7595Re: Feeding A Magnetic TX Loop
- Jun 12, 2010Ah Yes -- now I recall the capacitive tuning/matching
network using two caps, one a dual section. That's what
MFJ uses in their loop tuners. I may just
build one up someday. I run an FT-817ND and always was
an advocate of low power. It sure simplifies capacitor
As a result of recent illness I have given up my house
which was ham heaven and moved into an assisted living
residence where towers and wires are out of the question,
but a loop will provide a very satisfactory antenna.
I've got most of the materials ready and just need spring
to arrive -- it's late this year in Calgary!
--- In firstname.lastname@example.org, Jim Dunstan <jimdunstan@...> wrote:
> At 01:41 AM 6/3/2010 +0000, you wrote:
> >--- In
> >toddroberts2001@ wrote:
> > >
> > > Hi All,
> > > I am wondering if anyone has tried locating the feed loop
> > > or Gamma match next to the tuning capacitor and if
> > > they had success with this arrangement?
> > >>
> > > 73 Todd WD4NGG
> > >
> >The portion of the loop opposite the capacitor is the only real
> >place to get a low impedance feed point which the gamma match
> >requires. You would have difficulty feeding the loop anywhere
> >around the capacitor because of the very high voltages there.
> Hi Irv,
> It is not really difficult to couple to the loop at the tuning
> capacitor. The circuitry is simple ... the problem is as you say ...
> dealing with the high RF voltages. It also relates to the amount of power
> you run. If you run QRP no problem.
> >Believe me, it would greatly simplify the construction of the
> >magloops if the feedpoint and capacitor could be colocated -- thats
> >why you never see it in magloop articles.
> The reason you don't see it done is that it requires non-traditional methods.
> MFJ made several versions of a Mag Loop Tuner that operated in this
> fashion. Simply connect the loop to the 2 stand-off insulators. the tuner
> acted as the base as well as the tuner and it could sit on the table next
> to the rig. I didn't particular like the idea of the mag loop sitting a
> couple of feet away from me ... even though I was only operating 10 watts
> I extended the distance. The version I built separated the loop from the
> tuning capacitor/coupling unit by about 8 feet using home brew parallel
> feed line.The loop was about 3 ft in diameter and I ran 10 watts output (I
> used a Kenwood TS-50 running at the low power output setting) no
> problem. it worked just as well as the same loop fed in the more
> traditional way at the low impedance side. If I fed the same loop at the
> low impedance side I could easily run 50 watts .... but then I had the
> inconvenience of not being able to tune the loop and adjust coupling from
> the operating position. By the way ... the loop was fastened to the
> balcony railing and the tuner/coupler was just inside the window to the
> apartment. Both loop arrangements had the same efficiency (e.g.
> output). The difference was that feeding the high impedance point
> dramatically lowers the 'destruction' point hi hi.
> It is not a matter of will it work. It works! ... It is just not easily
> done with traditional components. Modern day Amateurs love coax .... and
> coax is incompatible with high impedance feed. If Mag loops were popular
> back in the 1930's I am sure that is how it would have been done (that is
> tuning and feed at the same point).
> Jim, VE3CI
> [Non-text portions of this message have been removed]
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