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