Further information about fixes for Harmonics, Spurs and IMD

Removing spurs

Raj VU2ZAP has confirmed that surface mount components can be used in the LPF after the 45MHz filter.

He used SMD Yellow shielded inductors 331nH  x 2 + 51pf to ground.

Summary of recommended fixes to address unintended spectrum products

  1. Replace K1, K2 and K3 with Axicom 12v relays (low current models are fine) to remove harmonics to acceptable levels in most rigs on most bands.
  2.  Install a 45MHz filter across TP13 (v3 board).   Ashhar Farhan VU2ESE inserts a 0.3µH inductor in series with a 10 pf capacitor across TP13 on the v4 board.   This is on the output of the 45 MHz IF amp going to the front end of the mixer.   The inductor comprises 8 turns on a T30-6 toroid (to give 0.3µH or 300nH).   Or use Raj’s alternative as above.
  3. Consider also changing out L5 and L7 with shielded surface mount inductors (yellow type).  See this article.

 

Leave a Reply

Your email address will not be published. Required fields are marked *