Re: Topband: Cage wire performance

[Jim Brown]

On 1/4/2021 7:05 AM, Kenny Silverman wrote:

I will be converting a wire inverted-L to a T top loading on a 75’ tall wire 
hung from a tree. To improve the bandwidth, I was wondering about going to a 
2-wire “cage” for the vertical section.


Hi Kenny,

I added a second wire to my Tee many years ago; at first the vertical 
section was about 80 ft, now it's closer to 100 ft. My spacers are sort 
of random, on the order of 8-12 inches. It did, indeed, increase the SWR 
bandwidth. I'm using a lot of on-ground radials of varying lengths.


73, Jim K9YC
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Re: Topband: Cage wire performance

[GEORGE WALLNER]

Kenny,
For the Baker Island KH1/KH7Z DXpedition I developed a 43 foot "T" antenna 
with spreader wires (Fat Vertical) with sloping top loading wires. It 
performed very well. I have been using a 65' version at C6AGU for the past 
two years and it has been performing very well. (There is a picture of it on 
the C6AGU QRZ.com page.) NEC modelling indicates higher gain (6 dBi) and 
wider bandwidth, BUT making the antenna "fat" lowers its radiation 
resistance, which places greater demands on the ground system. (Both on 
Baker and C6AGU the antenna was standing in salt-water.)
The C6AGU antenna feed-point impedance was measured at 9 - 130j Ohms. (I use 
a remote tuner.) If you measure a much higher resistive component, it could 
indicated that you need to improve the GND system.

GL and 73,
George,
AA7JV/C6AGU


On Mon, 4 Jan 2021 10:05:47 -0500
 Kenny Silverman  wrote:

Hello and HNY!

I will be converting a wire inverted-L to a T top loading on a 75’ tall wire hung from a tree. To improve the bandwidth, I was wondering about going to a 2-wire “cage” for the vertical section. I’m actually modeling a skinny triangle where the wires connect at a point on the top, but with a 4 foot spread of the wires near the ground. This adds about 15-20 kc to the 2:1 bandwidth per the model. 


Will a 2-wire section like this always behave as a wide/fat conductor or do I 
have to worry about voltage/current in Each wire?

Regards , Kenny K2KW 
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Re: Topband: Cage wire performance

[Rob Atkinson]

The problem with cages isn't electrical; the thing to consider is
physical.  If you are in an area where you can have ice you have to
consider if your cage and its supports are strong enough to hold ice
under high winds.   You don't want a relatively inexpensive wire cage
to pull down more costly supports that are a lot harder to rebuild.
Good idea to build in a weighted antenna that will sag to the ground
under a lot of ice, or a fail safe that is easy to fix.

73

Rob
K5UJ
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Re: Topband: Cage wire performance

[Kenny Silverman]

Hi Dave,  thanks for the analysis. I was using your number 3 model, though I 
had a small slope in the top wires. When I flattened the top wires I too was 
getting about 100kc at 24 ohms. 

I will to do a sensitivity analysis to see what works best for me. Where I set 
down the 60 radials (laying on the forest floor) I can’t get the top wires flat 
due to overlapping tree canopies. The only place with a clearing is above my 
house and I can’t put the vertical there. 

Also thanks to all the input on and off the reflector!  I will look at the 
relay option if my idea doesn’t work.  I’m running low power so my rig’s tuner 
can help if I don’t get 100 kc

