Bob,
Maybe you're talking about two different sources of noise. The
background you hear when the AF gain is set very low is a known problem
which seems to be coming from Orion's audio section. The workaround is
to use less sensitive headphones or to put in an attenuator in the
headphone wire to cut down the sensitivity.
The noise you should hear on a dummy load is what you'll hear on any
receiver. As you may know, it comes from thermal and other sources of
very weak noise in the front end of any receiver. (Even with a perfect
frontend, you'll get 300 K thermal noise from the dummy load.) If you
don't hear this on any rig, it just means that there is not enough
gain. Orion's AGC system (in default setup) operates to bring up the
noise more than you may be used to in other rigs. You can cut back the
RF gain to reduce the noise level -- if you're not going after
ultra-weak signals.
Does this account for your problem?
73, Martin AA6E
--- Robert Carroll <rlcarroll@patmedia.net> wrote:
> The Orion receiver is the best I have used, but there is an aspect of
> it I
> don't understand and don't particularly like. I think back to some
> of the
> early transistor portable radios-about 1959 or so. The sound from
> these
> sets was pretty good, but when you turned the volume control fully
> down so
> that you couldn't hear a station there was still a audible
> shhhhhhhhhhh
> noise from the speaker. With my Orion if I connect a dummy load to
> the
> antenna input I still get a "shhhhhhhhh" which is clearly audible on
> the
> speaker or headphones. Any real signal input is enough to overcome
> this
> background noise, but to me it is annoying. When I crank down the
> audio
> gain on my MP and Pro, all audio background noise disappears. With
> the Orion
> I find that when the AF gain gets very close to zero on the bargraph
> there
> is a click and the shhhhhh is gone, but at the 2-3% point it is back
> and
> increases with the AF gain control. Activating NR removes most of
> it.
> Cranking back the RF gain control lowers it, so I assume it is
> generated by
> DSP activity of some sort. To me over a period of time on cw using
> headphones this background noise is fatiguing. I wonder if this is
> the root
> of some of the "noisy receiver" complaints that appear from time to
> time.
> Has anyone else noticed this? Is it a necessary "feature" of the
> digital
> processing being used?
>
>
>
>
>
> Bob W2WG
>
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>
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