While testing my new build it seems that the 8 way RF Switch has failed. No matter what frequency I transmit it appears on all 8 outputs at the same level - very low at -40dBm (with attenuator in circuit set at -20dB).
I have checked output from attenuator on 1255MHz and it is -16.5dBm, so taking into account the -20dB setting on attenuator and 2dB loss it will be around 6dBm, so all OK there.
It did seem OK at first, but I found that when moving the sma connector from one output to another on a number of occasions the Pi would restart. I then noticed that I received a slight 'tingle' from the sma connector (which was connected to the spectrum analyser) when I was in contact with the 0V line on the Portsdown, so it looks like there is an earth loop here.
Could this destroy the RF Switch chip and cause the Pi to restart ?
Regards,
Nick.
8 Way RF Switch failed and Pi Restarting.
Re: 8 Way RF Switch failed and Pi Restarting.
Nick
It sounds like one of your power supplies feeding the Portsdown or your Spectrum analyser PSU is either not earthed or has a high leakage current. A lot of test equipment has mains filtering consisting of capacitors from live and neutral to earth, this can cause quite a high leakage current to appear on the case and ground connections on your SMA connectors if the earth on your mains wiring is faulty.
Now if the PSU feeding the Portsdown has no earth, this would cause the leakage current to pass through the SMA connector and raise the common mode potential that could take out the 8 way switch.
If you put a DVM between Spectrum analyser chassis and your Portsdown PSU without them being connected together you might see quite a potential difference that should not be there.
73
Andy
It sounds like one of your power supplies feeding the Portsdown or your Spectrum analyser PSU is either not earthed or has a high leakage current. A lot of test equipment has mains filtering consisting of capacitors from live and neutral to earth, this can cause quite a high leakage current to appear on the case and ground connections on your SMA connectors if the earth on your mains wiring is faulty.
Now if the PSU feeding the Portsdown has no earth, this would cause the leakage current to pass through the SMA connector and raise the common mode potential that could take out the 8 way switch.
If you put a DVM between Spectrum analyser chassis and your Portsdown PSU without them being connected together you might see quite a potential difference that should not be there.
73
Andy
Re: 8 Way RF Switch failed and Pi Restarting.
Thanks for the reply Andy.
I have checked for voltage and can't read anything. At the moment the problem seems to have gone away (no Pi restating and no more 'tingling').
The PSU is a 25A one (PS-30M) that I use for my HF rig and my RA amplifiers for 2Mtr, 70cm and 23cm DATV - these are only connected when I am using them. It is earthed.
However, the RF switch is well and truly fried. All outputs measure between 6 and 10 ohms to output, and when powered the voltage to the RF switch is only a little over 1 volt - the 5V regulator is untouchable. The control lines have the correct voltages on them.
Hopefully will be able to replace the RF switch and maybe regulator and SKY amplifier this weekend.
I was hoping the problem would still be present so I could trace and hopefully cure it. I don't like intermittent problems - they have a habit of coming back, so will look further into this - don't want to fry any more bits.
I have checked for voltage and can't read anything. At the moment the problem seems to have gone away (no Pi restating and no more 'tingling').
The PSU is a 25A one (PS-30M) that I use for my HF rig and my RA amplifiers for 2Mtr, 70cm and 23cm DATV - these are only connected when I am using them. It is earthed.
However, the RF switch is well and truly fried. All outputs measure between 6 and 10 ohms to output, and when powered the voltage to the RF switch is only a little over 1 volt - the 5V regulator is untouchable. The control lines have the correct voltages on them.
Hopefully will be able to replace the RF switch and maybe regulator and SKY amplifier this weekend.
I was hoping the problem would still be present so I could trace and hopefully cure it. I don't like intermittent problems - they have a habit of coming back, so will look further into this - don't want to fry any more bits.
Re: 8 Way RF Switch failed and Pi Restarting.
Problem found while testing the RF board after replacing the chip.
The intermittent fault was found to be the connections for the mains plug in the extension that the analyser was plugged into. They made a very poor contact with the plug prongs, especially the earth one which had virtually no connection, but was OK when I tested the earth loop resistance a few days ago. They were so poor it was impossible to tighten them up (see photo), so now in trash bin.
The intermittent fault was found to be the connections for the mains plug in the extension that the analyser was plugged into. They made a very poor contact with the plug prongs, especially the earth one which had virtually no connection, but was OK when I tested the earth loop resistance a few days ago. They were so poor it was impossible to tighten them up (see photo), so now in trash bin.
- Poor Connections.
- Useless Power Connections..jpg (1.4 MiB) Viewed 2034 times