I've had my Omni VII for 3 years now. I find it to be an excellent radio
especially in weak signal DXing and contesting. It is different than most rigs
I've used due to the way the DSP and AGC is implemented. I find the main
function of the RF gain is to first change the AGC threshhold and then to
reduce the gain as you get farther into the control. I almost never use the RF
gain set at 100% on HF except maybe on 12 and 10 meters. Most all rigs have
much more sensitivity than is needed for HF work and the OMNI VII is no
exception to this. I normally set the RF gain to the point that the S-meter
reads about 1 S-unit above the ambient band noise. You will notice as you turn
down the RF gain control the band noise decreases as the AGC threshold is
increased yet the actual signal stays pretty constant. Apparently the AGC
threshold at 100% RF gain is so low that it amplifies the noise as well as the
signal so the rig appears to be noisy but it is really not. Actually, weak
signal DXer's have know for years that cutting off the AGC and backing down
the RF gain and increasing the AF gain can help in hearing the weak ones no
matter what radio they have.
Another important feature to use is the AGC decay time adjustment button.
According to the review by the RSGB the AGC decay times are:
OFF - 10ms (with this DSP radio it's never really completely off)
FAST - 35ms
MED. - 350ms
SLOW - 2.5 sec
Attack time is 1ms for all settings.
The function of AGC is to maintain a constant level of audio from varying
levels of signals. It increases the gain of weaker signals and reduces the gain
of stronger signals. The decay time is how long this gain change lasts. You can
see if you have QRN and AGC set to slow, a big static crash will reduce your
gain for up tp 2.5 seconds. That's not good for trying to hear the weak ones!
Normally I use Slow for SSB and Medium for CW but I find FAST or OFF is better
for hearing the weak ones in the presence of QRN. During the 160 contest this
past weekend there were extremely strong signals spaced every 200-300Hz and
Saturday night QRN levels at S-7 to S-9! At times I had the RF gain on 0% and
the AF gain to 100% and I could easily hear the weaker S5 and below EU signals
in the midst of the din. Sometimes the DSP noise reduction also helped. I
have no low noise RX antenna.
The Omni VII may not have the very best 2kHz 2 tone dynamic range but its
80-84db (depending on who ran the tests) appears to be enough, at least at my
station. I had no trouble running them on 160 with the big boys close to me on
either side and have experienced no problem hearing the weak signals coming
back to me on my QRG. I find no indication of phase noise being a problem
either.
Test reports and reviews are all well and good but there is no substitute for
actually using the radio in real live operating conditions. My Omni VII passes
this test very well and I'm extremely pleased with its performance.
Other who are more technically competent than I can probably address the issue
of AGC in a DSP radio like the Omni VII to greater detail and accuracy. I can
only report what I find in actually using the radio.
73,
Puck W4PM
Message: 2
Date: Sun, 31 Jan 2010 19:49:08 -0500
From: <waltk8cv4612amos@att.net>
Subject: Re: [TenTec] Omni VI+ the best and other great radios
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Message-ID: <DEF81FD45C6444B2BBCE250C0E9DE69F@waltk8cv>
Content-Type: text/plain; charset="iso-8859-1"
Not being smart enough to know the difference ............... but, the old
Omni-6 with the same antennas and time frame is a world quieter in BAND NOISE
than the nice new Omni 7, no matter how I twiddle the options or RF gain
control, there you have it! Phase noise, maybe, it just seems way to sensitive
and by the time I get rid of the band noise the signals went with it! The K-3
and Orion 2 are every bit as good as the old omni-6 ........... go figure! Fun
trying them all though :-) MAYBE it is the different architecture ?
Walt K8CV Royal Oak, MI.
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