[TenTec] Re: Orion rf gain and inherent noise

[Grant Youngman]

> From my point of view, it would seem the receiver should be quieter
> But, it would seem that listening to the receiver with the
> antenna off and the rf gain all the way off you would hear the base
> level of noise in the receiver.  If this level weren't there, would we
> be able to copy weaker signals better?

I'm not sure what the source of that slight increase in background 
noise level is with the RF gain all the way down.  It sounds to me 
like a gain increase somewhere else in the system.  But internal 
receiver noise such as it is (pretty low) does not appear to be a 
limiting factor, and you wouldn't be looking for weak ones with the 
RF gain backed off anyway.

The "RF" gain doesn't go anywhere near zero.  (I wonder if this is 
really an IF gain block in the DSP).  At the lowest gain setting, a 2 
uV signal is still very audible.

Without doing any rigorous signal to noise measurement, the radio 
hears well below 0.1uV, and, with the preamp on, signals at 0.05uV 
and below are clearly discernable (CW, 1Khz bw).  Your'e never 
going to find a band that quiet in any case.

At the spec points of 0.18uV with the preamp on and 0.5 uV with the 
preamp off, signals are strong, clear and well aboveinternal noise.  

I'd just leave the RF gain alone.  You'll hear whatever is out there to 
be heard.

In passing I managed to confirm that the S-meter is set for S-9 with 
right at 100uV at the antenna. (SUB receiver selected to a different 
antenna).

Grant/NQ5T