[time-nuts] Chinese NTP Time server

Sun Dec 22 23:20:07 UTC 2019

Sorry, that should have been '10base2 ethernet card'

On Sun, Dec 22, 2019 at 11:16 PM Adrian Godwin <artgodwin at gmail.com> wrote:

> Voltage converter might be one of these  :
>
> https://www.we-online.com/catalog/datasheet/177920521.pdf
>
> You can also sometimes find a similar device on an old 10baseT ethernet
> card, where it generates a -9V supply.
>
> On Sun, Dec 22, 2019 at 7:04 PM Brian Lloyd <brian at lloyd.aero> wrote:
>
>>
>>
>> On 11/26/19 09:28, xaos at darksmile.net wrote:
>> > Hello everyone,
>> >
>> > Does anyone here know about this item:
>> >
>> >
>> https://www.ebay.com/itm/Brand-New-NTP-Time-Server-GPSDO-GPS-Disciplined-Oscillator-GPS-Clock/362758051388?hash=item547610963c:g:yFIAAOSwgztdgfM9
>> >
>> >
>> > George, N2FGX
>>
>> OK, I ordered one. I missed the part about the 10MHz output being
>> "optional". (Optional? Really?) So I ordered one and it arrived 2 days
>> ago. Delivery took about 3 weeks. Looks nice, well packed, no damage. It
>> includes an active GPS antenna with about 20' of RG174 and a 12VDC
>> wall-wart. Unit, antenna, and PSU, nothing else. No doc and no software.
>> No problem ... so far.
>>
>> Plugged it in. Power supply LED comes on and the Sync LED is flashing at
>> about 2Hz. About 20 seconds later the SV LED comes on. about 2 minutes
>> later the Sync switches to 1Hz. I am guessing it has achieved some sort
>> of lock. I connect the 10MHz output to my FA-2. Of course, no 10MHz
>> output. (More on this later.) I plugged it into the network. Looked at
>> my DHCP server. No IP address assigned. Huh. How do I find this thing on
>> my network?
>>
>> eBay message back to the seller. Seller sends me a link to a zip file
>> with the software and doc. The first 'uh oh' is that all the file names
>> are in mandarin. I must admit, I find <mandarin>.pdf and <mandarin>.exe
>> amusing. I have an old laptop that dual-boots Linux and Windows just for
>> this sort of thing, i.e. annoying software that only runs on Windows. I
>> extract everything from the zip file and try things out. One of the
>> programs shows just an ip address of 192.168.0.100 and has three windows
>> separated into dotted-quads. Could this be the tool that sets the IP
>> address, subnet mask, and gateway? I run the PDF that opens with a
>> picture of the unit through google translate. OK, yes, that is what the
>> program does. There is a picture of the window and, guessing at the
>> examples, I was right, IP addr, mask, and gateway. With 5 buttons to
>> click on in varying orders, it tooks me several tries to finally get it
>> to change its IP address to one on my network. It is now pingable.
>>
>> I look at some of the other programs. These are mostly in English, being
>> open software, and do things like let you look at the status of the GPS
>> receiver. After successfully setting the IP address of the unit, I was
>> able to run the utility 'PowerGPS.exe' and have it report GPS status
>> from the box.
>>
>> So I pointed ntp on my linux server at the box as a server. It synced
>> right up and chose it as the primary ntp source. Clearly it works just
>> peachy as an NTP server and is running in my network that way. Now to
>> tackle the lack of 10MHz output.
>>
>> Opening up the box it clearly has a 10MHz OCXO so getting something out
>> the 10MHz BNC connector should be fairly straight-forward. Examining the
>> bottom of the board, the path from the OCXO to the 10MHz BNC output is
>> pretty clear. It goes through a single buffer op-amp and then drives the
>> BNC jack. The only problem is, the op-amp is missing. The pads are for
>> an SO-8 package. Following the traces it is pretty clear it is a
>> standard, single-op-amp pinout, i.e. :
>>
>>  1. n/c (null)
>>  2. inverting input
>>  3. non-inverting input
>>  4. V-
>>  5. n/c (null)
>>  6. output
>>  7. V+
>>  8. n/c (null)
>>
>> Lots of parts could go there. Looks to me like it should probably be
>> something like an LT1227. The op-amp is operated at a gain of 2 with a
>> 100ohm FB resistor and 100ohm to ground. This should be pretty stable
>> with 100ohm pretty much swamping any parasitic capacitance in the FB
>> loop. The input is a 300 ohm/300ohm voltage divider so the overall gain
>> of the stage is unity.
>>
>> Input to the buffer from the OCXO is capacitively-coupled as is the
>> output. There is a 50ohm resistor in series with the output. The
>> unloaded voltage output of the OCXO is a 3.5V positive square wave.
>> After passing through the buffer it is probably supposed to approximate
>> a 3V p-p sine wave. (At least, that is what the marketing verbiage
>> suggests.)
>>
>> The board is already populated with linear +5v and -5v regulators (74L08
>> and 74L09 respectively) and associated bypass/filtering. +5v is present
>> at pin7. No -5v is present. Tracing the board back to the source of the
>> -V at the input to the -5v regulator, one arrives at an empty 4-pin
>> through-hole area marked u14. This has +7.5V on pin 2 which also feeds
>> the input to the +5V regulator. Pin 3 is the -V output that feeds the
>> input to the negative analog regulator. So the 64-dollar question is:
>> does anyone know of a chip/module that is a 4-pin, 0.1" pin spacing,
>> single-output, inverting regulator module, producing -7V from a +7V
>> input? I need to find something like that to populate this board and get
>> the 10MHz output. I haven't been able to find anything on Mouser or
>> Digi-Key. I am guessing that this is something that already exists as a
>> module but ...
>>
>> Yes, I have asked the seller about the parts to populate the board or
>> the option of returning it and getting one already populated. If the
>> seller tells me to go pound sand I would like to manage to make this
>> work anyway.
>>
>> Hmm ... if I DC couple the input and run the op-amp with a single-ended
>> +5v supply, it might work without the negative supply at all. My only
>> worry would be latch-up because the input would be going right to the
>> negative rail and approaching within 1.5V of the positive rail. OTOH,
>> most op-amps now are pretty immune to latch-up. Just thinking aloud
>> here. I am sure someone here has some ideas about getting this to work.
>>
>> Thanks in advance for humoring me.
>>
>>
>> --
>>
>>
>>  <https://www.lloyd.aero>
>>
>> Brian Lloyd
>> 706 Flightline
>> Spring Branch, TX 78070
>> brian at lloyd.aero <mailto://brian@lloyd.aero>
>> +1.210.802.8359
>>
>>
>>
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>