Uhf antenna tuners

Discussion in 'General Technical Questions and Answers' started by WY4K, Oct 9, 2017.

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  1. WY4K

    WY4K Ham Member QRZ Page

    I was looking around for uhf antenna tuners. I didn't find many.

    Then I got to thinking that an antenna tuner could give a good swr at the tuner but by the time the rf traveled to the radio that the match could be off depending on the length of the connector from the radio to the antenna tuner.

    Am I right or does the tuner match the antenna to 50 ohms at the tuner and then there is no change in the 50 ohms of impedance as it travels from the radio to the antenna tuner?

    I am asking this question because I seem to remember that you can place a 200 ohm load on one end of a coax and you can read different values of impedance based on wavelengths as you move along the coax or transmission line.
     
  2. WA3QGD

    WA3QGD Ham Member QRZ Page

    How did u get an EXTRA class License?I'm sure you would like to know so read it for yourself "Jones Antennae Book" First step for your education in RF frustration get a "Dummy" load might be amazed at the number of RF devices it can and should be used on.Yes it's free and online see the part's that refer to Surge Impedance.
     
    OH2FFY and N6QIC like this.
  3. KL7AJ

    KL7AJ Premium Subscriber QRZ Page

    Two things:

    It's infinitely easier to get a perfect match at the antenna at VHF/UHF frequencies than at HF....especially if you're trying to work MULTIPLE HF bands.. No excuse not to get as good a match as possible at VHF. Secondly, at VHF/UHF, it's generally more important to have a good match than at HF, because the line losses are greater. (S/N on receive falls apart faster with lossy transmission lines, as well).
     
    N6QIC likes this.
  4. W1VT

    W1VT Ham Member QRZ Page

    Tuners are dirt simple at 10GHz--you just stick a bunch of screws in the waveguide spaced 1/4 or 1/8 a wavelength apart. A wavelength is physically different in waveguide versus free space, so it does help to make that calculation. Similarly, I've fed a 2.4 GHz horn dish feed with a short section of waveguide so I can tune the system with tuning screws. I usually make my horns out of sheet brass, though I have also made them out of double sided circuit board.

    Zack W1VT
     
  5. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Yeah, impedance varies along a transmission line but SWR doesn't, other than getting lower towards the source end if the line has loss.

    I've never used a UHF "tuner." Why would you need one?

    UHF antennas can be easily trimmed for a great match without any kind of tuner. Unless you're really good at microwave practices and techniques, any kind of UHF tuner will introduce loss you probably don't want. Easier to adjust the antenna.
     
    W7UUU and N6QIC like this.
  6. WY4K

    WY4K Ham Member QRZ Page

    Once the antenna tuner matches the antenna and transmission line to 50 ohms, then the 50 ohm match from the transmitter to the antenna tuner will be good whether I connect the transmitter and antenna tuner with 1/8 wavelength of 50 ohm coax or if I use 1/4 wavelength of 50 ohm coax.

    Thanks

    This makes me want a vhf and uhf antenna tuner because I have a set of yagi antennas and their swr is above 2 to 1 or greater at the ends of the band. A 1:1 swr at 146.5 MHz does not do any good when you want to operate a 144.6 MHz and the swr there is 3:1.

    I would like a tuner to make the transmitter happy even though I would not be getting the best radiation from the antenna.

    It should be pretty simple to make a vhf tuner so I may give it a try.
     
  7. N6QIC

    N6QIC Premium Subscriber QRZ Page

    You tune with the tuning section of the antenna. Usually tuned with a gamma match on a vhf yagi antenna.

    gamma_match.jpg
     
  8. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    What kind of antenna is 1:1 at 146.5 and 3:1 at 144.6?

    I've never even seen a 2m antenna (beam or otherwise) like that, and I've used 2m for 52 years.

    My 2m beam (M2) is 1.5:1 at 144.0 and 1.7:1 at 148 MHz, and everything in between.

    What kind of beams are you using?
     
  9. AI3V

    AI3V Ham Member QRZ Page

    I use a "antenna tuner" on the output of a mirage d1010 amp (10watts in 100 watts out)

    NOT because my vswr is greater than 1:1, but because by the time you get to 432 MHz it's a rare amplifier that actually outputs maximum power into a 50+j0 load.

    We won't talk about how a 1:1 indicated vswr is almost certainly not a real 1:1, that's a story for another thread.

    General electric/erricson call it a "z" match, it's a simple pi network, and a directional coupler/diode detector, arranged to measure forward power after the z match.

    You simply tune the z match for maximum forward power, while monitoring the amplifier collector current so you don't exceed the transistor ratings.

    It's pretty much a standard item on ge and Motorola repeaters.

    Rege
     
  10. N2UHC

    N2UHC Ham Member QRZ Page

    A UHF antenna tuner? Why? The best way to do it is to make sure your antenna is matched, then you won't even need a tuner.
     

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