Wednesday, 11 November 2009
I have been experimenting with HamCap. It uses the VOACap engine to produce propagation maps and charts. As an experiment I have created a series of band-by-hour charts for the UK - now updaetd for January 2010.
These are based on 100W to a dipole at 35ft, with a smoothed sunspot number of 17. They are all short path too. You can try them here.
I think that 20m looks a bit optimistic with propagation way after sunset - time will tell!
Will sunspot 1029 still be active when it comes back around the sun later this month? Will 10m open up again for CQWW CW like it did for CQWW SSB in late October? Find out more about this and the best HF bands to use in November in this month's podcast. Use the link above or search for G0KYA on iTunes.
Friday, 23 October 2009
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 www.solarcycle24.com.
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.
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 http://www.snowdonia-radio-company.co.uk/
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
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
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
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
Wednesday, 16 September 2009
On 160m (1.8MHz or Top Band), look for short-skip and DX openings at night. Again, no daylight skip is 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 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, again, lower critical frequencies may mean that it is difficult to work other UK stations while perfectly possible to talk to European stations.
20m (14MHz) is likely to be the best DX band between sunrise and sunset. The bands may occasionally open after dark, mainly 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. Once again, 15m may struggle to open during times of low solar flux. Both bands are likely to close after sunset.
12m/10m (24MHz/28MHz) will continue to be disappointing bands at this point in the solar cycle. There may be many days where there are no signals at all, although occasional brief openings to DX may be possible, especially if the solar flux heads towards the high 80s/90s.
Are sunspots disappearing completely? Some scientists think so. But a large spot is just around the back of the sun and should swing into view around September 20th. Find out more about this and the best HF bands to use in September in this month's podcast.
Also available on iTunes
Sunday, 9 August 2009
A look at HF propagation conditions for August 2009, including the solar and geomagnetic data for July 2009, Sporadic E and how to work stations VQ9JC on Chagos Island and 5N0OCH in Nigeria. All this plus a band-by-band round-up of what you can work and hear.
Also available on iTunes
Thursday, 30 July 2009
A project at my local club (Norfolk Amateur Radio Club) turned into a bit of a nightmare recently. The project was simple - let some of the youngsters make a 2m Slim Jim antenna out of 300 Ohm ribbon cable.
We had made plenty of these before and they work well. You cut a piece of white, translucent ribbon cable of about 60 inches long and bare the wires at both ends by about half an inch. You then twist the ends together and solder, giving you an overall length of 59 inches.
Then you cut a one-inch slot on one side about 18 inches up from the bottom. Feed it across the two elements about two inches from the bottom and there you go – except we didn't.
For this exercise we had bought some black, heavy duty 300 Ohm ribbon. When we made them up they came out on an MFJ analyser at about 136MHz – they were obviously too long.
After much messing around I decided that the only reason must be that the velocity factor of the black ribbon cable is different to the translucent stuff.
Out with a calculator and I reckoned it was about four inches too long. We decided to shorten one – carefully – until we got it right. We could then use it as a template for the rest.
We ended up with a length of 53 inches, with the slot 16 inches up from the bottom. This gave a virtual 1:1 – 1:1.5 SWR at 145MHz.
My prototype Slim Jim has now been put in a piece of white piping from the local hardware store with the silver top off a room spray on one end and the end off a toothpaste tube on the other.
It looks quite good and cost about £5 all in.
So if you are going to make a Slim Jim from ribbon cable do bear in mind that the length will depend on the type of cable you use.
Here is the latest HF Propagation Podcast for June/July 2009 as featured on "This Week in Amateur Radio". Solar activity remains very low with virtually no visible sunposts. The Summer (in the Northern Hemisphere) is characterised by lower MUFs during the day than in winter, but higher MUFs in the evening/night. 14MHz may stay open later in the evening than it does in Winter. Sporadic E conditions are excellent, giving good short-range openings on 14, 21, 28 and 50MHz, occasionally getting up to 144MHz.
Also available on iTunes
Friday, 3 July 2009
I quite like the Hustler 5-BTV vertical. It is rugged, well made and gives you five bands in one antenna.
BUT - you must make sure you have a good earth radial system if ground mounted. Putting a single earth stake in will work, but it will be quite deaf. Adding radials makes a big difference. They don''t have to be resonant. As they are lying on the ground this detunes them anyway - just make sure that they are as long as the antenna is high.
In fact, there is no hard and fast rule about radial length, apart from more shorter ones are better than fewer longer ones.
The golden number to aim for is 120 radials, but that isn't really practical. As you add radials you will notice the SWR change and the performance improve, but as you add more the effect will be less - the law of diminishing returns. By the time you get to 48 -64 you probably won't see much difference.
