[ICOM] IC-756 - CW problem - and on Christmas yet!

[Sheldon Daitch]

I'd suspect that most commercial dummy loads are not very
good radiators.  I looked over the Bird dummy load specs and
don't see any numbers related to isolation, but based on my
experience with the smaller dummy loads, say, 5KW and smaller,
the Bird versions seem to be sealed units.

My gut feeling is that most of the radiation leakage with a TX, feedline
and dummy load set up is through the cabinet of the transmitter, and
perhaps somewhat less, leakage via the coaxial line.  I think we might
find that the level of leakage from the dummy load is probably the lowest
of the three.

At one location, we had a 100 kW dummy load that was essentially steel
resistance wire, in the form of a lossy transmission line.  I guess it was
about 16-20 back and forth runs between end points, folded over
transmission line.  In theory, it should not have radiated very much,
but it really wasn't much of a dummy  load, rather, it was a fair antenna.


73
Sheldon
WA4MZZ

"Jan C. Robbins" wrote:

> Dummy loads are antennas, Gary; they ALWAYS radiate, even when they're
> grounded (which they're usually not).  To prove the point, set yourself
> up on 14.195 when rare DX is operating there.  Attach a dummy load to
> your rig.  Set power out to 50w.  Call the DX station and see how long
> it takes until you're told to "listen up" or called a lid.
>
> It is perfectly possible to work DX on a dummy load, just as it is when
> there is a dummy like me on the OTHER end of the coax.
>
> Happy New Year!  May it bring all on the list health, happiness, and the
> last one for Honor Roll.
>
> 73 Jan
>
> Gary Fiber wrote:
>
> > OK Jan I got your point but have to say most every call I took in the
> > eleven years at Icom a dummy load usually negates the RFI problem.
> > Yes we used to get run off Channel 16 on the marine bands as the IFR
> > loads radiate very well. Anyway his trouble is solved.
> >
> > Gary K8IZ
> >
> > At 09:40 AM 12/26/2004, you wrote:
> >
> >> Good for you Carl!
> >>
> >> The problems--and your solutions--are common ones for those of us who
> >> run mobile--dropping voltage, Icom DC cables, RF on the coax (yes,
> >> Virginia, dummy loads do radiate), etc.  Glad it was that
> >> straightforward!  Happy New Year; look for you on CW.
> >>
> >> 73 Jan N0JR
> >>
> >> Carl Vangsness wrote:
> >>
> >>> Thanks to everyone for all the good suggestions. As with everything
> >>> electronic, there was more than one issue.
> >>> 1. MFJ Mighty Lite power supply sags from 13.8 vdc no load down to
> >>> less than 11.4 vdc during normal CW keying, down to 10.6 vdc during
> >>> keydown of more than 5 seconds. I will begin immediate search for
> >>> better power supply.
> >>> 2. DC cable from PS to 756 running parallel to and inches away from
> >>> antenna cable exiting LDG tuner. After doing power supply voltage
> >>> measurements, problem went away. Then came back after repositioning
> >>> tuner and Rigblaster.
> >>> Brilliant ham radio solution: aluminum foil wrapped around power cord
> >>> (Icom's unshielded basic two large wires) to get it  past the length
> >>> near the antenna cable. Result: nice 20 minute CW full power QSO with
> >>> KCØSHU near Denver. (I'm near Minneapolis.)
> >>> I do have some other lack-of-ground issues with shack in basement
> >>> near any true earth to plant a ground rod in, but that continues to
> >>> be a work in progress.
> >>> Again thanks to everyone on the forum for their help and
> >>> encouragement and a good New Year to all.
> >>> 73 de Carl WCØV
> >>>
> >>>>
> >>> ----
> >>> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
> >>> Win a new Icom IC-756 PRO III and help QSL/QTH.net
> >>> Details at: http://mailman.qth.net/
> >>
> >>
> >> --
> >> "There is no end to what you can accomplish
> >> if you don't care who gets the credit."   Anon.
> >>
> >> ----
> >> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
> >> Win a new Icom IC-756 PRO III and help QSL/QTH.net
> >> Details at: http://mailman.qth.net/
> >
> >
> > Gary Fiber K8IZ
> > GROL PG-19-6691
> > Washington State Resident
> >
> >
> > ----
> > Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
> > Win a new Icom IC-756 PRO III and help QSL/QTH.net
> > Details at: http://mailman.qth.net/
> >
> >
>
> --
> "There is no end to what you can accomplish
> if you don't care who gets the credit."   Anon.
>
> ----
> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
> Win a new Icom IC-756 PRO III and help QSL/QTH.net
> Details at: http://mailman.qth.net/