AM Mobile Noise

[WU2D]

I have decided to try some noise reduction work on the Nissan. My mobile adventure with the ARC-5 station was fun but my ears are still ringing from the ignition noise! These modern fuel pump and ignition and computer systems are pretty nasty.

I figure that I was losing a good deal of sensitivity due to the nasty popping noise coming from my main ignition harness. I fashioned a two turn loop and put it on the end of a chunk of coax and attached this to the ARC-5 receiver. I sniffed out most of the noise to the main harness. How to fix this?

Jamie, KF2VM suggested shielding rather than trying to use snap on beads. Anyway, here is my first shot across the bow. I have not completed the wrap or even bonded everything, but it is a start.

Any suggestions?

Mike WU2D

[Mike/W8BAC]

Finding parts and installing will be the biggest chore. I once made a Volkswagen air cooled 1600 cc engine completely silent (no small task). In the eighty's it was a big job. Cars today are even noisier.

As far as ignition cables go I agree with Jamie. Beads aren't going to do anything. You're going to have to shield each wire. Old wires tend to leak  because of insulation breakdown or damage. Make sure the wire is in really good shape before you wrap it. I used RG-214 shield (used mil surplus). If you have shielded spark plug covers that's a big plus. If not you might check the junk yards. These usually screw on to the plug wire end. Attach the shield and your good to go. You might be able to find what they call resistor spark plugs that are a bit quieter. Remember, the spark plug itself makes a bunch of noise.

Some of these newer ignition  systems have a coil pack for each plug wire. The old stuff had one coil and a distributor. A feed through cap helped quiet the collapse of the coil on ignition. Covering the distributor cap to shield it was a big job that hopefully you won't have to deal with.

Alternators wine and fuel pumps buzz and weer. Most of this stuff can be fixed with feed through caps. I think Estes is still in business through GC ELECTRONICS. Check around on the web. Every thing you silence will bring a new noise to s9. It is a test of endurance Mike. Good Luck.

Mike

[W2JBL]

     start by bonding the whole car with braid (tinned 1/2"-1" copper preffered). terminate them in large ring terminals and 1/4" or larger bolts with big flat washers. scrape the metal for each connection clean of any paint. that means hood, trunk lid and doors/hatchback to body in two places- left and right accross the hood/trunk hinges,top and bottom for doors. then move on the the exhaust system at the tailpipe end(s). if you are lucky enough to have a real frame then put braid accross each rubber body/frame mount. if you have metal bumpers bond them too at each end. then on the the engine block, and battery negative terminal. bond the case of the car's ECM (computer) to the body too. if you are front wheel drive and unit body bond the engine/transmission crossmember/pan accross each rubber mount too. are you having fun yet? 

     now it's time to look at the installation- is every radio bolted down or in a metal to metal bracket secured to the vehicle floor, body or dash and also bonded by braid? yep- you need to do that too. how is your antenna mount grounded and attatched? all should be metal to metal, and bonded to the frame/body,  congrats- after all that you can start to run down noise from the engine, fuel pump, your cellphone charger (which will put you off the air) rear window defogger (clevelry disguised resistive noise generator), and seat warmers. ain't HF mobile fun? i think you are using ARC-5 stuff- if so there are some truly excellent series diode noise limiter circuits for the receivers.

    fuel pump noise is nasty, and best handled by a brute force PI section filter right at the pump in BOTH pos and neg leads. you will have fun building it. ferrite clamp on cores do little at HF. you need a lot of them to do anything at 3.9MHZ. igintion noise is nasty too, but not as much on modern vehicles. if you have a distributor and long plug wires the sheilded wires are the best way to go. no distributor/coil on plug is normally very quiet.

     following these tried and proven procedures i can take the noise in most vehicles down by about 20DB. you will also find your antenna tunes easier and you get out a bit better. choice of vehicle has a lot to do with it. the bigger the better. unitbody is quieter and gets out better than full frame. police package cars have the bonding (or most of it) allready done. a receiver with a good IF noise blanker is a nice thing to have on board too, allthough i have had good luck with the tube type blanker circuit from the Collins S-line, which uses a seperate "noise" antenna (i put mine under the hood). it eliminates the "blocking" caused by strong adjacent signals.

[flintstone mop]

I owned a Toyota truck with a four banger and I did the bonding of the vehicle body and running ground strap from the engine block to the vehicle body and frame. The last bit of noise was the injectors. After I grounded them to a separate ground I was able to use 17M. The funny thing about that, was they were all connected together on the engine block, but after moving the connection to the chassis ground I had less than S-1 noise. Before moving was S-9.
Resistor spark plug wires help to reduce the noise too.
Fred

[WA1GFZ]

Mike check connections going through firewall. Bonding is a big deal. Also make sure you use real good coax between antenna and rig.
RG58 is junk. RG223 is only fair. You could slide braid from RG224 over RG223 and maybe terminate only 1 end.

