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| low power 125khz receiver |
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| David Hess:
--- Quote from: vk6zgo on March 12, 2019, 07:57:57 am ---Selectivity is another question, as there are the twin problems of adjacent channel rejection, & obtaining sufficient bandwidth at 125kHz to preserve the modulation. Cross modulation from high power MF AM Broadcast transmissions is another likely trap, not to mention that from SMPS. The dynamic range of a receiver operating on voltages of the order of 3.6v is unlikely to be able to handle interference from even quite distant lightning strikes, either. --- End quote --- This is also why I suggest using tuned circuits. Not only do they contribute to selectivity, but they also double the available voltage compliance. Thinking about it more, I would also use a power detection stage with a one shot to only activate the later stages including the data slicer after a potential signal is amplified. FM modulation would be easier to deal with. All of the above could be done to save power but linear operation would not be required before detection. |
| vk6zgo:
--- Quote from: David Hess on March 12, 2019, 11:22:53 pm --- --- Quote from: vk6zgo on March 12, 2019, 07:57:57 am ---Selectivity is another question, as there are the twin problems of adjacent channel rejection, & obtaining sufficient bandwidth at 125kHz to preserve the modulation. Cross modulation from high power MF AM Broadcast transmissions is another likely trap, not to mention that from SMPS. The dynamic range of a receiver operating on voltages of the order of 3.6v is unlikely to be able to handle interference from even quite distant lightning strikes, either. --- End quote --- This is also why I suggest using tuned circuits. Not only do they contribute to selectivity, but they also double the available voltage compliance. Thinking about it more, I would also use a power detection stage with a one shot to only activate the later stages including the data slicer after a potential signal is amplified. FM modulation would be easier to deal with. All of the above could be done to save power but linear operation would not be required before detection. --- End quote --- In my opinion, a radio without tuned circuits is just a detector. The OP hasn't mentioned size, but most people have a fixation on miniaturisation. That is counter-indicated in this case, as compact, high value RF inductors are lossy. This is tolerable when you haven't put strict limits upon the DC current draw of the complete device, as active gain can make up for these losses. |
| David Hess:
--- Quote from: vk6zgo on March 13, 2019, 02:59:06 am ---In my opinion, a radio without tuned circuits is just a detector. --- End quote --- I agree but I assume the OP was thinking of relying on the selectivity of a tuned antenna. I would use tuned circuits for their other advantages as well in this case which help with low power operation. --- Quote ---The OP hasn't mentioned size, but most people have a fixation on miniaturisation. That is counter-indicated in this case, as compact, high value RF inductors are lossy. --- End quote --- Lossy is actually an advantage if it limits Q to an acceptable value. I would have anticipated increasing the loss to lower the Q in this case anyway. |
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