9 MHz 6 Pole 250 Hz Crystal Filter Model 221

Special 250 Hz filter with the passband centered on 500 Hz rather than 750 Hz. Same as 219 except for the passband frequency.


Center Frequency 9.000500
6 dB BW, Hz 250
Shape Factor, 6/60 dB 2.4:1
Insertion Loss, dB 10.0
Ultimate Rejection, dB 85+
Z in & out, Ohms 200
Number of Poles 6

Additional Information

From Scott Robbins, W4PA, on the Ten-Tec Reflector February 17, 1998:

As regular readers of the reflector, you've probably seen the thread about a group of hams contracting with our filter manufacturer, through Ten-Tec, to have an alternate center frequency 250 Hz 9 MHz I-F filter built for use with the Omni-VI and Omni-VI Plus. Tyler Barnett, N4TY, gathered the group and then contacted us about the possibility of Ten-Tec's engineers providing our filter manufacturer with the needed specs and to see if we could obtain a reasonable price for the filter as well.

The idea for an alternate passband center frequency CW filter is not a new one. We did a survey via the Internet reflector about a year ago to see where our Omni-VI owners run the offset in an attempt to determine whether it was feasible for us to offer alternate passband center filters for the transceiver. This was after a couple of groups of hams had contracted independent of us with our filter manufacturer to build a 9 MHz I-F, 500 Hz bandwidth, 500 Hz passband centered filter. (Which, of course, was fine with us as we had no interest in doing them ourselves).

Our standard 9 MHz I-F filters are passband centered at 750 Hz. This becomes somewhat problematic when running the Omni-VI or VI-Plus at a lower CW offset (400-550 Hz). Using a low offset, when 250 Hz bandwidth filters in both I-F's are cascaded together the signal tends to slip off the edge of the filter.

After some discussion with the filter manufacturer they indicated to us that despite the filter being a "special order" item that they would be willing to extend us our usual quantity discount for the new filter. Which, I must admit, we were surprised and pleased to hear! The main sticking point in the past for us to offer alternate passband centered filters was the possibility that we would have to stock the item at a significantly higher price than the rest of the crystal filters we offer for the Omni-VI/Omni-VI Plus.

We'll be offering the new filter at $89, same price as all other crystal filters available for the Omni-VI/Omni-VI Plus. The specs for this filter are the same as the #219 250 Hz CW filter, except the passband is centered at 500 Hz rather than 750 Hz. Who benefits? If you often use a pair of 250 Hz filters, with a low CW offset, you may find this filter to be to your advantage. If you usually run the offset at 600 Hz or higher, you'll find no benefit from having the new #221 in place of the #219.

This is not a "one-time" offer; we will be stocking this filter as a permanent addition to the line.

(note: my #221 filter has a measured center freq of 450hz - N1EU)

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