There are two specific opinions I presently hold regarding medium wave radials buried in the ground and fanning out from a vertical antenna.
There are two specific opinions I presently hold regarding medium wave radials buried in the ground and fanning out from a vertical antenna.
I am stating the opinions now as a way of checking them out, to see how much agreement or non that you may provide.
First, I believe radials must be done in even numbers, with a minimum of two.
“Two” in this case means that from the center-point, at the vertical, one radial points (let’s say) north, the other south.
In actuality these radials are a single long wire tapped in the dead-center by transmitter ground, thus defining a “stunted” dipole, whose two sides would be in opposite phase.
Every “set” of radials thus added to a circular area is a repeat of the stunted dipole, thus the need for even numbers of radials.
An unevenly numbered radial would extend from the vertical off toward some direction, but would have no opposite out-of-phase partner, and would thus either off-set the tuning, directionality, or possibly radiate.
My second opinion has to do with whether the radials are bare wire or insulated wire. Some writers have said that it doesn’t matter if radial wires are insulated underground, but I believe the insulation capacitively separates the bonding between dirt and wire. To say it the other way, I believe that wire to dirt contact makes a closer capacitive bonding than would occur with insulated wire.
I will appreciate your point of view on these matters.
Bare Your Wire!..
Shouted the Part-15 Crier.. Let My R.F.’s Go! Allow them to flow freely so my voice can be heard.. 😉
Electric fence wire works great! And it’s cheap.. Holds solder and lays done nice if ya roll it out right from the spool..
10 radials ~20′ long is about as good as it gets. More is better but the added effort isn’t really worth it..
3 would work if they were spread out evenly. 2 just ain’t enough..
From Your Experience
That is a great page from your experience, Mr. 12v.
I believe, without duplicating the experience, that you have found some real-world limits.
Earlier tonight I was wondering if 1/4 wavelength radials beneath a 3-meter antenna would really know what to do.
They wouldn’t know.
10 radials, 20-feet long. Sounds right.
That’s 5 criss-crossing stunted dipoles, by my way of saying it.
Which Is All Very Nice
All discussion on these subjects is interesting, but the original questions raised in my opening post remain unaddressed.
I am beating the drum right now to bring some attention to what I’ve asked.
I’m trying to fill in missing detail from my electronic point of view.
Grounding Precision..
I don’t see it being as important as the radiator, as for length(s). I’m sure that ground resonance is good but for the power levels that we work with, any kind of return works. Working in any fraction of wavelength just isn’t worth it..
The near field is where we need to collect a return because we don’t make a whole lot to begin with. Outside of a 20′ radius, the levels are so small and not worth worrying about..
I figure an unbalanced ground area “could” make a system somewhat directional towards the area with the best/most ground area but it would be insignificant, IMO. We get what we get with our very short radiator..
Un and Dis
I am unsatisfied and dissatisfied with response so far to my original questions.
Your input, 12Vman, is all very agreeable by me, but it does not cover all the detail of everything I asked.
One of the issues, whether insulated wire adds a layer of capacitance from that very insulation when put in the ground, is addressed in an article I found somewhere where the author “expects that insulation adds capacitance to wire used for grounding”, so the thought has passed through another mind.
While holding the questions open for further comment, allow me to post another question.
Are all of these descriptions synonymous?
Ground simulation, artificial ground, synthetic ground, floating ground, and virtual ground (?)
Insulated or Not
To address your second point all I have to offer is my thinking which went into my decision to use insulated radials.
Insulated copper wire (#12 THHN) was chosen because the insulation provides some protection from corrosion not afforded to bare wire. Bare wire would allow for ohmic contact with the soil until the layer of corrosion forms and even with this the thickness of the corrosion would be much less than that of the insulation so it appears that capacitive coupling would be greater than with the plastic insulated wire. The question now becomes “how much greater and does it matter?”. I have no answer to offer.
Here’s some anecdotal information concerning my outdoor antenna system. The radials (12) were installed with 4 of them buried about 1-2 inches in the sod. Four were laid on the soil and covered with mulch, and the remaining four were laid on the soil with no cover. Because of animal activity the four which were covered with mulch are constantly being pulled up on top of the sod. I slit the soil and buried two of these four and noticed an immediate increase in field strength of 0.3 dB at my monitoring point. My plan is to bury the other two in the next few days and I will watch the FS. So far, this is very weak evidence that burying the radials increases the FS since there are so many other things which can affect this but if burying the other two increases the FS by about the same amount this would tend to support this conclusion.
Neil
New Twist
Thanks Neil for pointing out the corrosion problem with metal to dirt contact. One tends not to foresee these things, which take experience or wise counsel to know about.
Based on related observation involving metal, water, plumbing, and the like, I guess the corrosion sets in right away, based on rain fail and other electro-chemical actions.
How fortunate, because I have a lot of insulated heavy-gauge copper wire.
Hi Carl!
I had 16 radials and they were insulated
wires about as thick as lamp cord.
Some radials were ten feet and some were
20.
Things didn’t seem that great when I was
working with 4 or 6 radials, but by the
time I got up to 16, it was REALLY getting
out. I also had that huge top hat, which
was probably part of the equation.
For whatever it’s worth,
Bruce
Radials On Hold
Thunder bangs are getting closer and closer, so I’d better shut down. I hear things crashing around, it’s either tree branches coming down or hail.
