I have a Yaesu FT-817 and a couple of SLA batteries, but I haven't got a 2m beam. I used to own a 4el quad by Jaybeam which was brilliant, but sold it as I thought I would never use it again – duh! I looked at a few manufacturers' websites, but £50 for a 5el Yagi seemed a bit steep for one-day's operating.
So I decided to make my own. I wasn't interested in outright gain, but wanted something which was a) small and light, b) cheap and c) offered a little gain and some front to back.
The answer tuned out to be a Moxon rectangle beam. This is a two-element beam offering about 3dBd gain and massive 30dB front to back
If you head over to http://www.moxonantennaproject.com/wb5cxc/wb5cxc.htm you can find out all about it.
There is even a PC-based calculator that you can download.
So I headed off to B&Q and came back with 2m of white PVC trunking, two connector unions, and some PVC glue. I added some 2m PVC coated copper wire that I had, an S0239 socket and some 3.5mm heatshrink tubing – that's it. About £10 all in.
I modelled the beam for 145MHz and came up with the dimensions shown below. I then cut the PVC pipe accordingly and soldered/glued it all together. I used the heatshrink tubing to connect the ends of the elements. If I were making another one I would use a drinking straw first to strengthen them, although they seem OK with the tubing on its own.
Using my MFJ analyser I found that it resonated at about 136MHz – damn! I think this is because the velocity factor of PVC coated wire is about 94-95% and the computer simulation assumes bare wire.
So out came the junior hacksaw and I cut everything down to 94% of the original. This gave me a beam with about a 1:1.2 – 1:1.5 SWR across 2m. I fitted the beam to a 10m fishing pole (about 2m down from the top) using a couple of cable ties and hauled it up. I used 20m of Mini8 coax, but later that day found that it had a measured loss of about 2.4dB on 144MHz. Switching to RG213 reduced this to about 1dB.
So does it work? Yes, and quite well. I was able to hear the GB3VHF beacon at about S1-2 (148.20 km (92 miles) away). Swinging the beam around made the signal vanish into the noise. I could also hear the PI7CIS beacon in the Netherlands (JO22DC) - 221.11 km (137.4 miles). Swinging the beam vertically brought in repeaters from up to 60 miles away too. This was under flat conditions and I was unable to raise anyone on 144.300MHz SSB, more's the pity.
So for a total cost of about £10 a great little lightweight beam.
Still very few sunspots at the moment, but lots of coronal hole activity! This month I also take a look at WinCap Wizard from Tabersoft. You can listen by clicking on the headline or search for G0KYA on iTunes.
Solar flare activity has been low, but even a small change in the Interplanetary Magnetic Field (Bz) swinging south was enough to cause the HF bands to misbehave.
This was characterised during the International Marconi Day event on 26 April. The morning was not too bad with DX from the Caribbean and VK being workable on 20m in the mid morning. By afternoon is was EU only.
May 1 should see the start of the Sporadic E season. This is characterised by very strong signals in the 14-50MHz bands, with very occasional openings on 2m.
Look for very strong signals on 10m and 6m, which will suffer from heavy QSB. As the Es clouds move the countries you are able to work will change.
Peak times for Es are mid morning and mid to late afternoon, although look in the evening too.
Daytime MUFs are likely to be lower than those of winter. Older books suggest this is due to the ionosphere heating up with resultant lower ion densities. But other theories suggest that this is due to a change in ionospheric chemistry between winter and summer.
The so-called “Seasonal Anomaly” is now thought to be due to a large summer electron loss rate caused by an increase in the molecular/atomic composition of the ionosphere and the reaction rates being temperature sensitive.
It is not all bad news though. Night-time MUFs may be higher in summer than those in winter. Note that DX on the low bands, if possible, is unlikely to occur until around midnight or the early hours due to the late sunset.
So let's look at each band and what you can expect.
On 160m (1.8MHz or Top Band), high levels of static and solar absorption mean that the band will not really support sky-wave contacts during the day. During darkness, short-skip openings may occur, but DX may be a rarity. Occasional openings can occur during the hours of darkness, especially around local midnight/early hours.
80m (3.5MHz) will generally follow the characteristics of Top Band with high levels of static, but will also provide good openings out to around 250 miles during the day. Absorption will grow to a maximum at midday for inter-G contacts. DX capabilities will be poor to fair during the hours of darkness.
