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.
----- Original Message -----
From: "Tim Duffy K3LR" <email@example.com>
To: "Towertalk" <firstname.lastname@example.org>
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
> 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
> Tim K3LR
> 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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