[Milsurplus] Radio interference

[Rian Robison]

It seems to me that should work.

I would first try grounding the tail pipe at the rear with a clip lead to see how that helps.  The tail pipe can be a good antenna that carries noise from the engine (grounded there through the engine block and braid to the frame (around the an engine mount)...which makes a good above ground, radio freq. wise, feed point for the tail pipe with an open (Hi-Z point) at the rear of the vehicle.  Most tail pipes are hung with a rubber straps (insulators) between the frame and a clamp around the pipe itself.  The radio antenna is then installed near the rear of the vehicle where the tail pipe is radiating engine noise (quite nicely) which of course isn't a good thing.  I would suggest a copper strap jumper at each hanger (with some slack to permit the hanger to continue doing its job of keeping noise from vibrations off the vehicle chasis).  I would also put a ground clamp within a few inches of the rear of the pipe should a hanger (with a ground strap you install)  is not within 4 or so inches of that end.   I have done this over the years and it sure helps quiet things down.

Another thing is to try is to install both a .01 and 20 or so MFD cap (in parallel) on each side of the power feed point at the radio to see if some of the noise is coming from them radiating noise near the radio (since you have dynamotors I doubt there is noise feed-thru from them to the radio via the power supply).  I assume you are using both a positive and negative lead (both fused)  all the way from the battery (the negative fuse protects the radio from the starter cranking current should the negative to the engine block open).  Using the vehicle frame only, for the negative lead, introduces noise to the radio because the negative lead (the frame) has engine, generator,etc. noise on it.  Running a negative lead (even in addition, where the radio negative appears on its case/chasis) shorts out most of this noise.

It used to be common practice, when using a steel chasis for RF or quality audio, to run a copper wire through the middle (or so) of the space under the chasis and tie all grounding points to it (it was the next best thing to a common ground point).  Many RF amplifiers were unstable because the builder didn't do this.  Using braid for plate leads was another problem point (braid becomes lengthly parallel wires after being in service for awhile from dirt and corrosion) but this is another subject.

Good luck, I hope my long wind helps.

73,
Rian
W6SVU 

-----Original Message-----
>From: POWERMWT at aol.com
>Sent: Aug 16, 2006 8:53 PM
>To: milsurplus at mailman.qth.net
>Subject: [Milsurplus] Radio interference
>
>I have problem with radio interference with my TCS radio in the back of my 
>1944 MB-NAVY-MZ-1 radio jeep.
>
>It has a 6 piece sheet metal suppression system that covers the ignition 
>wires & plugs, coil and distributor, as well as filters (capacitors) for the coil, 
>ignition switch, starter switch, generators (2) and regulators (2). 
>
>When the engine is running at the 900-1000 RPM required for keeping the 
>batteries charged, the static is too much to hear anything (like 1530 talk radio). 
>Yet, with the engine off, the reception is excellent. This leads me to believe 
>I have some sort of interference with the ignition system. 
>
>I have an old article on how to make a 4" diameter loop probe connected to 
>the antenna and ground to locate the interference by listening with the 
>headphones. 
>
>Is this the best method to find the interference? 
>
>Regards,
>Mark Tombleson
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