Great idea!
For an antenna I'm designing, I need a 150 ohm phasing line and had
concluded
that 3 x 450 ohm or 2 x TV 300 ohm open wire line in parallel was the
cheap and cheerful way to get there (Pout < 150W). Thanks also on the tip
for
measuring the velocity factor with the MFJ -- I had been thinking
of measuring lengths as open or shorted quarter waves, but your way is
easier.
Best Wishes,
Bob, N1RC
-----Original Message-----
From: owner-antennaware-digest@contesting.com
[mailto:owner-antennaware-digest@contesting.com]
Sent: Monday, December 18, 2000 4:53 AM
To: antennaware-digest@contesting.com
Subject: Antennaware Antenna Modeling Digest V3 #37
Antennaware Antenna Modeling Digest Sunday, December 17 2000 Volume 03 :
Number 037
In this issue:
[antennaware] Twin-Coax-Cable as single feed line to 1/2 impedance
Re: [antennaware] Twin-Coax-Cable as single feed line to 1/2 impedance
Re: [antennaware] Twin-Coax-Cable as single feed line to 1/2 impedance
[antennaware] FSM
Re: [antennaware] Twin-Coax-Cable as single feed line to 1/2 impedance
See the end of the digest for information about antennaware-digest
----------------------------------------------------------------------
To: <antennaware@contesting.com>
Date: Sun, 17 Dec 2000 05:12:21 -0000
From: "Billy Ward" <billydeanward@hotmail.com>
Subject: [antennaware] Twin-Coax-Cable as single feed line to 1/2 impedance
Greetings Group,
I would like to have this groups input on something that I have been working
on today.
Today was not the first time that I've toyed with this idea but I performed
the experiments again that I have done a few times with the same results as
before. There was a question posted on another forum about some ideas for
low-loss coaxial cable and I offered some information as a POSSIBLE
solution.
This is it:
The Idea was to use two 72-Ohm Belden cables in parallel to obtain 36-Ohms
to match a 32-Ohm 1/4 wave ground-plane antenna. In doing this, the I
squared R losses would also be 1/2 unless there is something that I am not
seeing. Since the tests show that it works, if I qualified the tests
properly, I would have no doubts except that I have been a Ham and a RF
engineer for almost 40 years and have never heard of running two cables in
parallel.
I used an MFJ-259-B and measured the Characteristic Impedance of three
lengths of Belden 72 ohm cable.
One of them was Three Feet, one was 12 Feet and the other one was 18 Feet.
They measured 71.2-, 71.3 -and 71.2-Ohms. I then measured the velocity
factor using the "Distance to Fault Mode" to determine the electrical length
of the cable in inches and and then divided that figure by the actual length
in inches.
The Velocity Factor measured at .80, .80 and .79 blinking to .80
After making up 3 parallel cables by fitting both cables into a single
Pl-259 at each end just as you would to make a co-phasing cable for CB
radios, I made the measurements again. The impedances were almost exactly
what I expected at 35.7, 35,7 and 35.4.
The Velocity Factors were a little further from the single cable figures
than were the impedances, measuring at 82.3, 82,4 and 82.0. I figured that
this was because the losses from the insulation was divided among the two
cables causing the Velocity to be just a little faster than one cable.
I am familiar with Conjugate Matching and realize that there is really no
practical reason for using this cable arrangement in order to radiate 100%
of the power delivered by the transmitter less the power dissipated by the
cable losses.. Also the amount of power saved by halving the losses of
cable that is already low enough is not worth the time it takes and the
extra cost of the cable to bother with it. However, to stir up a discussion
on the other forum, I offered this idea. So please NO preaching about why I
do not need to bother with this idea. It is just a fun thing for
discussion.
In your opinions, are there any flaws in this being a viable feed line.
Billy
_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com
------------------------------
To: <antennaware@contesting.com>
Date: Sun, 17 Dec 2000 12:07:51 +0000
From: Clive Hollins <gfv91@dial.pipex.com>
Subject: Re: [antennaware] Twin-Coax-Cable as single feed line to 1/2
impedance
Yes you can do this- I have used similar arangements
of paralleling cables of the same and different
impedances to match antenna feed point impedences.
and to match phased arrays. The only problem you
need to be concerned about is the power handling
capacity of each of the cables.
