Some years ago I acquired some superb…and originally very expensive…SEI Crystal Filters on 1.4MHz.  I knew I had a USB and LSB pair, but didn’t know which was which and had no idea about the correct termination impedance.  What I needed was SEI Crystal Filter Data…which no one had.  There have been lots of questions on the internet looking for it too, no one has it.  I recently came across an SEI Crystal Filter data book and thought I’d scan it in…so those who need it can find a copy.  It’s under ‘Miscellaneous’ on my ‘Downloads’ page.

It covers the following filters:

100KHz – QC1170, QC1170A, QC1171, QC1172 and QC1173

1.4MHz – QC1112F, G, H, J and K plus QC1113B

1.6MHz – QC1112A, B, C, D and E plus QC1113A and QC1193A, B, C, D and E

10.7MHz – QC1062A, B, C, D, E, F, G, H and J plus QC1121A, B, C, D,E and F

My filters

SEI Crystal Filters

The two filters I have, pictured right, are the QC1112V and QC1112Z…not mentioned in the SEI Crystal Filter Data book!  However, the bandwidth is written on each filter; they are 3.2KHz wide each.  The frequency is also listed as 1.4MHz.  I’d already used my Raspberry Pi Wobbulator to discover which one was USB and which was LSB…I used a cunning process of elimination to deduce that 😉

They seemed to be quite low impedance and I think it isn’t too much of a ‘leap of faith’ to assume they are part of the QC1112 range in the book.  At 75 ohms termination the passbands are perfect and they look like really good filters.

You need to remember that these filters, now available as surplus, cost a fortune to make…they were for professional communications equipment where expense was not as much of an issue as it is with amateur equipment.

So, you can now dig out those filters you got at a rally and use them in a homebrew receiver or transmitter…the filter performance will be outstanding.

The various SEI crystal filters were used in a number of different receivers, and transmitters.  The 10.7MHz filters were mainly used in FM equipment…but they also make great roofing filters for homebrew receivers.

I have many pages of SEI Crystal Device Data to scan and upload…when I have another few hours to spare.