Keep your ground connections short if you want them to work

Earlier today I got an email from an SWL with a KiwiSDR & AirSpyHF+. He was complaining about very high noise / RFI levels, even though he lives in a rural area much like myself (he was comparing his noise levels to what he sees when using one of my online KiwiSDR receivers).

We exchanged a few emails back and forth, so I could understand his setup. He has a 80 ft T2FD and 500 ft sky loop antenna, so comparable to some of my antennas. I asked him if the coax shields were grounded, he said yes. OK, I asked how. 

"I have a very nice ground it is a 8-ft rod into the ground and it is connected with the 12 gauge copper wire to the coax cables."

I explained that the connection from the ground rod to coax shield needs to be as short as possible. Ideally a few inches. How long is it? If it is many feet long, the inductance will be high, and it will not work as a good ground connection.

"Apx 12 feet". 

Hmm... So he shortened that to 9 inches, and reported the RFI levels dropped down to as low as if no antenna was connected to the radio. Ideal background noise levels.

He was pretty happy 😀

So the moral of the story is, if you want your ground to work, you need to keep the connection to it as short and low inductance as possible.

Comments

  • I made some simple brackets that clamp to the ground rod and have 3/8" holes. I put "F" bulkhead barrels in the holes and that becomes a splice point, ground point, a bit of a lightning arrestor point. The ground is zero length.

  • I do nearly the same thing, I got a bunch of CATV F connector grounding blocks off eBay, attached directly to my ground rods. Short, direct, and low impedance.

  • I had grounding blocks and they weren't reliable outside, so I switched to the bulkheads, cheaper too

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