Thursday, March 22, 2007

1:1 baluns

I've been very fond of using vertical antennas on my little island excursions. The nice thing about these antennas is their simplicity. Just a few wires held up by a fishing pole or fiberglass mast and you've got your radiator. The last remaining problems that I've got with this approach is keeping the RF out there at the antenna instead of following the coax back into the radio. Usually, a few turns of coax will provide enough of an impediment to keep the problem manageable, but I been thinking I could do better.
The Buddipole systems each have a Triple Ratio Switched Balun (TRSB). This device serves two purposes: (1) it has an isolation transformer to keep the RF off the coax, and (2) it has a tapped second transformer that allows you to match your 50 ohm feed to an antenna with a lower impedance such as 25 ohms or 12.5 ohms. (It also has a switch position for a 50 ohm load, too.) Since the Buddipoles are shortened verticals for the lower bands, being able to match these lower impedances is very helpful and, as such, I believe the TRSB is a must have accessory for any serious Buddipole user. I should also have something similar (but simpler) for my fishing-pole verticals.
What I need is just a simple box with a 1:1 balun wound around a toroid. There are lots of simple designs in popular books like Understanding, Building, and Using Baluns and Ununs. All you need are the parts and a little patience.
I purchased from The Wireman kit 836 that has the following description:

CQ "Lew McCoy" heavy duty balun kit for balanced line to coax, heavy load. Kit contains 3-T200-2 or 1 T300A-2 iron powder core, fiber glass tape, #635 polyimide wire, instructions.

My kit contained 3 of these toroids--though I dropped one on my new kitchen floor and now I have only 2 {sigh}. Of course, you can get better prices for some of this stuff. Check out the prices at on their
Toroid page. Looks like I can get three of these T200-2 toroids for $12!
I plan on making two 1:1 baluns around the two toriods I have left (assuming I don't drop any more on the kitchen floor) and put them in small boxes that I can place at the feed point of these fishing-pole verticals. Hopefully, I'll have some time between now and my trip to Maine in April so I can try them out at the K1P special event station.
In other news, there has been some progress on our plans for a Dayton get-together for ham bloggers. The tentative plan is for anybody interested (bloggers or those who read us) to meet at 6 PM in the lobby of the Crowne Plaza Hotel on Thursday, May 17th. This will be immediately after the conclusion of the Contest University event. So far Steve Weinert (K9ZW), Jeff Davis (KE9V), and yours truly are planning on meeting at that time. This is the first "official" announcement for this. Pass the word!
Finally, assuming my cough will subside enough (I'm still fighting this stupid cold! Can you believe it?!), I'll be in the CQ WW WPX contest this weekend working on my QRP DXCC total. Of course, if QRP at the very bottom of the sunspot cycle becomes too depressing, I'll either hang it up, or switch to 100 watts. This is a contest where everybody-can-work-everybody. Even if you're not keen on contesting, this is a fun one. Just use a signal report (59, of course) and a sequential serial number for the exchange. See you on the air!


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