Re: Ref: QRSS Ultimate 2: Reference Frequency keeps changing.
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Hi Roger
There were less than 400 U2 kits were produced, so it is the least known of any of the series (Ultimate, Ultimate2, Ultimate3, Ultimate3S).?
Do you have an oscilloscope, or access to an oscilloscope? It would be very valuable for fault-finding.?
The fact that your 125MHz frequency is changing every time, and by wild amounts, seems to indicate an issue with the calibration. This could either be due to the AD9850 DDS not working properly (not generating the required calibration frequency during the calibration process), OR, there is an issue with the GPS 1pps signal.?
You did not mention what GPS you are using. Many GPS modules have 2.8V logic level outputs and these will need pull-up resistors or proper level conversion. Pull-up resistors generally work but some GPS modules can be sensitive to having the right value resistor, and anyway pull-up resistors decrease noise immunity. The QRP Labs QLG1 GPS removed all those problems because it has a logic level converter onboard to produce 5V logic outputs.?
Regarding the DDS module, it is possible that the blue trimmer potentiometer on the board was dislodged. This trimmer sets the threshold for the comparator which turns the DDS sinewave into a 5V logic squarewave for the Ultimate2. There is an article here about how to adjust the trimmer:?
Failing all else... you could have a deceased AD9850 DDS module. I believe these AD9850 DDS modules are still available on eBay and elsewhere.?
73 Hans G0UPL
On Mon, Oct 23, 2017 at 9:09 PM, Alan G4ZFQ <alan4alan@...> wrote: Roger
With a deafening silence from respondents, I take it that the DDS module is goosed. But thanks to all those who thought of replying.
I guess it is not a common occurrence. I could not answer.
I might suspect the DDS or the GPS? Or the micro...
Maybe not too many here know the U2? The firmware and configuration might be a lot different.
73 Alan G4ZFQ
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