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

Hi Ron,

Swapping cables and such like was the first thing I tried.

Unfortunately it looks like the LAN8710A chips on both Beagle boards are fried.

I'm not sure what has happened. The first board was definitely not my doing, but the second could have been whilst I was swapping cables and boards around. Either way, I think it would be hard to pin the failure on Seeed after they have been running OK for this length of time.

At least I've been able to confirm that the KiWi boards still work, which was my main concern, so that's good news.

I've ordered up another couple of BBG boards to quickly get me up and running again (I had just ordered some metal cases prior to the failure, so I've held off from buying BBB's in case they are not compatible) and also a few LAN8710A chips to see if I can repair the existing BBG boards and keep them as backups, as I've nothing to loose if I mess them up during the rework process.

I was thinking that if I get the old BBG's working again I could just buy some KiWi boards to use with them. But actually it seems that it's probably cheaper to wait and get a whole kit via Massdrop than buying just the KiWi boards from Seeed.

Fingers crossed that I can get it all up and running again without too much hassle :-)

Regards,

Martin - G8JNJ

I have found that If you set the AGC threshold value to -80dB it sounds a lot nicer on the Airband :-)

Hi John,

I like the new TDoA maps in v1.238, I think I actually prefer them to the original :-)

Thanks for the quick fix.

Regards,

Martin - G8JNJ

Hi Colin,

Good luck when trying to measure the IMD performance, especially using the single tone method.

Here are my measurement results, note that I'm using amateur grade kit to measure it, so there may well be errors creeping in, but I have spent more than 6 months gradually optimising the test setup, so that I can obtain repeatable results and at the very least 'compare like with like'.





Note that the calculated values using the two tone and single tone methods don't match, and the difference varies depending upon the amplifier configuration, so its not possible to apply a simple formula to bring them into agreement.

Wellbrook quote an OIP2 of +70dBm and an IOP3 of +40dBm for their 'old style' amplifier which the Wellgood is based upon, and an OIP2 of +90dBm and an IOP3 of +55dBm for their 'new style' amplifier.

My results indicate the Wellgood to be somewhere around an OIP2 of +57dBm and an IOP2 of +37dBm, which is not a million miles away but could be better.

It maybe that if I'd used slightly bigger ferrite cores and optimised the bias I could have matched Wellbrook's figures, or it could be that George has not quite got the transformer winding correct WRT the way the overwinds are placed on the binocular core with its three (possible) separate magnetic paths.

Bottom line the LZ1AQ is better than the old style Wellbrook, but the new style Wellbrook may be as good as, or better than, the LZ1AQ.

Regards,

Martin - G8JNJ

Ah yes I missed the other thread, I got confused because I'd been following a similar conversation on another forum regarding the loss of Google maps.

They had suggested Leaflet (an open-source JavaScript library for mobile-friendly interactive maps) https://leafletjs.com/ as being worth looking at, but I'm sure there are many other contenders too.

I think this decision may actually cost Google more than they may gain in the long term, and it's not as though they really need the money either.

Regards,

Martin - G8JNJ

@ Kovalr

Yes, some time ago I asked Kari if he could include the ability to map GPIO ports to specific antennas so that it would be easier to accommodate binary switching of banks of relays as you have done. Unfortunately he hasn't so far) been able to do this.

You have two (or maybe more) options. You could modify Kiri's code to switch more than one GPIO pin at a time when an antenna is selected, or alternatively use some diodes to provide simple logic to 'steer' switching signals from each GPIO output to drive one or more relays at a time or as otherwise required.

I use the second method, as I'm not really a software guy and diodes are cheap.

Regards,

Martin - G8JNJ

Hi John,

I have a test setup running on http://g8jnj.proxy.kiwisdr.com:8073/ with two AM signals being modulated by a CW recording.

TEST TEST TEST 1234567890 THE QUICK BROWN FOX JUMPED OVER THE LAZY DOG

The two signals are at different levels

3598.00KHz @ S3

4548.00KHz @ S5

I can get good decodes (just) on 4548.00 with 50Hz BW and a threshold of 42 but 3598.00 is too weak.

I'll leave it running so please feel free to use it for your own tests as required.

Regards,

Martin - G8JNJ

https://github.com/OH1KK/KiwiSDR-antenna-switch-extension


https://github.com/OH1KK/KiwiSDR-antenna-switch-extension/blob/master/docs/ant-switch-backend-beagle-gpio.txt

This extension uses Beagle GPIO pins

P8 pin 11 - GPIO_45 - Antenna 1
P8 pin 12 - GPIO_44 - Antenna 2
P8 pin 13 - GPIO_23 - Antenna 3
P8 pin 14 - GPIO_26 - Antenna 4
P8 pin 15 - GPIO_47 - Antenna 5
P8 pin 16 - GPIO_46 - Antenna 6
P8 pin 17 - GPIO_27 - Antenna 7
P8 pin 18 - GPIO_65 - Antenna 8 (not available in webui yet)
P8 pin 19 - GPIO_22 - Antenna 9 (not available in webui yet)
P8 pin 26 - GPIO_61 - Antenna 10 (not available in webui yet)

When you install the extension it will ask you which interface you wish to use.

Regards,

Martin - G8JNJ

Hi Paul,

You can also trade the overall notch depth against the notch bandwidth by varying the L/C ratio.

In most cases you don't need to have more than 10 to 20dB notch depth in order to bring the worst offenders down to an acceptable level.

Here's a couple of filters I made using SMD parts. If you remove the 5.6R resistors and are using components with a good value of Q (L >40)
you can obtain >20dB notch depth.




This is the frequency response with the resistors fitted.



Regards,

Martin -G8JNJ