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

Hi All,

Just some brief notes regarding the installation of a 15 way D connector on the Seeed metal case in order to bring out the GPIO port for use with an antenna switch.

The ventilation slot cuts out very easily and only required a small amount of filing in order to make the connector shell fit.

First the pinout I used



End view of case



Top view of connector



Wiring to GPIO ports



Side view



Hope this is of some use to others.

Regards,

Martin - G8JNJ

Hi All,

Just some brief notes regarding the installation of a 15 way D connector on the Seeed metal case in order to bring out the GPIO port for use with an antenna switch.

The ventilation slot cuts out very easily and only required a small amount of filing in order to make the connector shell fit.

First the pinout I used



End view of case



Top view of connector



Wiring to GPIO ports



Side view



Hope this is of some use to others.

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

I replaced the LAN8710A (PHY) chips on the two original Beagle boards and they now work correctly.

I had a bit of a problem with the second board as the LAN8710A is a 32-pin QFN/SQFN surface mount package with a fairly large heatsink pad on the underside. I thought I'd got it hot enough with the hot air gun on the rework station, but unfortunately three of the pads lifted off the PCB from one corner when I removed the chip :-(

Fortunately I managed to repair the missing tracks and the chip works OK :-)

However the second new Beagle board I got from Farnell still refuses connect. I've tried just about everything with it, but it just won't cooperate. I've checked the same image I've loaded onto it on two other Beagles, which have both started up and connected to the router, so I don't think it's a MAC address conflict as the same problem would have occurred. So I'm 95% certain there is a problem with the new Beagle board.

I've still got enough spare chips to try swapping the LAN8710A, but I think it's probably better just to send it back to Farnell and get a replacement board.

So it looks like the Ethernet port is the Beagles weak spot.

Regards,

Martin - G8JNJ

I replaced the LAN8710A (PHY) chips on the two original Beagle boards and they now work correctly.

I had a bit of a problem with the second board as the LAN8710A is a 32-pin QFN/SQFN surface mount package with a fairly large heatsink pad on the underside. I thought I'd got it hot enough with the hot air gun on the rework station, but unfortunately three of the pads lifted off the PCB from one corner when I removed the chip :-(

Fortunately I managed to repair the missing tracks and the chip works OK :-)

However the second new Beagle board I got from Farnell still refuses connect. I've tried just about everything with it, but it just won't cooperate. I've checked the same image I've loaded onto it on two other Beagles, which have both started up and connected to the router, so I don't think it's a MAC address conflict as the same problem would have occurred. So I'm 95% certain there is a problem with the new Beagle board.

I've still got enough spare chips to try swapping the LAN8710A, but I think it's probably better just to send it back to Farnell and get a replacement board.

So it looks like the Ethernet port is the Beagles weak spot.

Regards,

Martin - G8JNJ

Hi Stu,

I agree you have to be careful with ESD paths, especially if you have big external antennas and live on top of a hill :-)

The first KiWi was obviously connected to the antenna etc. when it failed. However the second one only had the ethernet and DC connectors plugged in when it broke.

I have taken great care to ensure that the RF ground on the antenna and mains / DC supply ground are all at the same potential, including adding supplementary ground rods and suitable bonding cables.

My KiWi's have a spark gap (GSD), ESD discharge, 30MHz LPF filter, BC band notches, RF limiter and transformer isolation. All contained in a custom built module that I use to provide additional protection on the RF input.

You also have to be careful with DC supplies (especially the double insulated Switched Mode types - the ones with only a two core mains cable). These often contain an RF filter network consisting of a Y capacitor network across the incoming AC supply and to the supply ground, which is also often the DC ground. The net result is that the DC ground 'sits' at 1/2 AC supply potential (but at very low current).

However when you first plug in the DC connector to any kit that already has a ground return path, an appreciable current can flow from the Y capacitors to the ground of the kit the supply is being connected to for a fraction of a second. This can be enough to pop any sensitive devices.

I always make sure any DC supplies have a proper connection between the AC ground and DC ground to try and prevent this problem. However this can result in additional RF interference unless the RF, AC and DC grounds are all at the same RF potential (not the same as supply potential) or are isolated by means of RF choke baluns (or a combination of both).

It takes a lot of effort to try and maintain safety and ESD protection whilst at the same time trying to minimise RF interference paths. If you also have UPS's in circuit it becomes even harder :-(

I think my second KiWi popped when I was repeatedly plugging and unplugging the network cable whilst trying out different tests. I can only think that I must somehow have cross connected some of the pins or got the screen of the RJ45 shorted against something it shouldn't have.

Regards,

Martin - G8JNJ