Monday, December 7, 2015

YoctoAzEl - "RFI be gone"

As I've mentioned in some previous posts I had two forms of RFI from placing my Yocto-3D sensor mounted on my large 50 Mhz Yagi.  One was RFI from the Ethernet via a CAT6 line run up the tower (yeah that didn't seem like a good idea at the time either, but I resolved that, easily).  This RFI was effecting my Receiver.  The fix for that was posted earlier this last week on this blog.

The other was from RFI when I transmitted QRO 1.5Kw at 50 Mhz.  This sometimes caused intermittent drop out of the down link signal from the sensor to it's base located next to the Yocto-Ethernet.

This was going to be a little tricky I thought, but I found that the down link was just fine from the Yocto-Ethernet (the RFI problem I already resolved).

I bought a little Aluminum box from Bud industries that is a NEMA 4 box.  If you don't know what that is google it.  This box is 6"x3"x2.5".  I also bought some Belden 9842 which is two twisted pair in a 90% braided shield, and a 100% tin foil shield.  Not cheap and not easy to find.  The price was $1.65 USD per foot.  But this stuff is practically bullet proof.  With an EXCELLENT jacket on it.  Perfect for rotating around my tower on COLD days/nights. 

Next I attached the shield to the inside of the new Aluminum box with a small screw.  Just inside the box where the Water Tight Cable Grip is mounted (with a 9/16" hole through the box).  

Then Epoxied two plastic stands to the inside of the alum. box and attached the sensor head to those and soldered the 4 wires to the Yocto-3D.

15 feet of cable is what I used.  The other end runs into the Steel NEMA 4 box I've talked about on this blog before related to this project.  on the outside of the box I added a Toriod doughnut of mix 43 about 2" wide or so and ran the cable through that 4 times and then on into the NEMA 4 box where I had another Toriod of the same mix/size and numbers of wraps.  I grounded the shield of that end at the entrance of the box as well.  And ran the 4 wires to the Yocto-3D base.  I added two snap-on mix 43 ferrites just before where they go to the base.

Now I'm running 1.5kw again and there's no down link interuption on the sensor data anymore.

SOOOO I'm keeping my fingers crossed that this will resolve the last of the RFI.  In all it really wasn't that big of a deal to resolve.  The hardest part was finding the parts I wanted to use, and getting them shipped here in a timely fashion without spending too much.

All in all I think it was worth the effort and 4 extra trips up/down the tower to resolve it. :-)

Here's a few pix of the work I did.

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