Copper vs Stainless?
 

Pardon an ignorant sailor butting in here but I have a question about
antenna material. I have been experimenting with home brew QFH antennas to
receive 137.5 Mhz weather satellite images. I built one out of copper
tubing that works great. I can get good pictures from Hudson Bay to Puerto
Rico. Then I tried to duplicate it with stainless tubing to use on the
boat. The two antennas and baluns are identical but the stainless version
has less than half the range. Any suggestions on how to modify or tune it
to improve reception?

Or, failing that, what effect would powder coating the copper one have?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

I understand that you are the resident authority on QFH antennas. Can you
help with this problem?

--
Glenn Ashmore

"Glenn Ashmore" wrote in message
news:HyEEd.16418$EG1.2863@lakeread04...
Pardon an ignorant sailor butting in here but I have a question about
antenna material. I have been experimenting with home brew QFH antennas
to
receive 137.5 Mhz weather satellite images. I built one out of copper
tubing that works great. I can get good pictures from Hudson Bay to
Puerto
Rico. Then I tried to duplicate it with stainless tubing to use on the
boat. The two antennas and baluns are identical but the stainless version
has less than half the range. Any suggestions on how to modify or tune
it
to improve reception?

Or, failing that, what effect would powder coating the copper one have?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

On Tue, 11 Jan 2005 07:55:19 -0500, "Glenn Ashmore"
wrote:

I understand that you are the resident authority on QFH antennas. Can you
help with this problem?

Hello Glenn,

I've had some experience with the QFH, Glenn, but I don't consider
myself an authority. However, I'll try to help you with the problem,
but first I'll need to know the form you used in your model. Is it
the self phasing type, with the inductive bifilar longer than the
capacitive one? Or are both bifilars of the same length and fed with a
power splitter and a 90° hybrid? If it is the self phasing type what
diameter is the tubing? And have you reviewed my data on the subject
that appears in Reflections?

If both the copper and stainless steel models are fabricated in
exactly the same form there shouldn't be much difference in
performance due the different materials. I don't believe the
difference in resistivities of the two materials should have a
significant effect on their performances, unless your bifilars are
made with very small diameter wire. If you used the self phasing type
the tubing diameter should be approximately 3/4", in which the
difference in resitivities would be absolutely insignificant.

So Glenn, give me the details of your QFH so that I can be of more
help.

Walt, W2DU

You are talking a little over this sailor's head but I think I got the jist
of it.

The antennas are basically Bill Sykes and Bob Cobey's design.
http://www.askrlc.co.uk/. I did change the ratio of height to width a
little but verified the dimensions with John Copens' calculator.

The loops are different lengths so I would say it is self phasing. Both
antennas are 3/8" tube but the copper is .065" wall and the stainless is
..028" wall. Also at corners I used long Ell sweat fittings on the copper
tube and bent the stainless on a 3/4" radius but the total centerline
lengths are within half a mm on both antennas.

I have tried two different balun designs. One is Paul Hayes design
http://web.ukonline.co.uk/phqfh/phbalun1.pdf built inside a film can and
the other just 4 turns of RG58U around the 1 1/2" support column. The RG58U
balun worked better than the film can (probably due to my poor workmanship)
but the relative performance between the two antennas was the same.

I did read your QFH article in Reflections 2. Even understood about half of
it. :-)

I have plenty of stainless tube and building these things and seeing how
they work is fun so starting over from scratch would not be a problem.
Would 3/16 solid rod work better?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Walter Maxwell" wrote in message
...
On Tue, 11 Jan 2005 07:55:19 -0500, "Glenn Ashmore"
wrote:

I understand that you are the resident authority on QFH antennas. Can
you
help with this problem?

Hello Glenn,

I've had some experience with the QFH, Glenn, but I don't consider
myself an authority. However, I'll try to help you with the problem,
but first I'll need to know the form you used in your model. Is it
the self phasing type, with the inductive bifilar longer than the
capacitive one? Or are both bifilars of the same length and fed with a
power splitter and a 90° hybrid? If it is the self phasing type what
diameter is the tubing? And have you reviewed my data on the subject
that appears in Reflections?

If both the copper and stainless steel models are fabricated in
exactly the same form there shouldn't be much difference in
performance due the different materials. I don't believe the
difference in resistivities of the two materials should have a
significant effect on their performances, unless your bifilars are
made with very small diameter wire. If you used the self phasing type
the tubing diameter should be approximately 3/4", in which the
difference in resitivities would be absolutely insignificant.

So Glenn, give me the details of your QFH so that I can be of more
help.

Walt, W2DU

On Tue, 11 Jan 2005 13:56:47 -0500, "Glenn Ashmore"
wrote:

You are talking a little over this sailor's head but I think I got the jist
of it.

The antennas are basically Bill Sykes and Bob Cobey's design.
http://www.askrlc.co.uk/. I did change the ratio of height to width a
little but verified the dimensions with John Copens' calculator.

