[time-nuts] Quadrifilar Helix Antenna

[Rob Kimberley]

I had a go at making one in 1986 for a broken NBS unit (huge two 19" RMK,
single channel GPS), which had been damaged in transit. Used small sections
of semi-rigid coax soldered together. 

It worked well enough to track SVs and get data we needed.

Rob K

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Azelio Boriani
Sent: 08 June 2012 21:29
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Quadrifilar Helix Antenna

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_A
> ntenna_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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