[Elecraft] [All] K9YC's RFI Tutorial Bears Fruit

[Al Lorona]

Now and then I have used Jim K9YC's "A Ham's Guide to RFI, Ferrites, Baluns, and 
Audio Interfacing" as a reference but very recently I finally read the whole 
thing straight through, and it finally dawned on me that Jim advocates putting a 
common-mode choke right at the feedpoint of the antenna. The reason he gives is 
that most 'balanced' antennas are not in perfect balance due to the antenna's 
surroundings, and this imbalance makes the feedline pick up more noise. Much of 
his paper consists of measured data of many kinds of chokes, but I built what 
seemed the simplest effective choke -- 15 turns of solid THHN electrical wire 
bifilar wound on a #31 toroid-- and put it near the feedpoint of my  dipole.

I say 'near' because for mechanical reasons the closest I could put the choke 
was about 12 transmission line feet from the feedpoint. I use all-homebrew 500 
ohm open-wire line.

I finally got the antenna up Saturday and  have been tuning around the low bands 
and it appears that my noise floor has indeed dropped. Whereas in this noisy 
location I have had the REF LVL of the P3 set to -114 dBm on 40 meters for some 
time, I now have to drop the REF LVL to -118 dBm to move the noise floor to the 
same location on the bottom of the display. There is a similar outcome on 80 
meters. But man, I just picked up another half S-unit of noise floor last 
weekend. 

This K9YC is a smart man. Another change I've made since reading his entire 
paper was replacing  my 'shielded' speaker cables (which nonetheless were always 
bothered with RF buzz whenever I transmitted on 40) with simple unshielded 
twisted pair, and it looks like my buzz problem is pretty much gone. 

Two changes which have improved the station by a lot. Thanks, Jim.

Al  W6LX