The loops are different lengths so I would say it is self phasing. Both
antennas are 3/8" tube but the copper is .065" wall and the stainless is
.028" wall. Also at corners I used long Ell sweat fittings on the copper
tube and bent the stainless on a 3/4" radius but the total centerline
lengths are within half a mm on both antennas.

I have tried two different balun designs. One is Paul Hayes design
http://web.ukonline.co.uk/phqfh/phbalun1.pdf built inside a film can and
the other just 4 turns of RG58U around the 1 1/2" support column. The RG58U
balun worked better than the film can (probably due to my poor workmanship)
but the relative performance between the two antennas was the same.

I did read your QFH article in Reflections 2. Even understood about half of
it. :-)

I have plenty of stainless tube and building these things and seeing how
they work is fun so starting over from scratch would not be a problem.
Would 3/16 solid rod work better?

Hello Glenn,

I've finally found time to review your QFH design, and find it quite
close to that which I designed for the wx sats, now the polar-orbiting
NOAAs (TIROS-N).

The design for the NOAA wx sats follows the data at the bottom of Page
22-14 in Reflections 2, in which diameters D1 and D2 at 137.56 MHz are
34.0 and 37.7 cm, respectively. Yours are 35.6 and 36.4 cm,
respectively. The perimeter dimensions P1 and P2 for the wx sats are
221 and 244 cm, respectively, while yours are 222.8 and 236.2 cm,
respectively. The height of the longer of the two bifilars in the QFH
of the wx sats is 0.260 lambda, or 56.7 cm. I was unable to determine
the height of your model.

The element tubing diameter in the wx sats is 1.918 cm, or 0.755",
while yours is 3/8" (0.375"). We actually used 3/4" tubing on the NOAA
wx sats.

Have you measured the terminal impedance of the quadrifilar? If it is
to radiate optimum CP at the operating frequency the impedance must be
very close to 50 ohms. Observe the Smith Chart plot, Fig 22-10 on Page
22.13, and note the cusp in the impedance plot at 0.95 +j0. During the
development phase of the QFH I found that this impedance proved the
self-phasing was working properly and was achieving excellent circular
polarization. If the cusp was off from this point the circularity was
jeopardized, as proven by measurements.

The reason I mention this is because one of the vital parameters in
obtaining the + and - 90° phase relationship between the two bifilars
to obtain the self phasing is the diameter of the elements. It is the
difference in the inductance of the elements, due to the difference in
physical lengths, that obtains the 90° phase relationship, and the
diameter of the elements is crucial to the correct element inductance.
So if the cusp of the swept input impedance plot is very far off from
50 + j0 you can expect that the circularity to be jeopardized.

Now to answer you original question concerning the use of copper or
stainless steel, I would not expect to see a significant difference in
performance between the two, especially considering the diameter of
the conductors. The difference in loss resistance between the copper
and stainless steel would be insignificant at this frequency when
considering the diameter involved.

Please let me know if I can be of any further help.

Walt Maxwell, W2DU

On Tue, 11 Jan 2005 13:56:47 -0500, "Glenn Ashmore"
wrote:

You are talking a little over this sailor's head but I think I got the jist
of it.

The antennas are basically Bill Sykes and Bob Cobey's design.
http://www.askrlc.co.uk/. I did change the ratio of height to width a
little but verified the dimensions with John Copens' calculator.

The loops are different lengths so I would say it is self phasing. Both
antennas are 3/8" tube but the copper is .065" wall and the stainless is
.028" wall. Also at corners I used long Ell sweat fittings on the copper
tube and bent the stainless on a 3/4" radius but the total centerline
lengths are within half a mm on both antennas.

I have tried two different balun designs. One is Paul Hayes design
http://web.ukonline.co.uk/phqfh/phbalun1.pdf built inside a film can and
the other just 4 turns of RG58U around the 1 1/2" support column. The RG58U
balun worked better than the film can (probably due to my poor workmanship)
but the relative performance between the two antennas was the same.

I did read your QFH article in Reflections 2. Even understood about half of
it. :-)

I have plenty of stainless tube and building these things and seeing how
they work is fun so starting over from scratch would not be a problem.
Would 3/16 solid rod work better?

Hello Glenn,

I've finally found time to review your QFH design, and find it quite
close to that which I designed for the wx sats, now the polar-orbiting
NOAAs (TIROS-N).

The design for the NOAA wx sats follows the data at the bottom of Page
22-14 in Reflections 2, in which diameters D1 and D2 at 137.56 MHz are
34.0 and 37.7 cm, respectively. Yours are 35.6 and 36.4 cm,
respectively. The perimeter dimensions P1 and P2 for the wx sats are
221 and 244 cm, respectively, while yours are 222.8 and 236.2 cm,
respectively. The height of the longer of the two bifilars in the QFH
of the wx sats is 0.260 lambda, or 56.7 cm. I was unable to determine
the height of your model.