In a test, I tried a 5BTV mounted on a single three foot ground stake - it was very, very deaf, although the SWR was fine. It was at least three S points down on a dipole and a Windom.
Adding just six 26ft radials made a big difference - it equalled the dipole and Windom and actually beat them at times.
A ground mounted vertical like a Hustler or Butternut is only half an antenna - put down a decent radial system and it will really improve.
I first measured the coax losses of 30ft of RG58 with an MFJ 259 analyser, which were as follows:
3.6 MHz: (0.6db)
7.1 MHz (0.7db)
14 MHz (1.3db)
21.2 MHz (1.4db)
I then took SWR readings on five bands - below are the SWR figures as measured at the bottom of the G5RV's ladder line with an MFJ 259 analyser. The figures in brackets are the SWR readings as measured in the shack after a run of 30ft of RG58.
Using the calculator at: http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=12232 the final figure is therefore the calculated total loss taking the measured loss and SWR loss into account.
3.5MHz: 2.0 (1.7) - 0.646dB
3.6MHz: 3.0 (2.2) – 0.724dB
3.8MHz: 4.2 (3.6) – 0.823dB
7.0MHz: 2.2(2.2) - 0.784dB
7.1MHz: 2.4 (2.3) – 0.806dB
14.150MHz: 4.5 (5.7) – 1.954dB
21MHz: 3.9 (9.6) – 2.83dB
28MHz: 3.6 (12.4) – 3.862dB
29MHz: 3.2 (9.5) – 3.397dB
As you can see the antenna was only really a good match at the bottom end of 80m and on 40m. The total loss gets worse as you go up in frequency. At 28MHz the combined loss was 3.8dB - you are losing half your power.
But the worst case scenario of 25ft+30ft of generic window line at an SWR of 12.4 on 28MHz is only 0.405dB.
So the conclusion is, a G5RV fed with RG58 coax is fine for 80m and 40m, but losses mount as you go higher in frequency. If you want to work the higher bands think about using open wire feeder all the way to the tuner. You then have a doublet with much lower losses.
Wednesday, 17 June 2009
In the next round of tests I used the same 9:1 Un-Un wound using PVC covered cable and a T200-2 toroid. Note in the photograph that the PVC tape is only used to keep the turns neatly arranged.
If you want to build your own follow these instructions:
Building a 9:1 unun
Note: you could also use a T130-2 toroid, but that will be limited to a maximum of about 75-100W.
This time I erected a 10m high fishing pole and attached a 65ft quarter wave antenna for 80m in an inverted L fashion. That is, 10m up and then 9.8m out to the nearby summerhouse.
This was arranged away from the house and fed with 12m of RG8 coax, a single earth stake and two 20ft radials at the feed point..
Here are the SWR readings at the end of the coax:
3.5MHz – SWR 3:1
3.65MHz – SWR 4.2
3.8MHz – SWR 5.9
7.10MHz - SWR 13.6:1
10.1MHz – SWR 2.5:1
14.2MHz – SWR 3.3:1
18.14MHz – SWR 1.8:1
21.2MHz – SWR 2.4:1
24.9MHz – SWR 1.9:1
28.5MHz – SWR 1.2:1
From this you can see that by shortening the wire to 65ft from the original 85ft you gain 80m, but lose 40m. The rig (FT2000) would quite happily tune seven bands with its internal ATU.
Here are the quick comparison results against my 80m Windom and parallel-fed dipoles in the loft for 40m, 20m, 17, and 10m.
Not as good around the UK as the Windom - probably due to the maximum current being in the vertical section. Modelling shows the antenna to be down about 10dB on a low dipole.
Lithuania similar. Other EU and Italy similar. Bulgaria down 2 S points
Similar – inverted L has slight edge at times. Slightly noisier
Better than Windom by about 1 S point.
Much better than Windom, dipole and mag loop around Europe via Es, by about 2 S points. Slightly more noise (+ 1 S point).
From this I can see that I need to do more tests, especially on 20m, but for an all-in cost for the antenna of about £15-£20 it shows promise. If you have a tree then the up and out idea with a 65ft wire looks quite good. A way to get 40m back would be to put a 40m trap in the wire at the 10m mark.
If you don’t fancy making your own UnUn you can buy the whole antenna from the Snowdonia Radio Company for £35 inc P&P – see http://www.snowdonia-radio-company.co.uk/srcproducts.html
My first tests were with my 85ft end fed and were not too encouraging. These are the SWR results I got using an MFJ analyser:
from these you can see that the rig would be able to match the long wire on five bands. On test it would not match on 80m, although when run as a W3EDP through my external ATU it works well.
