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Discussion of precise time and frequency measurement

Re: Z3801A questions

Joseph Gwinn

Sat, May 20, 2023 3:37 PM

Re: time-nuts Digest, Vol 229, Issue 21
On Sat, 20 May 2023 03:30:25 -0400, time-nuts-request@lists.febo.com
wrote:

Message: 1
Date: Fri, 19 May 2023 20:17:49 -0500
From: Mahlon Haunschild k4oq.radio@gmail.com
Subject: [time-nuts] Z3801A questions
To: time-nuts@lists.febo.com
Message-ID: 1D775F50-375D-48AB-A340-79A5E3906A45@gmail.com
Content-Type: text/plain; charset=utf-8

Hello list. Just joined and, after reading the list archives, I
feel that I Am Not Worthy to ask these questions, but here goes.

I’ve had a Z3801A just sitting around for years now and, the other
day, I finally decided to experiment with it a bit. I already had
a 26dB Andrew antenna and a Vicor 48V 2.9A power supply for it, so
I put the antenna on the back of the receiver with some N adapters,
wired up a serial cable to an ancient ThinkPad running SatStat,
placed the whole rig in the back yard, and turned everything on.

To my astonishment, after placing it into survey mode, four hours
later, it had completed its sky search and had switched over into
position hold, with a TFOM of 3 and a FFOM of 0. Since all I
wanted it for was to use as a freq reference, I thought it was good
to go.

The next day I tried it again. No go. The Z3801A acted like it
had developed an internal power supply short because it was causing
the Vicor to go into current limiting, with zero volt output.

I’ve read the material on 56V vs 48V switching supply startup for
these, and I will them that next. Failing that, I’ll troubleshoot
the power supply.

It appears that a long time ago someone reverse-engineered the
power supply design and published a schematic for it, and Google
found it somewhere in https://xdevs.com/doc/HP_Agilent_Keysight/
https://xdevs.com/doc/HP_Agilent_Keysight/ but is it on the web
elsewhere?

If all else fails I’m tempted to yank the two DC-DC converters from
the power supply board and power the whole thing with a suitable
AC-DC triple-output switcher (specifically, a Nemic Lambda
LWT-50H-5FF, which is on hand). Has anyone done this?

Lastly, I’m considering trying an Oncore UT+ instead of the VP to
get its better front-end filtering. Opinions?

I'd bet that at least one electrolytic capacitor de-formed while the
unit was on the shelf, and then failed when power was re-applied
after all those years. So look at all electros, and replace any that
seem off.

Joe Gwinn

Re: time-nuts Digest, Vol 229, Issue 21 On Sat, 20 May 2023 03:30:25 -0400, time-nuts-request@lists.febo.com wrote: > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Fri, 19 May 2023 20:17:49 -0500 > From: Mahlon Haunschild <k4oq.radio@gmail.com> > Subject: [time-nuts] Z3801A questions > To: time-nuts@lists.febo.com > Message-ID: <1D775F50-375D-48AB-A340-79A5E3906A45@gmail.com> > Content-Type: text/plain; charset=utf-8 > > Hello list. Just joined and, after reading the list archives, I > feel that I Am Not Worthy to ask these questions, but here goes. > > I’ve had a Z3801A just sitting around for years now and, the other > day, I finally decided to experiment with it a bit. I already had > a 26dB Andrew antenna and a Vicor 48V 2.9A power supply for it, so > I put the antenna on the back of the receiver with some N adapters, > wired up a serial cable to an ancient ThinkPad running SatStat, > placed the whole rig in the back yard, and turned everything on. > > To my astonishment, after placing it into survey mode, four hours > later, it had completed its sky search and had switched over into > position hold, with a TFOM of 3 and a FFOM of 0. Since all I > wanted it for was to use as a freq reference, I thought it was good > to go. > > The next day I tried it again. No go. The Z3801A acted like it > had developed an internal power supply short because it was causing > the Vicor to go into current limiting, with zero volt output. > > I’ve read the material on 56V vs 48V switching supply startup for > these, and I will them that next. Failing that, I’ll troubleshoot > the power supply. > > It appears that a long time ago someone reverse-engineered the > power supply design and published a schematic for it, and Google > found it somewhere in https://xdevs.com/doc/HP_Agilent_Keysight/ > <https://xdevs.com/doc/HP_Agilent_Keysight/> but is it on the web > elsewhere? > > If all else fails I’m tempted to yank the two DC-DC converters from > the power supply board and power the whole thing with a suitable > AC-DC triple-output switcher (specifically, a Nemic Lambda > LWT-50H-5FF, which is on hand). Has anyone done this? > > Lastly, I’m considering trying an Oncore UT+ instead of the VP to > get its better front-end filtering. Opinions? I'd bet that at least one electrolytic capacitor de-formed while the unit was on the shelf, and then failed when power was re-applied after all those years. So look at all electros, and replace any that seem off. Joe Gwinn