Topband: RF in the DX Eng. NCC-1 (and a fix)

[Rob Atkinson]

Merry Christmas and Happy New Year:

On 160 m. (probably due to the close proximity to my inverted L) my
NCC-1 rx antenna phasing box would snap crackle and pop on transmit,
most likely the result of RF getting into the nine relay coils inside.
If you employ phased rx antennas and a tx antenna, all in a small
space, running over 1 KW you may have noticed this also.  The stock
box has some small bypass caps on the DC supply line in, and the T/R
control line in, but they were not enough to keep RF out entirely.
The fix for me was a small 100 micro-Henry choke inside the box in
series with the floating center of the T/R line, along with a 0.015
mfd cap on the cold side of the choke to ground, and a pair of the
same chokes  in series with the DC +,- supply line into the box at its
entrance.  The DC supply jack has an adequate amount of stock bypass
capacitance so I didn't add any more.  0.1 mfd if I remember
correctly.  These fixes quieted the NCC-1 down for me and were a lot
easier than trying to bypass each relay coil to ground with
capacitors.

73

Rob
K5UJ