Wednesday, 17 June 2009

Long wire and Un-Un part 2


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

To understand how to construct an unun lets build a 9:1 version. You will need a T-200 (red) toroid and three pieces of wire, each 24 inches (60cm) long . It will also help if you a small plastic box with an SO239 socket mounted at one end and with two wing nuts or mounting posts at the other. In the UK you can buy a small plastic box from Maplin which is watertight with a rubber seal, yet inexpensive.

It will help if the wires are different colours, although that isn't critical if you have a multimeter available. It just makes it a lot easier to follow these instructions.

For the sake of this explanation I'll assume that you are using green, red and black pieces of wire.

Put the three pieces of wire together and wind them carefully onto the T130-2 toroid. Place the wires (left to right) green-black-red, and wrap nine turns on to the toroid.

Try not to let the wires overlap.

You should end up with a toroid with three wires extending from the left winding and three wires extending from the right.

Now twist and solder the left black wire with the right red wire. This can be covered with PVC tape once complete.

Now twist the left green wire with the right black wire. Strip the ends of the two wires, twist and solder them together leaving the length about 2” long from the toroid.

Finally trim and strip the remaining right green wire and solder another 5” piece of green solid wire to it.

Now take the left green wire and right black wires that you twisted together and connect them to the centre pin of the SO239 socket – this is the input side and will connect to your radio via a length of coax.

One of the green wires is now soldered to the ground connection of the SO239 socket. The other end of the wire you soldered on (which is connected to it) becomes the earth connection for the unun and typically goes to a ground stake and ground radials.

This leaves the remaining red wire which connects to the other wingnut and will become the connection for the antenna.

If you are worried about the wires unravelling you can either use PVC tape to hold them in place or plastic cable ties.

So how do we use an unun? Lets look at a typical example.


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.

80m
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.

30m
Lithuania similar. Other EU and Italy similar. Bulgaria down 2 S points

17m
Similar – inverted L has slight edge at times. Slightly noisier

15m
Better than Windom by about 1 S point.

10m
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

Long wire and Un-Un part 1

I have been playing with a 4:1 unbalanced-unbalanced transformer and a long wire. The theory is that the Un-Un reduces the impedance at the feed point to a point that your internal ATU can cope with.

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:

1.9MHz >30
3.6MHz: 10
7.1MHz: 3.0
10.1Mhz: 5.7
14.150MHz: 2.4
18.1MHz: 2.9
21MHz: 2.6
24.93MHz: 2.0
28MHz: 5.7

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.

HF Propagation report - Summer

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

World Radio - an online ham radio magazine


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.

Go to http://www.cq-amateur-radio.com and click on the WORLDRADIO link at the top left corner of the page.