Not always. It may be considered poor design but if the in/output goes directly to a differential amp with little or no 'padding' to chassis (creating the comparison to 'different'), it may have a floating ground and actually cause problems if connected to ground.
In the case of Motorola radios, you'd have to ask them why, but never assume that either side of a speaker (for example) is chassis grounded, or you'll blow up a very expensive audio amp (like on the popular GM300). A careful resistance test should be done before connecting audio ground to chassis. In general, we agree that chassis to chassis bonding SHOULD be encouraged to reduce noise (and is electrically safer having everything at the same ground potential). But it does NOT always solve problems. I've seen cases where one (presume a computer to radio) chassis-chassis connection made the problem worse (ground looped hum), because it introduced more noise into the radio, even if plugged into the same power source (should have been equal grounding already). Audio isolation transformers were the solution, pass only the audio. It might be against common practice, but reality trumps theory. Chassis to chassis grounding may have any range of results (but certainly try it). And in the case of RF, remember what may be good DC ground isn't always RF ground. Ask any mobile HF operator (striving to get very low RF resistance to ground to improve antenna efficiency). ;-) With RF, more grounding (overkill) is often MUCH better and always use plenty of low RF resistant metal because of skin effect (braid or at least multi-strand, not solid wire). A lot of the crud generated by electronics is actually low level RF so it should be treated as such. Fortunately, it also works well at DC to audio frequencies as well. Rick WA6NHC -----Original Message----- From: Jim Brown On 11/1/2011 4:57 PM, Rick Bates wrote: > Note that on some computers, chassis ground is NOT audio ground and I'd > suspect the same is true of some radios (true for at least one of my > Batwings). It SHOULD be. If it is not, the mfr goofed. THAT'S what a Pin One Problem is! Further, unless the audio interface is BALANCED, audio return will always be referenced to the chassis, but it may be a lousy path. > Chassis to chassis bonding may increase noise in that case. WRONG. This is another of those widely held misconceptions that is WRONG. Chassis to chassis bonding is ALWAYS good practice, and ALWAYS minimizes buzz and RFI. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
