NEW! The multiband trapped EFHW HF antenna

The 20-17-15m trapped EFHW

Ever since I first published the details of the original monoband EFHW people have been asking me can you design a multi-band version? My stock answer has always been "no" – I couldn't see how I could.

Anyway, this had been bugging me for some time. I tried modelling a version that could use parallel-fed half-wave radiators, but it didn't work.

I had always dismissed traps as these are used on quarter-wave radiators so they wouldn't work on a half-wave design – or would they? Turns out they do. I started modelling an antenna in MMANA-GAL and found that you could make a 20-15-10m EFHW using traps for 10m and 15m. But you would need a variable capacitor to bring the EFHW tuning unit to resonance.

This actually makes sense as the end of an EFHW is at the same impedance as the end of a quarter-wave vertical, so a trap does the same thing on a half-wave design. All you have to control is the feedpoint impedance.

Doh! – why didn't I think of that earlier?

The result is my first working prototype of a 20-17-15m multiband trapped EFHW, which seems to work well. I have updated the PDF to show how this was done. Development work has continued and one can now be built with a single matching box that doesn't need a variable capacitor at all, just the original coax capacitor.

Download the PDF with the complete EFHW story.

International Marconi Day, April 20 2013

Saturday 20th April 2013 is International Marconi Day when stations around the world celebrate the birthday of Guglielmo Marconi.

It is also a good opportunity for you to gain a very nice certificate. All you have to do is work the requisite number of award stations and send in a log extract - you don't need QSL cards.

I am giving a talk to Kings Lynn Amateur Radio Club about the best way to win the award and you can download the presentation in PDF format (14Mb). It is aimed at UK operators.

I shall be helping to run GB0CMS again this year at Caister Lifeboat. There is short video that looks at the equipment the club used to make 165 contacts in 24 countries on Saturday 30 April 2011. And another for the 2012 event when we made more than 500 contacts.

See http://www.youtube.com/watch?v=Z41FLKaT7eY and http://www.youtube.com/watch?v=C8ZRW0q6SyI

You can also view my propagation predictions online.

You can find out more at: http://www.gb4imd.org.uk/

Origins of the term "CQ"

Have you ever wondered where some of our radio terms come from?

Some say that SOS stands for "Save our Souls" - which it doesn't. The Morse phrase ... --- ... was chosen as it was very distinctive and unlikely to be misread. It doesn't stand for anything.

So what about CQ? I've heard it described as "Come Quick" but that doesn't make sense.

But a chance conversation with someone while working in the US has cleared this up. He is multi-lingual (unlike me) and although he is not a radio ham, knew immediately what it could stand for.

CQ is Cherche Quelqu'un - literally the French for “looking for someone”

This makes sense as a lot of radio terms have French origins - the Coastguard still says "securite" for important information.

So there you have it - the origins of CQ. Or is it?

Pol G3HAL sent me an update. According to Wikipedia:
Land telegraphs had traditionally used "CQ" ("sécu," from the French word sécurité^[1]) to identify alert or precautionary messages of interest to all stations along a telegraph line, and CQ had also been adopted as a "general call" for maritime radio use. However, in landline usage there was no general emergency signal, so the Marconi company added a "D" ("distress") to CQ in order to create its distress call. Thus, "CQD" is understood by wireless operators to mean, "All stations: distress." Contrary to popular belief, CQD does not stand for "Come Quick, Danger", "Come Quickly: Distress", or "Come Quick — Drowning!"; these are backronyms.

This sounds more likely.

The Morse Crusade

I had an email today from Ian G4XFC, founder of the Morse Crusade. This concentrates on the Koch method of teaching Morse. The Crusade has been running since September 2011 and is starting a new campaign this year to promote the learning and use of good readable Morse.

Any site that promotes the use of Morse code is good in my eyes - I use Morse a heck of a lot and it is my favoured mode for working DX, although I struggle with my speed increasing and decreasing as I either use it more or let it drop for a month.

I've worked some choice DX that I would never have been able to work with SSB, using up to 100W CW and an assortment of compromise antennas at this surburban QTH. This is what prompted my "Stealth Antenna" book.

Anyway, you can find out more at www.themorsecrusade.g5fz.co.uk

Keep Calm And Work Some CW

I had a tremendous response to the "Keep Calm And Work Some DX" T-shirts I designed for Cafepress.

These joined the Marine Radio Room clock, which has sold well around the world. For a bit of fun I have now added a "Keep Calm And Work Some CW" shirts and mugs too.

You can find them at  "The Radio Room" on Cafepress

Short path propagation charts from the UK

I have now updated my short path HF propagation charts for the UK for the next three months – November, December and January.

These have been created using the latest smoothed sunspot numbers from NOAA in the US and HAMCAP.

October was a fantastic month for 10m propagation with most of the world being workable at times. Early November saw a dip in the solar flux index, which manifested itself as poorer conditions overall.

But the flux has been climbing steadily over the past few days and is back in the 130s again so 10m is opening up nicely.

We just have to worry about solar flares and coronal mass ejections, which could be a fly in the ointment. Solar flares can bring short-lived D layer absorption, while coronal mass ejections, if earth facing, can bring about depletion of the F layer for many days.

Look out for a high solar flux index (>120) and a low K index (0 or 1) at www.solarcycle24.com for the best HF conditions.

The low bands are also coming into their own with the extended periods of darkness in the northern hemisphere.

Keep an eye on 80m – there will be good openings on 80m, and 40m has been open to parts of the US way past sunrise over the last week.

December should be a good month for the low bands, including Top Band (160m) although probably not as good as we have seen a few years ago around solar minimum.

The November propagation chart can be found at: www.infotechcomms.co.uk/propcharts/november/ 

A link to all of the charts can be found top right.

Video of trip to K6KPH, California

I was lucky enough to visit the Maritime Radio Historical Society's old KPH sites at Bolinas and Point Reyes, California, in September.

If you haven't heard of these they were the transmitter and receiver sites for KPH - the mighty Pacific coastal station that sent Morse code and RTTY to ships and point-to-point services until the late 1990s.

Both sites are now restored and they also run K6KPH - an amateur station. They were kind enough to let me operate some CW as well, letting me make contacts across the USA on 14MHz.

You can find out more at: www.radiomarine.org

I shot a seven-minute video while I was there too - you can see us working G3LDI back in the UK on 20m CW. Go to https://www.youtube.com/watch?v=Wj-IwYPrtTM