Noise figure feature

[G4WIM]

Hi guys
I thought I'd have a dabble with the noise figure tool built into the PD4 - it looks really useful and I already have a suitable noise source.

Seems I have run into a problem as GPIO26 seems to sit high at 3.3V from power up and does not show any signs of a 10Hz signal to gate the noise source.

Also I see only a single line on the NF meter - the wiki imples there should be two (noise on / noise off). This single line moves up and down at approx 1Hz

Maybe I'm doing something wrong or my GPIO output is defective ?

Any pointers ?

73 Tim

[g0mjw]

It works for me. I assume you have the latest software properly configured. It uses the Lime, if that is not there or not detected it might be a problem. Oh, and just in case, GPIO26 is on pin 37 but the noise source uses GPIO physical pin 26.

Mike

[G4WIM]

Hi Mike

thanks for the quick reply - clearly I've messed up some how.

I've checked I have the correct FW in my Lime (V1.30) and I'm pretty sure I'm on the correct GPIO (gpio26 physical pin 37 of 40).

GPIO26 goes high from power up and stays high so my noise source is active all the time - interestingly noise on and noise off both show -51dB even if I unplug the DC to the noise source.
Updating to LIME DVB gives the same results. The PD4 has the latest FW 202209280.

All very odd

73 Tim

[g0mjw]

Tim - it is PIN26. Not GPIO 26 !

[G8GKQ]

As Mike says, physical pin 26 (GPIO 7, WiringPi 11, Portsdown 25-way interface pin 7). Confusing, but the table on this page should provide clarity https://wiki.batc.org.uk/Portsdown_4_GPIO_Connections

Dave

PS - Just checked on a new build and all working. No Lime required for the switching volts to operate.

[G4WIM]

Thanks Dave / Mike

Sorry for the 'newbee' questions.

I now have a switching noise source and yes I've always found the Pi4 a little confusing as to naming conventions etc.

This time I was led astray by the wiki which said GPIO26 which on my Pi4 chart implies pin 37.

All clear now with pin 26 of 40 which is actually GPIO7

Still not out of the woods though when I press calibrate it reports device gain between - 0.5dB and +0.7dB but unplugging the noise soruce makes no difference - I suspect the RF path to the Lime rx might be at fault.

Another question - underLime Config menu 37 I assume LimeRFE Mode Rx and LimeRFE should both be enabled - correct ?

Lime RFE RX atten = 0dB

73 Tim

[G4WIM]

Ok - all good now.

I'm using an RFD2305 noise source and had left a 10dB on its output meaning its ENR was below that of the Lime RX.

Had to be something simple - so now I can check my 24cm mast head LNS.

Many thanks for a great piece of work.

73 Tim

[G8GKQ]

Hi Tim

Please could you point me at the place on the Wiki where it says GPIO 26?

I can only find references to GPIO pin 26. I tried to make it clear, but maybe I have missed it somewhere.

You should leave the LimeRFE Disabled unless you have a LimeRFE https://www.crowdsupply.com/lime-micro/limerfe connected.

I did all the testing with Lime Mini Firmware 1.30, but LimeDVB firmware might work.

Dave

[G4WIM]

Hi Dave

this is what mislead me - I took GPIO pin 26 to mean GPIO 26 not realizing what it actually meant - maybe GPIO 7 on physical pin 26 would be a little clearer ?

Noted about the RFE being disabled.

Regards Tim

https://wiki.batc.org.uk/Noise_Source_PSU

Switching
Q1 is a p-channel mosfet and is used to switch the supply on and off. The switching signal from GPIO pin 26 on the Portsdown Raspberry Pi 3 or 4) turns an NPN transistor on or off to switch the MOSFET. The exact types of transistors are not critical. The MOSFET should be able to handle 100ma and 30v. The NPN transistor needs to be able to handle 30v.

[G4WIM]

One other thing - using my RFD2305 in 5dB ENR mode (10dB attached) doesn't work as the Lime can't see the noise.

Removing the 10dB so having a 15dB ENR seems to help.

Out of interest I'll compare my PD4 results against those from my RFD NGA system to see how they compare.

73 Tim