Base Can you detect RF currents flowing on your antenna system?

[bob85]

about 30 years ago we had 11kv cables through the yard with a large transformer on a pole 5 houses up from me in our field that fed the whole estate,
they took those away and the 3 phase we had on poles in the street

The feed to the houses has always been underground as far back as i remember,
we are still on a different phase to our neighbors either side,

we have 3 systems, no external earth on old properties,
TNS that uses the sheath of the armoured cable for earth like mine &
PME that uses a combined neutral & earth wire on new properties.

 

[M0GVZ]

All you need to test for RF currents on your feedline is one of these, a flourescent light tube.

Key up, put it near your feedline and it'll light up to a varying level of brightness depending on how much current is flowing on the outside of the braid.

 

[Shadetree Mechanic]

This is interesting how the grounding may or may not come from the utility. The neutral would have to come from what ever transformer your feed comes from I would think. The neutral is tied to a ground bar inside the breaker panel on the house. There is a ground rod outside where the feed goes into the house to the breaker box.

I read an article one time about electrical safety and the biggest killer of electricians is the ground rod connection when it is disconnected when the power is on. Be careful if you ever have to re do or modify the existing ground rod connection to the house in order to connect station ground to it. I will see if I can find the article. I think it was an OSHA statistic or something. Put a clamp meter on the ground wire to verify or turn the house off just incase.

Our power lines run along the street directly in front of the house about 50 feet away. The house was built in the early 60s and the power feed must have been updated in the 80s. The single top wire goes to a "Pole Pig" down the street and then the three wires below it supply the houses on the street with two legs of 240v and the neutral to make 120v. The feed for the house runs down the pole and underground and around to the back of the house to the meter.

Years ago when my kids were young, we would sometimes play catch with a football in the front yard. Sometimes I would kick the ball straight up and over the top wire on the pole. Has to be at least 40ft. This was a big hit at the kids birthday party. My kids would bet the other kids that I could do it and then they had to see it. Then one time it hit the top wire with everyone standing there. Nothing happened but I never did it again. Haha!

 

[Marconi]

Here is another video that shows a guy testing and comparing 2 antennas that looked to produce the same signal pattern, and then comparing these two with and without Common Mode Current mitigation.



I think this video is showing us much more detail for the noise and the signal than I could ever see just using my radio. I might agree we could see a little reduction in noise on his screen. Maybe if we look real close we could even see a small improvement in the RX signal too. If this is the only difference we sometimes read about, no wonder I was never able to detect any differences just using my radio.

Back in the days when I had a very lossy feed line on my Starduster, on occasion I could actually detect that I was able to hear weak signals that some of my local buddies...claimed they did not hear. I actually worked that 10 year old feed line on my SD for nearly a year, and I never realized it until a neighbor called my attention to my low signal and then some other buddies all agreed my signal was low, but they all heard me just fine, and some said they saw no signal at all when I keyed up and talked.

 

[bob85]

Eddie

This guy is using the SDRplay RSPduo, I have the RSP1a single rx version using the same SDR uno software,

This test is not at all representative of what's possible in local noise reduction
for multiple reasons,

The test is on longwave where his coax & power cable to batteries ( his noise antennas ) are a tiny fraction of a wavelength like using a half inch long coax at 27mhz,

he also puts the choke in the wrong place, it should be at the feed-point for best results,

and the amplified rubber duck antennas are right there next to the potential noise sources hung in the window,

he sees about 3db improvement in the snr where the coax is even shorter relative to wavelength & 6db higher up the band where coax is longer relative to wavelength if you look at the snr display,

much more is available with external antennas & noise from sources near your unchoked coax,

signal strength over distance follows an inverse square law,

you can't expect to see much improvement even putting the choke in the right place when the antennas are so close,

when your antenna is away from noise sources &
your coax runs significantly closer than the antenna to a local noise source &
your coax is long enough to act as a good antenna been usually at least 1/2wave long @27mhz &
you put the choke in the right place,

you can see much more improvement than this guy sees doing the test as seen in the video on longwave with crappy little amplified ducks hung in the window.

And theres more!
He has no mast or ground wire to act as noise antennas near the house like many stations,

If noise is been received on mast and or ground wires which are seen in parallel with the coax braid,
just isolating the coax won't fix your noise,

some people think chokes don't work for rfi or noise or antenna pattern because of the half assed installation techniques most people use,

they make a choke even if its correctly made for 27mhz or buy a line isolator & it seems to do nothing much at all so they don't work,

( RADIALS & MAST ISOLATION INCLUDING ANY GROUND WIRES & CHOKE ) all three together, or you could be wasting your time,

Another reason you did not see much change back in the day is noise from chinashit power supplies & chargers, computers & internet home hubs & such has got MUCH worse over the years,

Hams are packing in with radio because of local noise making operation from their home QTH unbearable to them.