[Premium-Rx] WJ-8711A encoder noise elimination

[Steve Pappin]

Re: WJ-8711A encoder noise elimination and initial findings

The work that I am doing is based on initial findings from Dallas Lankford. 
Digital noise from the 8711A tuning encoder shaft actually extends well 
below 15 MHz and raises the overall noise floor. This has the effect of 
making the 8711A less sensitive. Depending on any number of variables this 
might become more or less of an issue. Systems using remote high gain 
directional antennas might not be affected. Systems with local antennas, 
short feed lines, or active antennas will definitely be affected.

1) Unmodified WJ-8711A: To measure noise from the 8711A's encoder shaft I 
used an HP8924C and HP RF probe 1 meter from the front panel of the 8711A. 
Measurements were taken at 15 MHz and 30 MHz. Ambient noise was 
approximately 2 dB uV. Total encoder noise measured was 32 dB uV at 15 MHz 
and 27 dB uV at 30 MHz.

2) Modified WJ-8711A: I established a ground at the base of the encoder on 
the front panel by removing the mylar, adhesive, and chem film. I 
re-installed the star washer and encoder shaft nut. I then added thrust 
washers and a spring washer to the encoder shaft. I removed the anodized 
finish from the back of the tuning knob. I installed the tuning knob. Noise 
levels dropped by 30 dB uV at 20 MHz and 25 dB uV at 30 MHz. Digital noise 
is no longer detectable at 1 meter. The noise floor dropped significantly 
across all of the bands.

The final configuration is TBD. The thrust and spring washer solution seems 
to provide the best results. It provides the least drag, friction, wear, and 
noise. I am using stainless steel hardware. The modification can be easily 
removed and it looks professional. Only a very thin border around the 
encoder shaft needs to be cut in order to establish a ground. The 
modification can be performed without opening the radio.

Best Regards,

Stephen Pappin
PCS Associates
2033 San Elijo Avenue #272
Cardiff by the Sea CA. 92007 USA
Ph: +1-760-487-8951

WEB site: www.pcs-associates.com