[TenTec] CW filters Omni-C

[Marinus Loewensteijn]

Recognizing a wealth of expertise on this mailing list I like to invite your input on something that has kept me occupied for the past few days.

I like to add a CW filter to my Omni-C. TenTec has sold out of the 217 (500 Hz) and still has the 218 (1.8 kHz) and 219 (250hz). In planning is a replacement manufactured by Inrad.

The consensus seems to be that the 500 Hz is more frequently used than the 250 Hz.

Have been looking at a few alternative options from Inrad, the 8 pole 1000 Hz #766, the 8 pole 400 hz # 759 and the 4 pole 600 Hz #763. Looking at the curves on the old Inrad website I see that the 1000 Hz filter has approx 4dB insertion loss, the 400 Hz approx 9 dB and the 600 Hz about 2.5 dB. 

The Omni-C has a filter board that can take the 1.8 khz and the 500 Hz filter. This board has an amplifier to offset the filter losses. The 1.8 kHz filter position has a 1 dB amplification and the 500 Hz filter position has a 7 dB amplification.

(The 250 Hz filter has an approx 14 dB loss)

I am thinking about using the 4 pole 600 Hz filter: I feel it will provide better IMD / dynamic range performance because it can go in the 1.8 kHz slot. This should go well with the 500 Hz audio filter which is built in.

Am I missing something / have an error in my reasoning?

Many thanks, 73, Marinus, ZL2ML






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