[Elecraft] K3S XREF GPSDO recommendation needed

[Clay Autery]

While the Bodnar GPSDO will run off "station power" as long as it sees 
less than 14 vdc at the external DC (5.5mm x 2.1mm (+ to center pin) 
connector, anything above 5 vdc is dumped as heat into that tiny little 
chassis.

It will ALSO run fine (and preferred) at 5 volts DC from EITHER the USB 
port OR the External power connector.

Here is what I do:

1) I don't have the GPSDO connected to the computer via USB when I am 
not ACTUALLY setting it via software.

2) I can run it from a USB cable connected to a "charge only" port on my 
computer connected hub OR from ANY port on the USB hub I use for "power 
only" and no connection to a computer. BOTH of these hubs have 12 VDC 
external power supplied STOCK by a 12 vdc switching PS (wall wart). "I" 
power them from the station power supply (13.9 VDC) via an LM317 based 
adjustable DC regulator that I set at precisely 12 VDC.

3) Alternatively, I can power the GPSDO via the Ext Power connector with 
5 VDC from EITHER a USB cable hacked on one end to add the 5.5mm x 2.1mm 
connector (to the aforementioned USB hubs), OR via a twisted pair cable 
with 5.5mm x 2.1mm connector on one and and the other end terminated to 
connect to the 5VDC output of the regulator I mentioned earlier that 
primarily powers the HP 58516a GPS Antenna Splitter/amp.

Bottom line... I eliminated the switching supplies from the picture and 
feed the GPSDO 5vdc to minimize the waste heat dumped into the GPSDO 
chassis.

As an aside, and verified with Leo Bodnar, you can switch the GPSDO from 
computer connected to power ONLY WITHOUT cold booting the device (you do 
not have to power it down).  With the unit connected to the computer via 
USB, simply connect some other 5vdc power source to the Ext Power 
connector (USB or other as described above)  You now have 5 vdc going to 
both USB and Ext Pwr connectors.  THEN, disconnect the USB connection to 
the computer.  The unit is now on EXTERNAL DC only, no data/computer 
connection.

I then perform an additional step...  I plug a pwer only connection BACK 
into the USB connector (to a charging-only or a power-only USB hub/power 
bus), and then remove the power cable from the Ext Pwr connector.

Why? To remove the possibility that the computer connection might feed 
something back into the GPSDO and affect its frequency outputs.

73,

______________________
Clay Autery, KY5G
(318) 518-1389

On 06/05/18 09:31, Grant Youngman wrote:
> I’ve been using one in the station for a long time (starting years ago before the K3 came along).  Started with an HP Z3801, and replaced that with an HP Z3816, when the 3801 went to heaven.  I currently use a bit more modern (and more compact) Trumble Thunderbolt.  All of those have worked fine.
>
> If I needed a new one, I’d probably buy the Bodner since it’s compact, appears to be a well regarded device, and will run off the station 12V DC supply.  These are available in the US from Airspy (and maybe others) at https://v3.airspy.us/product/lb-gpsdo-1/ <https://v3.airspy.us/product/lb-gpsdo-1/>
>
> Grant NQ5T
> K3 #2091, KX3 #8342
>
>> On Jun 5, 2018, at 10:04 AM, David Box <dobox at suddenlink.net> wrote:
>>
>>
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