Monday, October 18, 2010

Spectrum and Band Occupancy

Dan, KB6NU, has some good reasons to worry about 300-3000 MHz competition for amateur bands.
American Radio Relay LeagueImage via Wikipedia
Right on.  At least frequencies below 300 MHz are under less pressure, which is a relief to us HF & 2M troglodytes.  Still, vigilance is required.  Support ARRL.

There is a problem with the VHF and higher bands that doesn't get a lot of attention.  Amateurs are not very good at utilization.  The bands are almost always completely empty, and this makes them targets for commercial use.  Around here in CT, the 2M repeater segments are mostly allocated and unavailable for new applications, but they are still unused most of the time.

Multiple PSK31 transmissions on the 20m digimo...Image via WikipediaBy contrast look at 14.070 - 14.073 kHz. I can often copy dozens of PSK31 QSOs in progress there in 3 kHz of spectrum.  Also look at the cell/CDMA bands that support 100s of "QSOs" in a few MHz all the time.  Hams do need to pay more attention to band occupancy.

Tuesday, October 12, 2010

BARTG RTTY result

My first ham contest in a long time was the BARTG RTTY affair in March.  I just checked up on the results and found where I fit into the grand scheme of things.  I don't feel bad about it, though there's a lot of room for improvement! (These are the 328 "non-expert" full contest entries.)

Sunday, October 10, 2010

More U-verse work

I did some more testing on U-verse vs HF QRO operation today.  The main results are reported at http://aa6e.net/wiki/Uverse, which is going to be where the data from this work is accumulated.  We only give the late breaking news here.

As expected, winding the incoming DSL line on a ferrite core (8 turns, type 77) has helped a fair bit -- allowing a doubling of amplifier power on a good range of frequencies.  We also see that the U-verse DSL does not show any problems for QRO at 20 meters and up.  80 and 40 (and 160) are going the be the troublesome bands.

But we have more countermeasures we can try.  That will be for another day.

I also have trouble with my carbon monoxide detector going off.  (It's very loud!)  And pickup in my computer loudspeakers is annoying on 40 M.  All this will yield to filtering.

Wednesday, October 06, 2010

Uverse vs 80 meters

So, we've finally got to the point of some stability with Uverse in the house for TV, Internet, and telephone service.  That is, without doing much ham radio.

I discovered a nice tool, U-Verse Realtime, which lets you show many parameters of your Uverse operation. It's free software for Windows machines, and it seems to work in my virtual Windows XP machine.  (VMware under Ubuntu Linux.)

The first bit of science is to measure my "bitloading".  That shows what parts of the frequency spectrum are being used for the underlying DSL connection.  The results:

The chart shows that frequencies between about 100 kHz and 3.7 MHz are used for download (yellow), while 3.7 - 5.0 MHz are used for upload (green).  There is a small higher region, about 5.3 - 5.5 MHz also allocated to download.

The increasing line attenuation with frequency is apparent.  (At least, if you believe that "bitload" has something to do with signal power.  I don't really know that.)  The electrically measured line length from the Uverse node is 2554 feet, which puts me in the lowest of 3 service tiers.

OK, second science test.  The active DSL spectrum includes the 80 and 160 M ham bands.  What's the interference potential?  This is not a simple question.  The interference from Uverse's DSL connection might not be much of a problem.  Why?  The received signal is going to be weak (indicated line attenuation is 21.6 dB.) The locally stronger transmitted signal, 3.7 - 5.0 MHz, is mostly outside the 80 M band, although there could be problems between 3.7 and 4.0 MHz, in the SSB band.  Fortunately (?), the 80 M band is naturally so noisy that the interference might not be noticeable.

The thing to worry about, I think, is interference to Uverse service.  I ran a very short test at ~3536 kHz CW.  I was downloading a large file over the Internet and listening to an HDTV program in the other room.  Transmitting with ~90 W output caused no apparent problems.  Transmitting at ~850 W killed the DSL connection pretty quickly.  Download stopped, and the TV image froze. It took about 70 seconds to reacquire the signal after transmission stopped.  (At least nothing was destroyed!)

This is all very preliminary.  We will need to improve the wiring and experiment with ferrite chokes -- probably on the incoming DSL connection.  There is no guarantee that kilowatt 80/160 M operation will ever work, but it might...

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