Re: [time-nuts] Z3801A OCXO manual trimming

Someone mentioned the right non-lazy approach with a summing/offset opamp. Do agree. But then just for a try use a V supply and a 10K. I seem to recall tracing the DAC to an opamp. The EFC line is pretty easily accessed. Its one of the little coax cables. The other even lower risk approach is

[time-nuts] Z3801A OCXO manual trimming

Success! I disassembled the oven and adjusted the OCXO frequency up about 5 Hz. Lady Heather reported the DAC changed from +99.99% with no lock to -90% with lock to GPS. Hopefully I did not increase the frequency too much. The long term aging/drift direction has been down - which caused the

Re: [time-nuts] Z3801A OCXO manual trimming

Hi Assuming you can break the EFC lead to the OCXO, you aren’t going to damage anything inside by feeding the EFC line with +/- 5V. If you are going to tear open the OCXO, the line will need to be pulled anyway. Without knowing what they drive the EFC line with, it’s hard to know if the

Re: [time-nuts] Z3801A OCXO manual trimming

Hi The control range should be +/- 5V if I remember correctly. If it’s not, the only other standard would be 0-5V. There is zero logic in running a wider swing mod to an OCXO at a lower EFC range. It indeed sounds like the DAC has trouble. Bob > On Mar 6, 2018, at 1:24 AM, Mark Sims

Re: [time-nuts] Z3801A OCXO manual trimming

Crazy thought.Could you just force a DC offset into the EFC assuming the internal varicap is not out of range. It would be simply adding a resistor to pull up or down to see if you can get a bit of pull and allow the dac to move back in range a bit. Its a band aid. I know its sort of crazy.

[time-nuts] Z3801A OCXO manual trimming

I'm not sure what the Z3801A uses for EFC range. Heather uses the EFC relative command to report the EFC setting. That command reports values from -100% to 100%. There is a command that reports the DAC input in counts, but nothing documented that shows volts/count. Since the DAC is at -2V

Re: [time-nuts] Z3801A OCXO manual trimming

/installing antennas including one of my GPS antennas. From: Mark Sims <hol...@hotmail.com> To: "time-nuts@febo.com" <time-nuts@febo.com> Sent: Monday, March 5, 2018 7:36 PM Subject: [time-nuts] Z3801A OCXO manual trimming Or, it you are sure it's the OCXO,  go

[time-nuts] Z3801A OCXO manual trimming

Or, it you are sure it's the OCXO, go shopping for a new one.There is a reputable seller with them (the double oven version) for $100 on Ebay. A couple of things to try... monitor the EFC voltage, power up the unit, and see if it is changing as it attempts to lock. If it does not, you

Re: [time-nuts] Z3801A OCXO manual trimming

The easiest solution would be to drill a hole in the right place in order to access the screw that covers the trimmer hole of the inner OCXO housing. Does anyone have a disassembled double oven 10811 at hands and could take the required measures plus check if any vital parts of the outer oven are

Re: [time-nuts] Z3801A OCXO manual trimming

Hi Either tear into the OCXO or go shopping for a new(er) GPSDO. The Z38xx devices all had a lot more in common with each other than they did differences. The OCXO design changed from the 10811 to various more modern designs. The disciplining process seems to have remained pretty much the same

Re: [time-nuts] Z3801A OCXO manual trimming

Crazy thought.Could you just force a DC offset into the EFC assuming the internal varicap is not out of range. It would be simply adding a resistor to pull up or down to see if you can get a bit of pull and allow the dac to move back in range a bit. Its a band aid. I know its sort of crazy. But

Re: [time-nuts] Z3801A OCXO manual trimming

Thank you, Hal, for these links and to others for your comments. Setting the oven temperature on a turning point appears tedious. Perhaps there is enough range in the frequency adjustment to put the oscillator back on frequency - or close enough for the EFC to be effective. If not, I may have

Re: [time-nuts] Z3801A OCXO manual trimming

I dug in deep and there is an adjustment. Thats the great news. The bad news was never able to put the oven back together. It was a mess. The insulation stuff deteriorated. (Might mean over heated oven) The various wires going to the oscillator are wrapped about 4 times around the oven. I am sure

[time-nuts] Z3801A OCXO manual trimming

Oops... I checked and the Z38xx devices don't have a DAC setting command. It was the UCCM GPSDOs that have a SCPI command for controlling the DAC manually, - > When I press "D" Lady Heather replies: Manual disciplining not supported by this receiverpress ESC