Regards , Kenny K2KW 

> On Jan 4, 2021, at 1:18 PM, Dave Cuthbert  wrote:
> 
> 
> 
> Kenny, your model might have a problem with the acute antenna between the two 
> vertical wires. I ran EZNEC simulations to test this and compare against a 
> single vertical wire T reference antenna. Your antenna shows similar 
> bandwidth, but a different input resistance. 
> 
> Antenna 1 reference antenna
> 75' vertical wire
> from there extend two horizontal 35'wire
> SWR bandwidth normalized to the antenna input resistance of 23 ohms
> SWR bandwidth is 118kHz
> 
> Antenna 2 your antenna
> perfect GND, #12 bare wire, current segments are 1'
> 1' vertical wire from GND
> from that wire two wires extend to 75' separated by 4' at the top
> At 75' the two wires are joined 
> From each 75' wire extends a 48' wire
> SWR bandwidth normalized to the antenna input resistance of 16 ohms
> 2:1 SWR bandwidth is 100kHz
> 
> Antenna 3 your antenna modified to conform to the NEC included angle rule
> perfect GND, #12 bare wire
> 1' vertical wire from GND
> from that, 2' horizontal wires extending opposite one another
> two wires extend from the ends of those two wires to 75'
> at 75' the two wires are joined
> from each 75' wire extends a 52' horizontal wire
> SWR bandwidth normalized to the antenna input resistance of 25 ohms
> SWR bandwidth is 106kHz
> 
> Antenna 4 single vertical wire with a horizontal flat top wires
> perfect GND, #12 bare wire
> 75' vertical wire from GND
> from that, 2' horizontal wires extending opposite one another
> two wires extend horizontally from the ends of each of those two wires to 22'
> SWR bandwidth normalized to the antenna input resistance of 23 ohms
> SWR bandwidth is 72kHz
> 
>Dave KH6AQ
> 
> 
>> On Mon, Jan 4, 2021 at 5:07 AM Kenny Silverman  wrote:
>> Hello and HNY!
>> 
>> I will be converting a wire inverted-L to a T top loading on a 75’ tall wire 
>> hung from a tree. To improve the bandwidth, I was wondering about going to a 
>> 2-wire “cage” for the vertical section. I’m actually modeling a skinny 
>> triangle where the wires connect at a point on the top, but with a 4 foot 
>> spread of the wires near the ground. This adds about 15-20 kc to the 2:1 
>> bandwidth per the model. 
>> 
>> Will a 2-wire section like this always behave as a wide/fat conductor or do 
>> I have to worry about voltage/current in Each wire?
>> 
>> Regards , Kenny K2KW 
>> _
>> Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
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Re: Topband: Cage wire performance

[Kenny Silverman]

Hi Clive,  thanks for the input!  The existing 75 foot inverted  L measures 26 
ohms X=2 using 60 x 100 foot radials. This is very close to what the model 
calculates. 

Regards , Kenny K2KW 

> On Jan 4, 2021, at 10:12 AM, cl...@gm3poi.com wrote:
> 
> Kenny a lot will depend on your ground system. If it is very good then that 
> extra bandwidth may help.
> But if it is just medium quality, there will be sufficient loss not to bother 
> until and if you improve your ground system. Try the bandwidth without the 
> extra wires and see how it compares with the predicted bandwidth. 73 Clive 
> GM3POI/GM3X
> 
> -Original Message-
> From: Topband  On Behalf Of 
> Kenny Silverman
> Sent: 04 January 2021 15:06
> To: TopBand List 
> Subject: Topband: Cage wire performance
> 
> Hello and HNY!
> 
> I will be converting a wire inverted-L to a T top loading on a 75’ tall wire 
> hung from a tree. To improve the bandwidth, I was wondering about going to a 
> 2-wire “cage” for the vertical section. I’m actually modeling a skinny 
> triangle where the wires connect at a point on the top, but with a 4 foot 
> spread of the wires near the ground. This adds about 15-20 kc to the 2:1 
> bandwidth per the model. 
> 
> Will a 2-wire section like this always behave as a wide/fat conductor or do I 
> have to worry about voltage/current in Each wire?
> 
> Regards , Kenny K2KW 
> _
> Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
> 
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Re: Topband: Cage wire performance

[Dave Cuthbert]

Kenny, your model might have a problem with the acute antenna between the
two vertical wires. I ran EZNEC simulations to test this and compare
against a single vertical wire T reference antenna. Your antenna shows
similar bandwidth, but a different input resistance.

