[TenTec] Omni VI plus - noise & INRAD filters

[Jim Reid]

Aloha Yuri,  You wrote,  in part:

> Procedure to verify this is: turn your LP and DSP off, disconnect the 
> antenna, turn your RF gain full up: see if you will hear high pitched 
> hiss/noise from audio. 

> On my Omni VI+ this happens when I turn my RF gain past 3 o'clock. 
> 
> Let me know if you get the noise or not.

Yes,  Yuri,  I do get the noise,  whether the antenna input
terminal to the Omni VI+ is left "open" or terminated in
50 ohms.  BTW,  the S-meter reads zero deflection.  And,
yes,  perhaps even in the background,  below or at the level of
rigs RF stage internally generated noise,  I can hear
a faint   "whine".  But read on.

Now,  if I connect my 10 meter beam,  a dead band this
morning in KH6 land,  the noise level output increases
quite noticeably,  and the S-meter reads 1.5;  perhaps due
to the  very high x-rays flux coming from the Sun these past
 hours;  actually began some 20 hours or so ago.

In fact,  at this moment as I make this measurement,  the
x-ray flux has nearly reached M-class level,  at 
1949 UTC,  the x-rays are at C9.9 level!  Yesterday,
at this time,  about when I was reporting no X band noise
deflection on my Omni S-meter,  the x-ray flux was over
an order of magnitude lower,  in fact about 13 dB lower!!

Not surprising then that I have S-meter noise deflection
now,  hi.

What you are hearing with your RF gain up,  and the antenna
disconnected,  is the noise generated in your  front end RF
stages of the Omni.  But,  so what,  as soon as you connect
to the real world,  via your antenna,  you hear a much higher
real world noise environment, which overwhelms your
RF stages internally generated noise  and that very weak
"whine" tone you hear.  It is gone with the antenna bringing
in all the real "band" noise.

And of course,  going to lower bands,  the back ground noise
from any of my other antennas is higher yet:  S 2.2 on 21290,
for example.

BTW,  if you repeat these tests,  you MUST use an antenna
resonant at your test frequency.  That is it must be very
close to 50 ohms pure R,  or 1.1 or so vswr;  otherwise,
you will not get the solar and galactic noise matched into
your receiver.  That is why a 40 meter antenna used on
10 meters seems so quiet!  It is,  because it is coupling
neither much signal nor noise into the 10 meter tuned
circuits,  hi.

Oops,  just made another interesting "discovery".  My beam is
pointed almost exactly to the Sun's present azimuth direction
from Kauai just now:  Sun at 85 degrees azimuth,  beam at
about 60 degrees,  toward the US mainland from out here.
And if I rotate the beam 90 degrees,  the S-meter deflection
drops a unit!  So,  QED,  there is more noise from the Sun today.

I sure would not be concerned in real operation with the Omni
about the noise level I see coming from the internal circuitry.
There is a LOT more coming from the antenna operating
within any of our HF bands.

73,  Jim,  KH7M





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