From: Didier Juges <[EMAIL PROTECTED]> Subject: Re: [time-nuts] Allan Deviation -> continuing saga... Date: Sat, 28 Oct 2006 08:44:27 -0500 Message-ID: <[EMAIL PROTECTED]>
> Magnus Danielson wrote: > > Look at the AD8561 datasheet first. The 74HC4046 is much slower than the > > AD8561 and the higher output slewrate of the AD8561 is certainly good to > > keep > > jitter down. The 74HC4046 is worse for that aspect. > > > > What I would rather critize Didiers schematic for is the lack of decoupling > > caps. This is good for many reasons, but it includes keeping the rise and > > fall times up and thus the slewrate up and thus the jitter down. > > > > > There are decoupling caps everywhere, I kept the schematic simple. Implicit components is obviously a bit hard to comment on. > Same, the counters actual wiring is not depicted, it is straight from the > Texas Instrument data sheet. Those where a bit more obvious, since there isn't that much variations to hook those up to acheive the /128 functionality. You could get /256, but that output is not synchronous so you would expect higher jitter. A 74F74 would solve that thought. > I also have a 200 ohm pot across the OCXO > output to adjust the drive level into the 390 ohm resistor not shown. In series I assume. > > I would measure the actual phase-stability and phase-slope of the IF > > transformer solution with aspect to temperature. You may want to lower its Q > > value to flatten the phase-response. You loose in selectivity but gain in > > phase-stability. > > > I have planned to do that. The transformer I am using is quite > temperature stable, and the Q is controlled via the 390 ohm resistor, > which may or may not be the optimal value from a Q standpoint. It is > close to the best value from a drive level standpoint, to make sure I do > not overdrive the comparator. I did not observe a measurable change in > resonance frequency when blowing a hot air gun at it from a distance, > even though my measurement method was crude (adjust the drive frequency > using a SG503 and peak the voltage, use scope to monitor). Good to hear. I have a decent network analyzer to help me out for such experiments. On the other hand I have a lack of space in the lab which effectively prohibits such experiments so... > I could use the 5370 to measure the phase shift while I blow hot air on > the circuit (transformer and comparator), or I could make a small hot > box with a light bulb and a variac, put the OCXO and clock shaper in it > and use my HP3478B voltmeter and a thermistor to record temperature, and > plot delay and temperature via the GPIB while I crank the temperature, > then I could plot delay vs. temperature. Good idea! > The opportunities to experiment are endless... I will never have time > for all that, I better retire now :-) Indeed. I get more toys^H^H^H^Hinstruments next week. Cheers, Magnus _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts