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[TowerTalk] W0IYH Feed line Choke Performance

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Subject: [TowerTalk] W0IYH Feed line Choke Performance
From: (Tim Duffy K3LR)
Date: Mon Aug 18 16:19:16 2003
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

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