parnass@ihu1h.UUCP (Bob Parnass, AJ9S) (10/04/84)
Why is ICOM'S 250 Hz Filter Cheaper Than Its 500 Hz Filter? ICOM offers 2 narrow CW filters for the 9 MHz 1st IF in the R71A general coverage receiver: 1. FL-32 (500 Hz @6 db, 1.5 KHz @ 60 db). Price = $60. 2. FL-63 (250 Hz @6 db, ? @ 60 db). Price = $48.50. The 500 Hz filter worked ok in my older R70. Why is the more narrow filter CHEAPER? Does anyone have any experience with either filter in the R71A? -- =============================================================================== Bob Parnass, Bell Telephone Laboratories - ihnp4!ihu1h!parnass - (312)979-5414
andy%aids-unix@sri-unix.UUCP (10/08/84)
From: Andy Cromarty <andy@aids-unix> The cost of a filter is usually less dependent on its bandwidth than on (a) its shape factor (ratio of the 6dB and 60dB bandwidths) and (b) the IF stage (more specifically, the frequency) for which it was designed, at least for a crystal filter. This is because for any given frequency the crystals cost about the same whether they're 250 or 500 Hz apart; the thing that costs more is *more* crystals (aka more "poles"), which does not alter the 6dB bandwidth but improves the shape factor. Improved shape factor corresponds to an increased ability to select against strong stations on a nearby frequency. In addition, filter cost varies with frequency, since it is generally harder to build an IF stage with good gain and selectivity at a higher frequency -- that's the reason most superhet receivers use a low-frequency IF stage somewhere along the way, most often at 455kHz. (They use the high-frequency IF stage(s) for image rejection.) This would predict that the more expensive component has a better shape factor and/or is for a higher IF frequency. If that isn't the case, then I'd suspect either (a) different filter technology (there are other sorts of filters, such as ceramic or mechanical filters for low IFs) or (b) an artifact of the production process, such as improved production efficiency through automation (the sort of thing that Yaesu claims is responsible for the remarkably high feature/cost ratio for the FT-757GX transceiver) or larger volume production of one filter than the other. [Corrections and additions are invited.] 73, Andy N6JLJ
hoffman@pittvax.UUCP (10/10/84)
I have an R71A with the 250 Hz filter and find that it performs very well. Between that filter, the passband tuning, and the notch, I can isolate even the most crowded of CW signals. Now, if only I were more proficient in CW! :-) It even does an acceptable job of picking those 85-hz shift RTTY stations out of the multiplexed transmissions. ---N3CVL -- Bob Hoffman Pitt Computer Science