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Those Darned Electrons!

S

szicree

Well Known Member
Today I finished the wiring harness for my radio and intercom and thought I'd try it out. Since there are no other electrics in the plane yet I hooked up a little 12v battery charger to the intercom in the hopes of being able to put on a headset and hear my backseater make fun of me for sitting in an airplane in a garage. Well, it all seems to work but has got the most intolerable hum. Not some little background thing, but a big loud hum! I followed the wiring instructions to the letter when building the harness, even checking continuity across all connections as I went.

So here's my question: I notice in the manufacturer's literature (PS Engineering) it says that the device needs a minimum of 13.8 volts to operate properly and my little charger only reads 11.6. Could this cause my hum? If not, then what? Geez, I don't want to fool with that harness anymore with all it's microscopic Sub-D pins! Help.

Steve Zicree
RV4
 
sounds like you heard the A/C hum of your converter. Try a 12v battery ... even a small 12v battery will do.
 
Batteries don't need smooth DC for charging so your charger's output oscillates between 0V and probably around 17V or so. Very very noisy! A good source of smooth 12V DC is an old computer power supply.

Conor
RV-9A 90990 wings
 
Today I went looking for a power supply at the local electronics store. When I told the guy what I wanted it for he suggested I get a cigarette lighter plug and a bunch of lamp cord so that I could just plug into my car. 3 dollars and 10 minutes later I hooked it up to the plane. You guys were right about the AC hum. Everything is quiet and perfect now. This is the first electrical device in the plane and it feels pretty cool to see it work. Incidently, once I wire up my com radio, will I be able to hear stuff in my garage?

Steve Zicree
RV4
 
be careful with the radio ... you need to make sure you have a antenna and good gounds so you don't "blow" the radio.
 
The transmitter needs a "load", otherwise you will get a reflected wave that can wipe out your transmitter. You won't hurt the reciever but NEVER key the transmitter without an antenna.
Mel...DAR
 
Oops

Mel,
I keyed it twice momentarily just to see if my ptt was working. Is my radio toast?!?

Steve Zicree
 
szicree said:
Mel,
I keyed it twice momentarily just to see if my ptt was working. Is my radio toast?!?

Steve Zicree
Click to expand...
A couple of truly 'momentary' key-ups shouldn't toast it, theoretically! And if you weren't "screaming" into the mic, that would reduce the load on the finals somewhat also.

The newer radios tend to be somewhat less sensitive than older ones: the final amplifiers are a bit less fragile, and some have a self-limiting circuit that recognizes high SWR and reduces transmit power.

I'm not entirely sure that the aviation guys have made to the 20th century technology wise though :rolleyes:
 
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