Excellent observations Puck. I run an Option III with the lower center
frequency CW roofing filter, and the 221 lower CF 250hz N2 filter and love
it...but the NR on it is just not what it can be on a newer rig.
Would love to try one side by side with this, but don't think I'd be able to
send it back.
73,
Art, K0R0
481
-----Original Message-----
From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
On Behalf Of H. M. Motley, Jr,
Sent: Monday, February 01, 2010 5:49 PM
To: tentec@contesting.com
Subject: [TenTec] Ten Tec Omni VII
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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