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[TowerTalk] Antenna Tuners

 To: [TowerTalk] Antenna Tuners n4kg@juno.com (T. A. Russell) Sun, 09 Mar 1997 23:33:06 EST
 ```Bill - The answers to your questions are YES and YES... BUT, before you get too concerned, you need to look at the alternatives and calculate the losses. It's not very practical to place an antenna tuner at the antenna unless you have some way of remotely tuning it. Commercial practice is to put the tuner at the transmitter if the SWR is under 3:1 at the antenna. The additional losses due to SWR are quite small with an SWR of 3:1 or less at the antenna. The ARRL antenna books (older ones anyway) had a set of curves of additional loss due to mismatch as a function of SWR and lineloss of the cable (when properly matched). (Or, check the HANDBOOKS) Most of the energy is radiated by the antenna but some amount is reflected back to the transmitter/tuner which will NOT look like 50 Ohms to the reflected wave (since there was an SWR and the tuner was adjusted to provide a match between this impedance and the 50 ohm transmitter output) SO, there will be a reflection at the tuner back to the antenna where most of the energy will be radiated and a smaller amount will again be reflected back to the tuner, etc, etc. This process will go back and forth (at the speed of light) until all of the power is either radiated from the antenna or dissipated as heat in the transmission line. The lower the SWR at the antenna and the lower the loss in the line, the less the power lost as heat in the line. For many years, I have tuned my 80M dipoles to CW and use a tuner on SSB with a 5:1 SWR at 3.8 MHz. Using 500 ft of 3/4 inch CATV hardline to feed this antenna, the additional loss due to SWR is less than 1 dB. (I don't have the curves here at the computer.) These antennas have worked a LOT of difficult DX on 75M SSB! de Tom - N4KG . On Sun, 9 Mar 1997 21:12:01 -0600 w5ec@digitalexp.com (Hawkins, Bill) writes: >Hi Yall >A recent posting reminded me that I have had a question for >a long time which I have never asked. So here it is. >Suppose I put up an antenna, generally the best I can afford. >I feed it the best way I know how. >I hook it to my antenna tuner to which I hook my rig (oldtimers >talk for transceiver). >I tune the tuner so the rig shows a perfect match and happily talk >away. > >Here's the question. >Unless (a BIG unless) the feedline is a perfect match for the >antenna, ain't I just fooling the rig and matching it to the feedline >while the feedline is still probably mismatched to the antenna >and bouncing reflected power all around? > >Another question. >Unless everything is properly matched (a BIG unless), >Shouldn't the antenna tuner be at the antenna and the >feedline tuner be at the rig? > >Any words of wisdom? > >Thanks >Bill W5EC > > >-- >FAQ on WWW: http://www.contesting.com/towertalkfaq.html >Submissions: towertalk@contesting.com >Administrative requests: towertalk-REQUEST@contesting.com >Problems: owner-towertalk@contesting.com >Sponsored by: Akorn Access, Inc. & N4VJ / K4AAA > -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com Sponsored by: Akorn Access, Inc. & N4VJ / K4AAA ```
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