[Robalo]

from service manual

Rci 2950dx white noise correction

PLL 2 VCO voltage
radio on freq 24.890 in AM RX mode
connect multimeter to TP10 (just to left and below X2 Crystal)
adjust L14 for 1.0 volts DC +/- 0.1
recheck at 29.699 for equal or less than 4.5 volts DC
PLL 1 VCO voltage
radio on freq 24.890 in AM RX mode
connect multimeter to TP11
adjust L13 for same 1.0 volts DC
recheck at freq 32.000 for less or equal to 6.5 volts DC

 

[delta]

I have many rigs and ham sets. I use a Ranger 2995dx and it's just fantastic on 10-11-12 mtrs. I'd say better than my chipswitched Lincoln
With my interceptor 10K and my astatic echomax mic it's really does the business on CB bands. No trouble with white noise at all...
Ranger RCI-2995DX Amateur 10 & 12 Meter Base Station from Ranger Communications

 

[dudmuck]

from service manual

Rci 2950dx white noise correction

PLL 2 VCO voltage
radio on freq 24.890 in AM RX mode
connect multimeter to TP10 (just to left and below X2 Crystal)
adjust L14 for 1.0 volts DC +/- 0.1
recheck at 29.699 for equal or less than 4.5 volts DC
PLL 1 VCO voltage
radio on freq 24.890 in AM RX mode
connect multimeter to TP11
adjust L13 for same 1.0 volts DC
recheck at freq 32.000 for less or equal to 6.5 volts DC

Proper alignment is one thing.

But if you think its the PLL causing the noise, it certainly can be.
For any superhet receiver, any noise on the local oscillator will be heard, perhaps even with no received signal. The only way to be sure is put a good spectrum analyzer on TP3 to see how clean it is. Or disconnect the PLL output and inject a known good signal at the same frequency to see if its better.
The PLL could be dirty for several reasons.
* the loop filter could be too wide bandwidth (loop filter is resistors and caps around TP11)
* IC3 is not a low-noise op amp
* noise on the power supply lines, or noise radiating in from some other part of radio.

But is also likely white noise could be from other parts of radio. Could be from the AM demodulator circuit, or audio amplifier.
A good AM receiver with no man-made noise on the antenna should sound like pop-corn type noise when there is no signal, not like an FM receiver which sounds like white hash without signal.