Friday, 27 January 2017

A shortened multi-band End-Fed Half Wave (EFHW) antenna for 80-10m

The 80-10m EFHW
This is a shortened multiband antenna, about 23m long, for 80m-10m that offers low SWR (1.3:1) on 80m and 40m, and below 3:1 on 20, 15 and 10m. The antenna has almost 300kHz bandwidth on 80m between 3:1 SWR points. But performance is down about 8-12db on a dipole on 80m.

This design came from attempts to find an 80m antenna that could fit into a small space. This was because Norfolk Amateur Radio Club likes to take part in the 80m Club Championship (we won in 2016), but many members don't have enough space for a full size (132ft) dipole or the 100-102 feet needed for a G5RV or W5GI antenna.

This antenna lets you get on to 80m in a horizontal distance of about 12m (40ft) when used as an inverted sloper with the apex at 8m, although you'll be down a couple of S points on a dipole. But if the other station is 59+20dB, you'll be about 59 +5 or 10db, so all is not lost!

I take little credit for this as it was outlined in PD7MAA's and IK0IXI's blogs after extensive work on the antenna in the Netherlands. However, there was little on their blogs in terms of its performance or SWR characteristics. Hence this write-up.


Download the 80-10m EFHW antenna guide

Update 29/1/17:
I've updated the guide to look at replacing the coil with a 7MHz trap and also putting the antenna up as an inverted V.  The trap and about 14.2m of insulated wire would improve the 80m performance a little, if you have the space, but possibly at the cost of the 14MHz performance. Surprisingly the MMANA-GAL model suggests the inverted V would be worse for 80m NVIS communication.

Update 09/02/17
I thought I would bite the bullet and took the wire and loading coil off and replaced it with about 130ft of insulated wire. This needs some final tuning, but gives a low SWR across 80 and 40m, and SWRs below 3:1 across the higher bands. Performance seems to be similar to a 100-foot W5GI dipole. I'll add the actual SWR figures to the PDF. This is OK if you have the space. The last 10m (33ft) of wire has to go along a wooden fence at my QTH.

Monday, 9 January 2017

HF and solar conditions continue to decline

I've now updated my hourly HF propagation charts for the UK for the next three months.

The charts, with real time solar information, can be found at http://www.infotechcomms.net/propcharts/
You can definitely see the effects of the current poor solar conditions. As the charts are produced by VOACAP it is suggested we use the smoothed sunspot number (SSN) for the calculations.

In January 2016 the SSN was 44.8, but this month it is just 29.2. In fact, the actual daily sunspot number is even lower than this at around zero to 11 with a solar flux index in the low 70s.

Given that at sunspot minimum we wouldn't expect the solar flux index to drop below 66 you can see that we are very close to the kind of conditions we can expect over the next few years.

NASA says the current sunspot cycle is the smallest since cycle 14, which had a maximum smoothed sunspot number of 107.2 in February of 1906.

The current prediction for sunspot cycle 24 (this one) gives a smoothed sunspot number maximum of about 101 in late 2013.

The next sunspot minimum is currently predicted to occur around 2019-2020.

The solar maximum for cycle 25 is predicted to be around 2025, possibly with a monthly smoothed maximum sunspot number of around 60-65. If true, this is almost down to Dalton Minimum levels.

What we are seeing is that the ionosphere is currently struggling to regularly open up to DX at frequencies much higher than about 18MHz. Around the UK we are even finding 40m (7MHz) closing to inter-G contacts by early afternoon, if it opens at all.

This means that 80m (3.5MHz) and 60m (5MHz) are coming into their own, although both are struggling with inter-G contacts by late afternoon.

A succession of coronal holes and their associated high-speed solar wind streams are also causing disruption to the ionosphere. While these are typical of this point in the sunspot cycle they are generally not helping DX at all.

This week's high K indices have been caused by such a hole, although the solar wind has mostly had a north-facing Bz field, which is less likely to couple with the Earth's magnetic field, and we have't seen the very high K indices that indicate severe auroral conditions.

Lastly, readers might be interested in a new HF propagation tool based on the ITU's ITURHFPROP software and developed by Gwyn G4FKH. The URL is http://www.predtest.uk

The 'Area Coverage' predictions have been available for some time, but a new Point-to-Point prediction tool is now available. Clicking on the link starts the process, when the form is filled out a series of plots are available depicting propagation between the required Tx. and Rx. sites.

New features include various colour schemes for the plots allowing users with colour preferences to make the best viewing choice for themselves.

Steve G0KYA

Monday, 2 January 2017

Some Christmas QRP HF operating

Elecraft K1 on 40m QRP frequency.
The period from Christmas to the New Year is traditionally the time for the GQRP “ Winter Sports”.

I don't take this too seriously as there are plenty of other calls on my time, but it is an opportunity to get on the air and work a few stations with 5W CW or 10W SSB.

This year got off to a good start with a contact on 23rd December with SK6SAQ at Grimeton in Sweden – home to the Alexanderson alternator that puts out a 200kW signal on 17.2kHz.

SAQ also has a special event callsign so it was good to get operator Kjell in the log using 5W from a Yaesu FT-991 into an outside EFHW. I really must visit Grimeton one day.

I also dragged out my Bencher paddle as I was sending some awful Morse with my Kent single lever I think I was getting key bounce so will have to take a closer look. The Bencher was fine, which was good news.

After Christmas I turned to my Elecraft K1, which I finished in the summer after owning the kit for about 12 years!

This brought CW QSOs with Peter OM0WR in the Slovak Republic on 7.029MHz with 5W into my loft-mounted zig-zag dipole.

The YT160TESLA QSL card.
Then it was YT160TESLA on 20m celebrating 160 years since the birth of Nikola Tesla in Serbia. I really want their QSL card which looks great and worked them on 40m in March. As they went QRT at the end of 2016 it really was a last chance.

I have an Icom IC-7300 on test, which belongs to my local club and that brought 9A1700SBD in Dubrovnik, Croatia, although it took 25W to get through.
The view across the rooftops of Dubrovnic, Croatia.

2016 was the 1700th anniversary of St. Blaise, patron saint of Dubrovnik – if you ever get the chance to go there, do as it is absolutely beautiful.

Station LZ463PP then went in the log with 10W from the IC-7300 and a W5GI dipole on 17m SSB, so still QRP. It was celebrating 463 years of Saint Patapii.

Finally I had a nice (but weak) QSO with Ian EA7JUK in Lubrin, Spain on 20m CW using 5W from the K1 and an indoor dipole. Ian's UK call is G0WHX.

The Reverse Beacon Network proved everything was working!
Sunday 2nd January marks the QRPARCI New Year's Day Sprint, but I really didn't expect to hear anything from the US due to rotten HF conditions. If I do I'll update the blog!

So, I heard a lot more stations than I worked, but I had fun – which is what it is all about.