Re: GPSDO ubitx ?

Rafael Diniz

Hi Ashhar,

Is there a way to know if the Si5351 correct got the 25 Mhz input?

I still did not do the 10 MHz to 25 MHz circuit (I bought a GPSDO with
10Mhz output from ebay). Any way I can buy a 10 MHz to 25 MHz
transverter already assembled?


On 11/19/20 12:48 AM, Ashhar Farhan wrote:
I tried something a year ago or so. I was attempting to reduce the
phase noise on Si5351 using an external oscillator instead of the
internal oscillator.
So, this is how it worked. 
1. You take a 10 MHz TCXO, (subsitute this with a GPS source for a
GPSDO) and divide it by 2 in a 74HC74. The output is rich in harmonics
at 5 MHz.
2. You feed the 5 MHz square wave into a triple tuned bandpass filter
at 25 mhz to isolate the 5th harmonic. This will be weak, add an
amplifier of 16 db to bring it up.
3. Feed this to the xin input of the Si5351.
Now, your Si5351 is GPS disciplined.

On Thu 19 Nov, 2020, 7:35 AM Rafael Diniz, <
<>> wrote:

Very interesting Jason! Tks!


On 11/17/20 10:47 AM, Jason Pirok wrote:
> I just bought one of the VFO/SigGen kits from QRP-Labs and they
> already have a GPS disciplined option for it if you want to try it
> out. It is only 1PPS but apparently does the job. I haven't built my
> GPS kit yet so I can't give any personal details atm. You have to
> provide the 5v supply on your own so that is some extra work.
> Just a thought in case you hadn't seen that project yet.

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