The AM Forum

http://mysite.verizon.net/jkelly/hpsdr/k2sdr_160.wmv

and I just plugged my new Excalibur reference board that I wired today.
This is very cool.

That is FINE BUSINESS!

Later I tuned into WWV on 10 meters and changed the display to phase mode.
I watched the phase dance around a bit and then enabled the external reference.
The circle of dots forming phase information got smaller meaning less phase noise and jitter.
This external reference board is required for diversity. It also allows me to pipe in a GPS locked reference of even higher quality with a simple jumper change.
The Mercury designers found the aux clock input provided better operation than the external input programmed into the FPGA. This requires a jumper change and the addition of a small wire to route the clock to the aux input. There are different input types allowed by FPGA internal structure so the designers just picked the wrong type.

Does that box take phased enhanced clock slaves?

The reference board does a couple things. It has a clean 10 MHz VCXO that drives the clock bus through some clock drivers. It has an hc4046 phase detector so you can use it to tune the VCXO locked to an external source.
There are a pair of LEDs on PD2 that you monitor as you tune. Or you can move a jumper and route an external RF signal in through an amplifier to the clock driver chips that drive the clock bus.
The clock bus (pin C16) wants to see a 3.3 volt square wave so the board uses 74AC04 drivers resistor ORed to drive C16. The C16 pin could be driven by an external source as long as it is 3.3 volts low impedance.
I was going to roll my own but the kit was cheap considering it included the VCXO. It took a few hours under the microscope to build it though.
So to answer your question. I think yes as long as it is 3.3 volt swing.
In time I'll interface my Thimble Thunderbolt

Hi Frank,

Impressive demo. I'm still not sure if your using a 10MHz input slaved to a GPS receiver and a VCXO or just a VCXO?

Most of all I'm wondering how you did a full motion screen shot like that? I have seen it done for product demos but I figured it was animation. I would like to learn more. Thanks

Mike

Mike, there are several sw packages that will do video screen capture of your computer. Just Google it.

Frank, it's preferred to reverse the phase advance and then cross-correlate the two. The resultant is used as a phase retarding voltage and can be locked quickly. The voltage swing is not enough though. They're really missing the boat on this one.

Thanks Steve, I didn't know this kind of software existed much less how search for it. A new tool in the box! I like it!

Mike

No just a free running TCXO. HPSDR guys didn't want to mess with a PLL when you could just pipe in the GPS source. I wanted to use the XOR in the 4046 to lock since no signal would sit at center control voltage. But again way put another pll in series the GPS source. Now the 4046 is just used as a tuning aide when you calibrate the TCXO.
Sorry for the confusion when I posted VCXO which was the wrong term.
Today I tuned in WWV on 15 MHz. Higher frequency seemed to have lass phase changes. when I monitored phase on P SDR display it went between a dot and small circle so the oscillator is pretty darn close out of the box. I've worked on standards so know they need to burn in at least a month so maybe I'll calibrate it during the summer.

Frank, you said,


And,


I have a Brandywine GPS receiver that gives me a very accurate 10MHz that is piped through an attenuator and used as the standard for my SDR-1000 and a few other pieces of test gear. I have the concept but when you talk above about "piping in the GPS source" without a GPS receiver I get lost? I can see how a temperature controlled crystal oscillator would be a good choice as well. After initial lock and a few hours run time the 10MHz signal from the Brandywine is rock steady and clean as a whistle. It has been running 24/7 for a few years now.

Mike

Sorry to confuse you Mike.  GPS source I mean to say a 10 mHz oscillator locked to the 1 PPS coming out of the GPS RX. The Excalibur has an RF input buffer amp converted to 3.3 volt logic level required by the Atlas clock bus. A simple jumper move the source can be changed to external. After the buffer amp is some 74AC04 buffers to drive the atlas bus. Atlas was designed to have impedance controlled traces. I wonder if I should have a look at the waveform to see if it needs a load resistor at the end of the bus. I keep the Metis board at the end for downloading firmware through JTAG chain.

Frank - you think this HPSDR with 2 receiver channels integral to the A/D chip would work with this diversity program?

The devloper hasn't yet implemented the 2nd channel in his firmware code, but 350 smackers for a dual channel RX is pretty tempting.

http://uvb-76.blogspot.com/p/sdr-project-mk1.html

Well the first issue is software support. That will depend if it is accepted by the masses and the right software people who are willing to share code.

Look at the dynamic range of the internal DDC of that IC. When HPSDR first started looking at this design they wanted to use a DDC from a cell phone.
Mark WA1QHQ told me they had crappy dynamic range which the designers learned  so they decided to stuff the function in an FPGA. I have not picked up a second Mercury yet  but there will be a production run this summer.

Has anyone ever run a ENOB test over the full frequency range for the candidate A/D's?

Rocky had diversity capability a/o version 2, out several years ago. Unfortunately, further development was discontinued.

Good point. I think the LTC parts are real.
I don't think the guy who did the softrock project ever shared the software so it died on the vine. I think he also did a QEX article.
I think there is a 4RX version coming to HPSDR. That will run into some cash to buy 4 receiver boards.