...the WA2SRQ studies are on several places on the net including K1TTT's
most excellent web site
I have toyed with the idea of making these as a side business... as a
happy user of "WA2SRQ baluns" for years... and no bugs!
I would be interested to know if there is a market for these... I am
looking for a small business, have a few mechanical tweaks W1CW and I
added to the basic design - probably would sell them on eBay or in the
Please reply direct to me on this one!
Tim Duffy K3LR wrote:
> HI Paul!
> You are correct, it would be interesting experiment and some day I will take
> 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
> 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.
> Tim K3LR
> "Paul Christensen, Esq." wrote:
>>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
>>>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
>>>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.
>>>TowerTalk mailing list
> 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.
> TowerTalk mailing list