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Half-Wave End Fed tuner from these parts?

Discussion in 'Homebrew and Kit Projects' started by W0EA, Apr 24, 2009.

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  1. W0EA

    W0EA Ham Member QRZ Page

    Hey guys, I just scrounged up some great reactive components and I want to make a half wave end fed antenna tuner with them. I also have another capacitor for what its worth. How would I go about hooking these up and is there enough "juice" in them to make a good matching network?

    The inductor is 40uH the whole length and I assume the cap is probably a couple hundred pF. Any ideas?


  2. W4CBJ

    W4CBJ Ham Member QRZ Page

    Half-wave End Fed tuner fromthese parts?

    Firstly (as the British would say) The variable capacitor looks (to me) like it is a receiving capacitor (closely spaced) plates, probably about 360 pF (mmF). This would limit the power to the tuner to 100 watts or less . (Arcing when not in resonance). The inductor would need to be "tapped" or a roller to change the inductance to what may be required for a specific hook-up. Feeding an end-fed half wave antenns results in a very high input impedance. My suggestion is to read an (ARRL) or other radio amateur's handbook to familiarize yourself with these simple circuits. There are generally three (3) configurations for feedind various antenna input impedances. Depending on what band (frequencies) you want to work, an end-fed antenna is the worst choice. A random length would be better. This is all explaned in the handbook(s) and is quite simple. Let us know how you make out. 73 Joe W4CBJ
  3. KB9BVN

    KB9BVN Ham Member QRZ Page

    On my homemade EFHW tuner, I used a T130-2 toroid with 18 turns of 20ga bell wire on it, and a 365pf vari cap.

    I then wrapped two windings on the T130-2 and connected the ends of that to the coax to my rig.

    Look here:

    and here:

    I have always made these with toroids. I have not made one with the air inductor you show. I imagine it can be done but wow...40 uH might be a bit much. The inductance in mine runs about 3uH to maybe 4.5 uH for my 20m and 40m versions.
  4. W0EA

    W0EA Ham Member QRZ Page

    Yeah, I've seen the pages with the toroids... I have a bigger toroid here that I used for making baluns I could use but I'm not sure I have an analyzer that could tell me the inductance on it if used it. I might be able to find one (I go to an engineering school for heaven's sake right?!)

    Ideally, I'd like it to work like the PAC Electronics 10/20/40 - or at least 20/40. I know it uses a coil along the line somewhere, but it allows you to use full halfwave length wires on any other band too. I think I'll make another trip up to the W9NAA shack to see if I can find a L-C meter.
  5. AI3V

    AI3V Ham Member QRZ Page

    You can use those parts to make your tuner, Just go easy on the power. Even 100w might be pushing things.

    If the cap arcs, or the coil melts, You went too far!:eek::D

  6. W0EA

    W0EA Ham Member QRZ Page

    LOL yeah, I have 20w max on my rig anyway :p (Ten Tec Argonaut V)
  7. W4CBJ

    W4CBJ Ham Member QRZ Page

    Half-wave End Fed Tuner

    Actually, measuring inductance or capacitance is quite simple. All you need to do is purchase (OUCH) or build a Wheatstone impedance bridge. Very inexpensive and easy to do. I went to engineering school and they did not even mention anything about it (mechanical). Without it....let me tell that I never graduated from 'magician's school'. 73 Joe W4CBJ

    Italian: ingegnere meccanico
    German: maschinenbauingeniur
    Dutch: mechanisce ingenieur
  8. K9STH

    K9STH Ham Member QRZ Page

    You can also measure impedance or capacitance with a Grid Dip Oscillator ("grid dip meter").

    A simple way of using the inductor is to tap it about every 5 turns. Do this by pushing in the wire on each side of where you want to put the tap. Then you can either install some kind of switch to chose the tap or, even simpler, use an alligator clip on the end of a piece of hookup wire and physically move the tap.

    Glen, K9STH
  9. W0EA

    W0EA Ham Member QRZ Page

    I did a bit more research and rather than make a limited L network, I'm just going to use all 3 components and do the classic T configuration (C-L-C). My main issue is that my current tuner (MFJ-941E) is just too big to carry around. I've got it opened up now and the caps would fit in my project box (4"x4"x3") well and the switch has lots of positions, and I could use my little coil for the inductor, which according to the ARRL ( has a good range of inductances.

  10. W4CBJ

    W4CBJ Ham Member QRZ Page

    Half-wave End Fed Tuner

    Yeah....but...the Wheatstone bridge if properly constructed and calibrated will read out the actual capacitance or inductance very accurately in comparison with a "good" 'store bought' bridge. 73 Joe W4CBJ
  11. W0EA

    W0EA Ham Member QRZ Page

    Just thought if they were not any better than T's, companies would just make L networks - but most tuners (from MFJ anyhow) are T networks...
  12. K5UOS

    K5UOS Premium Subscriber QRZ Page

    Old Idea using L Network

    I can't add anything about L Networks. Many things having to do with electronics and antennas are compromises based on what is available or what environment we are in. The L network is one of those simple, versatile solutions to a common problem.

    The link is a clever use of an L network.

    The project is referred to as dual band operation but I use my 40M HB 1/4 wave on 15M. I can get 3 band from a single radiator.

    I have a mini version using fixed L and C for camping but use an HB L network with roller most of the time.

  13. G3TXQ

    G3TXQ Ham Member QRZ Page

    I like the L-match for the reasons WA8KJP gave. But manufacturers prefer the T-match because it can match a given range of load impedances using smaller values of capacitance than are required for an L network, and high-pF wide-spaced variable capacitors are expensive to make.

    Here's an example for matching a 25+j0 ohm load at 2MHz:

    L-match: C=1600pF L=2uH
    T-match: C1=100pF L=34uH C2=82pF

    Then again, you only need one variable capacitor in an L-match :)

  14. W4CBJ

    W4CBJ Ham Member QRZ Page

    Half-wave End Fed Tuner....

    Maybe the "Don't ask, don't tell" rule ought to apply to amateur radio, too. HI 73 Joe W4CBJ
  15. AI3V

    AI3V Ham Member QRZ Page

    The L will need to be rewired for some solutions, The T tends not to!

  16. AE5JU

    AE5JU Ham Member QRZ Page

    I've seen that same tuning cap from a number of sources, and listed variously as 10-380, 10-400, 9.6-365.
  17. W0EA

    W0EA Ham Member QRZ Page

    Ok so here's what I did, I scrapped the tuner build and traded my big tuner for a smaller MFJ model. If I go with a half wave wire on it, could I expect similar results to the PAR antennas? (it seems these things work like magic!)
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