); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY [EMAIL PROTECTED] wrote: > > In a message dated 11/2/2007 17:51:33 Pacific Daylight Time, > [EMAIL PROTECTED] writes: > > >>> H'm... and if you really want the full +/-10V range, fitting a regulator >>> and op-amp into the 2V of available headroom requires an LDO and a >>> rail-to-rail output op-amp. >>> > > > > Hi guys, > > I've been following the discussion about increasing the Fury EFC range from > 0-5V to -10V to +10V with great interest! > > I just had an idea on how to avoid all the issues potentially introduced by > using an Opamp circuit. > > Let's take a step back and see how much EFC voltage deviation is really > required: > > 1) let's assume we use an HP 10811, so temperature stability is very good > and certainly requires less than +/-2.5V range to compensate for (on the MTI > double oven units we typically see less than 100uV deviation on the EFC due > to > temperature!). > > 2) Now let's assume an aging of 5E-08 per year - certainly good OCXO's will > be better than this. 5E-08 per year at 10MHz is about 0.00137Hz aging per > day. > > 3) For 10811's I have measured a range of 4Hz for a 5V EFC change, so let's > assume it's EFC gain is 0.8Hz/Volt. This into 0.00137Hz/day means a voltage > change of 0.00171V per day. > > This means a -2.5V to +2.5V EFC range would be enough to compensate for > about 8 years of aging on our well-aged theoretical OCXO, so going to +/-10V > is > probably much more than needed. > > 4) So why don't we just run the OCXO ground at +2.5V instead of 0V, and run > the Fury ground at 0V? > > This means the Fury's EFC output (0V to 5V) looks like a -2.5V to +2.5V > range to the OCXO due to the OCXO's ground being offset by 2.5V. > > The 10MHz output of the OCXO can be easily transformer-coupled into Fury as > someone has said earlier, so no problem here. > > Offsetting the OCXO ground by 2.5V should be possible by adding a -2.5V low > noise regulator to the system. EFC current is very low, so a low noise > negative voltage reference may be used to generate the -2.5V. > > No need for opamps, complex bipolar voltage regulators, etc. Of course any > noise or drift in the -2.5V regulator would show up in the EFC voltage as an > error. > > What do you think? > > bye, > Said > > > Said
Another consideration is that for 10544A's and similar oscillators which are only intended to drive high impedance loads( >= 1K) a simple 2 transistor cascode buffer (or maybe a 10811A style common emitter stage with series feedback in the emitter circuit) may be required to allow them to drive a 50 ohm load or an RF transformer satisfactorily. A cascode buffer has higher isolation than a common emitter stage. Bruce > > > > > > > > ************************************** See what's new at http://www.aol.com > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
