Friday 23 October 2009

Making sense of 10m propagation

What's this? G stations working VK on 10m at sunspot minimum? Jordan and Thailand audible on 10m on a 65ft end fed?

That can't be right!

Well, it looks like it is. So why did 10m suddenly open up this week?

I think we need to look at a number of factors. First the solar flux was 72 so obviously no massive increase in solar UV output has caused it.

But it is October and this is a peak month for DX. The ionosphere in the Northern Hemisphere is cooling down, becoming more dense and the chemical composition changes too in the Winter compared with Summer, giving us a greater ion density.

To quote J K Hargreaves' “The Solar Terrestrial Environment”: You get an increase in NO concentration and a decrease ion loss rate due to the removal of water-cluster ions and a change in chemical reaction rates due to the temperature change.

In fact, if you feeling really awake read the whole 414 pages – I am sure the more I read the less I understand!

Anyway, so is that the whole story? No!

At the time of the openings the he Bz (Interplanetary Magnetic Field) was pointing south which means that solar wind was coupling with the earth's magnetic field and hot ions were pouring in.

Hence the 6m aurora the previous night – see

The three-hourly K index reached 4 showing the effects of these ions on the earth's magnetic field.

So what we probably saw was a pre-auroral enhancement and that condx on the upper HF bands while good, are going to get worse. I'll let you know if I was right.

And they say that a high K index is bad for propagation – not always at the outset though.

Snowdonia Radio Company SRC X65 65ft end fed

I bought one of these at a local rally. It is a 65ft wire and a 9:1 UN-UN. The guy who sells them is very friendly and is an ex Royal Signals op (I think). At only £30 it is barely worth making your own. I set it up as an inverted L with a 10m fishing pole. So it was about 9m up and about 10m sloping down to my shed, tied off with fishing line so that the end was about eight feet off the floor. I used a single ground stake and six 20ft radials.

Here are the results:
SWR measured with MFJ 269 at end of 30ft of coax.
Single earth stake and six 20ft radials

3.5MHz – SWR 3.5:1
3.6MHz – SWR 4.4:1
3.8MHZ – SWR 6.2:1
7.10MHz - SWR 4.8
10.1MHz – SWR 2.6:1
14.2MHz – SWR 2:1
18.14MHz – SWR 1.7:1
21.2MHz – SWR 1.9:1
24.9MHz – SWR 1.7:1
28.5MHz – SWR 1.3:1
29.6MHz – SWR 1.9:1
50.1MHz – SWR 1.9

On–air comparison with 135ft Windom (OCF)

Similar signal strengths to Windom around UK, sometimes 2-4 S pts down, but 1-2 S pts. less noise. Holland down 2 S points. Germany 1 S pt better.

Similar to Windom on PA and DL, F similar, IK similar, G similar.

UA 1 S pt better on SRC, IK better by 1 S pt, YO similar

Similar – inverted L has slight edge at times. Slightly quieter

Better than Windom by about 1 S point, sometimes better, sometimes worse.

All signals better by 1-2 S points

Much better than Windom, dipole and mag loop, by about 2 S points. UA three S pts better. Slightly noisier. 5B4 beacon 2 S pts better.

I was very surprised at how good it was on 10m – or my Windom is very bad. I think this could be a keeper. See

Update: In the CQWW SSB contest on 24/25 October I worked more than 20 countries using the antenna on 10m, including ZS9 - very good!

Wednesday 14 October 2009

HF Propagation Podcast, October 2009

Slight change to the format this month. I was very pleased to meet Carl K9LA at the RSGB Convention last week. Carl is an HF propagation expert and a fellow member of the RSGB's Propagation Studies Committee. I took the opportunity to talk with Carl about Solar Cycle 24. We also talked about the theory that galactic cosmic rays are affecting Top Band (160m) propagation during this solar minimum. You can listen to the podcast by clicking on the link above. Or you can search for G0KYA on iTunes.

Monday 12 October 2009

What is WSPR?

I gave a talk at the RSGB's National Convention on WSPR, what it is and how it is being used. I was asked if I could make the PowerPoint presentation available so here it is. It is quite a big download though - about 12Mb. Just click on the title to download it.

Sunday 4 October 2009

Propagation predictions for P29 DXpedition to Papua, New Guinea

Gordon G3USR asked me to produce some propagation predictions for the P29 DXpedition to Papua, New Guinea, that he is joining between 20.10.09 – 10.11.09.

I have used a combination of ACE-HF and W6ELProp, plus a bet of guess work to come up with the attached. It will be interesting to see how they work out.

Click on the main heading to download the PDF