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Antanna Tuners

Jun 24th 2013, 20:55

Marksail2

Joined: Apr 8th 2013, 00:09
Total Topics: 0
Total Posts: 0
I am a relatively new ham and have a general question.

Operating my Kenwood TS-2000, but not limited to this radio...It contains an internal antenna tuner. This radio as well as after market stand-alone tuners fit into the same catagory, ie: they don't tune in any band except HF. Like 2m for example. I am operating an antenna with a loading coil at the base. Band selection is done by selecting a 'coil' to short the coil and varying the length of the 'conterpoise' wire. On 2m I generally know I am tuned by watching an external SWR / Watt meter. With this method I can usually get in the range of 1.5 to 1. Once the radio is tuned to a HF frequency I use the manufacter's recommenadtions for whip, conterpoise length and coil for each band, then 'automaticlly' tune the antenna for optimum SWR etc.

My question... why are they NOT antenna tuners for bands above HF? I am assumig electrically they are possiable, but maybe not practical from a design stand point.

Tx,

Mark, KK4RVL
Jun 25th 2013, 03:15

AA6E

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Mark,

That's an interesting question! You're right that the general principles of matching are the same above 30 MHz as below, but you don't see the same kinds of tuners - on the market, at least.

A couple of reasons occur to me:

- Cable losses are much higher at VHF and higher frequencies. So the penalty of a high SWR on your coax is more serious. Loss that cuts your transmit power is bad enough, but loss that adds noise to your receiver is really bad. It's best to do your matching at the antenna so there's minimum loss in the transmission line.

-Matching with discrete components (L's and C's) is trickier at higher frequencies. Things are just very small. This makes wide impedance and wide frequency coverage harder to realize, especially at higher power. We might prefer to use transmission line transformers, stubs, etc. as tuning devices. They are easier to build.

73 Martin AA6E
Jun 25th 2013, 13:09

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

Some SGC tuners go up to 60MHz

http://www.sgcworld.com/productInfoPage.html

MFJ not only makes tuners that cover 6 meters, but they even have one for 144/222MHz

http://www.mfjenterprises.com/Product.php?productid=MFJ-921
http://www.mfjenterprises.com/Categories.php?sec=220

Ideally, for a VHF tuner to work adequately, it should be as close to the antenna as possible.

Zack Lau W1VT
ARRL Senior Lab Engineer


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