[TenTec] O II RF distortion in SSB audio

[Jim Brown K9YC]

On Sat, 26 May 2007 06:24:03 -0600, M. Todd Miskel wrote:

>Is it inherant that a hot front end like Orion is just more 
>sensitive to RF, or has TT missed the ball somewhere in 
shielding
>the Orion? 

Most "RF in the shack" has a "Pin 1 problem" as the root cause. 
I haven't looked at the Orion, but my Omni V has a pin 1 
problem.  My FT1000MP (which drives a Titan 425) has a pin 1 
problem that causes RF feedback distortion on 15M SSB with a 
dipole that is 150 ft from the shack! I've tamed it with 7 turns 
of the mic cable around a #31 2.4 inch toroid (FT-240). A #43 
toroid would also work on 15M. 

For a detailed rundown of "the pin 1 problem," see

http://audiosystemsgroup.com/RFI-Ham.pdf 

The link below shows how to test for RF susceptibility due to 
pin 1 problems. 

http://audiosystemsgroup.com/AESPaperNYPin1-ASGWeb.pdf

I used my HP 8657A to test my FT1000MP. It showed susceptbility 
at the mic jack just above 75M and around 15M. To do the test, I 
drove the shield contact as described in the paper, and listened 
to my radio on another receiver. The test is pretty simple. You 
modulate the RF generator with 1 kHz AM, and tune the generator 
over the range of interest. If you hear 1 kHz in the transmitter 
output, you have a pin 1 problem. 

73,

Jim Brown K9YC