[RFI] Mobile RFI Help Please

Mack McCormick w4ax.mack at gmail.com
Sat Sep 3 14:23:47 PDT 2011

I have a new mobile installation with spark plug noise on HF.

Here is the installation:
- 2003 Lincoln Navigator
- Kenwood TS-480HX (200 watt)
- Tarheel Model 200 Screwdriver Antenna fed with RG-8X. 2 inch receiver
mount bolted to the frame. SWR 1:1 on all bands.
- DC power directly from the battery with 0 gauge cable (fused). Very short
wiring runs.
- West Mountain ClearSpeech Speaker

The spark plug and possibly injector noise is loudest on 20M and has
improved since I've taken some steps. There is zero noise with the antenna
disconnected from the rig.

Here are the steps I've taken which seem to have helped on 75/40M but still
very noticeable on 20M. The rig ANL removes the noise but I would prefer not
to use it and instead fix the real problem. Also the ClearSpeech speaker
will remove the noise.

1. Ground strap from the engine to the body (it already had one factory
installed but I added a second strap)
2. Ferrite clamp on cores on the injector/spark plug DC wiring harness from
the car's PCM. 4 spaced apart on the main harness. I cannot get a ferrite on
each individual spark plug coil pack.
3. Exhaust strapped to the body in four places before and after every joint.
4. Tomorrow: I'll strap the body to the frame on all four corners.

All ideas on how to fix my spark plug RFI are most gratefully appreciated.
I've carefully read and followed the excellent advice of K0BG found on his


Mack de W4AX

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