HI Paul!
You are correct, it would be interesting experiment and some day I will take my
own measurements on coax single layer chokes and I will post my findings here.
However, in the mean time there are two excellent sources that have good
information on the subject. W7EL has some suggested single layer coax chokes in
the ARRL Antenna Book. WA2SRQ had a TowerTalk post some years back (should be
in the archives) where Ed gave a very detailed account of his tests related to
coax chokes.
73,
Tim K3LR
http://www.k3lr.com
"Paul Christensen, Esq." wrote:
> Tim,
>
> By chance, did you happen to measure the impedance of an air-wound choke
> consisting of many tight turns? On the low bands, it would be an
> interesting exercise to determine the equivalent number of air-wound turns
> needed on a given diameter in order to approximate the same impedance
> effectiveness as either the W2DU or W0IYH types.
>
> -Paul, W9AC
>
> ----- Original Message -----
> From: "Tim Duffy K3LR" <k3lr@k3lr.com>
> To: "Towertalk" <towertalk@contesting.com>
> Sent: Monday, August 18, 2003 1:41 PM
> Subject: [TowerTalk] W0IYH Feed line Choke Performance
>
> > I posted some of my experience concerning the W2DU type choke
> > performance a few weeks ago.
> > There were several requests for the test data.
> > I retrieved my lab notes taken from my HP Network Analyzer on October
> > 15, 2001.
> >
> > The W0IYH choke is made from 100 type FB-5622-43 beads on RG-142 with
> > silver plated PL-259's on each end.
> > The list is test frequency followed by impedance
> > 1.8 MHz 1152 ohms
> > 3.7 MHz 3483 ohms
> > 7.1 MHz 4115 ohms
> > 14.2 MHz 1783 ohms
> > 21.2 MHz 1280 ohms
> > 28.5 MHz 1234 ohms
> >
> > My tests with the W2DU choke:
> > 1.8 MHz 984 ohms
> > 3.7 MHz 1733 ohms
> > 7.1 MHz 1921 ohms
> > 14.2 MHz 1432 ohms
> > 21.2 MHz 905 ohms
> > 28.5 MHZ 423 ohms
> >
> > In 100% key down CW tests into a 50 ohm dummy load for 10 minutes I
> > found the W2DU to overheat (individual bead temperature exceeded
> > manufactures ratings) at 500 watts on every band. The W0IYH choke passed
> > the same test at 2000 watts and was well within the temperature
> > specification for each bead. I believe the W0IYH choke has adequate
> > safety factor for 1500 watt stations as long as the VSWR does not exceed
> > 3:1.
> >
> > There are lots of W2DU chokes in service and as you can see they will
> > work well. The W0IYH design is an improved version. As I indicated in my
> > September 1998 CQ Contest magazine article, I use the W0IYH design at my
> > station. They are on every feed point of every antenna, at the tower
> > mounted stacked antenna RF switch box and at the end of each antenna
> > feed line where it connects to the RF amplifier in the radio room. They
> > keep RF from flowing on the outside shields of the feed lines very well.
> >
> >
> >
> > If you are interested in ready to go chokes, completed W0IYH chokes are
> > available from Comtek Systems. Please contact them for price and
> > availability.
> > http://www.comteksystems.com
> >
> >
> > 73,
> > Tim K3LR
> > http://www.k3lr.com
> >
> >
> > _______________________________________________
> >
> > See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
> questions and ask for Sherman, W2FLA.
> >
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