A couple of 75 ohm cables in parallel will of course
give you 37.5 ohms at both ends, but if you use the
formula Zt= root(Z1*Z2) you can match that 37.5 ohms
to close to 50 Ohms using a lambda/4 length of coax
whose impedaence is 43 Ohms. e.g. a paralleled pair
of 90 Ohm cables-or any combinations that will give
you the same Z.
The classic example of an impedence transformer is
the 1/4 wave length of 75 Ohm used to match the 100
Ohms of a delta loop to any length of 50 Ohms.
Tried it once on 28MHz and it worked a treat!
de G8BOU/M5CHH/VE3CHH
Billy Ward wrote:
>
> Greetings Group,
>
> I would like to have this groups input on something that I have been
working
> on today.
> Today was not the first time that I've toyed with this idea but I
performed
> the experiments again that I have done a few times with the same results
as
> before. There was a question posted on another forum about some ideas for
> low-loss coaxial cable and I offered some information as a POSSIBLE
> solution.
> This is it:
>
> The Idea was to use two 72-Ohm Belden cables in parallel to obtain 36-Ohms
> to match a 32-Ohm 1/4 wave ground-plane antenna. In doing this, the I
> squared R losses would also be 1/2 unless there is something that I am not
> seeing. Since the tests show that it works, if I qualified the tests
> properly, I would have no doubts except that I have been a Ham and a RF
> engineer for almost 40 years and have never heard of running two cables
in
> parallel.
>
> I used an MFJ-259-B and measured the Characteristic Impedance of three
> lengths of Belden 72 ohm cable.
> One of them was Three Feet, one was 12 Feet and the other one was 18 Feet.
> They measured 71.2-, 71.3 -and 71.2-Ohms. I then measured the velocity
> factor using the "Distance to Fault Mode" to determine the electrical
length
> of the cable in inches and and then divided that figure by the actual
length
> in inches.
>
> The Velocity Factor measured at .80, .80 and .79 blinking to .80
>
> After making up 3 parallel cables by fitting both cables into a single
> Pl-259 at each end just as you would to make a co-phasing cable for CB
> radios, I made the measurements again. The impedances were almost
exactly
> what I expected at 35.7, 35,7 and 35.4.
>
> The Velocity Factors were a little further from the single cable figures
> than were the impedances, measuring at 82.3, 82,4 and 82.0. I figured
that
> this was because the losses from the insulation was divided among the two
> cables causing the Velocity to be just a little faster than one cable.
>
> I am familiar with Conjugate Matching and realize that there is really no
> practical reason for using this cable arrangement in order to radiate 100%
> of the power delivered by the transmitter less the power dissipated by the
> cable losses.. Also the amount of power saved by halving the losses of
> cable that is already low enough is not worth the time it takes and the
> extra cost of the cable to bother with it. However, to stir up a
discussion
> on the other forum, I offered this idea. So please NO preaching about why
I
> do not need to bother with this idea. It is just a fun thing for
> discussion.
>
> In your opinions, are there any flaws in this being a viable feed line.
>
> Billy
>
> _________________________________________________________________
> Get your FREE download of MSN Explorer at http://explorer.msn.com
>
> --
> FAQ on WWW: http://www.contesting.com/FAQ/antennaware
> Submissions: antennaware@contesting.com
> Administrative requests: antennaware-REQUEST@contesting.com
> Problems: owner-antennaware@contesting.com
------------------------------
To: <antennaware@contesting.com>
Date: Sun, 17 Dec 2000 09:17:47 -0600
From: Jay Terleski <wx0b@arraysolutions.com>
Subject: Re: [antennaware] Twin-Coax-Cable as single feed line to 1/2
impedance
Billy,
Hi, you have rediscovered an old trick.
If you look at ON4UN's book "Low-Band Dxing" you will see some arrays of
verticals using an element fed with parallel coaxial feebleness. To
match, and also create the magnitude of current needed for the array.
The triangle array is one such example. Of course in reality when you
try to build this array it creates a complex relay matrix, since we wish
to "steer" the array, but it works. Three towers in line is another
example.
There are other ways to feed this type of array using single coaxial
feed lines too.
But the point is that it is a common practice with phased arrays to use
parallel coaxial cables.
Reducing loss in the cable is not usually the concern, but I guess a
little less IR drop in an antenna feed line that has say 6 ohms of
impedance would be good. Say a mobile whip used on 160 meters. Here an
ohm of IR RF loss would be worth the effort to reduce.
Or guys on the 1750 meter band. These antennas probably can have a
fraction of an ohm of radiation impedance.
