[Mobile-Portable] Auto Ignition noise suppresion and mobil antenna matching

Fri, 15 Aug 2003 14:15:31 EDT

Roland, WB0AXN
I think we have all cursed ignition noise at some time or other.  Here are 
some suggestions: 
1.  If your radio has DSP, use it.

2.  Your xcvr's DSP may not be sufficient to eliminate it all, so buy a DSP 
speaker. I use AM-Com's CLEAR SPEECH speaker.  http://www.amcominc.com/
I would not be without it.

3.  Many auto mfrs. reduce vibrating metal parts, like fenders, bodies, 
frames, etc. with a piece of tar paper or fiber between the offending metal parts.  
Ford is notorious for this.  You can take a short length of braid from some 
old coax and using sheet metal screws, attach the hood to the fenders, the 
fenders to the frame, Everything to the body, etc., the frame to the exhaust 
system in several places (be sure not to drill holes in the exhaust system, use 
hose clamps) Don't forget brake and fuel lines, the "no holes" applies here also, 
and your noise floor may get better - - - - but no guarantee's.

4.  Electric fuel pumps are noisy as are ignition computer modules.  You 
could use RF chokes, filters or ferrite beads on the leads - - - - may not be 
necessary with DSP.  My diesel Mercedes computer rips up 40 meters so bad that I 
wished I had some ignition noise to hear but doesn't bother other HF bands.  My 
gas vehicles have some noise, but the DSP speaker takes it out along with the 
power line noise.

5.  Run your plus and minus DC leads for your xcvr directly to your car batt. 
 This usually helps.

6.  Purchase noise canceling ignition wires from http://www.magnecor.com/ , 
from their home page click on Product Information, then click on Technical 
Information, then click on CN Series which is recommended for "ham radio noise 
suppression," It is a spiral wound (180 turns per inch) nichrome wire that is 
wrapped around a ferromagnetic base and encased in silicone. - - - - Good Stuff.  
(My thanks to the hams who refreshed my memory on the proper web site for 
these wires.)  

7.  Shield your entire ignition system and run every input and output thru 
filters or "feed thru" capacitors - - - - Big Job and the insulation will 
breakdown with time and the high voltage spark will then short to the grounded 
shield.  

8.   Ask for help with your specific car and radio on the Mobil chat site 
that I copied on this e-mail.  ([email protected])    
There are a great bunch of Hams who are happy to help and may have already 
solved the same problem that you are experiencing. 

Regarding your question on matching your Hustler antenna mounted on your new 
truck's trailer hitch.  Make sure that your hitch has a low impedance ground 
to the body, chassis etc.  Some hitches use concentric rectangular tubing that 
inserts into a receiver that may not be very well grounded and subject to 
intermittent contact during road vibrations while others are a welded assembly 
that is solidly connected to your vehicle and needs no further grounding.  The 
antenna base matching coil that should work for you is a 16 turn open air bare 
copper wire coil of #14 AWG that is about one inch diameter and about 5 inches 
long. (you can firm up the coil with hot glue and popsicle sticks if desired). 
 One coil end connects to ground, while the other coil end connects to the 
Hustler's base feed point.  Make a six inch long jumper wire of # 18 with a 
small alligator clip on one end.  You then solder the wire on the center conductor 
of your coaxial feed line from the xcvr and then move the alligator clip 
along the coil until you can hear signals on your receiver the loudest, (that 
should be the "50 ohm" tap point for that band), clip the wire there and tune up 
your transmitter and check your SWR.  You may need to adjust the clip position 
on the coil slightly for lowest VSWR.  The coil setting will vary as you 
change resonators (bands).  The tap setting for lower bands like 40 or 80 meters 
will be towards the middle of the coil and high bands like 10 or 15 will require 
the tap to be near the coax feed side of the coil.  Your hustler resonators 
will need to be adjusted after installing the base matching coil by shortening 
the length of the adjustment rod that is on top of the resonator.  The 
matching coil adds some inductance, (i.e., electrical length) to your antenna and 
thus you must compensate for it by retuning (shortening) your resonator overall 
length. 

A screwdriver antenna will be more efficient than the Hustler resonator type 
of antenna and is easier to tune.  Take a look at one when the opportunity 
presents itself.     

You could obtain more accurate matching results by using an antenna analyzer 
such as the MFJ, I do and love it. 
73,
Terry, K7FE

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