electrical question NGC whatsoever..

[Chuck in Indiana]

Ok, I've been troubleshooting my communications radio in the airplane. I have a dedicated ground stud for the Nav/Com stuff. Com radio, transponder, encoder, and intercom. The com radio is headset only, and the mic and phone jack are insulated from the panel. I have the ground wire from the com radio and transponder in my hand, and they are both working. (!) What's up with that?
TIA, I'm clueless on this one.

[cruzziguzzi]

Ok, I've been troubleshooting my communications radio in the airplane. I have a dedicated ground stud for the Nav/Com stuff. Com radio, transponder, encoder, and intercom. The com radio is headset only, and the mic and phone jack are insulated from the panel. I have the ground wire from the com radio and transponder in my hand, and they are both working. (!) What's up with that?
TIA, I'm clueless on this one.

Are you confused that they are working in a perceived "un-grounded" state?

Case ground and cable back-up?

Possibly an antenna short - uniquely but do you have an SWR meter?


Todd.

[Chuck in Indiana]

Are you confused that they are working in a perceived "un-grounded" state?

Case ground and cable back-up?

Possibly an antenna short - uniquely but do you have an SWR meter?


Todd.

I tole you I was clueless..  The case is grounded. No, I don't have a steenkin SWR meter.. All I have is the "book" saying the connector numbered 1 is ground, and of course I did that when I first hooked it up. I'm *assuming* it isn't supposed to work without the ground hooked up, of course, but it seems strange to me that it does.

[StuCorpe]

Maybe the antenna (shield) wire is providing the ground. ?

[cruzziguzzi]

I tole you I was clueless..  The case is grounded. No, I don't have a steenkin SWR meter.. All I have is the "book" saying the connector numbered 1 is ground, and of course I did that when I first hooked it up. I'm *assuming* it isn't supposed to work without the ground hooked up, of course, but it seems strange to me that it does.

An auxiliary ground is pretty standard as many electronic devices get mounted in coated, painted... whatever clad pivoting and quick detach mounts. Think of devices- gauges- illumination working after you tap it... Almost always a flawed ground.


Todd.

[Guzzidad]

   I have no knowledge of the devices you are working with but I assume they are D.C. powered. D.C. negative is usually attached to ground. But the actual ground wire has a different function unrelated to powering your device. It just provides protection to the circuit in the event D.C. positive contacts the case of your device. It also provides personal protection by blowing a fuse or breaker. Confusing because D.C. negative and grounding wires are connected at the same points. Also, shielding wires should only be connected at one end. That one still has me confused.

[Kiwi Dave]

Also, shielding wires should only be connected at one end. That one still has me confused.

Usually only for analog audio.  If both ends are connected an "earth loop" may occur resulting in hum and other crud being introduced into the signal.

[flangeman_70]

Hey Chuck,

Your  question is a bit unclear but I gather you are saying all works normally but the dedicated ground is disconnected.

If yes you have ground (or near enough) somewhere else and this is pretty normal BUT that dedicated ground is a must to prevent noise from static charging when you start zipping through the air.

What exactly is the issue you are troubleshooting?

BTW I am a licensed avionics engineer.

Adam

[Kiwi_Roy]

The devices are powered by Positive and Negative wires, the metal case acts as a shield to keep electrical noise from the motor out of the radio and noise from the radio out of any sensitive instruments.
Your radio doesn't use the ground to supply the power as it would in a car.
The radio may well work without the case being grounded (funny term to use for an aircraft) but I think the idea is to bond the various bits together.

As Guzzidad says the shield is usually only connected at one spot to prevent current circulating.

If ever you work on HiFi you soon learn the importance of grounding at just one spot, if you don't the 60 Hz hum created by having two can overpower the tiny signal from the record pickup.

I work in process control Instrumentation the standard signal used to be 4 - 20 milliamps (4mA = 0%, 20mA = 100%), its possible to get quite significant errors in the signal if you don't follow the single point rule.

Oopps, Flangeman gave you the answer while I was scratching away

[Murray]

Most modern radio's etc use the case as a ground as well.

[frizzit]

To add to Murray, if it is case grounded and it is mounted in a vehicle to the chassis then it is grounded.

