18 February 2014

Triband Delta Loop antenna - some theory


Looking for an improvement in my station's configuration, I evaluated a number of antenna designs; the most important thing, wether some like to admit it or not, is what possibilities you have for installation. What type of ground, how high can you put it, is the surrounding space opened enough towards the horizon, are there elevated points you can use for support, what kind of weather it will have to endure, how can you properly make the safety grounding etc.

All these factors are very important in the choice of an antenna, and i'll come up with a quick example: a ground mounted L/4 vertical above salt water (let's say, on the beach of a small oceanic island) for the 40m band will put out a DX signal similar to an horizontal dipole mounted at about 30m high (horizontal antennas need height to obtain better gain at lower takeoff angles), and the dipole will need to be rotated towards the direction you want to work while the vertical is omnidirectional. If you look at the costs of building a 30m tall tower, adding a rotator to it and the mechanical challenge of making it stable in saltwater-impregnated sand versus the costs of a few wires and a 20m tall lightweight fiberglass pole, the choice is a no-brainer. However, move the same setup above a poor, dry ground (let's say, Sahara desert) and the horizontal dipole will be a much better antenna - and while you have a tower and a rotator you might as well make the dipole a 3 or 4 element Yagi and get an ever better signal.

What i tried to get is a versatile 20m/15m/10m antenna that offers good gain and is easy to build, install and work with. I have used full wave loop antennas before and liked them alot, especially for the rewarding performance/complexity ratio. You just need a wire, cut it at about 105% of desired wavelength, spread it as you can and off you go. When properly installed (vertically, as spread as possible), a closed loop antenna has some advantages over a dipole:

- slightly higher gain (about 2dB)
- less noisy
- less sensitive to height
- less influenced by the surrounding objects and enviroment


05 January 2014

YO9IRF station updates

Giving the fact that I had enough spare time the last two weeks, inbetween the little Christmas trip I took back to my home town of Ploiesti and the New Year's Eve party, I had the change to propery get my station back up on the air. Since I moved to the new location in June I didn't really have a proper setup and the few times I got on the air was with some modest balcony antennas.


Click to enlarge

The image above is a Google Earth mock-up of my current antenna setup. The red one is the HF dipole, the blue one is the VHF/UHF vertical and the green lines are the two feedlines.

The HF antenna is a an off-center fed dipole (OCFD) 41.8 meters long; this makes it resonate - when properly installed - on 3.5MHz, but on all it's harmonics also (7MHz, 10.5MHz, 14MHz, 17.5MHz, 21Mhz, 24.5Mhz, 28MHz etc). We usually feed dipoles at the center but due to the current/voltage distribution across the resonant wire, it will present a low (close to 50ohm) impedance only at the uneven harmonics (3.5Mhz, 10.5Mhz, 17.5Mhz, 24.5Mhz etc), while at the even harmonics (7MHz, 14Mhz, 21Mhz, 28Mhz etc) it will present a very large (theoretically infinite, practically a few thousand ohms) feed impedance, wich is very far from out 50ohm feedlines making the antenna unusable due to high feed mismatch.


27 November 2013

Steve Jobs influenced by ham radio

Steve Jobs and was undoubtedly one of the most influencial persons of the last 30 years when it comes to communications and computer technology, and his approach to both technological solutions and product marketing is something to be studied for many years from now. At the origins of what many call "Steve Jobs' genius" stands also the right enviroment and opportunities from his youth, and this interview shows how Jobs admits that as a kid, spending time with an amateur radio operator neighbour was an eye-opener for him towards electronics and how people percieve certain technology-centered products. The guy's name is Larry Lang and he was an enginer at HP at the time, and he showed Steve how to build Heathkit radios; unfortunately, his callsign eludes my Google-Fu. Skip to 05:40 into the video if you are looking especially for this part, but the whole video is worth watching if you have a spare 60 minutes or so.




Also, his partner since before Apple Computer ever existed, Steve Wozniak, is also a ham radio operator since he was 6, initally WV6VLY and then WA6BND. Wozniak built his first radio when he was 10 years old and his passion and enthusiasm for electronics and technology was one of the huge assets in the first days of Apple Computer. But don't trust my word, watch this video (after about 2 minutes in):


01 November 2013

HF One MKII - cheap mobile transceiver with SDR technology


HF One MKII is another big step towards a good and cheap HF QRP transceiver. Less than 8 months ago we saw the Xiegu X1M, a small 5W SSB/CW transceiver for HF that costs under US$ 300 and weights just 500grams, bringing serious competition to the Yaesu FT-817 for those QRP mountain hiking afficionados out there. This time, the chinese electronics industry brings us for about the same price - US$ 300 + shipping, a much more refined looking product based on SDR technology and with 10W power output.



Sure, the HF One MK II mostly looks like a mobile radio you would see in a taxi and not like true ham radio equipment, but this is just until you find out the best thing about it: because it's packing SDR technology it has I/Q outputs and the modest front panel can be replaced with a proper full-fledged software like PowerSDR, the moment you hook it up to a computer. Ta-daa, the meager black plastic box suddenly provides contest-class transceiver features.

28 October 2013

UT-100 - SDR USB dongle transceiver

The RTL2832 USB dongle recievers are already common knowledge among many radio amateurs and a way to introduce the SDR technology to everyone - although i'm not fond of it, given it's poor performance. We are basically talking about a TV-tuner using custom software that allows it to work just as a ham radio reciever, with the obvious limitations of a US$ 10 product no bigger than my thumb. Because they are cheap and they offer a wide frequency coverage though, they got really popular and manufacturers even started making them especially for amateurs.


Next need though would be transmit capabilities; enter the Hides UT-100, an USB dongle with transmit and recieve, the same wideband coverage, but with a heftier price - around US$ 200-230.



24 October 2013

Copy.com - 15GB of free cloud storage

Copy is the hottest thing right now in free cloud storage solutions. Yes, everybody loves Dropbox, Google Drive and Microsoft Skydrive are trying the same thing with moderate success, but none are really offering enough space to sync all your docs. Enter Copy, with 15GB of free cloud storage and the possibility to get infinitely more (still free), backed up by the data storage and backup giant Barracuda Networks and with a rapid growth during the last few months.


What is cloud storage ?

For someone who is not familiar with cloud storage yet, this is how it basically works: you install the Copy software on each of your computers, laptops, smartphones, tables and whatever else runs a compatible operating system and you designate a folder on each device and that folder will be copied and then kept in sync across all devices and also on the Copy servers. Whenever you edit a file on one device, the new version will be copied on the other devices as well, so if you add a new set of pictures for example on your tablet it will almost instantly be available on your desktop; of course, on mobile devices by default the content in only uploaded - so it won't clutter your smartphone with huge amounts of data and kill your dataplan, but if you want to download something from the cloud it's readily available. They have apps for Windows, Android and IOS so no issue there. You have the possibility to share some files or folders from your Copy folder to others, and while it's shared you also share the space taken: a 1GB file shared with 3 other users will be accesible to all 4 of you and will only take 256MB out of each one's space.


23 October 2013

The Red Tent - must-see movie for radio amateurs

The Red Tent is one of those great movies that masterfully combines action and drama with historic accuracy, keeping you both strapped to the seat to watch the story unfold and giving you something to think about afterwards. Contrary to what it might seem at first, it is not a light sunday afternoon movie and the entire setup - even if it was done almost 45 years old - is a fine example of cinematography and camera work. Adding to that some great acting, the names of two Oscar award winners - Sean Connery and Peter Finch as well as the ... beauty contest winner Claudia Cardinale, this is a recipe for a must-see movie.