N210 + UBX40: frequency instability

[Terry-G0EZY]

Hello. I have an N210 + UBX40 system with the intention to use it as a microwave tansceiver for amateur radio. The sytem is working using Ubuntu 18.04 and software from an American ham. Full multi-mode CW/AM/FM/SSB over the frequency range 10 MHz to 6 GHz. It also works (receive only) with Windows software SDR-Console from Simon Brown. The problem is frequency instability.  In receive mode, monitoring a known, stable transmitter shows the frequency jumping about often and randomly by several Hz. I get a similar effect when in transmit mode and monitoring output with a stable receiver. If I connect a GPS locked frquency reference (HP58503B) to the external reference, and enable the "External Reference" in the Linux software the problem seems to be solved. Unfortunately the Windows s/w doesn't enable external reference. I was very surprised that the internal oscillator in UBX board would have this instability (tested over the full range of the board 10 MHz to 6 GHz with similar results) and an external reference is required. Is the UBX40 faulty or is this expected?

[RobGeografo · Accepted solution]

Hi,

To answer your questions:

• The N210 has a frequency accuracy of 2.5ppm, which means that in the testing range (10MHz to 6GHz) the initial frequency accuracy oscillates around ± 25Hz. Worst case scenario is ±15kHz (see USRP-N210 Datasheet). The external reference that you locked has a HP SmartClock Technology which minimizes frequency drift maintaining accuracy to better that 100 parts per trillion.
•  In regards to the windows software, I am not sure why it is not working but the following link might be helpful: USRP Hardware Driver and USRP Manual

Cheers,

Rob

[Terry-G0EZY]

Hi Rob - Thanks for reply. That answers the question. The N210 needs a 10 MHz reference (GPSDO etc) to stop the +/- 25 Hz. The Linux transceiver program I am using enables an external reference.. but the Windows program doesn't. 

At least I now know that my UBX40 daughter board is not faulty! 

Regards

Terry

[anis345]

Hi Terry-G0EZY,

     I'm also trying to use SDR console for IQ data analysis obtained from VSA 5668R. However, there is no exclusive support for NI hardware in SDR Console as provided for other radios (BladeRF, HackRF etc.). I tried a few attempts by establishing a connection between both (through controller IP address) and interestingly found that on labview side, VI was listening the command sent from SDR console. However, IQ data sent from labview to SDR application is not being received on other end and simply an error is being shown. Probably, there is protocol mismatch or it needs certain drivers to acquire raw IQ data from VSA 5668R which could further be demodulated there.

     You have mentioned using USRP with SDR Console. Any assistance in this regard will highly be obliged.

Regards