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IC-746 FAQ
Inrad publishes basic performance curves of most of their filters on-line. An example of a
typical curve is:
http://www.qth.com/INRAD/graphs/116.gif
AB4OJ has a complete set of passband curves for Icom's filters on his WWW site at:
http://www.qsl.net/ab4oj/icom/filters/filters.html
Several companies have good on-line treatments describing basic filter characteristics,
complete with diagrams.
Corning Frequency Control has a very concise page styled in a glossary format at:
http://www.ofc.com/filters/definitions.html
(site not responding Jan-2002)
Vectron International also has a nice on-line treatment of filter characteristics at:
http://www.vectron.com/products/xtal/filter.htm - definition
The folks at Piezo Technology Inc. describe filter characteristics with attenuation curves.
http://www.piezotech.com/Technical_Information/techindex.htm
4.6
Why do filter "bandwidth" or "shape factor" matter?
Narrower bandwidths reject more noise and improve sensitivity. Wider bandwidths provide
better fidelity.
Narrower bandwidths also reduce the number of simultaneous signals the rig can "hear".
This reduces the AGC pumping action caused by nearby signals, particularly important for
CW and digital modes.
Smaller (tighter) shape factors reject more noise and improve selectivity. Larger (wider)
shape factors generate fewer problems/complaints with fidelity or ringing.
4.7
What is considered to be a narrow filter?
In the context of (and for the purposes of) this FAQ, a narrow filter is any filter that has a
smaller bandwidth than the stock 2.4Khz wide filters. However, most texts will describe a
filter as being narrow if its bandwidth is smaller than that of the desired signal.
4.8
What are narrow IF filters used for?
Usually, narrow filters are used to reject unwanted signals or noise. The narrower the
bandwidth, the less noise there will be and the better the sensitivity. You can lose part of the
desired signal in the process, but that may be preferable to the interference you're trying to
reject.
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2003-02-08