Jay, WX0B
Billy Ward wrote:
>
> Greetings Group,
>
> I would like to have this groups input on something that I have been
working
> on today.
> Today was not the first time that I've toyed with this idea but I
performed
> the experiments again that I have done a few times with the same results
as
> before. There was a question posted on another forum about some ideas for
> low-loss coaxial cable and I offered some information as a POSSIBLE
> solution.
> This is it:
>
> The Idea was to use two 72-Ohm Belden cables in parallel to obtain 36-Ohms
> to match a 32-Ohm 1/4 wave ground-plane antenna. In doing this, the I
> squared R losses would also be 1/2 unless there is something that I am not
> seeing. Since the tests show that it works, if I qualified the tests
> properly, I would have no doubts except that I have been a Ham and a RF
> engineer for almost 40 years and have never heard of running two cables
in
> parallel.
>
> I used an MFJ-259-B and measured the Characteristic Impedance of three
> lengths of Belden 72 ohm cable.
> One of them was Three Feet, one was 12 Feet and the other one was 18 Feet.
> They measured 71.2-, 71.3 -and 71.2-Ohms. I then measured the velocity
> factor using the "Distance to Fault Mode" to determine the electrical
length
> of the cable in inches and and then divided that figure by the actual
length
> in inches.
>
> The Velocity Factor measured at .80, .80 and .79 blinking to .80
>
> After making up 3 parallel cables by fitting both cables into a single
> Pl-259 at each end just as you would to make a co-phasing cable for CB
> radios, I made the measurements again. The impedances were almost
exactly
> what I expected at 35.7, 35,7 and 35.4.
>
> The Velocity Factors were a little further from the single cable figures
> than were the impedances, measuring at 82.3, 82,4 and 82.0. I figured
that
> this was because the losses from the insulation was divided among the two
> cables causing the Velocity to be just a little faster than one cable.
>
> I am familiar with Conjugate Matching and realize that there is really no
> practical reason for using this cable arrangement in order to radiate 100%
> of the power delivered by the transmitter less the power dissipated by the
> cable losses.. Also the amount of power saved by halving the losses of
> cable that is already low enough is not worth the time it takes and the
> extra cost of the cable to bother with it. However, to stir up a
discussion
> on the other forum, I offered this idea. So please NO preaching about why
I
> do not need to bother with this idea. It is just a fun thing for
> discussion.
>
> In your opinions, are there any flaws in this being a viable feed line.
>
> Billy
>
> _________________________________________________________________
> Get your FREE download of MSN Explorer at http://explorer.msn.com
>
> --
> FAQ on WWW: http://www.contesting.com/FAQ/antennaware
> Submissions: antennaware@contesting.com
> Administrative requests: antennaware-REQUEST@contesting.com
> Problems: owner-antennaware@contesting.com
- --
Jay Terleski
WX0B - Array Solutions
www.arraysolutions.com
------------------------------
To: <antennaware@contesting.com>
Date: Sun, 17 Dec 2000 16:10:13 -0000
From: "Billy Ward" <billydeanward@hotmail.com>
Subject: [antennaware] FSM
I am looking for one of those old Field STrength Meters that we used to get
through MARS and on the electronic surplus market back in the 50's and early
60's.
They were black wrinkle and had a large meter about 6 or 8 inches and a
single knob that tuned the HF band with a 6 or 8 foot telescopic antenna
Billy
_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com
------------------------------
To: <antennaware@contesting.com>
Date: Sun, 17 Dec 2000 10:52:48 -0600
From: Jay Terleski <wx0b@arraysolutions.com>
Subject: Re: [antennaware] Twin-Coax-Cable as single feed line to 1/2
impedance
My spell checker sold me on the use of Feebleness instead of Feed Lines.
Below.
Please excuse my feebleness.
Jay
Jay Terleski wrote:
>
> Billy,
>
> Hi, you have rediscovered an old trick.
>
> If you look at ON4UN's book "Low-Band Dxing" you will see some arrays of
> verticals using an element fed with parallel coaxial feebleness. To
> match, and also create the magnitude of current needed for the array.
>
> The triangle array is one such example. Of course in reality when you
> try to build this array it creates a complex relay matrix, since we wish
> to "steer" the array, but it works. Three towers in line is another
> example.
>
> There are other ways to feed this type of array using single coaxial
> feed lines too.
