[ARC5] Quick sensistivity comparison

[Bill Cromwell]

Hi Carl,

A couple of 'seat of the pants' observations from the peanut gallery.


On 06/13/2013 04:21 PM, Geoff wrote:
>
>
> Since you didnt specify mode or receiver bandwith those statements are 
> rather ambiguous.
> When dealing with vintage receivers that have only fair to poor IF 
> filtering I use the AM test for a 10dB SNR at 30 MHz at maximum 
> bandwidth for the models mentioned and even .25 to .5uV is a very rare 
> occurance. For CW I crank in whatever maximum selectivity is available 
> and of course sets with selectable filters will have different 
> results. And then measure MDS which is described as 3dB above the 
> noise but many, myself included, can hear well below that.
I have been playing with the soundcard based digital signal processing 
software. I noticed a long time ago I could hear and copy 100% signals 
that do not even tickle the S-meter on receivers. Now with the soundcard 
software I can see that some of those signals are hardly higher than the 
grass (noise) on the spectrum displays.

--snip---
>
>
> I disagree about SS having lower sensitivity at HF and it has been 
> proven many times by many people. The HRO-500 and others without PLL 
> phase noise are extremely sensitive with very low internal noise. 
> Those with a PLL vary considerably but most are very sensitive on a 
> test bench. It is when the wide open untuned front ends meet 
> hundreds/thousands of strong signals that the PLL becomes a noise 
> generator.
> You can hear the noise during a contest by monitoring outside of the 
> ham band and the backround noise will rise at the contest start and 
> fall at the end.
>
> Carl

I have a dual loop PLL, uP controlled Ten Tec RX-325 that exhibits the 
"features" you have mentioned. Just putting a Johnson Matchbox ahead of 
it helps. I'm working up a *real* front end preselector filter to put in 
that position.

73,

Bill  KU8H