40m (7MHz) will suffer from high static caused by high numbers of thunderstorms. Nevertheless, night-time openings should be reliable from sunset to sunrise. Local daytime openings will be possible on the whole. Night-time skip distances are likely to be between 500 and 2,300 miles.
20m (14MHz) is still likely to be the best DX band between sunrise and sunset, although the band will be noisier than the winter period and not as reliable for long-haul contacts. The higher MUFs at night mean that 20m may remain open during the evening to DX. Short skip may also be possible due to summer sporadic-E.
17m/15m (18MHz/21MHz) should provide a fair number of DX openings during daylight hours, especially to the southern hemisphere. Once again, 15m may struggle to open at times. Both bands are likely to close after sunset. Sporadic-E will provide good short-skip openings, predominantly in the May-June period.
12m/10m (24MHz/28MHz) are likely to be disappointing bands apart from Sporadic-E openings that will provide regular openings out to around 1,300 miles. Multi-hop sporadic-E openings are possible, providing relatively good, but short-lived paths to DX beyond this range. A typical multi-hop opening might provide brief contacts with the Middle East or USA, although they would be very hard to predict. Propagation via the F layer is unlikely to occur reliably until Autumn.
You can find HF short-path propagation prediction charts from the UK at:
http://www.infotechcomms.co.uk/propcharts/
You can also listen to Steve G0KYA's monthly HF propagation podcast on iTunes or at http://www.g0kya.blogspot.com/
Steve G0KYA RSGB Propagation Studies Committee
My HF Propagation maps for May 2010 have now been published. Please note that these don't predict Sporadic-E conditions, which should start around the 1st May. These will give short skip on bands from 14-50MHz, wtih occasional openings on 2m too.
Few sunspots at the moment, but lots of solar flare activity - boo! Find out more and also hear about the origins of Sporadic E in this month's Podcast. You can listen by clicking on the headline or search for G0KYA on iTunes.
Over the past month we had a solar flux low of 76 and a high of 92 (on 13th March). But we've also had some serious solar flares. We had a geomagnetic A index low of 1 on two occasions and a high of 28 in the first week of April.
In fact, the A index was still climbing as I wrote this and Auroral conditions were being recorded on 6m and 2m
We are still in the equinox period as far as HF propagation goes. These tend to be the best months for working North-South paths, such as UK to South Africa.
So let's look at each band and what you can expect.
On 160m (1.8MHz or Top Band), look for short-skip and DX openings at night. Little daylight skip will be possible due to absorption, but openings out to 1,300 miles and occasionally further afield can be expected at night with conditions peaking around midnight and again at sunrise (greyline).
80m (3.5MHz) will generally follow the characteristics of Top Band at night, but will also provide good openings out to around 250-300 miles during the day. These will lengthen to around 500-2,300 miles at night with fairly good DX opportunities at times.
40m (7MHz) Forty metres should open to DX in an easterly direction at sunset. Openings to the west should be possible after midnight and should peak just before sunrise. Contacts should be possible during the day, although lower critical frequencies may mean that it is difficult to work other UK stations while perfectly possible to talk to European stations. If the flux rises then 40m may open up to NVIS contacts around the UK, but 80m will be better.
20m (14MHz) is likely to be the best DX band between sunrise and sunset. The bands may occasionally open after dark, perhaps to the southern hemisphere. Good openings will be possible during daylight hours out to around 2,300 miles.
17m/15m (18MHz/21MHz) should provide fairly good DX openings during daylight hours, especially to Africa and South America, with 17m being open more often than 15m. If we get more sunspots 15m will become a great DX band, as it did at times in February. Both bands are likely to close after sunset.
12m/10m (24MHz/28MHz) These could be disappointing bands if the solar flux remains low. If the solar flux heads towards the high 80s/90s then openings will occur on both bands, although 24MHz will open first. If it breaks the 100 mark then expect to see some good DX openings on 10m. Expect to see Sporadic E start up at the end of the month, but more of that in May.
You can find HF short-path propagation prediction charts from the UK at:
http://www.infotechcomms.co.uk/propcharts/
You can also listen to Steve G0KYA's monthly HF propagation podcast on iTunes or at http://www.g0kya.blogspot.com/
Steve G0KYA RSGB Propagation Studies Committee