>
> But the point is that it is a common practice with phased arrays to use
> parallel coaxial cables.
>
> Reducing loss in the cable is not usually the concern, but I guess a
> little less IR drop in an antenna feed line that has say 6 ohms of
> impedance would be good. Say a mobile whip used on 160 meters. Here an
> ohm of IR RF loss would be worth the effort to reduce.
>
> Or guys on the 1750 meter band. These antennas probably can have a
> fraction of an ohm of radiation impedance.
>
> Jay, WX0B
>
> Billy Ward wrote:
> >
> > Greetings Group,
> >
> > I would like to have this groups input on something that I have been
working
> > on today.
> > Today was not the first time that I've toyed with this idea but I
performed
> > the experiments again that I have done a few times with the same results
as
> > before. There was a question posted on another forum about some ideas
for
> > low-loss coaxial cable and I offered some information as a POSSIBLE
> > solution.
> > This is it:
> >
> > The Idea was to use two 72-Ohm Belden cables in parallel to obtain
36-Ohms
> > to match a 32-Ohm 1/4 wave ground-plane antenna. In doing this, the I
> > squared R losses would also be 1/2 unless there is something that I am
not
> > seeing. Since the tests show that it works, if I qualified the tests
> > properly, I would have no doubts except that I have been a Ham and a RF
> > engineer for almost 40 years and have never heard of running two cables
in
> > parallel.
> >
> > I used an MFJ-259-B and measured the Characteristic Impedance of three
> > lengths of Belden 72 ohm cable.
> > One of them was Three Feet, one was 12 Feet and the other one was 18
Feet.
> > They measured 71.2-, 71.3 -and 71.2-Ohms. I then measured the velocity
> > factor using the "Distance to Fault Mode" to determine the electrical
length
> > of the cable in inches and and then divided that figure by the actual
length
> > in inches.
> >
> > The Velocity Factor measured at .80, .80 and .79 blinking to .80
> >
> > After making up 3 parallel cables by fitting both cables into a single
> > Pl-259 at each end just as you would to make a co-phasing cable for CB
> > radios, I made the measurements again. The impedances were almost
exactly
> > what I expected at 35.7, 35,7 and 35.4.
> >
> > The Velocity Factors were a little further from the single cable figures
> > than were the impedances, measuring at 82.3, 82,4 and 82.0. I figured
that
> > this was because the losses from the insulation was divided among the
two
> > cables causing the Velocity to be just a little faster than one cable.
> >
> > I am familiar with Conjugate Matching and realize that there is really
no
> > practical reason for using this cable arrangement in order to radiate
100%
> > of the power delivered by the transmitter less the power dissipated by
the
> > cable losses.. Also the amount of power saved by halving the losses of
> > cable that is already low enough is not worth the time it takes and the
> > extra cost of the cable to bother with it. However, to stir up a
discussion
> > on the other forum, I offered this idea. So please NO preaching about
why I
> > do not need to bother with this idea. It is just a fun thing for
> > discussion.
> >
> > In your opinions, are there any flaws in this being a viable feed line.
> >
> > Billy
> >
> > _________________________________________________________________
> > Get your FREE download of MSN Explorer at http://explorer.msn.com
> >
> > --
> > FAQ on WWW: http://www.contesting.com/FAQ/antennaware
> > Submissions: antennaware@contesting.com
> > Administrative requests: antennaware-REQUEST@contesting.com
> > Problems: owner-antennaware@contesting.com
>
> --
> Jay Terleski
> WX0B - Array Solutions
> www.arraysolutions.com
>
> --
> FAQ on WWW: http://www.contesting.com/FAQ/antennaware
> Submissions: antennaware@contesting.com
> Administrative requests: antennaware-REQUEST@contesting.com
> Problems: owner-antennaware@contesting.com
- --
Jay Terleski
WX0B - Array Solutions
www.arraysolutions.com
------------------------------
End of Antennaware Antenna Modeling Digest V3 #37
*************************************************
--
FAQ on WWW: http://www.contesting.com/FAQ/antennaware
Submissions: antennaware@contesting.com
Administrative requests: antennaware-digest-REQUEST@contesting.com
Problems: owner-antennaware-digest@contesting.com
--
FAQ on WWW: http://www.contesting.com/FAQ/antennaware
Submissions: antennaware@contesting.com
Administrative requests: antennaware-REQUEST@contesting.com
Problems: owner-antennaware@contesting.com
|