[frizzit]

https://www.cumulus-soaring.com/xcom/XCOM%20Aerial%20Dummies%20Guide.pdf

may help

[Chuck in Indiana]

Thanks to all for the explanation. Makes perfect sense now. Gotta love WG! 

What exactly is the issue you are troubleshooting?

Low volume, both transmit and receive.

[frizzit]

Could be a list of things:

Your antennae connection could be suspect causing a low power transmit receive.

Your Headset cable could be broken/almost broken along with the connections, as a cable ages it could bent to the point of almost breaking causing a high resistance connection attenuating the mic and speaker volumes to the transponder.

Power and grounding are always a player

How old is the equipment?

[flangeman_70]

Thanks to all for the explanation. Makes perfect sense now. Gotta love WG!  :thumb:Low volume, both transmit and receive.

If it isn't just the headset, pull the Headset jacks apart one by one. It is common for the tangs that contact the plug to vibrate lose and make contact in the receptacle. First sign is your symptom you describe.

Commonly fixed on big birds by potting with RTV3145 so they don't work harden especially on service jacks on engines and gear etc..

Let us know how you get on.

Adam

[Wayne Orwig]

Low volume, both transmit and receive.

Smear some dielectric grease on it. That will fix anything.

[sbaker]

Antennas ARE grounded.. The plane/car/bike is the ground plane of the antenna.. The 'stick' is the vertical radiator.. Clearly the case of the devices are also grounded. Try pulling the units out of the dash, disconnect the antenna and you should see the unit NOT come on..NOTE:  DO NOT press the transmit button without the antenna attached.  Then re-attach the antenna and see if the unit comes on.. It should... That will indicate that the Antenna is properly grounded and ergo, the radio is properly grounded....

[MGPilot]

The com in my German RF5B motorglider (www.rf5b.com) had marginal performance since the day I bought it. An avionics shop replaced the antenna and announced it fixed. Problem was, I couldn't tell the difference--and towers still complained that I wasn't coming in clearly at any significant distance.

Read up on the issue and decided that in my composite (wood & cloth) aircraft, they had never installed a properly sized ground plane. Further, with the shape of the fuselage, decided that it would be nearly impossible to do so.

Replaced the traditional antenna with a ribbon style dipole antenna (https://www.aircraftspruce.com/catalog/avpages/antennasystems.php). (I think that's the correct name.)

Crap.  Worked so well, I had to up my professionalism in talking to ATC, etc., if they could actually hear me now.

[Chuck in Indiana]

How old is the equipment?

No idea, although the intercom is new. I pulled it out of the airplane and it works if you blow into the mic,but voice is unintelligible. There was a broken wire on the ships radio mic tip at the solder joint. I repaired that, but still have the low volume issue. A friend gave me a junk radio.. last digit doesn't work on the display, the automatic dimmer doesn't work, but it's loud and clear in the same tray..

[charlie b]

Since your buddy's radio worked it sounds like it might be internal, as in an internal connection is loose, or, worst case kinda thing, a circuit board is cracked.

Like above, connectors take a beating so that's always a place to start.  Did your mic work with the other radio?

[LaMojo]

Sounds like the B+ voltage is low.  Could be the voltage regulator or a dead capacitor in the power supply circuit.  Maybe just a cold solder joint.
 

[Chuck in Indiana]

Since your buddy's radio worked it sounds like it might be internal, as in an internal connection is loose, or, worst case kinda thing, a circuit board is cracked.

Like above, connectors take a beating so that's always a place to start.  Did your mic work with the other radio?

Yeah, mic works. I sent the radio back to the manufacturer a couple of weeks ago on the basis of the junk radio working. The manufacturer said, "works fine, that'll be $125 please." Talked to him again last night, and he said send it back again and he'd take a more in depth look. 
I'm just trying to make absolutely sure the problem isn't on my end.

[Chuck in Indiana]

Sounds like the B+ voltage is low.  Could be the voltage regulator or a dead capacitor in the power supply circuit.  Maybe just a cold solder joint.
 

Thanks, I'll mention that to him..

[charlie b]

Yep, the problem with some of those connections is they work fine one time, then jostle it around or just let it warm up a bit and it goes bonkers.  Solder joints are especially bad for stuff like that, as you probably have experienced before.