Made some measurements on a 5065A optical unit. -There are 3 layers in the magnetic shield. -There is about 1/8" of insulation between the outer and middle, and between the middle and inner shields. -The C-field winding is wound on a cardboard form that fits tightly into the inner shield. -There is almost 1/2" of foamed insulation between the C-field winding and the cell and oven forms and windings. Per Poul-Hennings data a 3.25 deg C change of the outer shield will result in a 1 deg C change in the C-field coil. This equates to a 3.4X10-14 frequency shift when not using active current drive. If the outer shield is actively held to plus/minus 1 deg C then the shift will be held within plus/minus 1.05X10-14 as long as the ambient temperature stays within the regulating range of the PC liquid cooler. Cheers, Corby

Hi If the coil form really is plain old cardboard. I wonder what the impact of humidity is? With the heat rise and all the packing, it’s going to be a pretty indirect effect. It might be an issue on a unit that had been stored powered off for a number of years. Straight cardboard *is* an issue on RF coils in humidity. Bob > On Nov 27, 2017, at 12:34 PM, cdelect@juno.com wrote: > > Made some measurements on a 5065A optical unit. > > -There are 3 layers in the magnetic shield. > -There is about 1/8" of insulation between the > outer and middle, and between the middle and inner shields. > -The C-field winding is wound on a cardboard form that > fits tightly into the inner shield. > -There is almost 1/2" of foamed insulation between the C-field > winding and the cell and oven forms and windings. > > Per Poul-Hennings data a 3.25 deg C change of the outer shield > will result in a 1 deg C change in the C-field coil. > > This equates to a 3.4X10-14 frequency shift when not using > active current drive. > > If the outer shield is actively held to plus/minus 1 deg C then > the shift will be held within plus/minus 1.05X10-14 as long as > the ambient temperature stays within the regulating range of the > PC liquid cooler. > > Cheers, > > Corby > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

-------- In message <2B66D682-15CF-465F-9A34-D7F7E7929ED8@n1k.org>, Bob kb8tq writes: >Straight cardboard *is* an issue on RF coils in humidity. The C-field coil is DC only. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.

Hi Yup, I’ve never measured humidity on DC coils. I have done a lot of measurements on various combinations of cardboard and “stuff’ on RF coils. Bob > On Nov 27, 2017, at 6:36 PM, Poul-Henning Kamp <phk@phk.freebsd.dk> wrote: > > -------- > In message <2B66D682-15CF-465F-9A34-D7F7E7929ED8@n1k.org>, Bob kb8tq writes: > >> Straight cardboard *is* an issue on RF coils in humidity. > > The C-field coil is DC only. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > phk@FreeBSD.ORG | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence.

However the dimensions of the coil former vary with moisture content. Impregnation with waxes and other organic materials merely serves to slow down the rate of absorption and doesn't prevent it. Bruce > On 28 November 2017 at 12:36 Poul-Henning Kamp <phk@phk.freebsd.dk> wrote: > > > -------- > In message <2B66D682-15CF-465F-9A34-D7F7E7929ED8@n1k.org>, Bob kb8tq writes: > > >Straight cardboard *is* an issue on RF coils in humidity. > > The C-field coil is DC only. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > phk@FreeBSD.ORG | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

Hi The gotcha with coating (at least with RF coils is that the adsorption / desorption process gets really crazy. You may slow the “going in” part down to a week. The “getting out” part may turn into (many) months. That’s what makes the “stored on a shelf and then turned on” thing a mess. It takes a *long* time for things to stabilize. Again - this is all RF based. Some of what happens applies at DC. Some of what happens simply does not matter at very low frequencies. Bob > On Nov 27, 2017, at 6:41 PM, Bruce Griffiths <bruce.griffiths@xtra.co.nz> wrote: > > However the dimensions of the coil former vary with moisture content. > Impregnation with waxes and other organic materials merely serves to slow down the rate of absorption and doesn't prevent it. > Bruce >> On 28 November 2017 at 12:36 Poul-Henning Kamp <phk@phk.freebsd.dk> wrote: >> >> >> -------- >> In message <2B66D682-15CF-465F-9A34-D7F7E7929ED8@n1k.org>, Bob kb8tq writes: >> >>> Straight cardboard *is* an issue on RF coils in humidity. >> >> The C-field coil is DC only. >> >> -- >> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 >> phk@FreeBSD.ORG | TCP/IP since RFC 956 >> FreeBSD committer | BSD since 4.3-tahoe >> Never attribute to malice what can adequately be explained by incompetence. >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there.