Am Fm radio reception

[Matt Colie]

> Improper grounding will bite you frequently and people do not stop to consider it. What makes ours worse is we have 3 separate grounding systems
> in a GMC and most people do not stop to consider them.
>
> I did a demonstration one time for Dan Gregg. He attached a ground wire to the base of his Paterson Distributor and ran it to battery negative.
> I told him not to do it but he disagreed.
>
> The demonstration was to disconnect the starting battery negative cable from the engine block. Upon attempting to start the engine he promptly
> smoked the 12 ga. wire between the distributor base and the battery he had just installed. We replaced the wire and ran it to the engine instead of
> the battery.

I missed that show. I heard your talk at Elkhart, but I missed that show.

Matt
--
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit

 

[RF_Burns]

Ken,
I agree with your point about the engine block being the "Mother of all grounds" for the chassis electrical system.

However your demonstration to Dan Gregg also illustrates my point. Having the dash grounded by a separate wire directly to the battery is the same as
Dan connecting the distributor direct to the battery. If you have a fault in the main ground wire from the battery to the engine block, current will
flow though other paths which are not designed for nor capable of carrying the current flow to the starter.

Example, from the Neg battery through the smaller dash ground wire to the radio chassis... out the antenna shield to the antenna mount on the aluminum
body... from the body through the grounding braids to the engine block and to the starter. And just like your demonstration to Dan, something is
going to get hot.

I'm not sure why GM put a ground wire directly from the battery to the body as there are also heavy ground braids bonding the engine block to the
body. Maybe to reduce spikes from the high starter current during cranking? However the only "Electronics" in an as-built GMC was the radio.

It's been 45+ years since I worked in a car radio shop so I did need to go look at some photos of a 70's era GM car radio. They confirm my mind's eye
that the antenna connector was fastened directly to the radio chassis. I am quite sure the radio chassis is also power ground as I remember
connecting my negative power lead to the radio chassis on my bench. I do know that CB radios from the time had the power ground isolated from the
chassis. If GE had designed their two-way radios with a floating internal power ground, there would be no issue with running the radio power ground
to the battery, but both GE and Motorola radios were never designed that way.

Since most people now have aftermarket radios, I checked the Sony and Kenwood radios I have sitting in my shop. Both have the antenna shield and
power ground wire connected to the radio chassis.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

 

[bill wevers]

Happy Thanksgiving to all!
I have read with interest about radio reception problems in the GMC.
The Sony radio in my rig works great. I replaced the old whip antenna
on the roof with a new one mounted slightly behind the cab on the
aluminum roof. I ran the coax following the stock position down
the middle of the windshield to the radio input. The coax shield
is only grounded to the radio, not the body. The radio is powered by
the house battery.

There is some noise when the Progressive Dynamics charger is operating.
Unplugging the charger makes the noise go away. This is a problem when
listening to distant AM radio stations. During the evening I can clearly
receive KOMO Seattle 800 miles away. I can also receive KFI in Los Angeles.

Regards
--
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose

 

[Ken B]

I do not remember where that was. DuQuoin, or Pueblo, or maybe Bowling Green. It was quite a while back. I do remember we were also working on his
AC compressor. It might have been Patterson. It was a while back.

I really miss Dan. He was a good friend and he put up with my teasing him about everything from picking cotton to blowing up engines.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana