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am/narrow-fm/wide-fm/lsb/usb what else?
Al Klein wrote: On Sun, 09 Oct 2005 10:50:22 -0400, Dave Holford said in rec.radio.scanner: Al Klein wrote: But I can assume that all filters currently in production are symmetrical about the center frequency within 10% - because they all are. Certainly most current crystal filters Mechanical filters, ceramic filters, lumped-constant filters, op-amp filters ... any discrete piece of hardware that's supposed to pass a band of frequencies in the IF of a modern (within the last 40 years or so) receiver. are symmetrical about the centre frequency, as are most people symmetrical about the centre (externally at least, and I'm not going to quibble about the orientation since I'm sure you know what I mean) - I wrote 'carrier' frequency. If you put the carrier (no need for tics - carrier whether suppressed or not) at the center of the filter's bandpass, the filter is symmetrical about the carrier - if you put the carrier outside the bandpass of the filter are you going to claim that bandpass filters don't pass signals? The filter is symmetrical about any signal centered in the bandpass if the filter has a symmetrical bandpass - by definition. I'm not sure about current mechanicals (somewhere I have an old Collins filter catalog with asymmetrical SSB curves). Within 10%? None of mine were ever that distorted, although some of the Collins filters were about the most asymmetrical filters I've ever seen. They were designed that way. But the receivers were designed to work with "asymmetrical" filters. Just for fun I am currently listening to an LSB conversation on 3763 kHz with a 7.5 kHz filter and I cannot hear any sign of the conversation on 3765 - but, the noise is a bit higher due to the wider filter. I wouldn't normally do this but just had to try it. Of course, if I select DSB or ISB I get both signals, although the 3765 conversation is inverted and shifted in frequency. With what receiver and which filter? What kind of detector? I can design any number of receivers that will do what you claim, but that doesn't negate the fact that the standard filtered superhet SSB receiver will receive a signal on the "wrong" sideband if the filter is wide enough and the detector is set correctly. As I stated in my first posting, a Winradio. Oh, you mean that a DSP is capable of not hearing the opposite sideband. Nothing to do with filters. "Filtering" isn't always done by "filters". The rest of the paragraph is true if you are talking about 'the standard filtered superhet SSB receiver' provided that it is also fitted with AM filters which can be used in the SSB mode - not universally true. I can do it with my TS-450 but not my IC-706 for example. Not all receivers have the ability to select mode and filter independently. And my Honda can't receive ISB either. If we're comparing fruits, chickens don't count. You are saying exactly what I've been saying, except that you want to argue about it. Gotta go, lunch is ready. Dave |
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