[TenTec] OM7 on 40m in Europe

[DAVID HELLER]

----- Original Message ----- 
From: "Rick, NJ0IP / DJ0IP" <Rick at DJ0IP.de>
To: "'Discussion of Ten-Tec Equipment'" <tentec at contesting.com>
Sent: Thursday, March 01, 2007 8:19 AM
Subject: [TenTec] OM7 on 40m in Europe


> 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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