I then wound a 9:1 Un-Un (sometimes referred to as a magnetic long wire Balun) and tried again. Here are the results:
3.6MHz – SWR 28:1
7.10MHz - SWR 1.9:1
10.1MHz – SWR 3.6:1
14.2MHz – SWR 1.9:1
18.14MHz – SWR 3.8:1
21.2MHz – SWR 2.5:1
24.9MHz – SWR 3.5:1
28.5MHz – SWR 8.6:1
While 40, 20 and 15 metres were quite good I can't really recommend this as a multiband solution.
In all then, it is too long and not really worth playing with.
Daytime MUFs are likely to be lower than those of winter due to changes in the ionosphere. But night-time MUFs may be higher 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. Absorption will be high of the HF bands, as will noise. In all, not the best of periods for HF.
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.
Monday, 8 June 2009
They say that you can't get something for nothing, but that's not quite true. In this recession many magazines are struggling as advertisers look to their budgets.
The UK's "Monitoring Monthly" has folded, which is a great shame as it had some very interesting features. The editor Kevin Nice deserves a round of applause for having the guts to start the publication in the first place and I will miss it.
However, in the US someone has thought long and hard about this and has come up with the solution. If the biggest cost in a mazgazine is the print and distribution costs, why not make it an online publication - and make it free too!
The result is World Radio Online and do you know what? It is actually very good - and it doesn't cost a penny (or cent!)
Heres a sample from the current issue:
- USHAGAT: - a Low Budget DXpedition to Alaska
- VERTICAL TALES: Adding 17-Meters to a Hustler 6-BTV
- FISTS CW Club: An 11-Year Old’s View of Amateur Radio
- 10-10 INTERNATIONAL: Investment Strategy
- TRAIL-FRIENDLY RADIO: Plenty of ‘Enhanced’ Audio to Overcome Nature’s Soundtrack
- PROPAGATION: Changes in the Earth’s Magnetic Field
- AMATEUR SATELLITES: International Amateur Satellite News
- AERIALS: Antenna Efficiency
Take a look. I guess the more people subscribe the more advertisers will back it.
Thursday, 7 May 2009
I was first introduced to the range when I went to Florida on holiday and bought a Uniden HR2600 for about £50. This is a 10m-only rig with repeater shift and about 10w FM/25W SSB output and I loved it.
However, it didn’t get too much use in the sunspot minimum years and I decided to sell it – what an idiot!
Anyway, I have never been able to find another one to buy, so settled on the President Lincoln. There are loads of these on eBay for around £120 - £180.
The Lincoln covers 26-30MHz in eight bands. It is very similar to the HR2600 but doesn’t have repeater shift.
Unlike the Albrecht AE 485S I reviewed earlier it does have continuous 100, 10 and 1kHz tuning. You don’t get the memory feature of the Albrecht, but you do get a built-in SWR meter and a scan button. It also has an RIT, mic gain button and RF gain.
Switching to the ham band (28-29.7MHz) I was able to hear everything that my Yaesu FT-2000 could hear, including beacons in Italy, Slovenia and Norway. I worked a couple of stations on SSB and got 57 reports.
I had a bit of a problem with mine. After storing it in the loft for two years the tuning control was a bit odd – in some positions it was fine, in others it would either not change channel or actually go backwards.
You can get new tuning control switches, but they are hard to get hold off. One US expert suggested carefully drilling a small hole in the side of the switch (between the green segments) and squirting in switch cleaner.
I managed to get switch cleaner in the LCD display while doing this and had to strip it out and put in a new strip of white backing paper, courtesy of some glossy ink-jet paper. It now looks like new again!
It took a couple of applications of cleaner while rotating the switch to different quadrants, but it now works perfectly.
In all, the Lincoln is a great monoband rig for 10m, but is ideally suited to SSB and FM simplex. You used to be able to order a new “Superchip” from the USA that would give you repeater shift, but at £50 plus it costs half as much as an average rig. The Lincoln is a bit bulky, especially compared with the Albrecht 485S and you can’t easily work through 10FM repeaters either, but it works well on SSB.
I thought readers might be interested in a quick review of the rigs, starting with the Albrecht 485S. This is also sold as the Magnum 257 which has a blue display background and not orange. Typical prices are around £199, although they come up on eBay secondhand for about £100.
The power output on mine is about 12W.
This rig is quite small and out of the box covers 28 – 29.7MHz. Press two buttons though and it opens up to include 25.160 to 29.699MHz in “bands”.
It is here that the rig shows its true background. It is really a CB, with AM, FM and LSB/USB modes.
