More Re: [TenTec] Orion redefines the meaning of ... AGC OFF

[Bill Tippett <btippett@alum.mit.edu>]

K3BU wrote:
>That reminds me the "noise floor" thing in Orion. Disconnecting or shorting
the antenna terminals on Orion produced quite a bit of "noise floor."  This
appears to be a noise generated by the circuits (IF amp after mixer?) 
Turning the
preamp on, increases the noise slightly, without moving Smeter.

        It depends on what Threshold is set to of course.  Using a
50 ohm load directly on the antenna terminal, 350 Hz BW, AGC off
and preamp on, it does sound noisy at my normal AF setting.  Turning
AGC on, and adjusting Threshold up from the minimum, I find the noise
drops to a reasonable level at 2-3 uV.  Coincidentally, this is also
the level I normally used on 10 meters in the CQ WW contests this fall,
but I never felt I was missing weak callers and my results seem to
confirm this, of course my antenna gain of 22 dBi doesn't hurt either.
On 160, my Threshold setting is seldom below 20 uV even in the quietest
wintertime conditions.

        I do find NR makes a huge difference in background noise on my unit
using the above dummy load in both CW and SSB independent of the AGC
setting (including Off), so I'm puzzled by your comments about NR.  Did
you mean in listening on-the-air and not listening to a dummy load?  In my
actual operating I find I seldom use NR but quite often use the Hardware
NB which is one of the best Noise Blankers I've ever used.  It was very
effective in dropping the noise floor on 10m when signals were very weak
at the very beginning and end of propagation.

        ARRL's MDS measurements don't seem to indicate anything unusual
about Orion's Noise Floor and W8ZR reported the following:

>While I had the radio on my bench, I did two other tests. First, I measured
the 10 meter sensitivity, and found that I could copy (barely) a CW signal
of 0.2 uV with the preamp off. With the preamp on, I could copy a .02 uV
(20 nanovolt!) CW signal.

http://dayton.akorn.net/pipermail/orion/2004-January/000191.html

.02 uV is about -141 dBm if my math is correct, which is a bit
lower than ARRL measured at -134.4 dBm (10 meters, preamp on).  Of
course W8ZR did not specify BW and that could account for another
5 dB difference if he was using Orion's minimum BW (150 Hz) instead
of 500 Hz which ARRL uses.  BTW, Orion's minimum DSP setting of
"100 Hz" is actually 150 Hz.

        Anyhow, will be interesting to see your results!

                                                73,  Bill  W4ZV








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