Saturday, 31 January 2009

The 20m EH Antenna

The EH antenna attracts a lot of controversy - does it work and how? Is the coax doing all the radiating?

About two years ago I built a pair of EH antennas. I couldn’t really get either to work properly and they gathered dust in the back of the garage. In retrospect I should have used a choke balun near to the antenna. I moved house and couldn’t bring myself to throw them away, especially as I had bought a three-metre length of copper tube to build them that a cost of about £50.

Anyway, fast-forward two years and I thought I would have another go. I lent the small one to a friend to play with and set to on the bigger one.

I now have a 20m EH with two 20inch x 1.75 inch copper cylinders and a 10-turn tuning coil. It has a 10-turn choke 1 metre down from the antenna.

It is vertically mounted off a rafter in the loft and my other antennas are horizontal to cut down on cross talk/re-radiation effects. Does it work? Well, the 2.5:1 SWR bandwidth is just about 14-14.350MHz, the minimum SWR is about 1:1.4 and it hears almost as well as a dipole and a Windom, sometimes minus 1-2 S-points.

The noise level is lower too, which suggests little coax pick-up.

I have worked many stations, including Kazakstan and the recent Tunisian DXpedition with 59 reports - the latter on first try.

You can definitely see that fading is due to polarisation changes as one or other antenna improves as the other goes down. Does it work by Poynting Vector Synthesis? Don't know and may never know. Does it radiate from the coax? Don't think so (it has big choke near the feed point) and the fact that the field strength near the coax is less than my Windom and dipoles says something.

I have to admit that I am quite surprised. Earlier tests about two years ago were inconclusive, but I have learned that:

1. You need to earth the MFJ analyser to get reasonable readings.
2. You need the choke.
3. Make the tuning coil slightly longer than you think you need as you can always space out the turns to increase the frequency.
4. Spacing out the turns at the top of the tuning coil changes the resonant frequency, spacing out the bottom changes the SWR.
5. I did have it so that the maximum radiation according to the FS meter was the same as the minimum SWR, but this has changed slightly now that the antenna is on a different length of coax.

Does it work by Poynting Vector Synthesis? Probably not, but it does appear to work and the aim of this post was to encourage people toat least play with the design.

The noise level is lower too, which suggests little coax pick-up. I am only reporting what I am seeing. Build one according to the instructions and try for yourself. I was very sceptical and now I'm amazed.

For more details see http://www.eh-antenna.com/. You can get construction details at the EH Yahoo group (eh-antenna.yahoogroups.com)

13 comments:

  1. It would be interesting if you could use WSPR beacon mode to get some quantitative reception reports to compare with your dipole. One of these days I might make an EH myself but I can't make sense of the instructions.

    ReplyDelete
  2. I think that the EH antenna will perform better when placed on top of the roof, at least a half wave lenght above ground. 73, Paul PC4T

    ReplyDelete
  3. Yes, Keep playing with them - We are all learning (and sharing!) as we go along.

    I too agree that the top and bottom of the tuning coil have different effects, as you saw.

    Stu
    G3OCR
    (my call-sign inherited from, and in memory of, my Silent Key Father, who would have loved this, even though he'd never heard of an MFJ analiser in his day)

    ReplyDelete
  4. Just posted a link to you Steve:

    www.robbie.nildram.co.uk on "shack" page.

    Rob
    (M0RZF)

    ReplyDelete
  5. Nice write up Steve, i posted a link to your blog on the Code Warriors list.
    I think i will put my two EH's back up in the loft when i get time. :-)
    Bill G4KKI

    ReplyDelete
  6. Tnx for the nice article Steve!

    How much coax you have in the ugly balun?

    73 de Janne OH1SDR

    ReplyDelete
  7. Hi,

    The choke isn't an ugly balun, but 10 turns of RG58 counterwound through two ferrite rings glued together. It is the same choke I used for my Microvert experiments for "Stealth Antennas" and seems to work well.

    Steve

    ReplyDelete
  8. Hello Steve, Your live traffic feed is not too accurate, I'm in Glossop not Sheffield.
    What exactly do you mean by "counterwound" on your
    balun.
    73 Ken g8beq

    ReplyDelete
  9. Hi, sorry - the system gets it wrong quite a bit. By counterwound I mean wrap half of the turns one way then pass the coax to the other half of the toroid and wind them the other way. Hope that helps.

    Steve G0KYA

    ReplyDelete
  10. I have looked at the eh antenna group on Yahoo, but cannot find the construction details of of the antenna above.

    If you have a direct link it would be nice or what to look for.

    I'm thinking about making one for 20m, but there are not that many constructions details for 20m out there.

    vy 73 de AK4WQ / Soren

    ReplyDelete
  11. Hi,

    You need to look here:

    http://groups.yahoo.com/group/eh-antenna/files/EH%20Antenna%20Book/

    Steve

    ReplyDelete
  12. 40 Meter WSPR Comparative Testing a Dipole vs EH Antenna using Two Radios and xmitting at the same time yielded some interesting results:

    http://wsprnet.org/drupal/node/4112

    I'v got coil losses, maybe even PVC losses, that makes 'gain look a few to maybe 3 dB less ... I used 'link coupling' into the EH Tuning coil to avoid direct connection and thereby reduce feedline currents.

    de Jim WB5WPA

    ReplyDelete
  13. Hi Steve

    A week or two back I performed some comparisons on 40 Meters using the WSPR network testing a Dipole vs an EH Antenna by using two Radios and xmitting at the same time which yielded some interesting results:

    http://wsprnet.org/drupal/node/4112

    I've got coil losses, maybe even PVC losses, that makes 'gain look a few to maybe 3 dB less ... I used 'link coupling' into the EH Tuning coil to avoid direct connection and thereby reduce feedline currents. There are some pictures in the discussion on the link I posted just above.

    73, Jim WB5WPA

    ReplyDelete