[time-nuts] Very Accurate Delta Time RF Pulse Measurements
albertson.chris at gmail.com
Fri Jul 29 12:23:02 EDT 2016
Sounds like you want to build something rather then use some
instruments you can buy. I've thought a little about this too as I
want to make a LIDAR to measure distance using a laser pulse. In my
case I want both low cost and for the device to be very small and
light and run off a battery
I think the way to do this is to have a function generator that
creates a ramp function that moves from zero to some max volts in 100
ns. Then when the pulse arrives you use that to trigger a capture of
the ramp's current voltage into a sample and hold. Then later look at
the difference in the volts in each sample and hold. If the time
difference is longer than one ramp period then you need to also sample
the counts in a normal counter for each pulse edge.
I guess you might use a PIC to implement the above but I find it is
always easier to write software on a larger computer. The aded cost
of using more expensive device is nothing if it saves hours or days of
effort (and you are only building one unit.)
You could use the uP internal counter to measure the rough time
interval and whatever drives that internal counter would also drive
the ramp function generator
>> This is a little outside of time-nuts scope, but not by much. I'm
>> interested in finding the time between two rising edges above a set
>> threshold with preferably nS or high ps timing accuracy. Can this be
>> simply done with a few programmed Microchip PICs or with a good short
>> term OCXO clock? The issue I see is that a 10Mhz timing reference
>> with 1 cycle difference in time yields 100ns resolution, which is far
>> too large, so maybe a PIC can solve this.
>> This weekend project would be a multi-element antenna array, each with
>> a super-fast response log peak power detector fed into several PICs
>> for time of arrival. Whenever a nearby high energy RF pulse is
>> detected, the time of arrival between two antenna elements and hence
>> the direction toward the TX could be roughly computed. Some typical
>> log peak detectors have an 8ns input pulse response time, so I'm
>> hoping that rise times are similar between multiple detectors,
>> negating the delayed response.
>> There are time of arrival/AoA systems out there with synthetic
>> doppler, phased arrays, correlative interferometers, and phase
>> comparators, but it would be interesting to accomplish super wideband
>> AoA timing on two rising pulses with relatively cheap parts.
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Redondo Beach, California
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