George, Jim and all those who sent
wonderful direct to me replies on this;
It's touching to ask a question and get
such helpful replies from so many. I
appreciate it.
The long and short of what I see as
reality in this is I have an ongoing
problem with the 160M antenna and it is
not going to be resolved by correcting
this antenna alone. I've had to replace
the 160M wire maybe 7-8 times over the
last 7 or so years.
I'm using WD-1A wire and have always cut
them to the same length as the earlier
antennas that were INV-L but that close
tall tree is no more and I now have to
shoot the line over the closest tall tree
making it a sloper now, no more an INV-L.
At the Ocean's edge the hurricane winds
are at top speed and even strong storms
buffet the trees badly and it's a matter
of time when the more trees fall. There's
enough to probably last my time here but
I'll still have to use different trees and
there's no way to get each replacement
exactly as the one before had landed.
I was offered a beat-up but intact Vacuum
variable and am going to mount that at the
feed point and will adjust each
replacement antenna to be resonant at
1.825 and when the next time comes I have
to do it, it'll only be a minor thing to
re-adjust the VV. This solution will be
sufficient to handle 1500W when I'm
chasing DX.
I wish I had a permanent location to set
this up at so I could have a more durable
antenna but that will have to wait. I've
decided to move from CT and will choose a
retirement area that is rural and offers
me a better RX location. At the current
location (a salt marsh) I have a pretty
good TX signal, I'll just have to take my
time and make a fine radial bed when I
re-locate.
> Hi Gary & fellow Topbanders...
>
> It seems that Gary's 129 foot wire may be actually 133 to 136 feet
> long, depending on radials and ground conditions and whether the wire
> is bare or insulated.
>
> I did a quick model on a recent version of EZNEC and found that Gary
> may have to add series capacitive reactance of somewhere between -25j
> to -40j ohms to get to about 1835 KHz resonance with minimum SWR.
>
> XC = -40j requires about 2200 pfd series capacity.
> XC = - 25j is about 3500 pfd series capacity.
>
> The formula is XC = 1/(2 x Pi x F x C)
> Where F is in Hertz or Cycles
> and C is in Farads
>
> The voltage requirements are not too high but there will be at least 5
> or more amps of RF if you run power, depending on the impedance at
> your feed point. For safety sake I would use 2500 volt ratings on
> fixed caps and 3KV on vacuum variable caps. If you have a favorite
> center frequency, combinations of 200 to 500 pfd mica or door knob
> caps should be sufficient. If you use door knob style ceramic caps,
> use a lot of them in parallel, as they do not like high current.
>
> When done building a bunch of parallel capacitors for the value you
> require, try a KW for a few minutes at the desired frequency for
> minimum SWR and make sure there is no drifting of the value of XC
> (detuning of the series reactance). Then turn off the transmitter
> and go out and carefully feel the capacitors to make sure they are not
> very warm.
>
> I ran 3 - 4 amps through four 1000 pfd, 5 KV caps in series once and
> darn near blew them up.
>
> 73 & Good Luck
>
> George, K8GG
>
>
>
>
>
>
>
> > I just installed a replacement wire for
> > the 160 sloper. I made it 129' as was the
> > earlier one that came down in the winds. I
> > have to use a spud gun to get fishing line
> > over the tree tops and where the spud
> > lands, I connect the wire to the eye
> > fastener & reel it to the radial plate.
> > This time I had to use a different tree as
> > the earlier one came down in the last
> > hurricane.
> >
> > Now it is resonant at 1.785 and it is not
> > a problem at the lower end of 160 but
> > higher up it is. My problem is compounded
> > in that I also use this antenna for 10M,
> > 12M and the upper part of 15M. I need to
> > shorten it for use on these as well.
> >
> > It is too far away to shorten the wire and
> > solder a new eye on it and now it is too
> > cold to play with it on the tree (have
> > difficulty walking right now). So being
> > too long, capacitance at the feed point
> > might be my best answer. I have several
> > fixed vacuum & doorknob capacitors of
> > small pF to choose from that I can put in
> > line. Is there a formula that I might plug
> > data into to come up with the needed pF?
> >
> > Thanks & 73,
> >
> > Gary
> > KA1J
> > _________________
> > Topband Reflector Archives - http://www.contesting.com/_topband
> >
>
>
> _________________
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>
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