Aloha to all who have responded,
And many thanks also. Dan has, I believe, the best answer
for me, and also perhaps hinted at by others: press on and
don't be concerned about the apparant reflection delta readings, hi!
So this AM I have happily QSO'd away on 10 meter CW,
with somewhere around 40 to 50 watts reflecting that
and there between the amp and the tuner. I believe with
the low pass filter between the Bird coupler and the amp
output probably is a source of some reflection, and I also
have an RF Applications P-3000 watt/swr indicator between
the Bird coupler on the amp, and some 8 feet or so on the
way to the Palstar AT4K antenna tuner, which I am sure
does not mind some watts of reflected energy. I have,
at John, ON4UN's suggestion, put a couple of choke
baluns (which have ferrite beads within them, in series
with the line between to Bird on the amp and the tuner.
Have dicsonnected the MFJ-259B from the circuit, rather
than rely on the Hofi switch isolation at Dan's suggestion.
The impedance on the line, where the MFJ unit sits is
R=51, X=3, swr=1.0 when the Palstar tuner is engaged
and "tuned"; with the Palstar out, the MFJ reads its'
line insertion point as R=23, X=19, swr=2.5.
The latter number causes me to wonder if I should not
also take Dan's suggestion, and just take the tuner away,
and feed the Henry + low pass filter direct to the antenna
feed coax line. Could simplify my in-the-shack coax
runs a lot. My beam is Force 12 C4, and the impedance
down here in the shack is such that the vswr on the line,
without using the tuner, is never higher than the above 2.5
anywhere in our bands from 14000 to 29500 or so (at
least at that point where the MFJ analyzer sits when switched
in). Well it is higer on the 12 meter band, but not used here.
Notice that there is none of this reflection delta problem on
40 meters last evening, so, as has been suggested also, this
is confined to the upper bands where the coax lengths I
am using here in the shack are significant chunks of a 10M wave-
length, so the Z is going up and down, and who knows what
it is where the Bird and P-3000 sit; probably anything but
50 ohm Z, which is where they are designed to be, hi.
Without the tuner used in the 40 meter band, the amp/
filter output would see vswr's of 1.2 at 7005, but up to
5.2 at 7.3, but I never operate that high on 40.
There is another antenna -- a 1200 foot long, center V
dipole. It was supposed to be a V-beam, but as it
crosses a rather deep ravine, it does not seem to
form a beam, hi. But when the remote coax switch
sends the signal to that one on 160 and 80/75, I
go from the coax to, as Dan suggested, an Amidon
4:1 high power balun, then 450 ohm ladder line on to
the center feed point. This antenna on 160, w/o the
tuner presents a vswr to the MFJ point of 1.7 at 1800,
2.0 at 1855, and 2.9 at 2000kHz. Again, could perhaps
do without using the tuner; at 3500, get swr 1.4, and at
4000, 2.2.
So thanks again for all the new ideas and suggestions.
Will take the MFJ analyzer to the end of the main feed
coax, which could be connected directly to the back
of the Henry Ultra and see what I find at that point. Then
just may give Dan's method a go.
I presume I would then tune for max smoke up the feedline,
as measured on the Bird following the LPF, and just note
the reflected power for interest. If the Pi-L output of the
Henry does what I think it might, it will just turn the reflected
energy from the antenna mismathch right around, just as the
tuner would. So the forward reading of the Bird would be
true output plus the reflected power, correct? If the Henry
is properly tuned, that is, max possible forward reading on
the Bird for a given drive to the Henry from the Omni, I
think.
73, Jim, KH7M
--
FAQ on WWW: http://www.contesting.com/ampsfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|