BATC Forum

Hello,

I have just carried out my first test with Lime based Portsdown. This was on 437MHz and viewing the signal on a spectrum analyses.

I noted that when selected to MPEG-2 I get modulation, but when I select H264 after the carrier stops there is no modulation.

Have I missed some settings somewhere ?

Hi Nick

We need a lot more information if we are to be able to help you.

What modulator hardware? What SR? What FEC? What video source? What modulation? What video Format? What audio source? What audio hardware?

A photo of the touchscreen before you press transmit would suffice, with information about your hardware configuration and Portsdown software version (from "Info" on Menu 2).

73

Dave, G8GKQ

Hi Dave - thanks for the reply.

Requested photos attached.

I never had a problem like this with the FM Version of Portsdown I made - I expect I have something set wrong.

Regards,

Nick.

Hi Nick

Nothing immediately obvious there, but I have 2 suggestions to try:

• Please select Audio "Off" if you do not have an audio device connected.
• Upgrade your Portsdown software to the latest version (201903250) and then upgrade your LimeSDR Mini firmware (from Menu 3, Lime Config)

Let me know how it goes.

Thanks, Dave

Dave,

Setting audio to off had no effect.

I have updated Portsdown and Lime software to latest versions and still get no modulation on H264, but I do get a carrier now whereas before there was no transmission signal at all. Attached photos show what I am getting.
Regards,

Nick.

Dave,

I had an unused programmed card as supplied from the shop. It had an old OS on it, so I used a spare Pi and 3.5inch screen and updated it to the latest software.

I swapped this with the card in the Lime Portsdown transmitter hoping it would cure the problem - it didn't, but I have now noticed another strange problem.

When I transmit with H264 there is still no modulation, but also, when I touch the screen to stop transmitting, whilst the Tx LED does go off the Portsdown is still transmitting - the signal can be seen on the spectrum analyser.

Also, the Tx signal can vary from around -40dBm to -3dBm,

If I now switch to MPEG2 and transmit the spectrum analyser shows a modulated signal, and when I touch the screen to stop the Tx LED goes off and transmission stops OK. Same if I select carrier.

So, transmitting carrier or MPEG2 works OK. H264 is still giving problems.

Why it still transmits when the Tx LED is off is really strange.

I tried these tests at 1255MHz and 437MHz and got the same results.

I have no problems with setting different attenuations with the on board PE43703 attenuator - this seems to give the correct attenuations as set in the menu.

Regards,

Nick.

Hi Nick

The only possibility that I can think of at the moment is a hardware problem with the H264 encoder in your RPi. Please could you try the cards and Lime connected to your second RPI?

Dave

Hi Dave,

Just swapped the PI in the Portsdown and have the same problem - no modulation on H264 and transmission does not stop when I touch the screen, even though the TX LED goes off, i.e. its still transmitting when it should have stopped.

What could be causing that ?

Tried connecting the Lime to the PI by a short 10cm USB lead and it still works with MPEG2 but not with H264.

Is it worth taking the Lime out and trying it plugged into a PI with a 3.5inch screen to test it ?

Could the problem be caused by a faulty Lime ?

Regards,

Nick.

Just tested with the barest minimum - the Pi, a 3.5inch screen and the Lime connected directly to a USB port.

Got the same results - no mod on H264 and continues to transmit when I touch screen to stop. (Test on 437MHz).

The initial output level when on H264 was -16dBm but this then dropped to -46dBm (Lime gain 90 I think).

There does not seem much more I can test - is it time to obtain a new Pi and Lime ?

Regards,

Nick.

Nick

Please

• Confirm that you are using a LimeSDR Mini, not a LimeSDR USB
• Try it at SR125 H264
• Try it with S2QPSK modulation at SR125 H264
• Confirm that you are using a powered USB hub for the Lime
• Confirm that "Ugly mode" works. You can select this using Preset 4 on Menu 1

Dave