[RFI] TVI: suggestins needed! Help me

Bob Tellefsen n6wg at earthlink.net
Sun Nov 23 09:23:55 EST 2003

One thing to check.
How rf-tight is the transmitter case?
Run a piece of transmission line from your TV set to the transmitter.
Move the loose end of the transmission line around the transmitter to
see where rf energy leaks out.  Once rf is on the outside of your coax
feedline, no low pass filter can do much for you.
Good luck and 73
Bob N6WG

-----Original Message-----
From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com]On
Behalf Of Aldo Angeletti
Sent: Sunday, November 23, 2003 8:46 AM
To: rfi at contesting.com
Subject: [RFI] TVI: suggestins needed! Help me


we are three amateurs radio with different transceivers, 
  different antennas and ground systems but all with the
  same problem : moderate to strong interference to the video of the  
  TV channel B ( 61/68 MHz ) when we transmit on 21 MHz
  band ( 100 W ) ;in my case, the TV antenna is directly 
  connected to the TV Set ( no preamplifier on the feeding 
  line being the imput signal 1mV ).
  Connecting a Spectrum Analyser to the receiving TV antenna 
  I see the third harmonic that interferes with TV signal (it is 
  ~ 33 dB less ); connecting a Drake low pass filter the armonic 
  on HF cable decreases of 45dB but on TV cable:it has ,more 
  or less , the same amplitude .
  I tried a  TG-4 Line Isolators but nothing has changed, so I 
  have no other ideas.
  One of the test I tried it has been to use a dummy load instead 
  of antenna (Explorer 14 )and the TV channel was ok;the strange,
  in this case,is the behavior of the low pass filter:it does not work;
  all the armonics at the dummy load terminal keep the same 
  amplitude with or without it.Using a signal generator instead of the
  TX (Mark V) it works correctly cleaning all the armonics
  Can you help me ? 

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