[time-nuts] Quadrifilar Helix Antenna

Sat Jun 9 11:30:47 UTC 2012

Raj, it was not a trouble: on the contrary it was a good exercise. I made a
QFH some time ago but it was not quite successful. After this reading I
will try again. I have an Advantest R3765A vector network analyzer (40MHz -
3GHz) so I can tell if the antenna can work.

On Sat, Jun 9, 2012 at 11:36 AM, Rob Kimberley
<robkimberley at btinternet.com>wrote:

> 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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