Hi, Carl
Well, paying with your load on a Smith Chart, tuning out the -j11 only
improved the VSWR from 1.3:1 to 1.1 - not really worth doing! Also, you
would need a fairly large inductor to obtain 1 uHy of inductance with low
loss, and I expect that you would incur more loss in the inductor (that
would subtract directly from your transmitted power) than you would gain in
improved mismatch loss by improving the VSWR from 1.3 t 1.1!! Keep in mind
also that the inductor would also have stray capacitance to the enclosure
walls that will lower its Q ! I wouldn't do it! 1.3:1 is great!! Enjoy!!
You will help your overall performance much more by building a terminated
receiving loop - a KAZ, flag or pennant configuration to help your HEARING!!
MY KAZ loop did wonders for me!!
GL and have fun!
73,
Charlie, K4OTV
-----Original Message-----
From: Carl Braun [mailto:Carl.Braun@lairdtech.com]
Sent: Saturday, February 22, 2014 7:23 AM
To: Charlie Cunningham; 'ZR'; '160'
Subject: RE: Topband: Shunt feeding the Skyneedle - new developments
Charlie
Thanks for the tip. I may play with a bit of inductance just to see how the
system reacts.
Not sure if I can post a pic here but I'm including a shot of the panel and
the cap...hope you all can see it. The static bleed choke has been removed
and I'm awaiting PL 259 connectors from my friends at RF parts.
My crazy dog gets pretty loopy when we play with the Frisbee so I'm
considering a trial cut in the asphalt to see how easy or ugly the process
is. I hear the secret is all in the blade that's used. You Tube has some
videos showing the procedure for cutting asphalt...we'll see.
Thanks again
Carl AG6X
-----Original Message-----
From: Charlie Cunningham [mailto:charlie-cunningham@nc.rr.com]
Sent: Friday, February 21, 2014 8:18 PM
To: Carl Braun; 'ZR'; '160'
Subject: RE: Topband: Shunt feeding the Skyneedle - new developments
Hi, Carl
Well, I think that what you are doing with your radials should be OK. I
guess I'd rather get them under the asphalt if I could where they wouldn't
get torn up or b a trip hazard.
BTW I I was playing with your match on the Smith Chart and if you'll add
about 1 uHy inductance in series with the connector (SO-239?) where you
feedline leaves the enclosure, that will take you to 45 +j0, but I'd be
concerned about incurring more losses in the inductor than any tiny mismatch
loss from the -j11 term. I probably wouldn't do it.
73,
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Carl
Braun
Sent: Friday, February 21, 2014 10:56 PM
To: Charlie Cunningham; 'ZR'; '160'
Subject: Re: Topband: Shunt feeding the Skyneedle - new developments
I'm working on the radial field weekly.
Here is a theoretical question that results from my particular QTH. The
Skyneedle is situated near a secondary blacktop driveway that is in the back
of my property. I have to run radials over the blacktop to the rest of the
property and, in order to keep things kind of neat, I'm using
multi-conductor rotor cable as radials that travel over the blacktop. I
have both 6 conductor and 3 conductor control cable that I'm using. I strip
back the jacket at the radial ring...fan out the wires 3" apart and attach
them to the 1 1/2" copper pipe I'm using as a radial ring around the base of
the 'Needle'. Then the radial wires converge back into the cable jacket
then travel across the 10' blacktop driveway and then they are removed from
the cable jacket where they fan out into the dirt and are buried. Most of
these radial wires are 60' to 100' once they leave the jacket.
Any problem with what I'm doing here? I understand that it would be better
if they fanned out directly from the base but I can have 50+ wires traveling
over the blacktop.
I was even considering getting an asphalt blade and cutting some channels
into the blacktop...burying the jacketed cable into the asphalt and then
sealing then in so I'm not running over them or tripping over them when
playing Frisbee with the hound.
My Guatemalan yard worker has been burying radial wires for the last month
and thinks that I'm LOCO but he likes getting paid at the end of the day.
As we speak I have a total of 34 radials with the shortest being 30' with
the longest at 100'. Most of them are 60-70'. Four of them are tied into
my 40m phased array radial field comprised of 90-100 radials under each
antenna ranging from 40' to 80'. I can change the height of these verticals
from 33' for 40m to 66' for 80m. 1/2 wl spacing on 40 and 1/4 wl spacing on
80.
Carl AG6X
-----Original Message-----
From: Charlie Cunningham [mailto:charlie-cunningham@nc.rr.com]
Sent: Friday, February 21, 2014 7:36 PM
To: 'ZR'; Carl Braun; '160'
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@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@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@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@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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