G8JNJ

Interestingly I found that using screened CAT 5 cable actually made the noise levels on the VLF bands <50KHz much worse.

In the end I went back to using un-screened CAT 5 with 12 turns through a FT240-31 core (Mouser part number 623-2631803802) which was just as effective on the HF as it was when used with screened CAT 5 at frequencies around 20MHz, but didn't introduce the additional noise on VLF. I think the screen adds an additional ground loop, which the transformers in the Ethernet interface and external choke baluns can't fully isolate / filter because of the very low RF frequencies involved (just my opinion).

I also found that bonding the RF in and GPS connectors directly to the metal case at the point of entry reduced the HF noise floor by a further approx 3-6dB depending upon the exact cable configurations, but your mileage may vary.

Regards,

Martin - G8JNJ

Hi,

Just installed it and tried it but it doesn't work with the KiWi.

I tried playing some videos on YouTube and it worked OK with that.

So it can work but sadly not for the KiWi. Which is a pity as it would have been useful to open up receivers on different tabs, and then reroute the audio from each to separate destinations.

Regards,

Martin - G8JNJ

This morning I checked the other Beagle that I had repaired as it previously had a blown PHY chip.

Guess what......

R136 has gone open circuit on this board too.

So the digital ground and ESD ground are no longer connected.

R136 had the correct value marking, so it's gone open circuit whilst in service.

I revisited the other board that still showed no connection between the digital and ESD grounds.

I removed R136 in order to try and check the PCB tracks, but they all seemed OK.

Then I replaced R136 again with a 0 Ohm resistor.

Now the digtial and ESD grounds show 0 Ohms between them.

So whatever was open circuit now seems to have recovered.

I suspect that it could have been the tiny through board vias that are right next to R136 under the RJ45 connector.

All is now good again with both previously faulty boards :-)

I have a couple of theories.

1. A nearby lightning surge had blown R136 open circuit at some point.

2. If a power supply with a grounded outer on the DC connector is in use, and the center pin of the 5v DC connector accidentally touches the metal can of the Ethernet, USB, SD card or metal mounting pillars (or metal case if mounted via the pillars). Then it may burn out R136 (and possibly some PCB track).

Either of the above (or something similar) will result in the loss of ESD protection (and possible failure of the Ethernet port) and RF screening.

Regards,

Martin - G8JNJ

Whilst messing about with my Broken Beagles I noticed that the DC volts at the power supply had to be at around 5.4V to provide 5v at the Beagle.

On first inspection this seems to be associated with the RF filter on the DC input of the KiWi board, which is causing a voltage drop to occur (before it is passed to the Beagle) when the KiWi is drawing it's approx 600mA average running current.

Further experimentation is required to find the optimum input voltage in order to ensure a clean start up.

I'd suggest checking the DC volts on the Beagle header when it's up and running, to see what's actually being applied to the board.

Regards,

Martin - G8JNJ

Whilst messing about with my Broken Beagles I noticed that the DC volts at the power supply had to be at around 5.4V to provide 5v at the Beagle.

On first inspection this seems to be associated with the RF filter on the DC input of the KiWi board, which is causing a voltage drop to occur (before it is passed to the Beagle) when the KiWi is drawing it's approx 600mA average running current.

Further experimentation is required to find the optimum input voltage in order to ensure a clean start up.

I'd suggest checking the DC volts on the Beagle header when it's up and running, to see what's actually being applied to the board.

Regards,

Martin - G8JNJ