I'm surprised a post this old hasn't acquired several answers.
From the looks of it, you're working with an aircraft band AM modulated transceiver.
These radios have a "squelch" control. This control effects the CSQ line in the form of a base reference.
It could be internal or externally controllable depending on design.
In your case, it looks like you have not "preset" the squelch control.
If the squelch has not been activated, the receiver CSQ line thinks there is always a signal present.
You need to set the squelch with no input signal & the antenna port loaded with a 50 ohm load.
Presetting the squelch basically mutes the various audio amps that drive the speaker.
I think you'll find the CSQ line goes low when "squelched" and hi with an incoming signal.
It could oporate in the opposite sense as well.
Carrier squelch is based on a comparator having an adjustable reference. ie. the "squelch control".
The comparator is looking at input signal derived agc voltage & comparing it to the squelch control voltage.
When the agc voltage rises above a certain level, the comparator circuit changes the CSQ line.
Noise squelch is based on high pass filtered audio noise present at the output of an FM discriminator/demodulator.
The hi pass filtered noise is rectified and fed to a comparator.
During no input signal operation, the noise squelch produces the most "noise".
As signal increases, the hi-pass filtered audio level decreases due to "limiting" inherent in fm det.
At some point, the lowering of rectified hi frequency noise will fall below a preset and change the comparator.
Carrier squelch and noise squelch are used in parallel to minimize falsing of the squelch circuitry.
Together, these circuits qualify an incoming signal as a wanted signal or just noise spikes.
Each circuit will have different attack / decay times.
In some cases, the noise squelch circuit also provides a function usefull in a scanning receiver.
The fm detector used in noise squelch can also determine if a signal is centered on frequency.
If the signal is outside a given bandwidth, the receiver continues to scan even if the same signal could be demodulated by the AM detector.
That's long & short of it.
N2L
