Friday, 15 April 2011

The effects of a narrow IF filter

I installed a 500Hz filter into my IC-718. It was nice little screwing and soldering project:
The filter, FL-52A, ordered from RadioWorld Ltd.
I got it 3 days after ordering...not bad.
The IC-718, opened according to the instructions in the handbook. 
The opening of the board was a little bit tricky.
The filter is in place...

...and soldered at the other side of the board.

Ready! Hopefully things went right.
There were very clear installation instructions in the user manual....the installation took about half an hour.  Now to the shack for testing!

The result:
After the first hour of testing I had this QSO log:
What an hour! With 50-100 watts and a dipole. Obviously the DX conditions were quite OK that night, but I haven't experienced this kind of QSO efficiency before. One would think that a  razor sharp IF filter is for filtering out disturbing stations. Well, yes...but that's not all. Interfering stations per se isn't that a big deal for experienced CW operators, but this is:
  • The noise level decreases dramatically with a 500hz filter compared to the default 2,1kHz in IC-718. Stations that I could not hear with the wide filter, sound, although weak, chrystal clear! 
  • Related to that, the well-known AGC(Automatic Gain Control)- problem is not as big issue anymore, since it's now easier to block out strong stations, and thus keep the receiver sensitivite. This, together with the lowered noise floor became an asset in also PSK operation: some of the QSOs in the log above were impossible to work with the wide filter: they were not heard&seen at all!
  • Pile-up accuracy! With the narrow filter I can pin-point previous QSOs in order to plan my next shot. Three of the CW QSOs in the log above were worked rather easily in pile-ups.
I'm still a little pistol, with my home made dipoles and stuff. An excited little pistol. Do I dream of 1,5kW linears and yagi towers? Maybe some day, but now, honestly: no!


  1. 10 days after istalling the 500Hz filter I have catched almost 20 new countries and overseas QSOs are getting almost routine stuff...well, the filter was worth investing and installing!

  2. I have an Icom IC718 as my main radio and I love it. I may buy another for mobile/portable use.. :-) Grant ZL2AR