*Antenna 1 *reference antenna
75' vertical wire
from there extend two horizontal 35'wire
SWR bandwidth normalized to the antenna input resistance of *23 ohms*
*SWR bandwidth is 118kHz*

*Antenna 2 *your antenna
perfect GND, #12 bare wire, current segments are 1'
1' vertical wire from GND
from that wire two wires extend to 75' separated by 4' at the top
At 75' the two wires are joined
From each 75' wire extends a 48' wire
SWR bandwidth normalized to the antenna input resistance of *16 ohms*
*2:1 SWR bandwidth is 100kHz*

*Antenna 3 *your antenna modified to conform to the NEC included angle rule
perfect GND, #12 bare wire
1' vertical wire from GND
from that, 2' horizontal wires extending opposite one another
two wires extend from the ends of those two wires to 75'
at 75' the two wires are joined
from each 75' wire extends a 52' horizontal wire
SWR bandwidth normalized to the antenna input resistance of *25 ohms*
*SWR bandwidth is 106kHz*

*Antenna 4* single vertical wire with a horizontal flat top wires
perfect GND, #12 bare wire
75' vertical wire from GND
from that, 2' horizontal wires extending opposite one another
two wires extend horizontally from the ends of each of those two wires to
22'
SWR bandwidth normalized to the antenna input resistance of *23 ohms*
*SWR bandwidth is 72kHz*

   Dave KH6AQ


On Mon, Jan 4, 2021 at 5:07 AM Kenny Silverman  wrote:

> Hello and HNY!
>
> I will be converting a wire inverted-L to a T top loading on a 75’ tall
> wire hung from a tree. To improve the bandwidth, I was wondering about
> going to a 2-wire “cage” for the vertical section. I’m actually modeling a
> skinny triangle where the wires connect at a point on the top, but with a 4
> foot spread of the wires near the ground. This adds about 15-20 kc to the
> 2:1 bandwidth per the model.
>
> Will a 2-wire section like this always behave as a wide/fat conductor or
> do I have to worry about voltage/current in Each wire?
>
> Regards , Kenny K2KW
> _
> Searchable Archives: http://www.contesting.com/_topband - Topband
> Reflector
>
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Re: Topband: Cage wire performance

[Joe]

So this is more or less like the Bow Tie Dipole antenna that is used 
like in UHF TV antennas.


Sometimes two wires on each side like cat whiskers.
and other times a solid triangle on each side.

Now I wonder, is there a limit say ratio wise to length vs width at the 
far end, where you don't get any more bandwidth, or it no longer even 
acts like a dipole?


Joe WB9SBD

On 1/4/2021 9:32 AM, Richard (Rick) Karlquist wrote:


On 1/4/2021 7:05 AM, Kenny Silverman wrote:
where the wires connect at a point on the top, but with a 4 foot 
spread of the wires near the ground. This adds about 15-20 kc to the 
2:1 bandwidth per the model.


Will a 2-wire section like this always behave as a wide/fat conductor 
or do I have to worry about voltage/current in Each wire?


Regards , Kenny K2KW


Just a guess:  I would think with 2 wires, you would be fairly
successful with getting good current sharing, as long as there
wasn't some unbalancing effect, say due to having the vertical
running along side a tower.

With 3 wires, there is some reason to think that the middle
wire wouldn't carry much current if the three wires were
in a plane.  OTOH, if they formed a triangular cross section,
then it would seem likely that current sharing would be good.
In general, you want to emulate a round conductor, as opposed
to a strap.  When straps are used to make inductors, the
current crowds to the edges.  Round conductors don't have
such edges, hence they have good current sharing.

I don't believe NEC is good for modeling this.  You have
to use a tool called "HOBBIES" if you want to do this.
K6OIK has written some articles about this tool.

