1.9 kHz SSB Filter for Icom IC-746

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One thing I notice a lot during contests with my trusty Icom IC-746 (pre pro) is the splatter from power house stations nearby in frequency. I realize I can’t keep their splatter out if it falls within the passband of my receiver. However, I can at least try a more narrow filter to mitigate out of band energy.

The IC-746 comes with a 2.4 kHz wide filters for the first 9 MHz IF and for the second 455 kHz IF along with some wide options for AM and FM use.

I purchased this radio from a CW operator so it was no surprise what I found in the two 9 MHz optional slots: 350 and 250 kHz filters. They work real well for CW and, I suppose, the wider of the two would be good for RTTY work which I am just starting to use.

However, I do lots of SSB work and often get the AGC following the nearby signals rather than the one I want. So I really wanted to try out the 1.9 kHz Icom FL-223. It did not take long to find one on E-Bay from… Taiwan no less. In about a week I had my package.

I decided to keep the 350 Hz filter and replace the 250 with the 1.9 kHz unit.

That last picture was about the only way to quantify the difference between the two SSB bandwidths I now have. Here is it bigger…

Graphical results of 2.4 (bottom) and 1.9 kHz
Graphical results of 2.4 (bottom) and 1.9 kHz

These two filters, and the CW 350 and 250 kHz units for that matter, all run a little wider than you might expect, but that’s probably normal since frequency roll off is a slope.

Initial use reveals some affect on received audio, but really not all that much. I tuned in 160 meters and found some voices to listen too. I did notice slightly less fidelity when using the 1.9 kHz filter.

Does this mean I will have a better chance of keeping my AGC intact during close in SSB contest QSOs? I don’t know. Nothing will make this Icom 746 an Elecraft K3. However, this can’t hurt.

Sweepstakes is in a couple weeks so maybe I will give it a hard test then.

I only wish the Icom IC-746 had more filter slots.

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