Sunday, January 07, 2007

RF suppression

I recorded my first on-air QSO today using the new audio equipment, but not before I was forced to do some troubleshooting. I had already recorded from the radio to the iPod but had never transmitted while recording. When I tried transmitting today, the noise that came through the headphones was awful. Obviously RF was getting into the mixer.
I had expected this, actually, though I wasn't sure how it would be leaking in. (Few things work the first time. You didn't think it would, did you?) Rather than just start "trying stuff", I spent a minute looking over the setup to see what it might be. While it could have been the Shure microphone or its long cable, the more likely culprit was the power connection. I snapped three chokes around the power cable right where it enters the mixer and the noise disappeared completely! Here's that first QSO:
MP-3 of NE1RD with EA8BWW
I had similar problems with RF getting into things while on St. John. So, this summer I spent some time looking for chokes and reading up on RF suppression. In a previous post I mentioned Chuck Counselman's piece on common mode chokes (found here) which is excellent reading. The problem I was worried about then was RF getting into the laptop and confusing the power management circuitry (as it had on St. John). While testing has been minimal with HamMac, that problem doesn't appear to be happening with this new setup. Still, if it does rear its ugly head, I'm ready for it. I have a whole box of chokes packed for the trip (weighing only about 1 pound, they are great insurance against these pesky problems).
Everything is now broken down and repacked again. My mix of stuff still isn't right. The Pelican case weighs in at 49 pounds and the REI bag is now at 47 pounds, but I've not packed any coax, the MFJ analyzer is still sitting out, and only half my clothes are packed. The obvious place to reduce weight is in my selection for tools, though making that adjustment still might not be enough to bring me in under 100 pounds for the two bags.
I am packing both a Buddipole system and a Buddistick system in the REI bag. Together, they are probably 11 pounds (7 and 4 respectively). I've also got some extra accessories for both the Buddipole and Buddistick packed separately in that same bag. That's why this exercise is iterative: you throw everything you think you might need in bags and weigh them, then reduce the volume of stuff until you make your weight goal. It becomes a long series of trade-offs: "would you rather have A or B?" I've got about three weeks to make all these trade-offs, though I'll likely finish much earlier.
Finally, our first conference call in three weeks will be tonight in just a couple of hours. Lots has happened, and there is still lots to do. We added a team member officially today. Dave Bushong KZ1O will be helping us as a DXpedition pilot and backup Webmaster. The second role, backup Webmaster will provide some backup for me during the updates of the online logs. If, for some reason, our internet connection is not solid enough for me to update the web site from Montserrat, I'll try to forward just the log file deltas each day to Dave who will do those updates for me. That's the plan, anyway. Now, I just need to get that software finished!


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