Antenna Tuner

Discussion in 'Ham Radio Discussions' started by KC3EPA, Dec 3, 2020.

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  1. KC3EPA

    KC3EPA Ham Member QRZ Page

    I am sort of naive or limited on my knowledge
    I have an auto antenna tuner that I occasionally use for antennas that are not resonant such as some long wire antennas and sometimes in mobile for getting the lower bands.
    Currently I use a tapped loading coil as it seems to be easier.

    My question is if I have a resonant antenna but the impedance is let's say 25 ohms for a vertical and it is verified on the antenna analyzer at 25 ohms and no reactance to speak of.

    If I place an antenna tuner at the base of antenna will it work as a antenna match giving me the two to one ratio without the losses acting like a balun.
     
    KA4DPO likes this.
  2. NK7Z

    NK7Z XML Subscriber QRZ Page

    Hi,
    Anything you insert in line will create losses, so look to the tuner specs... Will it tune? It depends on the tuner... Again, look to the specs... 25 Ohms will give you a 2:1 SWR, I don't know of any tuner that will not tune that. If it were me, I would put the tuner in line. Any loss should be negligible.
     
  3. W9WQA

    W9WQA Ham Member QRZ Page

    a cross needle tuner/swr meter will let you do a lot and learn a lot.
    you gotta try stuff
     
  4. W4NNF

    W4NNF XML Subscriber QRZ Page


    As has been said, everything in the line can cause losses, but tuners are not generally a huge problem in that regard. ;)
     
  5. W1VT

    W1VT Ham Member QRZ Page

    Commercial tuners are typically compromises on the low bands like 80 and 160 meters. As a result the losses can be unreasonably high, say 25%, 50% or more when you have a combination of a very low impedance at the tuner and a very low frequency.
    The ARRL Product Review measures and publishes loss charts.

    If you want better low band efficiency and don't need a tuner that also works on the high bands a homebrew tuner can be an easy project for the beginner. Just scale the design and make the inductors and capacitors substantially bigger. All that talk about short lead lengths won't matter on 80 and 160 meters. A short 1.5" wire on 10 meters is a foot on 80M!

    Zak W1VT
     
  6. KI4IO

    KI4IO Ham Member QRZ Page

    Totally agree with Zak (W1VT).
    low-Z loads might require a slightly different matching network. See:
    http://www.somis.org/bbat_f1.jpg
    As Richard Measures (SK) has shown, you could use a switch, jumper, or banana Jack to switch from
    Hi-Z loads to low-Z loads if the antenna is used on bands which might have hi-Z loads.

    Enjoy the process
    Jerry
    KI4IO
    Warrenton, VA
     
  7. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    If the antenna is resonant on a single band then matching it to a 50 ohm source is not difficult. Two quarter wave sections of LMR-400-75 coax cable (that's 75 0hm coax) in parallel will create a 35 ohm matching section, that will match your 25 ohm load to a 50 ohm source. The only loss will be the loss of the coaxial matching section. No matter what you do, there will always be some additional loss introduced into the system, there are no free lunches. The matching section will solve the problem with the least amount of loss, and will be broad banded enough to cover an entire band.
     
  8. KC3EPA

    KC3EPA Ham Member QRZ Page

    My question is will a antenna tuner match a resonant antenna with a resistance that has no reactive components .The theoretical vertical could be any impedance from 20 to 500 ohms not that they exist without the normal losses with a antenna tuner used on non resonant antennas.Can it be used in such a case if the antenna tuner has a balanced output in lieu of a a hair pin or delta or gamma if the known feed point is resonant. OF COURSE AT BASE OF ANTENNA.A prime example is a 3 element beam that feeds the driven element and would be resonant but using a antenna tuner for a near perfect match if possible.
    I know how to do gamma and delta matches and know how to use 1/4 wave matching and balun and unos my question is the auto tuner .

    If you break down a gamma match into the electrical equivalent is is basically a I believe 2 coils and a capacitor which is similar to equivalent circuits in auto tuner .Remember I am talking a resonant antenna .
     
    Last edited: Dec 4, 2020
    KA4DPO likes this.
  9. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page


    If you break down a gamma match, it is an L network. You did say vertical antenna in your original post. If you are as familiar as you say you are with all of the aforementioned methods of impedance matching, then you know that a 25 ohm resistive load can only be modified by employing a pad. Or, if it is resonant, just use it as is, and let the transmitter deal with it.

    An auto tuner is an impedance transformer, no different than a manual tuner, and a quarter wave matching section is just another form of impedance transformer. Don't get warped by semantics.

    If the reactance is zero, then the impedance of your antenna is 25 ohms resistive. Haul out a Smith chart and prove it to yourself.
     
  10. KC3EPA

    KC3EPA Ham Member QRZ Page

    So you do not know answer.
     

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