This has now been sold as I have the CW filter for the IC-718 but I'm sorry to see it go. I'll keep this page here as I liked it so much and some of you might like to read my experience....
Just had it connected to the IC-718 on 40m this lunchtime and what a difference! Although 40m is not too packed at lunchtime (no QSO!) listening with the filter in is a totally new experience.
The FL-3 plugged into the audio-out jack at the rear of the rig and plugged the headphones into it and did some testing. Comparing the audio from the IC-178 and the FL-3 showed no discernable difference in straight through mode, all OK there.
Listening to a CW signal I switched on the filter pressed the CW switch and everything went quiet, not to worry. I tuned around a bit (slowly) and the CW I was listening to appears, very sharply. Measuring the audible bandwidth of several signals I got an average 200 Hz bandwidth. To qualify the claim, that is from the CW signal breaking the noise floor - peaking S9+ and back to the noise floor. With the filter out of circuit it was 3-4 KHz wide - amazing how wide the 718 really is!
Press the two CW buttons and I can vary the audio bandwidth so I can find the signal on the wide setting and then narrow the audio bandwith to 200 Hz. If I put the peak at the same frequency as my sidetone, I'm spot on frequency when I transmit (well +/- 100 Hz!).
The Auto Notch filter is a joy to witness! A whistle while listening to SSB, press the button and it's gone but the SSB is still perfectly readable. and not a processor in sight!
For an old piece of kit it's amazing and I think for late 1970's transceivers it was probably a pain having that narrow a bandwidth. Anyway, some history and bits.......
This is a late 1970's piece of kit from the much admired Datong (now an 'intelligence gathering' company) stable. The Datong Morse Tutor was the mainstay of learning CW back in those days and was bought by many clubs to share out. Actually, my experience of learning using one probably out me off CW in the first place but you can't knock the inginuity and quality of the build!
Any search for reviews on the FL3 will provide lots of information. All are praising the effectiveness of the filter and their ability to knock spots off almost all but the best modern DSP filters.
Only problem I have found so far is the power supply plug being a 3.5 mm mono type which shorts out the PSU (power supply) when inserting/extracting - silly!
For a full list of the products, manuals, circuits, PCB layouts and more visit the site of Nick B who seems to have been tireless in investigating Datong's kit.
Maybe we can get a modern PCB designed and buid a new one - MF10 filter chips are still out there!