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Crystal phasing & single signal reception
"gareth" wrote in message ... "Peter" wrote in message ... On Sat, 24 Aug 2013 21:06:59 +0100, "gareth" wrote: I wonder if some more experienced and senior (in the literal sense) amateur could explain to me one difficulty that I have in understanding single signal reception with the crystal phasing control? AIUI, the phasing control is adjusted so that the frequency that would give the audio image is phased out by being in the notch. If that is true, how is it then possible to adjust the BFO to a pleasant-for-you tone, because such adjustment will alter the CIO frequency? Surely the BFO has to be set in advance to be halfway between the serial resonant frequency and the notchable parallel resonant frequency? This is a query stimulated by my current project which is to build a boatanchor style RX, with a flywheel-loaded slide rule dial like that of the Eddystone EA12 The filter is operating on the incoming signal. The BFO frequency is applied to the output of the filter. Thanks, but I think that you may have missed the point. IMHO, Peter's reply is the correct opening statement of a response to your rather unstructured question. If you cannot then use this statement to seed and to refine your own thought process, it might be more helpful if you elaborated the point that you think he is missing. PA |
#2
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Crystal phasing & single signal reception
"Peter Able" stuck@home wrote in message
o.uk... "gareth" wrote in message ... "Peter" wrote in message ... On Sat, 24 Aug 2013 21:06:59 +0100, "gareth" wrote: I wonder if some more experienced and senior (in the literal sense) amateur could explain to me one difficulty that I have in understanding single signal reception with the crystal phasing control? AIUI, the phasing control is adjusted so that the frequency that would give the audio image is phased out by being in the notch. If that is true, how is it then possible to adjust the BFO to a pleasant-for-you tone, because such adjustment will alter the CIO frequency? Surely the BFO has to be set in advance to be halfway between the serial resonant frequency and the notchable parallel resonant frequency? This is a query stimulated by my current project which is to build a boatanchor style RX, with a flywheel-loaded slide rule dial like that of the Eddystone EA12 The filter is operating on the incoming signal. The BFO frequency is applied to the output of the filter. Thanks, but I think that you may have missed the point. IMHO, Peter's reply is the correct opening statement of a response to your rather unstructured question. If you cannot then use this statement to seed and to refine your own thought process, it might be more helpful if you elaborated the point that you think he is missing. Thanks. but the subject matter seems to have WHOOSHED over your head. |
#3
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Crystal phasing & single signal reception
gareth wrote:
"Peter Able" stuck@home wrote in message IMHO, Peter's reply is the correct opening statement of a response to your rather unstructured question. If you cannot then use this statement to seed and to refine your own thought process, it might be more helpful if you elaborated the point that you think he is missing. Thanks. but the subject matter seems to have WHOOSHED over your head. Mine too, I don't really understand what you're asking. The crystal filter is a bandpass filter. The phasing control affects the symmetry of the filter somewhat (but not really all that much). --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#4
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Crystal phasing & single signal reception
In message , Scott Dorsey
writes gareth wrote: "Peter Able" stuck@home wrote in message IMHO, Peter's reply is the correct opening statement of a response to your rather unstructured question. If you cannot then use this statement to seed and to refine your own thought process, it might be more helpful if you elaborated the point that you think he is missing. Thanks. but the subject matter seems to have WHOOSHED over your head. Mine too, I don't really understand what you're asking. The crystal filter is a bandpass filter. The phasing control affects the symmetry of the filter somewhat (but not really all that much). --scott The crystal by itself has a natural 'blow-suck' signal throughput, with a sharp notch just HF of the peak. The phasing control capacitor should be able to move the notch to the LF side of the peak, and also (to a limited extent) to move the notch a little closer to the peak (on either side). -- Ian |
#5
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Crystal phasing & single signal reception
"Ian Jackson" wrote in message
... In message , Scott Dorsey writes gareth wrote: "Peter Able" stuck@home wrote in message IMHO, Peter's reply is the correct opening statement of a response to your rather unstructured question. If you cannot then use this statement to seed and to refine your own thought process, it might be more helpful if you elaborated the point that you think he is missing. Thanks. but the subject matter seems to have WHOOSHED over your head. Mine too, I don't really understand what you're asking. The crystal filter is a bandpass filter. The phasing control affects the symmetry of the filter somewhat (but not really all that much). --scott The crystal by itself has a natural 'blow-suck' signal throughput, with a sharp notch just HF of the peak. The phasing control capacitor should be able to move the notch to the LF side of the peak, and also (to a limited extent) to move the notch a little closer to the peak (on either side). Ian, with your greater experience than mine, it is the concept of single-signal reception in which I am interested. Have you any clues about that, please? |
#6
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Crystal phasing & single signal reception
In message , gareth
writes "Ian Jackson" wrote in message ... In message , Scott Dorsey writes gareth wrote: "Peter Able" stuck@home wrote in message IMHO, Peter's reply is the correct opening statement of a response to your rather unstructured question. If you cannot then use this statement to seed and to refine your own thought process, it might be more helpful if you elaborated the point that you think he is missing. Thanks. but the subject matter seems to have WHOOSHED over your head. Mine too, I don't really understand what you're asking. The crystal filter is a bandpass filter. The phasing control affects the symmetry of the filter somewhat (but not really all that much). --scott The crystal by itself has a natural 'blow-suck' signal throughput, with a sharp notch just HF of the peak. The phasing control capacitor should be able to move the notch to the LF side of the peak, and also (to a limited extent) to move the notch a little closer to the peak (on either side). Ian, with your greater experience than mine, it is the concept of single-signal reception in which I am interested. Have you any clues about that, please? The only clue I can offer is that 'single-signal reception' is vague - but presumably self-explanatory, ie the filtering is very narrow, enabling you to receive only one signal (unless you have more than one on or very close to the same frequency). It's a term that I recall being around when I were a lad, but I can't say I've heard it much since. I guess it's been replaced by more scientific descriptions of how good the filtering is. -- Ian |
#7
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Crystal phasing & single signal reception
"Ian Jackson" wrote in message
... Ian, with your greater experience than mine, it is the concept of single-signal reception in which I am interested. Have you any clues about that, please? The only clue I can offer is that 'single-signal reception' is vague - but presumably self-explanatory, ie the filtering is very narrow, enabling you to receive only one signal (unless you have more than one on or very close to the same frequency). It's a term that I recall being around when I were a lad, but I can't say I've heard it much since. I guess it's been replaced by more scientific descriptions of how good the filtering is. Thank you, Ian. I have a vague memory of something in BadCon from about 40 years ago which related to setting up for single signal reception, which involved no further adjustments to phasing or BFO once it had been set. I am fairly sure, hence my enquiry that it involved phasing out the audio image as well as involving the peaking that comes from a single series resonant crystal. Hence my assumption that the BFO frequency must lie half way between the peak and the notch. I've no experience of such things. The HRO I had in my possession 20 years ago did not posses the crystal filter, but in an effort to speed up development of my RX project, it seemed to me that a single crystal filter would be an easier starting point than a ladder filter. |
#8
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Crystal phasing & single signal reception
Ian Jackson wrote:
In message , Scott Dorsey writes: Mine too, I don't really understand what you're asking. The crystal filter is a bandpass filter. The phasing control affects the symmetry of the filter somewhat (but not really all that much). The crystal by itself has a natural 'blow-suck' signal throughput, with a sharp notch just HF of the peak. The phasing control capacitor should be able to move the notch to the LF side of the peak, and also (to a limited extent) to move the notch a little closer to the peak (on either side). Yes, and that notch is useful for eliminating a single interfering CW signal. But it's not useful for multiple interfering signals or much at all for SSB. "Single signal reception" to me would imply a narrow-sloped bandpass filter but it sounds more like marketing than engineering. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#9
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Crystal phasing & single signal reception
"Scott Dorsey" wrote in message
... gareth wrote: "Peter Able" stuck@home wrote in message IMHO, Peter's reply is the correct opening statement of a response to your rather unstructured question. If you cannot then use this statement to seed and to refine your own thought process, it might be more helpful if you elaborated the point that you think he is missing. Thanks. but the subject matter seems to have WHOOSHED over your head. Mine too, I don't really understand what you're asking. The crystal filter is a bandpass filter. The phasing control affects the symmetry of the filter somewhat (but not really all that much). A single crystal-plus-phasing-control is NOT a bandpass filter. It is a SINGLE crystal that has a series-resonant peak and a parallel-resonant notch, and it is most certainly not a symmetrical response curve. The phasing control affects the frequency of the parallel-resonant notch. The reason for my query is that googling threw up the instructions for a Hallicrafters (SX42, I think) that suggested that the BFO could be adjusted AFTER the setting of the phasing control, when it seemed to me that such action would move the position of the notch AWAY from the audio image and thus lost the single-signal facility. But thanks for your contribution. |
#10
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Crystal phasing & single signal reception
A single crystal-plus-phasing-control is NOT a bandpass filter. It is a SINGLE crystal that has a series-resonant peak and a parallel-resonant notch, and it is most certainly not a symmetrical response curve. The phasing control affects the frequency of the parallel-resonant notch. The reason for my query is that googling threw up the instructions for a Hallicrafters (SX42, I think) that suggested that the BFO could be adjusted AFTER the setting of the phasing control, when it seemed to me that such action would move the position of the notch AWAY from the audio image and thus lost the single-signal facility. But thanks for your contribution. Gareth, The answer is quite simple; unless you move the VFO there will be no need to change the BFO setting. Adjusting the phasing control is akin to an IF shift control on a modern radio with the addition of a notch to the side of the passband which you can move with the phasing control. Adjusting it will have no effect on the frequency of the received signal merely the range of frequencies in the passband or the notch. The only reason that the BFO might need adjusting is pulling of the VFO which was quite common on early receivers due to poor supply regulation and the like. 73 Jeff |
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