TR and RF problem of the computer: Solutions

[Ve3bmv@aol.com]

In a message dated 97-02-14 15:14:32 EST, OH2MM writes:

<< Like K4MA and others, I have experienced a lot  
 of RFI to the computer when using TR with a  
 linear amp at OH0MM, EA8EA and PY0FF. 
 The symptom is the same: paraller port used for keying is
  locked in a permanent key-down position.  The
  locking can happen with only 80 watts output.
  >>

Just run into same problem when fired up on 20 m today. (160 m was OK with
full kw) Antennas in both cases are 20 ft above my head, verticals with
radials on the top of the roof. When transmitting on 20 m with more than 150W
the rig is keyed solid. Using par. port for keying and paddle. When I
disconnected DC power from the netebook (IBM Thinkpad 500) it got worse. I
took about 10" piece of braid and grounded the metal part of par. port on
notebook to the nearest screw on TS870 and problem is gone. I can run now
full power from Titan.  

I have noticed that pin 14 on LPT is NOT a 5+Volt pullup as might be
interpreted from TR Log manual. Pin 14 is a signal pin controlled by a gate
on par. port. That is typically tied up by resistor to +5V internally, but
there is a gate controlling the pin and it is also switchable between +5V and
0V levels. I have tied one too many circuits for pullup to this pin and as
soon as I closed the paddle contacts, pin 14 level droped to 0 and stayed
there. (keying dit-dah-dit-dah...) Manual states also that pin 14 is used to
control external relays. When using pin 14 for pullup for paddle contacts
only, it works ok. This could be contributing to the above RF problem. It
might be better to bring paddle pullup from real +5V. 

Don't "emulate" any other programs! This TR is a gem, just configuring for
two radio operation (same band), can't wait  to get it going!
73 de Yuri, K3BU, VE3BMV