As such it has some quirks that can be quite irritating to hams. Leaving it in ham mode and turning the tuning knob lets you move up and down the band in 10kHz steps. So far so good, but only if you want to work on 28.500, 28.510MHz etc.
If you want to work outside of these steps you have to press the “step button” which lets you switch to 1kHz steps. But now you have a problem. If you are on, say, 28.510MHz and hit the step button you can now tune from 28.510 – 28.519, but then it goes back to 28.510.
If you want to go 28.495 you have to switch back to 10KHz steps, move to 28.490 and start again.
This is really awkward and means that you can’t realistically use the radio mobile on SSB. However, its one saving grace is that it is brilliant for 10FM where 10kHz spacing is the norm.
The rig also has repeater shift, which is programmable. It took a few seconds to dial up 100kHz which is the standard and it will then happily tune 29.500 – 29.700MHz where the repeaters are –although I haven’t heard any European ones yet this season.
The rig also has an RIT, a noise blanker, a scan function and memories. On air it performed quite well, once you get used to the tuning.
The ability to scan the CB bands is also useful for finding out if 10m is about to open!
So, overall if you are looking for a lightweight, small mobile rig for 10FM it is brilliant. It is also OK for static mobile SSB work, but trying to move up and down the band while driving is recipe for disaster! Next the President Lincoln.
Update: I was able to buy some new buttons from Sharmans Wholesale for about £15 delivered.
Wednesday, 22 April 2009
Saturday 25th April 2009 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 gave a talk to my local club about the best way to win the award and you can download the presentation in PDF format (10Mb). It is aimed at UK operators.
You can also view my propagation predictions online.
You can find out more at: http://www.gb4imd.org.uk/
Pictured above are the operators at the Poldhu Amateur Radio Club who will be on this year as GB2GM.
Sunday, 8 March 2009
This a is a presentation I gave to my local club. It talks about finding DX, the modes to use, what you can do with QRP and CW and also looks at a number of antenna designs and what I found.
I have made it into a 3.8Mb PDF and you might find it interesting, even without the narrative that obviously went with it.
Download the presentation.
In an earlier post I talked about the Rybakov 806 vertical – basically, a 7.6m vertical end fed with a 4:1 un-un (unbalanced-unbalanced transformer), so giving a reasonable match across a number of bands.
In practice you MUST use an ATU to bring it down to 1:1.
Anyway, while playing with the design I tried wrapping the wire around an 8m fishing pole and had an idea.
If you push the pole up through the branches of a tree, taping each joint as you go, do you end up with a stealth antenna?
I think the photograph says sit all!
The pole is practically invisible and the leaves aren’t even out yet. Next to the matching box is a single earth stake and then two 20ft radials go left and right on the ground – you could bury them. I think it would work better with more radials.
My FT-2000’s built-in ATU was able to match it to 1:1 on 40-6m. The SWR on 80m is too high and the rig wouldn’t match it. Mind you signals were well down on 80m as the antenna is too short.
So how does it perform. On 40m it was either equal to or one S point down on an 80m 132ft OCF Windom on EU signals – you can just see the long leg of that in the photograph. Given the length is under a quarter wave this is quite good.
On 30m it equalled or outperformed the Windom slightly. This doesn’t surprise me as it is virtually a quarter wave on that band. The measured SWR was 3.6:1, which if you think about it is roughly 1:1 into 50 Ohms before it goes through the 4:1 un-un.
It was a similar story on 20m – equal to or just slightly down on the Windom.
The RR90 (Russian) beacon was down about 1 S point, the 4X6TU 9(Israel) and 4U1UN (New York) beacon was the same. VY2 (Prince Edwards Island) was down 2 S points. KQ2M (CT) was equal or slightly worse. K1RX (NH) slightly better.
It has to be said that compared with a dedicated half-wave horizontal dipole signals were generally 1-2 S points down, but that antenna is not multiband.
18MHz was barely open, but it was a similar story to 14MHz – roughly the same, some signals better, some worse.
21, 24 and 28MHz were not open, although as I have said before, it hears CB stations very well out to about 12-15 miles so I have high hopes for 10m.
So there you are - a stealth antenna that works from 40m – 6m for about £10 plus the pole. If you string the wire up into the branches you don’t even need the pole to be honest.
Wednesday, 18 February 2009
The equinox periods provide longer daytime periods than winter, but logically, shorter night-time periods too. These tend to be the best months for working North-South paths, such as UK to South Africa.
