Antenna Field Test Results Updated

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Recovering Loss

"The measured load resistance of my antenna system is 57 ohms at the feedpoint which indicates substantial ground R losses. Further investigation is underway concerning this."

There is a substance the power companies use to increase the ground conductivity where they slam ground rods into the dirt. It can be found at any hardware store or electrical supply shop.

Another method is to constantly keep the ground and especially the point where the TX connects to the ground rod and radial system, wet. I've seen some elaborate small irrigation systems setup using swamp cooler hose ran to each ground rod point and at the center. This will help reduce that ground loss..and keep the grass green and xyl happy. har har! :p


Ground Loss

Interesting suggestions from RFB but it may be that I would be fighting Mother Nature here. I found a ham radio site where they provide a table of ground resistance vs. radial number and size and for a 16 x 50 ft setup the R is typically 52 ohms. My measurement of 57 ohms for 12 X 10 ft radials also includes the loading coil resistance which I have not yet measured but if it is in the range of 15 ohms this would put the radial resistance at about 42 ohms which is in the ballpark of this. There is another source which is a program that calculates the radial resistance based on ground conductivity and using the FCC number for my area the program predicts 62 ohms resistance.

Next step is to measure the coil R and go from there.


Good Experimenting

This is really good stuff.

By the way, our street is full of all kinds of
messy RFI signals. The power lines are
terrible here. (They are intermittent, though.)

That's why, when I was on the air, I was
surprised that the neighbor on the right
800 feet away, could get my station on
a boom box in the house, and another neighbor about
500 feet to the left, could get my station
noise free on a GE Superadio. (During the
day.) I still can't believe how good my
station sounded in her kitchen. Then again,
the Superadio has a lot of pulling power.

Again, as someone who does a lot of listening
on the AM BCB, I have found that, even in very
noisy RFI locations, you can usually take a portable,
and null the noise out completely, or mostly.
You do have to have a good radio to do this. The
radio is doing a lot of the "work."

Thanks again, gentlemen.



Interference from household lights?

Most LED bulbs folks are buying today are packed with a power transformer in the neck of the bulb or behind the LED elements.

Input 110-120V is stepped down to 12V.

Yes, most of these bulbs are technically 12V.

Often these power converter boards are junk. They fail prematurely due to heat stress, high temperatures coupled with low air flow. RF interference from them is very high.

If you suspect one of these LED bulbs is causing interference, consider dissecting it. Remove the 110V power leads. Typically a simple snip with scissors will do along a thin cable bundled therein.

Patch a 12V power source either from a wall wart or from a 12V battery.

Power it up and test for interference.

I neuter one of these bulbs every few months. The power boards are truly hideous. Many "bad" bulbs that no longer work at 110V are just fine and dandy running 12V. So it is a dual purpose education.

Flood Light

Any chance the flood light that is at the end of a ground radial is adding or taking away from your coverage? I would say it could add to coverage, then again it really isn't a part of the antenna system as far as the RF is concerned.

 Barry of 1200 AM BBR - WQYY 664

Antenna Field Tests

This is a great thread! Precisely what new transmitter builders/buyers need to know! The loading coil is key. And, I understand, the more ground radials the better. At the several AM stations I worked at, we had 120, quarter-waves. At WZON in Bangor, our self-supporting tower was (still is) 500+ feet tall. 

This is just perfect for my AM tech folder! :-)



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