Wednesday, August 01, 2012

Handiham World for 01 August 2012

Welcome to Handiham World.

Troubleshooting 101

Last week's problem showed up when I was using my shack's two meter rig, which is powered by a switching power supply.  Let's just recap: It's the one that's typically used for the Handiham net each day. I'm located some distance from the N0BVE repeater system. (It's in the western part of the Twin Cities Metro while I am in the east.)  That means my reception of the N0BVE signal is not exactly perfect.  I can hear an annoying hiss in the background when the repeater is active, but that's easily eliminated with a flip of the switch on my external ClearSpeech speaker. This handy device has almost magical properties - really a very smart algorithm - that digitally cleans up the signal, virtually eliminating the noise. I don't like to leave it turned on all the time because I also enjoy listening to Minnesota Public Radio with the extended receive feature of the transceiver, and MPR has enough signal to be rock-solid perfect. It sounds best with the external ClearSpeech speaker's processing turned off.
One day I encountered an interesting problem. I had been listening to MPR when I last used the radio, and when I turned it on, that's the station I heard. Since I wanted to monitor the repeater instead, I flipped the memory to the stored two meter channel. Then, noticing that the ClearSpeech speaker was turned off, I slid its power switch to "on". At that very moment, the radio went dead - no power. I pushed the power button on the radio and everything was back to normal. I put up with this for weeks before finally getting the gumption to track it down.
The challenge was to guess what was going on.  Rick, W0IS, was right on the money when he wrote:
My educated guess is that the negative power lead for the speaker had gotten disconnected, but it still got power because it was grounded through the radio, either through the speaker connection, or just from the two chassis touching somewhere. But my guess is that the radio's negative power lead does not go directly to the chassis of the radio. There is some electronics between the black power wire and the chassis, and this electronics did not like the current running through it. I don't remember the details, but I had something similar happen with my FT-817 (or maybe it was a different rig). The black wire came loose, but it was still connected to the negative side of the power supply through the chassis. It worked, but there were some flukes, since the black wire did not go directly to the rig's chassis. Did I guess right? 73, Rick W0IS
Yes, and it turned out that the fault was in the ground side of one of those popular snap-together connectors in common use today. The connector was probably not properly installed in the first place, or else the spring tension inside was just so weak as to allow the ground side to lose contact if the connector was bumped or the power supply cable got moved in just the wrong way. It's worth noting that had the powered speaker had a grounded metal cabinet with a common grounding lug and had both the radio and the speaker been grounded to a common station ground, this problem would likely not have even shown up. As it was, the ground had been completed through the speaker's 3.5 mm audio plug's grounded side to the radio.  Obviously this is not the ideal way to power things!  In any case, the fix was as simple as it could be - just repairing the power supply DC cabling fixed the problem.
Station grounding is important, though. Grounding equipment to a common station ground can help eliminate RF circulating in places where it shouldn't be as well as protecting equipment from static discharges and keeping the gear at the same potential to avoid electrical shock hazards.
Email me at with your questions & comments.   
Patrick Tice, WA0TDA
Handiham Manager