Yesterday afternoon the OMNI VII arrived.
My XYL had committed me to being the designated driver for her and her
girlfriends' "night out", so that highly limited my time for playing with
the new OMNI.
I currently only have a 40m vertical (full size) and no other rigs to
compare the OM7 to (except a 20+ year old Argonaut 515 without any narrow
filters). Next weekend I will take the OM7 to one of our BCC contest
stations, DL1A on the west side of Munich. There we have beams on all bands
except 160. For comparing we have an FT-1000 MK5 FD, FT-2000, and Orion.
Being a 40m fanatic and living in Europe, I have become accustom to
disappointments when testing new rigs.
We have a multitude of shortwave broadcast stations which play havoc with
most receivers' front ends, beginning in the early evening, getting worse at
dusk, then slowly getting better towards midnight. Attenuation in the front
end helps, but it also attenuates the desired signal. This can be
significant if the desired signal is only S1 or S2. That's why the use of
an external preselector is popular over here.
Although I had no other "good" radios here to compare it to, I have recently
owned (within the last 2 years) two Orions, two K2's, an Omni VI+, and a
TS-480 (and tried a TS-850 but it fell over with intermod problems). The
comparisons shown below are based on memory, not on side by side comparison,
so take them with a grain of salt, your mileage may vary, etc.
Testing was done last night from 5pm until 6pm local, from midnight until
1am local, and again from 7:30 until 8:30 local this morning.
I was mostly just receiving and trying hard to find intermodulation problems
on the OM7.
The external preselector connected to the OMNI VII is a home brew bandpass
filter (not tunable), similar to the famous Braun preselectors, but not
quite as good.
Results:
* There was no blanket of noise across the 40m band (even without the
external preselector), like there are with so many other rigs. Even
switching the preamp on did not produce this adverse effect. THIS IS
SIGNIFICANT! For comparison, on this antenna:
* The newest K2 (S/N 4606) had about an S1 to S2 blanket of noise
across the entire band with preamp on. It was generally clean without the
preamp, except for peak problem times (dusk) where the attenuator or the
external preselector eliminated the intermod entirely.
* The TS-480 SAT had about an S5 blanket of noise across the entire
band with preamp on. With the AIP (preamp off) the radio was also pretty
clean, except for peak problem times (dusk) where I needed the attenuator.
I never tried the preselector on this rig. Of course the attenuator also
attenuates the desired signal but not as much as it attenuates the intermod.
* The OMNI VI+ was generally clean with perhaps an S1 blanket of noise
at peak problem times. The attenuator, but better yet, the external
preselector always eliminated it.
* The ORION was always clean in all circumstances on my antenna, and
on DL1A's 3-el beam at 100 ft., exhibits similar light intermod problems to
what I experienced with the OMNI VII using my vertical. These are completely
eliminated (on the ORION) by turning back the RF gain to 95%.
* OMNI VII Intermod: There were a few instances where there was a
strange carrier (obviously intermod) on the order of S2 to S5, but usually I
could eliminate it with 6dB (occasionally 12 dB) of attenuation. Of course
switching the external preselector in also eliminated it without reducing
the strength of the desired signal. These carriers would go on and off, and
I have no idea what was causing them, but it was clearly intermod because
just 6dB of attenuation would drop it several S-Units. Something somewhere
was mixing with something else. There were 4 or 5 frequencies where I
experienced this. The rest of 40m was clean, even with preamp switched on.
DO NOT INTERPRET THIS TO BE BAD. IT IS EXCELLENT. Most receivers are much
worse under these conditions.
* There was no pumping on strong signals like we experienced on the
FT-2000. To be fair, that was on DL1A's beam and I haven't tried the OM7
yet on that antenna (update next week).
* While I was on 40m, my neighbor ham (Freddy) was on 160m trying to
work the VK9NDX-pedition. He was running a healthy kilowatt (using my old
linear amplifier) and our two antennas are about 200 yards apart. When he
transmitted, the noise level would go up about an S unit or 2, but modulated
according to his SSB signal or to the cw signal - he used both modes. The
noise sounded a bit raspy. The preselector eliminated this. For
comparison:
* The TS-480 had about an S-8 increase in noise under these conditions
(in the past of course)
* I never noticed this on the OMNI VI (over a period of 4 or 5 years)
unless Freddy was on the same band as I was. Often he was operating SSB
while I was on CW on the same band. In that case I used my home-brew
tunable preselector which pretty much eliminated the problem.
* This morning I heard our BCC boys currently activating VK9NDX and
worked them first call (cw), barefoot, through a mini pileup.
* And to my pleasant surprise, the old Argonaut 515 could hear
everything the OMNI VII could, unless it was disturbed by strong QRM.
However I had to back off the 515's RF gain and play with its own built-in
preselector to avoid intermod.
Bottom Line: This radio is a true Ten-Tec!
There has been a lot of speculation on the reflector as to whether the term
"Distributed Roofing Filters" is real value-add or just marketing hype.
Coupled with careful management of amplification (signal strength) from the
antenna input through to the second mixer, it becomes very effective, but
one needs to understand this. It's a slightly different approach. It
clearly gets the job done, but I think Ten-Tec will have some missionary
work ahead of them.
Their main problem is, they did too good of a job in selling the industry on
the concept of "roofing filter" when they brought out the ORION.
Next update will be after testing on "real antennas" at DL1A.
73
Rick
DJ0IP (NJ0IP)
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