I have added the ability to include a known velocity factor into the Slim Jim / J Pole calculator, to help with building them with 450Ω or 300Ω feeder. Also, here is a tested and reproducible Slim Jim for 70MHz (4m) made with 450Ω balanced feeder:
Selim M0XTA went to Happisburgh Lighthouse for the Lighthouse On The Air weekend 2015. He set up a 70MHz station on top of the lighthouse, using a ⅝ λ vertical. I had a listen from home and could just make out a signal in the local noise I get on 4m at home, so I decided to go out portable and give it a try.
I set up a slim jim made from 450Ω feeder on a 10 metre fibreglass pole on a small local hill (away from the QRM) and used the Anytone AT588 with 50w on FM. There was some slow QSB, but we made the contact. He was 105 miles from me (see map). Not bad for no beams and FM!
I took a tiny bit of video on my phone, which is below.
Some amateur friends (that sounds odd, but you know what I mean!) were playing radio this weekend from the Kelvedon Hatch Secret Nuclear Bunker in Essex. I decided on Saturday to build a 70MHz Yagi and have a go in the 70MHz Cumulatives contest. I had some spare aluminium and wanted an antenna with good performance that wasn’t too bulky and therefore easy for portable operation. I decided to build a DK7ZB design as I have had great success with them in the past.
I decided on Version 1 on this page. Its a 12.5Ω design and has around 8.4dBd gain. The gain vs size is excellent, matching Yagi’s almost twice the length, except this one I can fit in the car. The compromise is the narrow bandwidth, and therefore tolerances were very small and build was rather critical. I adjusted the antenna slightly in EZNEC to suit my ½” tube. First tests with the antenna showed that it was a perfect 1.0:1 SWR at 69.5MHz and 1.7:1 at 70.2MHz. I trimmed 10mm off each element and that got it spot on 70.2MHz. We did well in the contest and a QSO map is available. We worked 40 stations in 2 hours, which I think is good for 70MHz. Our best DX was PA4VHF at 449km.
Thanks to George M1GEO for allowing me to use the site and Dave M0TAZ for the use of his mast!
I recently bought a Baofeng UV-3R+ 2m/70cm handheld. I always said I would never buy a Baofeng, but I wanted something cheap that I could throw about at work and not worry about. Anyway, we all know that you get what you pay for in life. It comes with a desktop charger, which had a problem. It has a USB cable and a small DC jack which plugs into the base itself. When I first plugged the DC plug in, it felt weird. It did work, but you had to fiddle with the plug to get it to make a connection. What happened is it had pushed the centre pin of the small DC socket backwards, because it must have not been central in the socket.
To fix it, I decided to drill a small hole above the socket, just big enough for the cable, cut the DC plug off and solder the wires direct to the PCB.
Fixed, no connection problems now!
Hmm, what to do on a bank holiday Monday? Well, we decided to purchase the aluminium to build a 15m and 10m Yagi about 6 months ago, so it was time to make something of it. Dave M0TAZ is building a 4 element 15m Yagi, and I am building a 3 element 10m Yagi. Dave started constructing his 15m beam this week. It is a DK7ZB 28Ω feed-point 4 element Yagi, with a forward gain of ~6.4dBd. The elements are tapered with 3 different sizes of tubing and the boom is 40mm square and 5m long. All that’s needed now is the feed-point arrangement and it’s ready for testing! Still, it looks great and is very rigid. Cant wait to get it on the mast! Here are a few photos for now…
Our club took part in Operation Bunker at the Kelvedon Hatch ‘Secret’ Nuclear Bunker at the weekend. Operation Bunker was a military vehicle, memorabilia and re-enactment weekend attended by vintage military personnel from all over the South East.
We operated the bunker special call GB0SNB from beside the main mast, using SSB, CW and Data modes. In total we contacted 368 stations in 47 countries around the world. Our best DX was into Chile at 11,330 KM on 14 MHz digital modes. I used my IC-7200 for data on Saturday, with my end fed half wave vertical on 20m and higher bands. On the Sunday, we used an IC-7100.
At the weekend, we took part in the RSGB RoPoCo (ROtating POst COdes) contest, which is always fun. We operated with Dave’s call, M0TAZ, from a portable location. Last year, we did really well, and we had zero errors in the log. Activity seemed a bit lower this year, but we did start 10 minutes late as Dave M0TAZ forgot to bring a key part of the equipment, the battery! We worked 47 stations in an hour and twenty minutes.
Its always funny when you are given odd exchanges. I remember last year we was given 001 to pass on rather than a postcode and this year was no different, with a few odd exchanges but we just passed them on as there’s not a lot you can do! We used my IC-7200 with a half wave inverted v, 11m at the centre.
Look forward to next year and I’m sure
we Dave wont forget the battery next time
I have always been a Linux fan and have owned a Raspberry Pi for some time which I use for all sorts of things. A new model was released in February, the Raspberry Pi 2 model B, so I got one. It’s quite impressive with its quad core 900MHz cpu and 1GB RAM.
Now my old model B+ was redundant, I decided to set it up as a home server to run some services that I was previously using a cheap VPS for. The server is at http://j0hn.uk and is pictured below.
The B+ has a 700 MHz (clocked to 800MHz) ARM1176JZF-S CPU, 512MB RAM and is using an 8GB micro SD for Storage. It is a very capable little machine and is running many server applications. Power is provided from an iPhone charger at present, but I am currently building a UPS for the Pi, but as of today, its been up since first boot, 26 days ago.
The Raspberry Pi is a great tool for all sorts. More info is at raspberrypi.org