73
Rick N6RK
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Re: Topband: Cage wire performance https://www.pi4cc.nl/album/80-160/slides/P5030195.html

[Peter]

Hi

An easy way to make a cage is to use black irrigation hose.
Just make some 30-50 cm diameter circles Drill 3-4 holes and ready to go
 https://www.pi4cc.nl/album/80-160/slides/P5030195.html 



Peter
PC2A
https://www.pi4cc.nl 




Op 4-1-2021 om 16:32 schreef Richard (Rick) Karlquist:


On 1/4/2021 7:05 AM, Kenny Silverman wrote:
where the wires connect at a point on the top, but with a 4 foot 
spread of the wires near the ground. This adds about 15-20 kc to the 
2:1 bandwidth per the model.


Will a 2-wire section like this always behave as a wide/fat conductor 
or do I have to worry about voltage/current in Each wire?


Regards , Kenny K2KW


Just a guess:  I would think with 2 wires, you would be fairly
successful with getting good current sharing, as long as there
wasn't some unbalancing effect, say due to having the vertical
running along side a tower.

With 3 wires, there is some reason to think that the middle
wire wouldn't carry much current if the three wires were
in a plane.  OTOH, if they formed a triangular cross section,
then it would seem likely that current sharing would be good.
In general, you want to emulate a round conductor, as opposed
to a strap.  When straps are used to make inductors, the
current crowds to the edges.  Round conductors don't have
such edges, hence they have good current sharing.

I don't believe NEC is good for modeling this.  You have
to use a tool called "HOBBIES" if you want to do this.
K6OIK has written some articles about this tool.

73
Rick N6RK
_
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Reflector


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Re: Topband: Cage wire performance

[Richard (Rick) Karlquist]

On 1/4/2021 7:05 AM, Kenny Silverman wrote:
where the wires connect at a point on the top, but with a 4 foot spread 
of the wires near the ground. This adds about 15-20 kc to the 2:1 
bandwidth per the model.


Will a 2-wire section like this always behave as a wide/fat conductor or do I 
have to worry about voltage/current in Each wire?

Regards , Kenny K2KW


Just a guess:  I would think with 2 wires, you would be fairly
successful with getting good current sharing, as long as there
wasn't some unbalancing effect, say due to having the vertical
running along side a tower.

With 3 wires, there is some reason to think that the middle
wire wouldn't carry much current if the three wires were
in a plane.  OTOH, if they formed a triangular cross section,
then it would seem likely that current sharing would be good.
In general, you want to emulate a round conductor, as opposed
to a strap.  When straps are used to make inductors, the
current crowds to the edges.  Round conductors don't have
such edges, hence they have good current sharing.

I don't believe NEC is good for modeling this.  You have
to use a tool called "HOBBIES" if you want to do this.
K6OIK has written some articles about this tool.

73
Rick N6RK
_
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Re: Topband: Cage wire performance

[clive]

Kenny a lot will depend on your ground system. If it is very good then that 
extra bandwidth may help.
But if it is just medium quality, there will be sufficient loss not to bother 
until and if you improve your ground system. Try the bandwidth without the 
extra wires and see how it compares with the predicted bandwidth. 73 Clive 
GM3POI/GM3X

-Original Message-
From: Topband  On Behalf Of 
Kenny Silverman
Sent: 04 January 2021 15:06
To: TopBand List 
Subject: Topband: Cage wire performance

Hello and HNY!

I will be converting a wire inverted-L to a T top loading on a 75’ tall wire 
hung from a tree. To improve the bandwidth, I was wondering about going to a 
2-wire “cage” for the vertical section. I’m actually modeling a skinny triangle 
where the wires connect at a point on the top, but with a 4 foot spread of the 
wires near the ground. This adds about 15-20 kc to the 2:1 bandwidth per the 
model. 

Will a 2-wire section like this always behave as a wide/fat conductor or do I 
have to worry about voltage/current in Each wire?

Regards , Kenny K2KW 
_
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