The 817 receiver filters were measured using computer software
called Gram that uses the sound card DSP as a spectrum analyser and
audio from the radio is fed into the soundcard. A noise generator is
applied to the receiver's antenna port. The volume needs to be
set with great care so the image can be understood. The first picture shows
the 817 when in either USB or LSB modes. The second is when the 817 is in
the narrow CW mode with the added Collins Mechanical Filter that is 500 Hz
wide
Notice the SSB filter appears to be about 2600 Hz wide. To strong
signals it appears to be much wider.
The Collins Mechanical filter IS narrow, and experiance shows it's
narrow to even strong ajacent signals. The Gram software shows it as having
about a 1000 Hz wide passband for even a strong signal.
Installing the Collins filter is a two step process not explained in the Manual. The filter installs with the filter up and there is a 3 pin and a 4 pin plug. Just line it up so the plugs will mate and plug it in. When your done with the Manual's installation you will discover the filter doesn't work. Now, while in the CW mode, tap the F key and select the list of 3 functions that includes NAR. Click on NAR and Bingo, your receiver is in narrow 500 Hz passband. This is so you can choose either the narrow filter or, use the wide SSB filter. Not sure why you would ever want that...
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