Saturday, November 27, 2010

U-verse Downs & Ups

Family watching television, c. 1958Image via WikipediaThe AT&T U-verse saga continues.  I was sad to find that, after my initial tests that showed I could run 80 M CW at 800 W, my latest round of tests showed really bad sensitivity.  I couldn't run over 20 or 30 W without causing the U-verse Residential Gateway (RG) to lose sync.  (That can mean a 1- or 2-minute TV and phone outage.)

After a bit of probing, it became clear that the RFI was entering on the internal home phone wiring.  Disconnecting it from the RG quieted the problem, but alas we are now very dependent on the U-verse VOIP service.  Disconnection is not an option, normally.  (Cell coverage is poor here - a story for another day.)

The AT&T installer had not fully appreciated my phone entrance system, which uses a special DSL surge suppressor that is bolted onto my Single-Point Ground system.  He ran his CAT5 cable from the wall plate straight into the RG. (That's OK for RFI, but not great for lightning surges.)  The house phones were fed via a circuitous route passing (backwards!) through the surge supressor, and generally making a nice RF pickup loop.

This afternoon, I pulled out half my station (the heavy part!) so I could get access, and rewired the phone system, adding ferrite chokes, etc.  Result: no trouble now with 800 W at 3600 kHz.  I'll do more tests later, when the contest goes away.

U-verse RFI tip:  You can use the ubiquitous DSL telephone line filters as an RFI choke.  These are transparent to telephone audio, but block the DSL frequencies.  (It's not clear whether they are effective at up to ~8 MHz that VDSL = U-verse uses, but it seems likely they are.)

More complete info will be at http://aa6e.net/wiki/RF_Compatibility.

Tuesday, November 16, 2010

Music from Outer Space - Design Tools

Design in your browser. An integrated web-based schematic capture and breadboard support system provided by Music from Outer Space.  It's oriented toward audio, not RF, but it's a cool site for simple designs.


(tnx jameco.com)

Wednesday, November 10, 2010

VAIO inverter surgery

My Sony VAIO (VGN-FS710/W) gave up the ghost last month. The screen went dark, and it emitted some screechy noises.  I figured what a hardware service call would likely cost, and I decided I quickly needed a new laptop to support my work at ARRL and other things. So I sprang for a new inexpensive Toshiba (Satellite L6460), which did not cost much more than that hypothetical service call.

Now, after my computing situation has stabilized, I had a chance to open up the VAIO to see what could be done.  There were some helpful disassembly hints on the Internet, and they were essential to avoid breaking things.  The culprit almost leaped out at me.  It's the tiny inverter card (above) that makes high voltage to run the fluorescent LCD back light.  The Internet (again) seems to be saying this is a frequent source of problems.  The HV rectifier was charred and broken, so obviously this was the problem.  It's a $50 part, and I hope replacing it will solve the problem.

I suppose there's a moral here.  I could have saved money, but incurred opportunity cost and risk, if I simply repaired the VAIO.  I'm happy to have a new, more powerful laptop. Still, the VAIO is handy because it has some critical features (like Firewire) that make it very useful for some of my work.

Update (11/12/2010): Thanks to lcdparts.net, I have a new inverter, and the VAIO is back in operation!

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