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Re: [softrock40] Re: It Works! (For some small values of 'works')

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  • Bruce Tanner
    I used a lot of these during my Novice years back in the 1950s! Basically ends up with a 75 ohm impedance which will work well enough for most applications. I
    Message 1 of 14 , Jul 25, 2012
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      I used a lot of these during my Novice years back in the 1950s!  Basically ends up with a 75 ohm impedance which will work well enough for most applications. I find that a tuner ahead of an SDR RX works pretty well. A trip to a Hamfest can probably bring one inexpensively to you or at least you could find a nice airdux coil and hefty variable capacitor to do a homebrew that would probably work for RXing. If you want to use it for TX as well it would be better to invest in a decent used one or even a new one from MFJ. They have some low power ones which are not all that costly.

      Bruce, K2BET
      On 7/25/2012 8:51 PM, Jerry Kaidor wrote:

      > Thanks for the suggestions. One point I'm not clear on is how to tune an
      > antenna and how to match an antenna's impedance to 50 ohms without more
      > equipment than I have. I'm reluctant to lay out a bundle on an antenna
      > analyzer. I could afford a modest SWR meter, but since I have only a
      > receiver, that's not going to help with tuning. (I've got a RX/TX kit,
      > but I'm reluctant to start building it until I'm successful with my Lite.
      > I ought to be successful with the 'easy' kit before I get into the tougher
      > one.)
      > I suppose that for tuning the antenna, I could wait until I find another
      > signal strong enough to receive with my un-tuned antenna, and then try
      > different capacitances to tune it, and I could randomly try higher/lower
      > turn ratios on a transformer, and just listen and see if the signal
      > strength changes.
      > Can someone point me to a source where I could read more about tuning and
      > impedance matching without a lab full of measuring tools? I'm totally
      > inept when it comes to antennae.

      *** OK,

      Here's the cheapest and dirtiest antenna I know of - the zip cord
      dipole. Say you're interested in 20M: the length is the name. Well, 20M
      is a full wave. A half wave is 10M long, a quarter wave is 5 meters long.
      Five meters, that's kind of like 15 feet. So you go get a hundred feet
      of zip cord, aka "lamp cord" at the hardware store. Unzip 15 feet of it.
      Tie a knot where the "unzipped" part starts. Voila, you have a 20M dipole
      with its very own feedline! The other end of the zip cord can be soldered
      to a PL-259.

      It won't be very exact - actually, it will probably be too long - but
      it'll work.

      My tool of choice for tuning such things used to be the grid dip meter
      ( before I got my MFJ259 ). Grid dip meters are dirt cheap at the ham
      swaps these days. Last month, I got a really nice Eico for $5! You
      make a little coil of wire to couple the GDO to the feedline, then tune
      for a dip. Cut the ends of the antenna until the dip is in the right
      place. Listen to the grid dip meter with your receiver.

      - Jerry Kaidor

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