As I mentioned in thesubject line I have an opt 3. I'm having a problem with my
swr meter circuit inmine, I think, so I thought I'd pose the question to the
list.
My station has been instorage for several yrs due to a move from one home to
another, and I'mjust now getting back on the air. After getting things set up
but beforegetting on the air, I swept the antenna system with my poor man's
network analyzer,and at 7100 the swr is about 1.3:1. So I figured I'm good to
go. Moving up theband to 7140, and still a 1.5:1 on the analyzer. The first SSB
transmission Imade, I immediately saw that the Omni 6 is complaining about swr
(3:1) andstarts cutting back on fwd pwr during voice peaks. Audio report from
the single contact I madewas pretty bad also. So I put a Dummy load in line,
and all is well.
I have a compromise 40 mtr ant in the attic of my 2 story house,and thought I
had rf coming into my shack common mode down the coaxshield, due to the way I
had to run the coax. A lot of RG-8 runs parallelto half of the dipole just a
few feet from it. I put 2 chokebaluns inline with 7 turns and 5 type 31 cores
12" diameter thatI found in one of W9YC's papers. I did this in 2 locations
along the lineas he also suggested in one of his papers to break up the line
like egginsulators, as he put it . Turns out it might not be what I thought
withRF in the shack ?
Next, I put a T-Match inline that has crossed needles. It also says about
1.5:1 during tune mode whenthe tuner is bypass mode, and swr is high (3:1) on
theOmni meter. It doesn't take long and fwd pwr starts to drop, asdoes the swr
on the Omni the longer I keep it in the tune mode. Networkanalyzer says 1.5,
T-Match says 1.5, Omni 3:1 Testing all the linesand connections from coax out
of antenna port on rear of Omni going to thedipole as a complete antenna system
including the T-Match in bypassmode as seen in normal operation by the Omni,
the analyzer still says 1.5:1,so this is not a bad piece of coax or jumper...
So I tuned the T-Matchto 1.0:1, and Omni is happy. I can use the T-Match
always, but I don't think this is proper since there may be an issue in the
Omni, and I'd rather find and fix the problem rather than put a Band-Aid on
it...
I'm starting to suspect that the swr detect and shut down circuiton the 9 MHz
board around U1A has a problem and has become hypersensitive. Any swr at all,
and the Omni starts to shut down, when thisshouldn't really start to take
effect until swr approaches 2:1 or maybe alittle higher. Just a guess.
This problem did not exist at the old QTHI have not taken the covers off the
Omni to try and removeand reseat connectors etcI have not tried to align the
fwd, 100 watt power set and current limit, nor reflected power adjustments.
I thought I’d ask here first to see if any ofthe Omni followers experienced
this type of problem with their rigs before ?
Regards
Jim T.WB8HMD
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