Subj:  RFI and a voice keyer...
Date:  Fri, Jun 23, 1995 4:48 PM EDT
From:  gswanson@arrl.org
To: cq-contest@tgv.com ('CQ-CONTEST REFLECTOR')


Greetings fellow contesters.

The following should be useful to some contesters who own the MFJ (Model 
432) voice keyer.

After we published a Product Review of the MFJ-432 voice memory keyer, a few 
people mentioned that they had RFI problems with their MFJ-432s. The Product 
Review testing had been done with outdoor antennas, and we did not notice 
any RFI problems--even at a multi-multi contest operation. RFI was not a 
problem at W1AW either, even during a code practice transmission with 
multiple kilowatt transmitters in operation (the bulletin antennas are 100 
feet or more from the station).

We conducted some additional tests on the MFJ-432 using a typical 100 watt 
transceiver and an indoor dipole about 6 feet away at its closest point. 
Sure enough, RFI could be described as severe, even at low power levels.

We easily eliminated the indoor-antenna RFI problem by wrapping the 
MFJ-432's input and output audio/PTT cables around a pair of FT- 140-43 
toroid cores.  Since we used an internal  battery to power the Keyer, we 
didn't have power supply cables to contend with.  Your installation may 
require a third core if using a power supply.

 Install the cores by winding 5 to 8 turns of cable around them and as close 
to the Keyer box as possible.  Once installed, we were able to run up to 
full power on 20 meters with the antenna's closest point only five feet away 
from the MFJ-432 Voice Memory Keyer.

FT-140-43 cores are available from Amidon, Palomar Engineers, Ocean State 
Electronics and other QST advertisers.

Since some may not get QST (shame!), here is the info for a few vendors:

Amidon Inc.
3122 Alpine Avenue
Santa Ana, CA 92704           
(714) 850-4660

Ocean State Electronics
PO Box 1458
6 Industrial Drive
Westerly, RI 02891
(401) 596-3080

Palomar Engineers
PO Box 462222
Escondido, CA  92046
(619) 747-3343

The above telephone numbers are accurate as of 23 June 95.

73!  Glenn Swanson, KB1GW
e-mail:  gswanson@arrl.org