[WU2D]

Thanks for all of the hard core ideas guys. It is going to take some time to try some of this!

See - Frank likes coax after all.. The double Faraday shielded coax is a radical approach. 

Frank, what about balanced line in the car? How would a tuner on the dash and pair of ceramic feedthroughs above my head going to the roof and ceramic standoffs  marching down the roof look? The ladder line could center feed a vertical copper loop.
Just kiddin..

Actually I am using some good coax now - I replaced the RG-58 with a high grade shielded foamed RG-8 and it actually fits through the trunk gap! Every 0.1 dB helps.

Mike WU2D

[The Slab Bacon]

Keeping the vehicle noise out of mobile rigs has always been a pain in the a$$. That is prolly why FM became so popular for commercial land mobile 2-way service.
                                              the Slab Bacon

[WA1GFZ]

RG8 is also junk. find some RG224 or hard line.

[WU2D]

RG-214 is an excellent choice in "RG-8 types" in the car because it has the right characteristics - Double shielded with two high conductor count braids, Tinned braiding for low oxidation, Hard Poly Insulation so it will not melt, a stranded center conductor for flexibility and finally a strong PVC jacket.

For loss and shielding however, the best RG-8 types include LMR-400, CushCraft UltraFlex, and some excellent Belden types. These all have the big solid center conductor, foamed insulation and double shielding usually with a braid over a solid aluminum shield. These will outperform 214. 

Some RG-8 is junk. Radio Shack RG-8 was notorious for having little or no shielding. Other brands and grades of RG-8 are very good.

Even 100 feet of RG-58 has a loss of only 3 dB at worst at 30 MHz. That would be 0.3 dB of loss at 80M for 10 feet of coax.

Mike WU2D

[The Slab Bacon]

Even 100 feet of RG-58 has a loss of only 3 dB at worst at 30 MHz. That would be 0.3 dB of loss at 80M for 10 feet of coax.
Mike WU2D

Mike,
       When going to lengths that long and using it for transmitting, keep in mind that with a higher powered transmitter the I-R losses of that small skinny-assed center conductor would be pretty bad. If using 58 for anything other than receiver antenna connections, I would keep the lengths sbsolutely as short as possible. The heavier center conductor of the "RG-8" types are much better suited to carry the feedlind current of a high power rig. Sometimes the published loss factors dont tell the whole story.
                                                     The Slab Bacon

[WA1GFZ]

When I'm doing RX testing in the shack on 75 with a 4 foot cable between the RX and the generator I can hear the strappers through RG58 shield and I am in the basement. solid shield is the best. double even leaks double with an insulator between shields is a bit better.

[k4kyv]

I don't operate mobile, but I have tried to sniff out line noise with a portable receiver.  Ignition noise from the car made the task almost impossible.  I found myself driving down the highway, gaining some speed, then putting the car in 2nd gear and pushing in on the clutch, and turning off the ignition and coasting down the road.  When the car is almost ready to stop, I  turn on the ignition, let out on the clutch to re-start the engine, reach cruising speed once again, and  let it coast some more.  I suppose someone behind me would think I was having car trouble.

A bicycle would work better if it weren't for so many idiot drivers on the busy highway.

A diesel should be noise-free, shouldn't it, since since the fuel in the engine self-ignites without spark plugs?

[The Slab Bacon]

A diesel should be noise-free, shouldn't it, since since the fuel in the engine self-ignites without spark plugs?

With the older diesels that have real mechanical fuel injection this is true. But.........this newer generation of computer controled diesels with electronic fuel injection may well have some of the same noise monsters as their gas counterparts.

                                                The Slab Bacon

[KD6VXI]

A diesel should be noise-free, shouldn't it, since since the fuel in the engine self-ignites without spark plugs?

With the older diesels that have real mechanical fuel injection this is true. But.........this newer generation of computer controled diesels with electronic fuel injection may well have some of the same noise monsters as their gas counterparts.

                                                The Slab Bacon

I have a 2006 Dodge Cummins Turbo Diesel.  It is VERY quiet.  I have a couple monoband radios in it now (mainly V/UHF), but I seem to remember the worst part about it was the "clock" frequencies of the various computers in it.

Injector noise can be heard, the injectors are pulse width modulated, I believe.  That is a changing noise, triggered by RPM, load and airflow at the time.  IOW, mashing the throttle another 1/100th of an inch takes care of that.

Honestly, I get more noise out of my GPS switching power supply that plugs in my cig plug than I do from the engine or it's electronics...  Except at those pesky clock frequencies.


KD6VXI
Shane