Sunday, March 30, 2014

ARNSW Home Brew Group - Smart phone and tablet apps for Ham Radio

Today at the ARNSW Home Brew group, a different kind of meeting. We turned to a survey of applications for Ham Radio that run on popular tablets and smart phone. Convener, Peter, VK2EMU rigged up an impressive camera on a tripod to project devices on to the big screen.

Peter showed a number of apps that generate audio tones, including sweeps, white and grey noise for measuring frequency response. We announced our plans to bring a tone source for an RF generator to iOS. I showed some phone apps including Morse and PSK31 decoding, antenna calculation and naturally I plugged my own free app for watching WSPR spots called WSPR Watch.

There was some home brew electronics on display with another great project from Stephen, VK2BLQ, showing a Drew Diamond design with the addition of a PIC based frequency counter.

The meeting did decline into a bit of an Android vs iOS discussion and we ended up discussing the demise of support for Windows XP and what that might mean for those who cling to it. I mentioned that people who see an iPad or iPhone as being out of reach should consider an iPod Touch as these start at AU$249 and run all the same software as an iPhone.

A huge turn out today, perhaps due to the weather, all kinds of interesting transport was on display, this one with space for your gun.

Today was also the last meeting with John, VK2ASU in attendance before he heads north to his new QTH. John has been a generous contributor to the group, net coordinator of the Home Brew nets over many years and super helpful to us newbies - we will miss you mate.

Sunday, March 16, 2014

iOS icon resizer script

Goodness, iOS 6 & 7 needs a lot of different icon sizes for a universal app. I wish Apple would support SVG. Here's my little script to resize a large icon down. It requires Imagemagick.

# Usage: bigicon.png
# You need to brew install imagemagick
filename=$(basename "$1")
echo "resizing ${filename}..."
echo "filename = $filename"
for size in 29 40 50 57 58 72 76 80 100 114 120 144 152
    echo "$filename$size.png"
    convert {$1} -resize $sizex$size $filename$size.png

This is a note to myself really.

Made an Unun for feeding end fed wire antennas

Following pictures and diagrams from M0UKD, I've built up a 9:1 impedance transformer sometimes called an Unun.

This transformer meant that a random wire strung up on the balcony could be quite easily tuned up and achieved a 1.1:1 SWR without too much trouble.

I guess the name Unun is an adaption of Balun which is balanced to unbalanced whereas this is unbalanced to unbalanced.

Here it is all boxed up. My thanks to Stephen, VK2BLQ, for the loan of his excellent drill press.

As a test, I hung out only a few meters of wire with a short counterpoise and the antenna analyser looked pretty good near 28MHz.

My plan is to get on air with this tomorrow night for the home brew group net.

Saturday, March 15, 2014

Got to talk a little about ham radio on ABC Classic FM

The WIA is doing some work on promoting Ham Radio and this week I had an opportunity to do my bit. I was invited to be a guest on Margaret Throsby's Midday interview on ABC Classic FM.

Here she is ready to ask me a wide range of technical questions in the relaxing Classic FM studio. (14 seconds to go!)

If you wish, you can hear the interview here. I got to talk about my love of the Ham Radio hobby and the Home Brew group along with many other topics of interest to me at least.

I'm used to doing short pieces of technology explanation and analysis so the prospect of being interviewed for most of an hour was somewhat daunting, but the music helps to break it up and Margaret and her team were lovely to deal with.

FT-897 vs KX3 transmission bandwidth

I'm trying to talk with old friend Ralph, VK3ZZC, who's in Melbourne, about 1,000km away. He's on 10m which is a band I've never used before - so that's an interesting experience.

So far, no luck, but Patrick, VK2PN, kindly agreed to a contact so I could make sure my signal is getting out. Recently I purchased a second hand FT-897, a portable rig with built-in high capacity batteries and have been using that. Patrick wasn't too impressed with the transmission and sent me this image from his panadapter.

He rightly complained about the out of audio band signal and urged me to go and get the KX3 for comparison. The FT897 is running 20W and the KX3 10 so the signal levels are different but take a look at this:

The KX3 seems to transmit much more in the right band and suppression of the opposite side band is clearly superior. It's a much better rig.

Now, the FT897 has an optional SSB filter which can be used on transmit and I'd be interested to know if that helps. Thanks Patrick and do check out Ralph's web site - it's most interesting.

Tuesday, March 11, 2014

Simplest antenna - open wire fed dipole

Spurred on by the ARNSW Antenna day, and illuminated by a comment from Mal, VK2BMS, that alerted me to the fact that I've been using my Emtronics EAT-300 tuner incorrectly; I had a go at the simplest antenna - a dipole fed with a slotted ribbon.

Cut for 10m, this tiny dipole is held out from the balcony on a 6m squid pole (the heavy half is inside so it doesn't fall off). The slotted 300 ohm ribbon was 30 cents a meter at Paddy's Market. I hold it away from the metal railing in a little string sling.

I've tried open wire feeder in the past but could never find a low SWR resonance point  - it turns out the EAT-300 tuner needs a link between the single wire terminal and one side of the balanced line. There's a dotted line printed on the box but I never understood what that meant.

I'm running 20W here but when I skeptically responded to a CQ call from Charlie, VR2XMT, in Hong Kong he immediately responded and gave me a 57 which is pretty good.

The open wire fed dipole seems much wider in bandwidth than a similar co-ax fed dipole.

Obviously, while an open wire feed works for me in a location where I can get from the antenna to the tuner without encountering much metal, it's not good for other antenna - shack arrangements.

Once again, using a squid pole to push the antenna out from the building makes a huge difference compared to being on the balcony with concrete and metal all around. I'm up high enough and the squid pole and antenna is thin enough to be virtually invisible from the ground.

Sunday, March 09, 2014

ARNSW Antenna Day

My sincere thanks to the committee at Amateur Radio NSW for organising a wonderful "Antenna Day" today at Dural.

The day was a relaxed mix of informative guest speakers (my special thanks to all of them), some hands-on construction, and Commander Al making puns and deafening us with his hooter.

We learned about many interesting antenna variations from dipoles to more elaborate multi-band antennas.

There was home constructed and some nifty bits of commercial gear including this cute little tuner from Elecraft.

Everything from 160m to 2m was discussed.

For a small price of $10 those interested got a very nice dipole coax centre insulator and time to put it together.

We were lavished with tea, cool drinks, a BBQ and in the afternoon ice cream and fruit!

It was a beautiful day all around as you can see here. Incidentally, the second hand store is very well stocked at the moment too.