Originally posted by Tepco
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Interesting issues for discuss, I want to make few comments about all this, from beginning of this post.
Operating frequency is absolutely non-related with recovery speed directly (but can affect it to some degree, depending on detector design, indirectly, some lower freq. machines are actually slower, but not all).Neither switch type used in demodulators can affect it directly in any way, but indirectly can.
Most important parameter defining recovery speed is design of post-detector filter stages. Just simple differentiator type circuit in some designs (diode limited and with reduced dynamic range), more complex bandpass filtering in others, usually DSP in anything recently built. Time domain response of this stage is crucial, but not only factor. As a rule, all faster detectors are built using some more sofisticated filter stages, all simple diferentiator types are slower.
Another thing to consider is demodulator type (not components used in it), single ended, like TGSL, or balanced. First type will “leak” DC\LF component in next stage, never mind, there is no DC or LF at this point. Well almost. LF component coming from GND is sufficiently attenuated in RX preamp and AC coupling after it, but higher freq. components generated during sweep over multiple targets may not always be. Especially if following filter is simple derivative stage, with relatively larger bandwidth and not so sharp roll off, this LF will fall into its passband. Balanced detector will perform better in general, or more aggressive band or high pass filtering at RX input can help with single ended design
(yes, 4053 is usually in balanced detector design, SMW or whatever version of it…)
Change filters (use some existing design), change demod, wach BW and gain distribution, you can get nice speed. Changing just time constants of existing filter is not recomanded, filter performance is limited and will affect motion response time too.
Operating frequency is absolutely non-related with recovery speed directly (but can affect it to some degree, depending on detector design, indirectly, some lower freq. machines are actually slower, but not all).Neither switch type used in demodulators can affect it directly in any way, but indirectly can.
Most important parameter defining recovery speed is design of post-detector filter stages. Just simple differentiator type circuit in some designs (diode limited and with reduced dynamic range), more complex bandpass filtering in others, usually DSP in anything recently built. Time domain response of this stage is crucial, but not only factor. As a rule, all faster detectors are built using some more sofisticated filter stages, all simple diferentiator types are slower.
Another thing to consider is demodulator type (not components used in it), single ended, like TGSL, or balanced. First type will “leak” DC\LF component in next stage, never mind, there is no DC or LF at this point. Well almost. LF component coming from GND is sufficiently attenuated in RX preamp and AC coupling after it, but higher freq. components generated during sweep over multiple targets may not always be. Especially if following filter is simple derivative stage, with relatively larger bandwidth and not so sharp roll off, this LF will fall into its passband. Balanced detector will perform better in general, or more aggressive band or high pass filtering at RX input can help with single ended design
(yes, 4053 is usually in balanced detector design, SMW or whatever version of it…)
Change filters (use some existing design), change demod, wach BW and gain distribution, you can get nice speed. Changing just time constants of existing filter is not recomanded, filter performance is limited and will affect motion response time too.
Many thanks!
)
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