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Author Topic: doublet marconi switch  (Read 729 times)
WS4E
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Posts: 234




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« on: July 13, 2009, 07:58:38 PM »

A number of times I have read that it is easy enough to just take a 80m doublet and connect the feed line together and turn it into a T(tee) Marconi antenna for 160m which will work reasonably well.

I am thinking about doing this with my antenna, but rather than trudge out and do this outside every time I want to work 160, I was thinking maybe a little switch or maybe even an automated relay could be made to short the feed line connectors together.

Has anyone ever built a switch to do this?  I am wondering what sort of relays/switches would be safe to use since there are some very high swr's occasionally.

Should I do this outside at the feed line or could a manual switch inside the shack on the coax work just as well?
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WB2WIK
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Posts: 20636




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« Reply #1 on: July 14, 2009, 09:09:53 PM »

I've done this for decades.

Using twin lead or ladder line as a transmission line for a doublet:

Install a cheap hardware store knife switch across the transmission line, right at the back of the tuner.

When you want to use the antenna as a doublet, leave the switch open.

When you want to use it as a Marconi, flip the switch and short the transmission line, and be sure the line is connected to the single wire antenna terminal of the tuner.  My tuner has a switch on the front panel to enable this, so I don't have to reach around back and change anything.

Have a very good ground system connected directly to the tuner chassis.  A good ground system would typically include an earth ground and radials -- the more, the better!

No need to do anything "outside," but the tuner should be very close to an outside wall of the shack, otherwise achieving any sort of decent RF ground can be impossible.

My hardware store knife switch was from Ace Hardware, purchased in 1968.  It still has the little sticker on the back: It was $0.79.

WB2WIK/6
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