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Archive for July, 2012

Aurora 15 July 2012

July 16th, 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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Posted in nature, radio

Tags: 144MHz DX science

K8GU/5 Field Day 1B1Op Battery

July 1st, 2012

I found myself in Santa Fe, NM, for Field Day this year to attend a conference. As I have shared before, I have mixed feelings about Field Day, but this was a genuinely good time. I first checked ARRL’s Field Day finder map and the local club’s web site for activity. Zilch. So, I remembered staying at the Fort Marcy Hotel Suites on several previous visits to Santa Fe. These condos are up on a hill overlooking town. Across the street is Hillside Park, with a couple of scraggly trees that might be suitable for antennas.

Instead of bringing the “usual” portable station, I brought a Small Wonder Labs SW-40, a K1EL K12 memory keyer (assembled especially for this trip), Palm Mini paddles, a 40-meter dipole, and a AA battery pack. The whole station took up less space in my luggage than my notebook computer and set up in 15 minutes. I got the dipole center about 4-5 meters off the ground and the ends sloped down to about 2-3 meters high…just enough to allow cars and small trucks to pass under them in the parking lot. Apologies for the photographs…they were taken with my cell phone (which is a regular old “dumb” phone).

The SW-40 did not appear to be transmitting correctly when I first hooked everything up. So, I pulled the cover off (packing a Leatherman tool is another good reason to check a bag) and wiggled some wires around until it fired up. Not an auspicious sign.

But, I did manage to operate for about an hour and make 12 or 15 QSOs. They’re logged in a notebook, but I haven’t looked at it since making the contacts. Virtually every QSO was a struggle. Low power (1.5 watts), wrong band (20 meters would have been better), a low antenna, and the fact that I hadn’t used the SW-40 for any QSOs in over 10 years, conspired to make thing difficult. Most operators pulled me right out once I was in the clear and zero beat (which I think was a serious challenge with the slightly drifty and definitely touchy SW-40).

My final QSO was with my old radio club from my college days, W8FT. The operator was my good friend Bill, AD8P, who worked hard to pull me out once he got my call right. After I packed up, I noticed that I had a missed call on my phone…sure enough it was from Bill. So, I gave him a call and we talked for a couple of minutes. “When he answered the phone, he said, `New Mexico?!?! I told Kelsey (N8ET) that’s what I had copied.'” We had a nice chat as I hiked back down the hillside into town and he pulled into his driveway after his FD shift.

I don’t think I’ve ever been so delighted with a Field Day effort of so few QSOs (except maybe my first Field Day, which was much more work for about twice the number of QSOs). Including the walk from my hotel to the park, setup, tear-down, and operating, I think the whole exercise took about 3 hours, and was tremendously FUN.