An EMI Spy?

 I've bought myself one of these kits from SDR Kits:

It's a german bit of kit marketed by Funk Amateur but sold in the UK by SDR Kits and is called the EMI Spy 2.0.

There's a load of bits and bobs in a neat box:

All of the SMD soldering is already completed, so in reality there are only a few components to solder to the board before assembly:

It went together really easily:

Once complete, there are 4 different antennas or probes you can use for EMI hunting.

This should prove a useful addition! I will report back once I've had time to try it out....

EMC 'n' all that Jazz

Well,

I've been having some issues when I TX on 6M CW. Very strange in that my Radio PC (the one sending the CW) shuts down - it doesn't crash - it performs an orderly shutdown.

This is definitely an RF issue as it only happens when the TX power is above a certain value.

So, by using a process of elimination, i.e. removing cables from the back of the PC one at a time and seeing if the problem goes away, I concluded that it's probably the HDMI cable to the monitor (well, one of the monitors) that's causing the problem.

This has lead me to question the effectiveness of ferrite suppression and other such gubbins.

Now, all of us hams will have purchased a bunch of clip on ferrites at a rally; these are supposed to be made of type 31 material which is rated up to 500MHz.

I mean something like this:

Now, these are designed to clip on a cable, effectively providing one turn through the ferrite. How well does that work then? So here's the spectrum analyser showing 0 to 100 MHz and a simple loop back from the generator to the input - no ferrite here:

So, lets now add a single turn of the clip on ferrite and see what difference it makes:

So the answer is, quite expectedly, not a great deal. So, let's increase that to 5 turns:

So, thats much more like it.

We have to conclude that clipping these ferrites onto cables around the shack is next to useless at HF - we need at least 6 turns through the material before we see any significant attenuation.

There are a number of larger ferrites available, using the same material, but bigger:

These will allow you to get multiple turns of coax or mains cable, or in my case a HDMI lead through the core, and most importantly they are also clip on.

I've tried a few combinations of different cores on my HDMI cable to see what works best; there are all sorts of other issues creeping in now though, like the resonant frequency of the cable itself:

The bottom picture above effectively gives me 6 turns by using 6 cores; the image above uses much more expensive cores and passes the wire through multiple times. They both have much the same impact.

So, I plan to add the cable above as an extension to my existing HDMI cable and see if the problem is solved.

Here's our very beautiful Elmo enjoying the fact that summer has finally arrived:

Local conditions.