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Equinox Emi Solved???


midalake

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37 minutes ago, sodbuster said:

Thank you for the advice Dave.  I will take it.  Aluminum foil prototype 🤞

I would add. Do a cellphone test close to your pod and see if your pod is effected. Then try the same cell phone test with with the alumn foil. ALSO I am using hard wired headphones! 

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12 hours ago, midalake said:

I would add. Do a cellphone test close to your pod and see if your pod is effected. Then try the same cell phone test with with the alumn foil. ALSO I am using hard wired headphones! 

As am I.  Using Sunray pro golds wired to rear of armrest as per Fisher F75.  

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"Did you happen to try different modes?  Also, I am using hard wired headphones "

I didn't try anything other than Park1, I knew that mode gave plenty of EMI pickup, so was a good choice for the 'hat test'.

I tried with wired headphones, and using the internal speaker, and there was no difference ( other than a funky metallic rattling as the hat sang along with the detector sounds. )

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  • 4 weeks later...

I finally got the opportunity to test the foil hat at the farm field with the microwave tower nearby.
Unfortunately, it was a fail. Absolutely no EMI reduction could be seen with the hat fitted, and grounding the hat had no effect. The 'strategy' of placing my body between the control box and tower still worked reasonably, I'm still optimistic that there's a solution somewhere.

Obvious problem: My foil hat is just that - there's a dirty great open hole at the bottom, that is an easy entry for microwave signals. So I will try and do the simplest experiment and just use a sheet of regular kitchen foil wrapped around as much of the control pod as practical. I can also easily join it to the detector ground with my dongle.
Another unknown is the internal wiring to the circuit ground. It's not inconceivable the ground on the USB port has EMI filtering on it, thus seperating it from the true circuit ground at RF frequencies. Hence connecting to it has no effect. Unfortunately, accessing the ground pin on the coil connector is not so easy. I have M12 plugs and sockets, and could make a short extension that would give me access to that pin, I've got to be neat, though, as the extra cable could just as easily make EMI pickup worse.
There's also the possibility of putting a proper braided wire screen on the coil cable, and joining it to circuit ground with the extension cable.

Another oddball idea: as my body will absorb EMI , can I improve 'body shielding' somehow. I have some foil-backed foam sheet that's for thermal insulation purposes. Could I fit a sheet of that stuff inside my coat ? I could easily hold it in front of the detector. It's a reflector, though, not an absorber, so may not be what's needed. Do I put the foil sheet on my back, or on my chest?

Which brings up the business of RAM : radar absorbent material. You've seen those photos taken inside EMI test rooms, where the walls are lined with spiky foam tiles, to absorb RF energy? They're made from carbon-loaded foam, so they conduct electricity, in a bad way. What they don't absorb is reflected, and the odd shape of them means the reflected RF gets spread around, and bounced onto another bit of the foam, to be re-absorbed, etc. So .... another experiment would involve using conductive foam sheet to cover the control pod. Experiments I've done in the past showed that those black plastic bags used for electrostatic protection of electronics boards/computer hardware etc are not very good conductors: good enough for their design purpose, but not much else. So not suitable for shielding. But the 'crunchy' foam used for storing computer chips is better.

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