[App_rpt-users] Bizarre Issue

[mike at midnighteng.com]

My experience has showed me that most problems like that were from some of
the following:

grounds that were suppose to be isolated (explicit) grounds chasing a
frame ground.

digital grounds that were not isolated.

or grounds that should have been frame grounds that were not (kinda
opposite of the above)

***
While I have seen some refer to them as ground loops, that name for it
does not always reflect what is really happening.
Audio paths in much of the older gear we use in repeaters, the audio
ground may not necessarily work correctly with a frame/power ground.

The originating problem is not necessarily in the connections/circuits you
see the error.

Just my observations over the years.

...mike/kb8jnm

> Got some kind of similar case.the audio of my system with 2 node on it was
> cracking out of no where, the only thing was a visit to the site for
> manitenance and a good look at the computer.. cleaning the fan, removing
> dust checking all connector..
> the thing was that we left a usb to keypad/mouse ps2 adaptor plugged in.
> We usely remove it. this was not even connected to a KB or mouse. but it
> was puting stress on the USB hub inside the computer.. So could it be that
> something internal of the mother bord is connected inside the computer on
> that hub? I am thinking of card reader like SD card??
> But thanks for the head up. will keep an eye on this ;-)
>
>
>
>
>
>
>> Date: Sat, 14 Feb 2015 21:15:13 -0600
>> From: n5zua at earthlink.net
>> To: App_rpt-users at ohnosec.org
>> Subject: [App_rpt-users] Bizarre Issue
>>
>>
>> Having worked with app_rpt for the past five years, I've run across most
>> of the common issues that everyone else has. But every once in a while,
>> I run across one that is so bizarre, I feel compelled to post it, so
>> others might know about it. Such was the case yesterday.
>>
>> I have a site with a cabinet with three repeaters in it. The two meter
>> repeater was installed last as an app_rpt repeater from the beginning,
>> and has never had any issues. The other two are 70 centimeter GE EXEC II
>> mobiles, full duplexed, connected to an RLC-4 controller, with the other
>> two ports being wire line interfaces. Since the wire line has been
>> having intermittent issues lately, I wanted to move the two GE radios to
>> URIs. I built two conversion cables, with a female DB-9 on one end (to
>> accept DB-9 male from radio to RLC controller), and a male DB-25 on the
>> other (to connect to the URI). This leaves the flexibility of going back
>> to the RLC-4, without rewiring everything. So, I get to the site and
>> plug everything in and I'm ready to set levels. But wait, whats this
>> gawd awful loud crackling noise on the transmit audio of both GE radios?
>> Is it present on the discriminator line of the receiver? No. Is it there
>> when the DB-9 from the radio is unplugged from the DB-9 coming from the
>> URI? No. Now things are getting narrowed down. How about swapping URIs
>> since there are three in the cabinet? No difference. What about swapping
>> USB cables? No change. But wait, plug the two meter repeater in to one
>> of the two new URIs, and it now has crackle. What!? It turns out the USB
>> hub on the computer motherboard is oscillating! This box had 3 hubs.
>> Moving both of the GE radios to a new hub solved the issue. I have never
>> run across this issue before, on the twenty-something number of boxes
>> that I have either built myself, or helped others build. I may never run
>> across it again either, but if I do, now I'll know where to look. By the
>> way, that noisy hub ... it works fine. I plugged the keyboard in to it
>> and used it without any issue whatsoever.
>>
>> Many thanks to KE5PTZ for tirelessly tracking this issue down, and
>> putting up with me pulling my hair out for hours on end while doing so!
>>
>> N5ZUA
>>
>> _______________________________________________
>> App_rpt-users mailing list
>> App_rpt-users at ohnosec.org
>> http://ohnosec.org/cgi-bin/mailman/listinfo/app_rpt-users
>>
>> To unsubscribe from this list please visit
>> http://ohnosec.org/cgi-bin/mailman/listinfo/app_rpt-users and scroll
>> down to the bottom of the page. Enter your email address and press the
>> "Unsubscribe or edit options button"
>> You do not need a password to unsubscribe, you can do it via email
>> confirmation. If you have trouble unsubscribing, please send a message
>> to the list detailing the problem.
>  		 	   		  _______________________________________________
> App_rpt-users mailing list
> App_rpt-users at ohnosec.org
> http://ohnosec.org/cgi-bin/mailman/listinfo/app_rpt-users
>
> To unsubscribe from this list please visit
> http://ohnosec.org/cgi-bin/mailman/listinfo/app_rpt-users and scroll down
> to the bottom of the page. Enter your email address and press the
> "Unsubscribe or edit options button"
> You do not need a password to unsubscribe, you can do it via email
> confirmation. If you have trouble unsubscribing, please send a message to
> the list detailing the problem.