The SMART Filter
The SMART Filter was perhaps the most useful accessory for the Ham Shack ever designed and built by N4YG. This filter was equally useful for SSB and CW operation. It used two chips, the S3528 and S3529, which are no longer available. If these chips were still available, or other similar chips could be found, N4YG would certainly be interested in knowing something about them. These two chips were both switched capacitor filters, S3529 a low-pass and the S3528 a high-pass. Together they formed a bandpass filter whose bandwidth could be varied from about 25 Hz to about 5000 Hz in steps of about 25 Hz. The filters were controlled digitally by an Intel(tm) 8749 microcontroller. An LED readout gave a visual indication of bandwidth. The filter could be optimized for either SSB or CW and the readout scale changed accordingly.
If you can obtain the S3528 and S3529 chips, N4YG would be interested in knowing the source. Also, if you have these chips, you could build your own SMART Filter. The schematic diagram and manual for the SMART Filter are available for download.
