Because you're using a shunt capacitor. This in conjunction with the inductive
reactance forms an L-network. As I said before, you need a series capacitor.
Move the tap to get 50 +jX and then add -jX.
Wes N7WS
On 10/15/2019 1:30 PM, Marty Ray wrote:
Thanks for the response Herb. I can
Marty,
You may be seeing errors in your readings due to broadcast pickup. This is
common when modern R+Jx measurement tools are connected to large antenna
structures. Others have described ways around this problem before here on the
topband chat.
Lee K7TJR OR
Thanks for the response
On 2019-10-15 4:30 PM, Marty Ray wrote:
I can obtain a good match using the 65 ft tap point, but my question
> is why my analyzer is measuring a change in the feedpoint resistance
> (real component of R + jX).
Because the *shunt* capacitor creates an L network with the impedance
(R +/- jX) at
FWIW, I had a shunt feed on my 97-foot Rohn 25 with stacked tribanders
and a shorty forty on it. I spent a long time trying to find a 50-ohm
tap point on the tower and was never successful, so I changed to an
Omega match, which was very easy to adjust once the local broadcast
station on 1550
m: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Marty Ray
Sent: Monday, October 14, 2019 7:45 PM
To: topband@contesting.com
Subject: Topband: Shunt feed question
I am shunt feeding a 70 ft Trylon tower with a Tennadyne T12.10-30HD LPDA at
70 ft and a full size 40m rotatable dipole at 79 ft
Thanks for the response Herb. I can obtain a good match using the 65 ft tap
point, but my question is why my analyzer is measuring a change in the
feedpoint resistance (real component of R + jX).
Regards,
Marty
> On Oct 15, 2019, at 3:19 PM, Herbert Schoenbohm
> wrote:
>
> Best to use a 3
Best to use a 3 or 4 wire cage feed and you will find the match easier.
You should tap the tower at 50 feet and work down till you find the sweet
spot. A 500 to 750 vac variable will take care of any measure inductive
component.
Herb, KV4FZ
On Tue, Oct 15, 2019 at 3:10 PM Marty Ray wrote:
> I
I am shunt feeding a 70 ft Trylon tower with a Tennadyne T12.10-30HD LPDA at 70
ft and a full size 40m rotatable dipole at 79 ft, (the top of the mast is ~85
ft). Both antennas have relays that electrically bond them to the tower when
the shunt feed is in use.
I have tried two shunt tap
Hi All,
Thanks again for your help back In December. KC4D’s 135’ tower (110 degrees
electrical length) with an omega match is up and running. There are 60 110’
radials though half go out 40’ and are coiled up until permission is arranged
to go on neighbors land. The shunt is a 4 wire cage
ft. and does change the SWR.
Jim - KR9U
-Subject: Topband: Shunt feed procedure?
Hi All, we’re planning on gamma loading a 130’ tower with a stack of StepIR
antennas using a cage for the shunt wire. We have modeled the tower. Question:
is the model sufficient to determine the gamma wire
Hi Tree, many thanks for the background on the dream beams! QSL on the
effective tower length. ON4UNs book says aunt feeding will work up to 140
degrees. My friend is doing the modeling and it’s hard to imagine we’re more
than 120 degrees. We’ll see. Fingers crossed
Regards , Kenny K2KW
>
Some anecdotal info on use of Steppir antennas on loaded towers.
I have never heard of anyone experiencing arcing. This also includes using
other antennas with isolated elements (like KLM). There just isn't going
to be a potential difference.
