Topband: Shunt feeding the Skyneedle - new developments

Fri Feb 21 22:56:25 EST 2014

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 at 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 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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