Sunday, September 03, 2006
More IC-7000 Manual Notch Filter
To start with, a picture of the display. I rather like it.
Unfortunately the IC-7000 user manual is rather opaque on the properties of the MNF. It does not give any indication about the tuning range of the MNF, neither about the width of the Narrow, Medium and Wide notch filter settings. By trial and error, I found that the tuning range is +/- 5kHz. The filter width is pure guesswork. But the IC-746Pro's manual notch is 70 Hz wide, and that might fit with "Narrow". So maybe Medium is 200 Hz and Wide is 500 Hz? My guess is as good as anyones.
Like I said there are two identical MNFs. You can choose one, the other, both or none (MNF Off). It can work together with the Auto Notch Filter as well. You can tune each filter independently within the (presumed) +/- 5kHz tuning range.
In AM mode the effect is startling. If the filters are centered in the tuning range, they will notch out the frequency you're on, and the signal you are tuned to will simply go away. Well...sort of, anyway. Now, if you are tuned to 730 and 729 is giving you a hard time, you tune one of the MNF filters 1 kHz downwards until you hear the interference being nulled. I don't know yet which bandwidth setting is best - narrow, medium or wide, but they all seem to work. Wide is not a worse choice than the other two. If there are other noise sources in the passband, try to tune the other MNF filter to notch it out.
ECSS mode is not as straightforward. As most will know, the USB and LSB bandwidths are asymmetric in shape, as opposed to the symmetrical AM bandwidths. So you need to tune the MNF not 1 kHz, but maybe 4 kHz, depending on the width of the SSB bandwidth chosen. Also, when using SSB mode to listen to AM signals, the AM detector and carrier are replaced with a product detector with the receiver BFO zero beat to the AM carrier. Maybe because of this I was not able to null the offending station the way I did in AM mode, but its signal level was nontheless significantly reduced. And the impact from splatter was reduced.