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Ed wrote:
Please educate me. I see one of these for sale on ebay that plugs into a crystal socket. I know that a lot of boatanchor IF's are 455Kc, does this generate the IF for old receivers, or is it a bandpass filter? There's an interesting-looking Hallicrafters 455kc crystal filter on eBay, I assume that's what Ed is referring to. The crystal holder has a neat lead seal with a Hallicrafters "h" impressed on it, to keep anyone from opening the holder. That type of filter is a prewar design (one-crystal filter), where the crystal was part of a balanced circuit before the first I.F. amplifier. It could be used with a variable "phasing" capacitor to null a heterodyne, or sharpen reception bandwidth. Most receivers used a switch-selected set of resistors across the single crystal filter to reduce the selectivity to permit 'phone reception. (for example: the Collins 75A-2 receiver) Better than nothing on a crowded c.w. band, but the ringing is annoying and tiring. Modern crystal filters are the lattice circuit type, where an array of crystals are used to get a flat-topped passband of the desired bandwidth. A "six pole crystal filter" has six individual crystals in the filter. 73, Ed Knobloch |
#2
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Exactly what I wanted to know, thanks Ed.
"Edward Knobloch" wrote in message news:yrRtg.12$pR4.8@trndny01... Ed wrote: Please educate me. I see one of these for sale on ebay that plugs into a crystal socket. I know that a lot of boatanchor IF's are 455Kc, does this generate the IF for old receivers, or is it a bandpass filter? There's an interesting-looking Hallicrafters 455kc crystal filter on eBay, I assume that's what Ed is referring to. The crystal holder has a neat lead seal with a Hallicrafters "h" impressed on it, to keep anyone from opening the holder. That type of filter is a prewar design (one-crystal filter), where the crystal was part of a balanced circuit before the first I.F. amplifier. It could be used with a variable "phasing" capacitor to null a heterodyne, or sharpen reception bandwidth. Most receivers used a switch-selected set of resistors across the single crystal filter to reduce the selectivity to permit 'phone reception. (for example: the Collins 75A-2 receiver) Better than nothing on a crowded c.w. band, but the ringing is annoying and tiring. Modern crystal filters are the lattice circuit type, where an array of crystals are used to get a flat-topped passband of the desired bandwidth. A "six pole crystal filter" has six individual crystals in the filter. 73, Ed Knobloch |
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