The element tubing diameter in the wx sats is 1.918 cm, or 0.755",
while yours is 3/8" (0.375"). We actually used 3/4" tubing on the NOAA
wx sats.

Have you measured the terminal impedance of the quadrifilar? If it is
to radiate optimum CP at the operating frequency the impedance must be
very close to 50 ohms. Observe the Smith Chart plot, Fig 22-10 on Page
22.13, and note the cusp in the impedance plot at 0.95 +j0. During the
development phase of the QFH I found that this impedance proved the
self-phasing was working properly and was achieving excellent circular
polarization. If the cusp was off from this point the circularity was
jeopardized, as proven by measurements.

The reason I mention this is because one of the vital parameters in
obtaining the + and - 90° phase relationship between the two bifilars
to obtain the self phasing is the diameter of the elements. It is the
difference in the inductance of the elements, due to the difference in
physical lengths, that obtains the 90° phase relationship, and the
diameter of the elements is crucial to the correct element inductance.
So if the cusp of the swept input impedance plot is very far off from
50 + j0 you can expect that the circularity to be jeopardized.

Now to answer you original question concerning the use of copper or
stainless steel, I would not expect to see a significant difference in
performance between the two, especially considering the diameter of
the conductors. The difference in loss resistance between the copper
and stainless steel would be insignificant at this frequency when
considering the diameter involved.

Please let me know if I can be of any further help.

Walt Maxwell, W2DU

Thanks. I am going to print this out and digest it over the weekend. I
will get back to you. The only test equipment I have is an old MJF 259 that
is very unstable at 137 Mhz.

Glenn

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Walter Maxwell" wrote in message
...
On Tue, 11 Jan 2005 13:56:47 -0500, "Glenn Ashmore"
wrote:

You are talking a little over this sailor's head but I think I got the
jist
of it.

The antennas are basically Bill Sykes and Bob Cobey's design.
http://www.askrlc.co.uk/. I did change the ratio of height to width a
little but verified the dimensions with John Copens' calculator.

The loops are different lengths so I would say it is self phasing. Both
antennas are 3/8" tube but the copper is .065" wall and the stainless is
.028" wall. Also at corners I used long Ell sweat fittings on the copper
tube and bent the stainless on a 3/4" radius but the total centerline
lengths are within half a mm on both antennas.

I have tried two different balun designs. One is Paul Hayes design
http://web.ukonline.co.uk/phqfh/phbalun1.pdf built inside a film can
and
the other just 4 turns of RG58U around the 1 1/2" support column. The
RG58U
balun worked better than the film can (probably due to my poor
workmanship)
but the relative performance between the two antennas was the same.

I did read your QFH article in Reflections 2. Even understood about half
of
it. :-)

I have plenty of stainless tube and building these things and seeing how
they work is fun so starting over from scratch would not be a problem.
Would 3/16 solid rod work better?

Hello Glenn,

I've finally found time to review your QFH design, and find it quite
close to that which I designed for the wx sats, now the polar-orbiting
NOAAs (TIROS-N).

The design for the NOAA wx sats follows the data at the bottom of Page
22-14 in Reflections 2, in which diameters D1 and D2 at 137.56 MHz are
34.0 and 37.7 cm, respectively. Yours are 35.6 and 36.4 cm,
respectively. The perimeter dimensions P1 and P2 for the wx sats are
221 and 244 cm, respectively, while yours are 222.8 and 236.2 cm,
respectively. The height of the longer of the two bifilars in the QFH
of the wx sats is 0.260 lambda, or 56.7 cm. I was unable to determine
the height of your model.

The element tubing diameter in the wx sats is 1.918 cm, or 0.755",
while yours is 3/8" (0.375"). We actually used 3/4" tubing on the NOAA
wx sats.

Have you measured the terminal impedance of the quadrifilar? If it is
to radiate optimum CP at the operating frequency the impedance must be
very close to 50 ohms. Observe the Smith Chart plot, Fig 22-10 on Page
22.13, and note the cusp in the impedance plot at 0.95 +j0. During the
development phase of the QFH I found that this impedance proved the
self-phasing was working properly and was achieving excellent circular
polarization. If the cusp was off from this point the circularity was
jeopardized, as proven by measurements.

The reason I mention this is because one of the vital parameters in
obtaining the + and - 90° phase relationship between the two bifilars
to obtain the self phasing is the diameter of the elements. It is the
difference in the inductance of the elements, due to the difference in
physical lengths, that obtains the 90° phase relationship, and the
diameter of the elements is crucial to the correct element inductance.
So if the cusp of the swept input impedance plot is very far off from
50 + j0 you can expect that the circularity to be jeopardized.

Now to answer you original question concerning the use of copper or
stainless steel, I would not expect to see a significant difference in
performance between the two, especially considering the diameter of
the conductors. The difference in loss resistance between the copper
and stainless steel would be insignificant at this frequency when
considering the diameter involved.

Please let me know if I can be of any further help.

Walt Maxwell, W2DU