I have helped several locals load their towers with
Hi All, we’re planning on gamma loading a 130’ tower with a stack of StepIR
antennas using a cage for the shunt wire. We have modeled the tower. Question:
is the model sufficient to determine the gamma wire height? Or is the
procedure to use a single wire to per the model height first to
...@contesting.com] On Behalf Of Marc
Wullaert ON4MA
Sent: Tuesday, October 10, 2017 1:43 PM
To: bob burton <n4...@yahoo.com>; topband@contesting.com
Subject: Re: Topband: Shunt Feed help
Hi BoB,
be careful with the c31xr as the 20m reflector is on the far end. maximum
voltage present there and mine
for a better isolator
73
Marc ON4MA
https://www.facebook.com/marc.wullaert.5
- Original Message -
From: "bob burton via Topband" <topband@contesting.com>
To: <topband@contesting.com>
Sent: Tuesday, October 10, 2017 2:22 PM
Subject: Topband: Shunt Feed help
Looki
I have used NEC4 to model my short 50 ft tower for shunt feed on 160,
80, and 40 meters. It has a small triband beam with all elements
grounded. The 160m shunt wire goes to the top, of course, and NEC gave
a good estimate of the impedance. On 80m, my first guess was pretty
close to 50 Ohms.
Looking for some shunt feed wisdom from the list. Trying to shunt feed 25G
tower ( 8-10ft sticks, 8ft flat top, base 18" out of the ground = total tower
89.5 ft) has a F12 C31XR just above the thrust bearing (@90ft) with 6ft 2" mast
above the tribander with a F12 D140 dipole (@96ft). Based on
I shunt feed my 54 ft free standing 3 section crank-up tower for 160m and 80m,
remote relay band switchable omega match. 2:1 SWR bandwidth is around 40+ kc on
160 and about 20 kc on 80.
3/8” solid gamma rod, 15” from a tower leg attached at about the 22 ft level,
the top of the bottom section
Steve, Space the cage wire should at least 24 inches under the belief
that the fatter the structure appears at RF to be the more bandwidth
will be obtained. Also consider at a minimum a ground screen of rabbit
fencing around the base of your tower to reduce your ground loses which
are
it becomes.
- Original Message -
From: Ralph Parker ve...@dccnet.com
To: topband@contesting.com
Sent: Thursday, December 18, 2014 7:59 PM
Subject: Topband: Shunt Feed - Insulated Elements on Yagi
Good question, Stan. I've wondered the same thing.
I have a 64' self-standing tower with a 3
I have never had an issue with this on any tower I have shunt fed that had
a Yagi at the top with insulated elements, but then again my insulators are
probably a lot better than the average ones used on commerical antennas. I
am thinking about shunt feeding a tower that is not mine and wanted to
Stan - For about 8 years, up until this past spring, my shunt fed tower
for 160 had a KT34XA (insulated elements, later upgraded to a KT36XA same
insulated elements) at the top and I never experienced any issue at all
running 1500 watts, even during a few contests where, as you know, you are
One of the factors for arc over is the diameter of the tower and
top support pipe diameter length.
A really FAT 1/4 wave tower may have 1000 ohms at the top, while a
skinny tower would have much more.
The higher the impedance, the higher the voltage to cause arc overs.
73
Bruce-K1FZ
Understanding what Bruce has posted would support the theory that a cage
feed tower is indeed fatter with a lower impedance and thus less
proclivity to arc over on the insulated elements.
Herb Schoenbohm, KV4FZ
On 12/18/2014 12:33 PM, k...@myfairpoint.net wrote:
One of the factors for arc
Concerning voltage breakdowns using yagi-loaded towers on 160 meters... I
have heard stories of arcing to beat the band, that included a fair amount
of destruction. I have heard stories of nothing needed for good operation,
even at QRO. All these stories have to exist in the same logical space.
On Thu,12/18/2014 4:59 PM, Ralph Parker wrote:
I have a 64' self-standing tower with a 3 el Steppir on it (insulated
elements) and a 40m linear loaded dipole (also insulated) on top of that.
I've worried that any high voltage on the ends of the boom might be harmful
to the drive motors in the
Greetings fellow Topbanders:
Please, an antenna question. For the last several years I have use a
Inverted L on 160. Rscently I became able to run more power (from 450
watts up to 1 KW output. At that point it appeared that I had developed
an arc somewhere in my antenna system, so I
The difference in an inverted L and a shunt-fed tower would have been
overwhelmed by any differences in the ground/counterpoise systems
underneath. How you deal with ground and radials/counterpoise on 160 is the
1000 pound gorilla in the room with no real competition.
Beyond that, if the bend of
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