Re: [time-nuts] Z3801A OCXO manual trimming

n...@npgcable.com said: > Does the oscillator have an adjustment? If so, is this somewhat accessible > without destroying the assembly? Are there pictures of the oscillator > assembly? https://www.realhamradio.com/GPS-oven-journey.htm https://www.realhamradio.com/z3801a-turning-point.htm

Re: [time-nuts] Z3801A OCXO manual trimming

Hi > On Mar 4, 2018, at 10:30 PM, Joe Hobart wrote: > > > Mark, > > When I press "D" Lady Heather replies: > > Manual disciplining not supported by this receiverpress ESC > > > Questions about the Z3801A: > > Does the oscillator have an adjustment? If so, is this

Re: [time-nuts] Z3801A OCXO manual trimming

Mark, When I press "D" Lady Heather replies: Manual disciplining not supported by this receiverpress ESC Questions about the Z3801A: Does the oscillator have an adjustment? If so, is this somewhat accessible without destroying the assembly? Are there pictures of the oscillator

[time-nuts] Z3801A OCXO manual trimming

Lady Heather has a command that lets you set the DAC voltage. It's in the "D" menu. Depending upon the firmware, you may need to disable disciplining first (also in the "D" menu). If the DAC command works to change the OCXO freq, the osc EFC and DAC are probably OK. If it does not, I'd

Re: [time-nuts] Z3801A OCXO manual trimming

Hi > On Mar 4, 2018, at 1:13 PM, Joe Hobart wrote: > > My Z3801A failed about a year ago (there was a warning the electronic > frequency > control was nearing a limit). > > Symptoms (most from GPS Control and Lady Heather: > > Frequency about 1E-8 low > > Time Invalid

Re: [time-nuts] Z3801A OCXO manual trimming

My Z3801A failed about a year ago (there was a warning the electronic frequency control was nearing a limit). Symptoms (most from GPS Control and Lady Heather: Frequency about 1E-8 low Time Invalid (many hours off) Date 6 months old DAC 99.9969 percent Life 72K Hours Lady

Re: [time-nuts] Z3801A OCXO manual trimming

t; On Behalf Of Bob kb8tq > Sent: Saturday, March 03, 2018 2:07 PM > To: Tom Curlee <tcur...@sbcglobal.net>; Discussion of precise time and > frequency measurement <time-nuts@febo.com> > Subject: Re: [time-nuts] Z3801A OCXO manual trimming > > Hi > > First off

Re: [time-nuts] Z3801A OCXO manual trimming

> Interesting point about the heater not working vs. the XTAL having drifted > too far. Any logs you made of EFC percent over the past few months or years will help verify the off-the-rail theory. Another thing to try -- turn-off the Z3801A for a couple of hours to let it cool. Disconnect the

Re: [time-nuts] Z3801A OCXO manual trimming

.net>; Discussion of precise time and > frequency measurement <time-nuts@febo.com> > Subject: Re: [time-nuts] Z3801A OCXO manual trimming > > Hi > > First off some basics about OCXO’s. > > In a single oven design, you have a heater th

Re: [time-nuts] Z3801A OCXO manual trimming

d frequency measurement <time-nuts@febo.com> Subject: Re: [time-nuts] Z3801A OCXO manual trimming Hi First off some basics about OCXO’s. In a single oven design, you have a heater that warms up the entire crystal and the guts of the oscillator. It is on all the time and it gets things u

Re: [time-nuts] Z3801A OCXO manual trimming

On 2018-03-03 3:56 PM, Tom Curlee wrote: What I don't understand is the purpose of what looks like another coil or heater wrapped around the Kapton printed circuit heater stuck to the inner case. This second coil/heater is 2 layers of 1/8" thick red foam wrapped completely around the inner

Re: [time-nuts] Z3801A OCXO manual trimming

Hi First off some basics about OCXO’s. In a single oven design, you have a heater that warms up the entire crystal and the guts of the oscillator. It is on all the time and it gets things up to a temperature that makes sense for a given crystal. It can be adjusted based on manufacturing data

[time-nuts] Z3801A OCXO manual trimming

Since the Z3801A is being discussed, I thought I'd ask about an issue I'm having with my unit.  I use my Z3801 as my working lab standard for the usual pieces of RF test equipment.  In the past year or so I've had the unit drop out of lock and go into standby mode.  Resetting/cycling power