On 160m (1.8MHz or Top Band), look for short-skip and DX openings at night. Again, no daylight skip is 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 miles during the day. These will lengthen to around 500-2,300 miles at night with fairly good DX opportunities at times. At this point in the cycle 80m should still provide good DX as absorption is still quite low. Local communciation should be good as long as the critical frequency stays above 3.8MHz - register for the digisonde data at http://www.ukssdc.ac.uk/ionosondes/view_latest.html
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, again, 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.
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. Once again, 15m may struggle to open during times of low solar flux, but could provide good openings if it rises above about 90-100. 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, especially in early spring/late autumn.
Friday, 6 February 2009
I have no idea why this is called a Rybakov 806, but essentially it is a 7.6m vertical fed with a 4:1 Un-Un (unbalanced to unbalanced transformer) as described by IV3SBE.
It works very well with a fibreglass fishing pole and can be put up in a few minutes. The pattern (right) is what you get on 20m.
You need to put down an earth stake, and it really, really needs radials – the more the merrier.
The idea is that the antenna represents a non 1:1 SWR match at all frequencies – 7.6m is chosen as it isn’t actually a half wave (high impedance) or quarter wave (low impedance) on any band. The Un-Un (see below right) transforms the impedance to something closer to 1:1 and therefore reduces coax losses.
Does it work? I have tried a 7.6m Rybakov at a few locations and yes it does. Is it as good as a dedicated resonant antenna – no. You get losses in the Un-Un and there will always be a residual SWR on the feedline, which adds to the losses. You will also need to use an ATU to get the SWR down to 1:1, although most internal ATUs can usually cope with the mismatch.
As a matter of interest, here is the SWR I found with the 7.6m vertical (with the 4:1 Un-Un) with a single earth stake and two 20ft radials:
7.50MHz - SWR 3.2:1
10.1MHz – SWR 3.6:1
14.2MHz – SWR 5.6:1
18.1MHz – SWR 5.4:1
21.2MHz – SWR 2.6:1
24.9MHz – SWR 2:1
28.5MHz – SWR 2.1:1
The radiation pattern on 10MHz and 14MHz is typical of a vertical and good for DX. It is not so good on the higher bands as the antenna is longer than a quarter wave and gets complex.
It is also rotten on 80m (SWR 330:10) as it is waaaaay too short – if you extend the wire to 8.6m it will be better on 40m but you may as well make it a proper quarter wave (about 10.4m).
In tests it could hear local CB stations that were inaudible on my Windom, W3EDP or horizontal dipole. I know most CBers use vertical polarisation, but it shows that it might be good for low-angle DX radiation on 10m too.
It is a bit short for 40m, but does work. It was ok on 20m - some stations louder than on a Windom at 30ft, some worse. Same on 17m.
For 20m–10m use I think you are better sticking to 7.6m. The modelling shows that the radials are critical. You may get different SWR readings depending on how many you have. A single earth stake might give you a low SWR, but will be lossy.
If you have little space and like experimenting it might be worth a go, but I never found it matched a proper half-wave dipole at 30ft. More radials might help –if laying on/under the ground they don’t have to be resonant, just make sure they are roughly the same length as the radiating element and aim for as many as possible (32+ is good). If you try this antenna with just a ground stake I think you will be disappointed.
Let me know how you get on.
Sunday, 1 February 2009
Mine was catapulted over the roof at this QTH. It goes out of the ground-floor shack window, straight up, over the roof and then down to the end of the garden where it is tied off with fishing line, leaving the end about 10 ft high. The counterpoise goes off at 90 degrees (see illustration).
At the last QTH it went 50ft up into an oak tree. It is very stealthy and a firm favourite of the QRP fraternity.
It consists of an 85ft wire fed against a 17ft counterpoise. Some books say that you don’t use the counterpoise at all on 10m. Others say that you use a 6.5ft counterpoise on 20m. You do need an ATU though.
Some even say that you should feed it as a balanced antenna through a balun, rather than as an end fed with the counterpoise connected to the earth terminal.
I have tried it both ways and it seems to work either way. The tuning is slightly twitchier using it as a balanced antenna.
The antenna works well on 80m and 40m and even gives a dipole a run for its money on 20m. I am writing this as I listen to US stations on 20m and Californian and Michigan stations are actually slightly louder on the W3EDP rather than the 20m dipole.
DX worked on this £5 wonder include 6W/DL4JS Senegal, YK9G Syria, VQ5XF Turks and Caicos, VP6DX Ducie Island and VQ9JC Diego Garcia.
The downside of the W3EDP is that it can be noisier than a dipole and watch for RF in the shack. Running it with an earth wire to a stake and a counterpoise my field strength meter shows that it isn’t too bad though. Try one.
Saturday, 31 January 2009
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)
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
Feel free to download them.
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)
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.
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.
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).
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.
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