Posts Tagged ‘144MHz’

UK Activity Contests

Every Tuesday evening the RSGB organises a VHF/UHF activity contest.  I have just in time submitted my entry for the low power section of last Tuesday evenings 50MHz contest. With just 3 QSOs logged there is no way on this earth that I’ll be anywhere but near the bottom! Having a V2000 omni vertical antenna, 5W, and a stroke damaged voice is no way to enter a 50MHz, UK based, contest! The V2000 and even 2.5W is great in the Es season (I work most that is around), but it is far from ideal working inter-G on 6m SSB.

Tonight is the 144MHz (2m) March leg of the UKAC. My small 3el beam should turn again now (manually) so I’ll see how long my voice holds out. 45 minutes to 60 minutes is usually my limit. Last week I was on very little time. My best DX seems to be around 200km with 5W on 2m in “normal” conditions.

At this time of the year there are fewer portable stations active but activity (SSB and CW) is usually very high so this is a good opportunity to work some new squares. People have been very friendly. If in the UK or nearby join the fun 2000-2230z on 2m.  I usually go QRT by 2100z because of the strain on my voice.

Just checked where I sit in the Jan 2015 AL section of the 50MHz UKAC. You guessed? Bottom! Well someone has to be!

Fredbox derivatives

Since my original Fredbox 2m AM design, a number of derivatives have been designed and built around the world. This is what our hobby is all about. Although the original Fredbox worked well and its results surprised me, it was always ripe for further developments, which is healthy. My Sixbox was a 6m version and at some point, when fitter, I’d like to make a simple 10m AM version for local natters.

See https://sites.google.com/site/g3xbmqrp3/vuhf/fredbox for the original Fredbox. Click on the schematic to enlarge. Other derivative ideas are on my website www.g3xbm.co.uk.   By the way, it got its name from Fred G8BWI who was a disabled local in the Cambridge area back in the 1970s. Fred was a regular contact and he could talk for hours and hours and hours and hours zzzzzzzzzzz. RIP Fred.

2m UKAC results

Last night I went on 2m SSB with 5W in the monthly UKAC activity contest. After 1 hour and 40 minutes I had to stop as my voice was gone (stroke).  Best DX missed was GI6ATZ in N.Ireland. I called him a few times without success.

In all 16 QSOs were completed showing that modest power and antenna from the home QTH is enough to enjoy the contest. Had I stayed on longer I’m sure I would have worked more squares. Quite a few stations in northern England worked too on the small, hand rotated, 3el beam, from the home QTH.

Looking at the map, I should have turned the beam towards the SW.  Hardly likely I’ll come other than close to the bottom, but that was not the point – it was good fun taking part.

2m stations worked with 5w/3el UKAC June 3rd 2014

The ‘C’ Word

Can I mention the ‘C’ word?

I mean contests. I refuse to call it sport radio as to me a sport involves sweating and physical discomfort. Sitting in front of a radio shouldn’t be uncomfortable. If it is you may need a new chair.Yes, there’s an element of competition, but that’s also true for growing the largest marrow. Anyway on to the point of this post.

Today was a first for me, the RSGB 144Mhz AFS contest was on and I thought I’d give away a few points, so instead of plonking the 5 ele yagi in the loft and leaving it in one place I put in on the end of my aluminium telescopic (wobble-o-matic) mast. The results were never going to be exceptional given I seem to live underground as far as rf is concerned but it was nice to give away a few points to those with higher real estate.

I’ve decided to give the UKAC contest a go as a ‘proper’ operator from a nearby hill and will use that kit with the FT-817 because I don’t have batteries for the IC-7000. If anyone is concerned if I’ve caught the contesting bug, I don’t think so, as today had most of the daylight spent at a local theatre and ‘A Muppet Christmas carol’. 200 kids, mince pies, snot and Marmite and someone dressed up as what looked like the Easter bunny with stick on horns. Both our kids were fairly sure it was Rudolph so that’s good.

QRB was Devon for me today, which was pleasing. All with 50w and a small yagi on the end of a pole. Lets see if I can improve on Tuesday night. Glad to see I’m firmly rooted to the bottom of the table though.

Aurora 15 July 2012

I was enjoying a leisurely sweltering summer Sunday afternoon in the back yard with Evan, Sarah, two Adirondack chairs, a kiddie pool, and the schematics for an IC-290A I have on the bench.  I came in to get a glass of water and while I was inside, I checked my e-mail (since I have some equipment for sale).  No prospective buyers, but I did have a message from Sean, KX9X, that he was working aurora on 6 and 2 meters.  I quickly plugged in the 2-meter rig and swung the beam around to the north.  Sure enough, there were raspy aurora signals all over two meters.  I quickly put N9GX (EN60) in the log for my first ever aurora QSO.  This was at least as cool as working K5QE on 2-meter Es with 10 watts.

So, I fumbled around a drawer and pulled out a cable to connect the TS-700S to the computer and fired up Audacity.  I made this interesting recording of KA1ZE/3.  I started out with the beam to the NE (45 degrees azimuth) with a strong auroral buzz on Stan’s signal.  Then I swung the beam around to the NNW direct path (345 degrees azimuth).  I’m in FM19la and he’s in FN01xt, which is exactly 200 miles (322 km) direct path.  On the direct (forward tropo scatter) path, there is still a hint of aurora, but the tone is a bit purer.  When I turn the rotor there is pretty bad hum from a (not unexpected) ground loop.

In order to better visualize a few things, I ran a short-time Fourier transform (this is the actual technical term for a “waterfall”) on the audio file.  I need to code-up a polyphase implementation of the FFT like that used in Rocky, but there are only so many hours in a day.  Click on the image for full-size.

There are lots of interesting details here.  First, you can see that the auroral scatter is both Doppler-shifted (lower in frequency) and Doppler-broadened (spread out from the central frequency) compared with the direct tropo scatter signal.  Second, you can see the ground-loop-induced hum at the low-frequency end.  Auroral backscatter comes from field-aligned plasma density irregularities embedded in the auroral convection flow.  Because most readers will be allergic to the vector math, we make the (somewhat gross) approximation that KA1ZE and I are transmitting and receiving from the same location.  Now, we can take a stab at estimating the flow velocity from the following equation:

Where delta-f is the Doppler shifted frequency (about 300-Hz from these data), c0 is the speed of light (300,000,000 m/s), f is the carrier frequency (144 MHz), and vflow is the flow velocity.  While we’re making approximations, if we round f up to 150 MHz, the twos cancel and we get the Doppler shift of 300 Hz corresponding to a flow velocity of 300 m/s (670 mi/hr).  Fast!  Because it is lower in frequency than the direct signal, we can also infer that the flow was directed away from us.

There you have it!  Science fair projects with your ham radio.


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