BATC Forum

I think I have found a bug in the sig gen. My Portsdown has the latest update installed. I have both the Pluto and Lime Mini SDRs installed.

Whilst checking the Portsdown sig gen frequency accuracy using a counter with a GPS disciplined clock, I noticed a problem when using the Lime Mini. The output is exactly 1MHz low of the displayed frequency; I used 1275MHz. It was actually a further 173Hz low, but that's just down to the Lime's onboard clock.

If I switch to the Pluto, it comes out on the correct frequency, ignoring the -14kHz offset due to the Pluto's 40MHz clock error.

My Lime is on frequency in DVB-S/S2 modes.

Can someone confirm this issue? Not a high priority for Dave, but I know some of us have been using the sig gen to align gear.

Clive

Hi Clive

Do you have the LimeDVB firmware loaded on your LimeSDR?

If so, that would account for the issue. The SigGen sets the Lime LO to 1 MHz below the desired frequency and then uses the internal oscillator to generate a 1 MHz signal that is applied as USB to the LO. This allows better control of the output amplitude.

The 1 MHz LO is not available with the LimeDVB firmware, so the only output is the LO; 1 MHz below the desired frequency. Unfortunately, I have been unable to find a reliable way of detecting the loaded firmware, otherwise I would implement a warning.

There is no problem with switching between the firmwares; I checked with the designers - it's an EEPROM with a 10,000 write cycle life.

It could also be that you haven't calibrated after a frequency change - this leads to poor LO suppression.

Dave

Hi Dave

Yes, I do have the Lime DVB firmware installed.

I have GPS locked HP sig gen to 2.06GHz and the not so accurate Pluto to provide a signal up to 4.4GHz, so I won't bother with switching the firmware unless I'm desperate for something more accurate above 2GHz.

I'd probably be better off using the second harmonic of the HP!

Thanks

Clive

Thanks Clive

I've updated the Wiki with this information. https://wiki.batc.org.uk/Portsdown_4_Si ... put_Device

Dave