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)

G5RV – flat or inverted V?

I did some tests recently with a G5RV in inverted V configuration. I was very disappointed. Don’t get me wrong, I know that the G5RV is a compromise antenna, but I found that some DX signals were inaudible compared with my 20m dipoles in the loft. Why?

Turns out that if you use a long multiband antenna as an inverted V it really changes the radiation pattern. The lobes contract quite badly and the radiation angle goes up dramatically. I lost about 7db east-west and the low-angle DX capability went through the floor.

An inverted V half-wave dipole doesn’t do this, so if you must have an inverted V for 20m, use a half-wave dipole, not a G5RV or OCF (Windom).

Save your inverted V G5RV or Windom for 80m where they seem to work quite well with high-angle radiation.

Above right: The red trace is a G5RV inverted V with the apex at 12m and the ends at three metres. The blue trace is a flat-top G5RV at 12m. These were produced with MMANA-GAL, an excellent program.

Thursday, 29 January 2009

Greyline Propagation


I few years back I was working on grey line propagation studies as part of my work with the RSGB's Propagation Studies Committee. For those who do not know what grey line is, here is a feature that was written for the RSGB's RadCom magazine. It is available in HTML form without images here or as an Adobe Acrobat PDF file with images (701kb) here.

Feel free to download them.

The first part of the research looked at trans-terminator propagation on 10m. That is, signal enhancements that are sometimes seen when signals arrive from areas to the west that are currently experiencing their local sunset. For this, Geoclock software was used (see www.geoclock.com), but the parameters are changed to show the illumination at both the D and F layers. This is done by following the instructions in the package. Signals were logged using DL4YHF's excellent Spectrum lab software (see www.qsl.net/dl4yhf).

The resultant data are processed using MS Excel and graphs can be produced like the one here. Enhancements were seen on signals from the OH9TEN and SV3AQR beacons, but it didn't happen every day. The phenomenon was called skip focusing.

Updates
You can also look at the latest trans-terminator results on 3210kHz (October 2005).
Radcom published the results of the first round of tests in May 2005 - you can download it in PDF format (500kb)

This is the original presentation on Greyline and the studies given to the RSGB Convention in 2005 (20Mb download - PDF.

Download the "3Y0X Propagation Predictions to G v Reality" presentation given at the RSGB's HF convention in October 2006 in either Adobe Acrobat PDF or Powerpoint formats (both 5mb). While not strictly about greyline it does show the effect of morning/sunrise enhancements on 80m very well. (October 2006)

Multi-band loft-mounted dipoles for 40, 20, 17, 15, and 10m


Amateurs are always after the Holy Grail - an antenna that will work on all bands, is inconspicuous, effective, but above all inexpensive. Unfortunately, you seldom find something that fits all these factors.

This antenna has nothing new about its design, but it does bring together quite a few useful ideas and characteristics.

These are:

• Fully no-tune antenna system for five popular HF bands

• Suitable for SWLS, QRP, M3 licensees and PSK31 operating plus occasional useup to 100W, but watch out for RFI at high powers. DO NOT USE A LINEAR!

• Uses non-inductive (zig-zag) loading for 40m

• Feed point balun reduces RF pick-up and interference making it quiet.

Maldol MFB-300 HF vertical antenna


The Japanese-made Maldol MFB-300 HF vertical is the latest antenna on the market to offer extremely wide-band performance, with a specified frequency range of 1.0-60 MHz.

There are very few antennas that can claim to work well across such a range and I was keen to see how it would perform. The benefits to a newly-licensed amateur, or one with very restricted space for antennas, are obvious.


The Maldol gives you access to all of the HF bands, plus 6m, and apparently all without the need for an ATU. I wasn't terribly impressed, but any antenna is better than no antenna I guess.

The MFJ-1786 Magnetic Loop Antenna


I have always been intrigued by small antennas. For those of us living in suburbia, seven element tribanders at 110 feet can only remain a dream. The quest therefore is always for electrically small antennas for HF that work.

Over the years I have experimented with magnetic loops, crossed field antennas and E-H verticals and have come to the conclusion that, for now at least, the magnetic loop seems to offer the best alternative to beams and dipoles if you have no space.

The MFJ-1786X is a 36-inch diameter aluminium loop that covers 10-30MHz. It can cover six HF amateur bands in one three-foot antenna, but the loop will also cover all the shortwave broadcast and utility bands in between as well. The loop is formed from 1.05-inch thick aluminium tube, which is welded to the loop’s variable capacitor so giving a very low loss connection – important for maximum efficiency.

If you thinking of mounting the loop in an attic do bear in mind that it can't be stripped down. Make sure that your loft opening can accommodate the 36 inches required or you will be taking a hacksaw to your ceiling!

Did Marconi really hear signals across the Atlantic in 1901?

As far as the history books and the general public are concerned, Marconi is the father of radio.But Marconi’s main claim to fame all rests on a simple premise — did he actually receive signals from Poldhu, Cornwall, UK at Signal Hill, Newfoundland on December 12, 1901?


Unfortunately, some say the evidence is stacked against him and people have argued about the success or otherwise of his achievement for years.


Read Steve's feature from the December 2007 issue of QST on the work of the GB3SSS experiment (3Mb PDF).

Propagation predictions for International Marconi Day

International Marconi Day (IMD) is a 24-hour amateur radio event held annually to celebrate the birth of Guglielmo Marconi on the 25th April 1874. The IMD event is not a contest: it is an opportunity for amateurs around the world to make point-to-point contact with historic Marconi sites using HF communications techniques similar to those used by Marconi, and to gain an attractive Award for achieving the requisite number of Marconi stations worked (see IMD Award ).

IMD is usually held on the Saturday closest to Marconi's birthday, when amateur radio stations are established and operated from original historic sites, or nearby. These stations are known as the 'Award Stations'. This year's event is on Saturday 25th April 2009.


I have calculated some propagation predictions from the UK to the various stations taking part to help you make contact and win your award.


Right: The Marconi Centre at Poldhu, Cornwall (or the "Macaroni Centre"as my kids call it!).

In search of Marconi – radio heritage in Cornwall


My wife called it a “geek’s weekend”. I can’t see the local tourist board adopting the title, but if you’ve ever been interested in technology and wondered how it developed, Cornwall is a great place to visit and find out.

Not only is this south-west corner of England the home of radio and satellite communications, but it’s also where the original world wide web was developed – back in the late 1800s.

Download the full feature in PDF format