30 to 1 RX

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KB2WVO, Aug 13, 2018.

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  1. KB2WVO

    KB2WVO Ham Member QRZ Page

    hello
    tryin to build a 30 to 1 balun RX. 50 ohm in 1500 ohm out.
    thoughts ideas . parts on hand. no it doesnt have to handle power.
    its RX only.
    t-200
    4 inch by 1/4inch core out of a RX'er..
     
  2. W4OP

    W4OP Ham Member QRZ Page

    If this is for wideband HF, I doubt you will get enough winding inductance with a powdered iron core. Ferrite would be preferred. In addition, an effective current balun is going to require 2 cores. One for the Z transformation and the 2nd for common mode reduction.
     
  3. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Unless you do something very special, such baluns usually only go in ratios that are the square of the turns ratio, so it would usually be 25:1 or 36:1.

    For "receiving only," you could use a smaller core and very small gauge wire. The number of turns required (as well as the core material) is based on the frequency range you're trying to cover.

    What frequency range is it?
     
  4. KB2WVO

    KB2WVO Ham Member QRZ Page

    RF.... lol
    i can try few diff freq's
    but looking around 50mhz. can even be in any part of the hf spec. if i need to build a few to get little better RX. then i can do that maybe lol

    the 2 circled. is 50 ohm to 1500 ohm.
     

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    Last edited: Aug 13, 2018
  5. KB2WVO

    KB2WVO Ham Member QRZ Page

    if i did math right. 1500/50 sq is around 7 wraps to 1. might get me in ballpark on a ferrite rod. problem is the rod is 4 by 1/4" out of a old rad shaft rx.
     
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Just noticed you wrote "rod."

    Try it and see what happens. I always use toroid forms for this stuff.
     
  7. SV1IYF

    SV1IYF Ham Member QRZ Page

    WB2WIC wrote: "...so it would usually be 25:1 or 36:1."
    One can also in-between by 11 to 2 turns = 5.5:1 ratio =>~30:1 impedance ratio.
    73 Nikos SV1IYF
     
    KB2WVO likes this.
  8. KB2WVO

    KB2WVO Ham Member QRZ Page

    so i wasnt to far off with my math. i got 7.5 ...what i will do is start with say 10. work down form there.. easyer to remove then add lol ..
     
  9. KF5LJW

    KF5LJW Ham Member QRZ Page

    Couple of things I have learned. Just built a RX only antenna for myself lately.

    1. Don't get hung up on trying to figure out antenna impedance, or exact ratios. That is a loosing game. Ball park number hits a home run on RX only.
    2. 75 Ohms' is a better impedance for RX only, easier to work with, and makes tip 1 even easier.
    3. Design for the lowest operating frequency, the rest works itself out. Determines how many primary windings are required. You will know you got it right if the primary turns required is 4 or less with 1 turn being perfect.
     
    Last edited: Aug 13, 2018
  10. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I'm confused by two posts here:

    First:
    thoughts ideas . parts on hand. no it doesnt have to handle power.
    its RX only.
    t-200
    4 inch by 1/4inch core out of a RX'er..

    T-200 is a toroid core description. T for toroid, 200 for diameter (.200").

    Then:
    if i did math right. 1500/50 sq is around 7 wraps to 1. might get me in ballpark on a ferrite rod. problem is the rod is 4 by 1/4" out of a old rad shaft rx.

    That describes a ferrite "rod," which is not a toroid.

    Which is it, actually?

    The winding would be different for each.
     

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