); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Can`t it be done with just 3 resistors? Cheers,.............................................Don C.
----- Original Message ----- From: "Bruce Griffiths" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]>; "Discussion of precise time and frequency measurement" <[email protected]> Sent: Saturday, November 03, 2007 10:19 PM Subject: Re: [time-nuts] Fury Interface Board: How about TI OPA277? > [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. _______________________________________________ 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.
