Topband: Shunt feeding the Skyneedle - new developments
Carl
km1h at jeremy.mv.com
Sat Feb 22 11:41:57 EST 2014
I suppose I missed that part while doing things around here but this is the
only pertinent info I can find from him. Nowhere does it say he has a 1:1
anywhere with the cap in the cabinet. Granted some of the posts are very
confusing as to where things are being measured.
----------------------------------------------------------
The j11 ohms is the best I can get period. I was able to get j0 when the cap
was outside of the steel enclosure with a better bandwidth. Maybe I should
throw my $400 enclosure and find a fibergla$$ enclosure. But as others have
indicated I should probably just live with it.
The swr at my given freq as tuned with the variable cap is 1.3:1 or
less...outside the enclosure the system had 1.0:1 swr readings and X=O over
what appeared to be a broader bandwidth...even with 42 ohms at the feed
point.
----------------------------------------------------------
So maybe you can explain where the 1.0 at the transmitter end with the cap
in the box came from?
Additionally the VSWR may/will change with added radials and ground moisture
conditions.
Im going out for several hours so no rush on the answers.
Carl
KM1H
----- Original Message -----
From: "Charlie Cunningham" <charlie-cunningham at nc.rr.com>
To: "'Carl'" <km1h at jeremy.mv.com>; "'Carl Braun'"
<Carl.Braun at lairdtech.com>; "'160'" <topband at contesting.com>
Sent: Saturday, February 22, 2014 11:03 AM
Subject: RE: Topband: Shunt feeding the Skyneedle - new developments
Well, I agree with all that, Carl. But Carl Braun, was reading "dead-flat"
1:1 at the transmitter end of his cable. I believe he is done!! The antenna
Q is what it is! As for "improving his 2:1 VSWR bandwidth" he could reduce
his radial field and increase his ground losses to improve his 2:1 "BW" -
but I believe that to be self-defeating!! I'm not "missing your point" - I
just don't see what you'd change to improve on a "flat" line! Carl is well
past the point of "diminishing returns"!
The math doesn't "lie"!
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Carl
Sent: Saturday, February 22, 2014 10:41 AM
To: Charlie Cunningham; 'Carl Braun'; '160'
Subject: Re: Topband: Shunt feeding the Skyneedle - new developments
Charlie youre continually missing the point; ignore cable loss period.
The only issue is what impedance does the amp see from lets say 1800 to 1900
KHz? AND can the amp load into it without a problem at full power? This is a
system issue, not just what is measured at the antenna and needs to be
addressed that way.
Put all that info into your program and post the results. Saying that a 1.3
VSWR at reasonance at the antenna is sufficient is too simplistic. Compute
the VSWR at the amp with whatever length of coax is actually used over the
lower 100 KHz with a range of " at resonance" VSWR's.
Carl
KM1H
----- Original Message -----
From: "Charlie Cunningham" <charlie-cunningham at nc.rr.com>
To: "'Carl'" <km1h at jeremy.mv.com>; "'Carl Braun'"
<Carl.Braun at lairdtech.com>; "'160'" <topband at contesting.com>
Sent: Saturday, February 22, 2014 9:57 AM
Subject: RE: Topband: Shunt feeding the Skyneedle - new developments
Well, Carl the looses in 70' or even 200' of LMR-400 are so low at 1.8 MHz,
even at 2.0:1 or 3.0 :1, if he can match it at the transmitter end of the
line, it really doesn't matter!
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Carl
Sent: Saturday, February 22, 2014 9:46 AM
To: Charlie Cunningham; 'Carl Braun'; '160'
Subject: Re: Topband: Shunt feeding the Skyneedle - new developments
That 1.3 is only at ONE frequency Charlie, he is not crystal controlled.
What is the 2:1 bandwidth at the amp?
Carl
KM1H
----- Original Message -----
From: "Charlie Cunningham" <charlie-cunningham at nc.rr.com>
To: "'Carl'" <km1h at jeremy.mv.com>; "'Carl Braun'"
<Carl.Braun at lairdtech.com>; "'160'" <topband at contesting.com>
Sent: Saturday, February 22, 2014 9:23 AM
Subject: RE: Topband: Shunt feeding the Skyneedle - new developments
I don't expect that ANY of those are valid concerns at 1.3:1 VSWR!!
-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Carl
Sent: Saturday, February 22, 2014 9:14 AM
To: Charlie Cunningham; 'Carl Braun'; '160'
Subject: Re: Topband: Shunt feeding the Skyneedle - new developments
Im not concerned by what is measured at the matching unit or a miniscule
cable loss; just what is transformed back to the amp and its ability to load
at full power without arcing, running out of or having too much fixed padder
C during QSY's. Contests do not stay just in the narrow CW 50 KHz "window"
and not having to use an external tuner is a big plus.
Ive always modified my amps to work with my antennas on 160 and 80/75.
Carl
KM1H
----- Original Message -----
From: "Charlie Cunningham" <charlie-cunningham at nc.rr.com>
To: "'ZR'" <zr at jeremy.mv.com>; "'Carl Braun'" <Carl.Braun at lairdtech.com>;
"'160'" <topband at contesting.com>
Sent: Friday, February 21, 2014 10:35 PM
Subject: Re: Topband: Shunt feeding the Skyneedle - new developments
Well, if I recall correctly, Carl, Carl said his feedline was about 70' of
LMR-400, so even at 2 2:1 or 2.5:1 VSWR, the excess losses in 70' of LMR-400
at 1.8 MHz are almost 0, so if he can match it OK at the transmitter end of
the line- no real point in making heroic efforts to achieve a "perfect"
match! He'd gain more by working on his radial field, and he really should
do that before doing any more tuning because improving the radials WILL
affect the antenna impedance.
73,
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of ZR
Sent: Friday, February 21, 2014 10:11 PM
To: Charlie Cunningham; 'Carl Braun'; '160'
Subject: Re: Topband: Shunt feeding the Skyneedle - new developments
The only benefit of getting it better would be a bit more 2:1 VSWR bandwidth
to keep the amp happy but even then there is sometimes a gotcha when tuning
an antenna.
Carl
KM1H
Subject: Re: Topband: Shunt feeding the Skyneedle - new developments
Well, you can do all that, Carl
But if your series variable capacitor is not maxed out (fully meshed) if you
can increase the capacitance enough to get to j0, you would be at 45
+j0 and on a 1.1:1 VSWR circle. No point int trying to do better than
that!!
Otherwise, just increase the series capacitance to bring that -j11 as
close to j0 as possible and take that! You'd be so near perfect that there
would be no real point in going further!
Your time and efforts might be better spent working on your radial field!
73,
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Carl
Braun
Sent: Friday, February 21, 2014 8:46 PM
To: Charlie Cunningham; 'Tom W8JI'; '160'
Subject: Re: Topband: Shunt feeding the Skyneedle - new developments
Thanks to all who replied
Tom W8JI, your comments on the metallic panel and the static bleed choke
make sense. I was so pleased with the FLAT SWR reading with the variable
cap outside the panel but I guess I can live with the slight SWR. (Thanks
Charlie K4OTV). I have a Nye Viking monster tuner but I hate to use it as
my Henry amp seems to load strangely when I have it inline so I think I'll
just live without it.
Can I add some coax (coiled) to bring the X down on the -j11 reading? I did
this with the old Telrex and brought the X right down and out of the pic.
I'm sure Ill need much more than I would on 14MHz but I think I'd like to
try anyway.
I'm still going to drop the tower down and add two more gamma wires to
create a cage and I still have the option of pulling the gamma wire(s) away
from the tower another 8-10 inches to add a few more ohms to the equation.
I'm having fun with the experiment.
Right now I'm hearing the beginnings of the SSB contest with N7GP, WD5COV,
W6YI with the big signals so far. XE is the only DX I've heard.
Lots of stateside calling stateside
Carl AG6X
-----Original Message-----
From: Charlie Cunningham [mailto:charlie-cunningham at nc.rr.com]
Sent: Friday, February 21, 2014 5:21 PM
To: 'Tom W8JI'; Carl Braun; '160'
Subject: RE: Topband: Shunt feeding the Skyneedle - new developments
Well, Carl
I plotted your 45-j11 load on a Smith Chart (normalized to 50 ohms) and it's
very near the origin on a 1.3:1 VSWR circle. Since you have a relatively
short feedline of LMR-400, You should be able to just tune it out at the
transmitter end of the line, and the LMR-400 line will be operating at such
a very low SWR (around 1.3:1 that the excess loss from a 1.3:1 VSWR at 160
is completely trivial and negligible! It may not be completely
"intellectually satisfying to have -j11 of reactance at the load, but it
should match easily and the antenna should work very well! Enjoy!
Sounds like that Array solutions static bleed is not as high in impedance as
we might wish! A large resistance might give you more satisfactory results!
GL! Enjoy!
73,
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Tom W8JI
Sent: Friday, February 21, 2014 8:02 PM
To: Carl Braun; '160'
Subject: Re: Topband: Shunt feeding the Skyneedle - new developments
Since then I've moved the variable capacitor inside the panel and mounted it
to a ¾" think Plexiglas sheet mounted to the back plane with nylon bolts and
washers. There is a 1" air gap between the Plexiglas and the backplane. I
now have seen the 42+j0 ohms change to 45 - j11 ohms...that's the lowest
reactance I can tune the capacitor for. Not really sure if its +j11 ohms or
- j11 ohms but I assume if the reading was + j11 I could continue to tune
it out with the capacitor but I cant.
Does the capacitor not play well with a steel enclosure?>>>>
Any enclosure will change things, especially a metallic enclosure. Just
readjust the cap.
<<<<The other strange situation I'm experiencing is when I connect my Array
Solutions static bleed choke to the feed thru insulator at the outside of
the panel to ground the resonant frequency jumps to 2.014 MHz at 25 +j0
ohms...remove it entirely and I'm back to my 45 - j11 ohms.>>>
The choke is completely unnecessary with a shunt feed tower. It won't help a
thing, so leave it out.
73 Tom
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