[time-nuts] Quadrifilar Helix Antenna

[Azelio Boriani]

OK here a summary of the IV3QBN article (original in Italian) on QFH:



This article suggests that instead of buying one, you can make your GPS
antenna. After two
antenna examples (fig.1 an Amsat plane spiral antenna and fig.2 a 9GHz
array of patches)
the author suggests to use a backfire quadrifilar helix, directly fed by a
50OHM coax cable.
The helix is only half a turn, but the pitch is much greater than the
classic helix.
The result can be seen in fig.3 and 4. The turn diameter must be an integer
fraction of the
lambda, as suggested by Kilgus [C. Kilgus: Resonant Quadrifilar Helix-IEEE
Transactions on
Antenna and Propagation. Vol AP-17, May 1969] and the length of the turn
must be 0.28 times
the lambda. To compensate for the reactive part of the antenna impedance,
the trick is to
make the wire pairs one longer and one shorter than the computed length so
that one is
seen as capacitive and the other inductive compensating each other. The 4
wires are soldered
on the outer conductor of the coax cable (bottom of the helix, GND) and on
top of the cable
two wires (one from each pair) on the center conductor and the other two on
the outer
conductor. This way the helix will radiate/receive from the top and the
gain will be
maximum in the 40degrees direction (radiation pattern in fig.3). You need a
piece of UT141
coax cable and 4 enamelled copper wires 1.5 upto 1.8mm in diameter. The
longer pair is
103mm in length and the shorter is 99mm, the diameter of the helix will be
30mm. See fig.5
for a detail of the helix. At the bottom the distance between the two pairs
is 5mm and the
length is 69mm (the shorter) and 73mm (the longer). In fig.6 you can see
how to solder the
top of the cable [but the detail is not so clear, IMHO]. The length [69 and
73? He doesn't
say explicitly] can be adjusted to trim the return loss but a network
analyzer or a sweep
is needed to check the result. The antenna is wound anticlockwise as seen
from the top. In
fig.4 you can see the HP8714ES analyzer result for the antenna [that the
author claims to
have seen after the first try, without adjusting anything]. To use this
antenna directly,
don't forget to put a DC blocking capacitor in order not to short the
antenna supply from
the GPS receiver or use a MMIC (MAR3, INA,ERA, MSA) [and a filter would be
best] to have
an active antenna.




On Fri, Jun 8, 2012 at 4:05 PM, paul swed <paulswedb at gmail.com> wrote:

> Good reads.
> Thanks Raj
> Paul
> WB8TSL
>
> On Fri, Jun 8, 2012 at 8:00 AM, Azelio Boriani <azelio.boriani at screen.it
> >wrote:
>
> > Meanwhile take a look at these:
> >
> > http://www.kunstmanen.net/WKfiles/Techdocs/RQHA/RQHA1999-1eng.pdf
> >
> > http://w2du.com/r2ch22.pdf
> >
> >
> >
> http://www.rish.kyoto-u.ac.jp/digitalbeacon/information/Building_QFH_Antenna_Guide.pdf
> >
> > http://ap-s.ei.tuat.ac.jp/isapx/2006/pdf/1E2a-5.pdf
> >
> > On Fri, Jun 8, 2012 at 1:04 PM, Azelio Boriani <azelio.boriani at screen.it
> > >wrote:
> >
> > > I have made a QFH but then found a Procomm GPS4 in Germany for a good
> > > price...
> > >
> > >
> > > On Fri, Jun 8, 2012 at 12:49 PM, Raj <vu2zap at gmail.com> wrote:
> > >
> > >> Not to worry Azelio, if you could tell us the gist of it. I thought
> > maybe
> > >> I could
> > >> try and brew one for my tbolt.
> > >>
> > >> At 08-06-2012, you wrote:
> > >> >I have tried to translate with Google (yes, I'm Italian but need time
> > to
> > >> >translate the whole PDF) but the result is very poor. If you can
> wait I
> > >> can
> > >> >prepare a short summary or a complete traslation (more time).
> > >> >
> > >> >On Fri, Jun 8, 2012 at 10:31 AM, Raj <vu2zap at gmail.com> wrote:
> > >> >
> > >> >>
> > >> >> I came across this article. I dont understand Italian!
> > >> >>  From RadioKit Elettronica 2003-03
> > >> >>
> > >> >> https://dl.dropbox.com/u/10377704/IV3QBN%20QuadHelix.pdf
> > >> >>
> > >>
> > >>
> > >> _______________________________________________
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> > >>
> > >
> > >
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