Hold those radials.
Yikes!
Bruce
All Clear
The storm began with a lot of bluster, rained furiously for a fair length of time, then settled down to a cooler, wetter night scene.
And the next day, here we are with a temperature around 50-f.
For radial school I am starting out “minimated”, to re-shape a word, using two radials pointed in opposing directions (west and east).
Because it’s an indoor, baseboard floating (above dirt) synthetic ground, the earth is at a distance.
I have a print-out of PhilB’s “Ultenna” description (Ultimate Part 15 Installation) which calls for installing 32 to 64 ground radials “at least 30 ft. long”.
The one thing I am borrowing at this time is the recommended length, “at least 30 feet long”.
Why 30-feet? Let’s think. 30-feet is three-times the length of the vertical (10-feet).
Based on the Ultenna guideline, 30-feet is declared our MINIMUM for length of radials.
Is there any benefit to going longer, say 40-feet, 50-feet?
What is the length of diminishing returns? Perhaps a 1/4 wave-length radial (based on frequency)?
The 1/4 wavelength at 1550 kHz is 158.5 ft, which might exceed the available space for placing radials, therefore our outer boundary is probably not a technical measure, but a space limitation.
Therefore the MAXIMUM length for our experimental test radials is 1/4 wave at frequency OR the maximum length possible based on available space, whichever is smaller.
Indeed with the baseboard tests at least 30 feet as a length for both wings of a two-radial floating ground, the AMT3000 matches the antenna by showing a 13V reading on the VOM and the peak signal seen on the Signal Analyzer jumps from 45 dBm up to 61 dBm.
However, the term “diminishing returns” doesn’t apply to the highest achievable length, but to “the length at which no signal improvement can be observed”.
I’m sure there are previous experiments on this question, and we’ll be looking over past postings on the subject.
16 x 1/8th wave radials is
16 x 1/8th wave radials is probably the best in our situation. at 1700 it would be 20ft at 1670 where i would run here is 22ft.
transmitter would be placed 1 meter above an earth level ground with a loading coil and a 3 meter radiator.
this is legal when you factor in how certified transmitters are tested and passed under 15.219
look up the chez procaster. it was certified 1 meter above a large solid ground plane with a ground lead attached to ground from tx ground lug and a 3m base loaded radiator.
with such a setup over good conductive ground and in a typical suburban setting getting can produce decent range.
we have seen an amt 3000 (see youtube video that was posted here some time ago) with such a setup get 3 miles to a car radio
Disclaimer:
rich i agree with your calculations (and respect your knowledge) and they serve a purpose but come out of your slide rules and calculators and setup a system for yourself in the real world before saying this doesn’t work.
thank you
Results from Baseboard
This thread is an off-shoot of the Indoor Antenna thread. Here the dialog is generally about ground radials.
For indoor transmitter installations one method for setting up a floating ground radial is to run a wire along the baseboard, which could be done rather neatly and inconspicuously. The idea was suggested in an article by a HAM operator, speaking to amateur radio people who may need to operate from an indoor setup. He said, “run wire around the baseboard and use it as a ground.” He didn’t give any other detail.
The first thing I found out is that it works, judging from an increased dBm peak observed on a Spectrum Analyzer.
Before trying the baseboard floating ground I was seeing 50dBm using the AMT3000 audio ground path as the only transmitter ground.
With a long random length wire on the baseboard center tapped to the transmitter ground the dBm jumped to 59dBm.
Then, after spending an afternoon in a confused state, I conjectured a measurement method taking into account the 10-foot antenna and the wavelength of the frequency to calculate a specific length for the floating ground, and “zing”, we made it to 69dBm!
Based on this experience I now believe that the length of radials does matter, even with part 15.
In the back of the mind I have another idea to try, which will keep this pursuit going on for a long time to come.
Great Stuff
If it was me, and I had a big
empty room in my house, I
would put the whole thing in
the middle of the room.
(This is a fantasy, of course.)
But anyway, I would lay down a
zillion radials, and put a
big honking tophat on the top
of the antenna pole.
I don’t know if being away from
the walls would do any good, but
it would be interesting to try.
My first working Part 15 AM
installation was inside my
front porch, which was mostly
surrounded by glass windows.
The transmitting antenna was
just 5 feet high. There was no
dedicated ground.
The thing still got out about
1000 feet. But at the end of
that distance, it was really weak
on the car radio. Then, for some
reason, in front of fire station
Number 5, about 1/2 mile away,
the signal would reappear, and
it would be pretty strong on the
car radio. This was with the
Ramsey AM-1, which was modified
for crystal control, on 1700 kHz.
Bruce, GNAT or FLEA 88.3 (Take your pick.)
This May Be Why
I suspect that large fire trucks act as great inductors that attract radio signals, which is obviously what happened in your experiment, FLEA 88.3.
As long as you’re dedicating a whole room to part 15 antenna/radials, I have several suggestions:
1) Punch a hole in the ceiling so you can get the final few inches of height. Most homes have 8-foot ceilings;
2) Bring a wheel barrow of dirt to dump on your room radials, add some salt and hose it a little bit.
Your wife’s call to report your crack-up will be done quietly, and your sense of surprise when men in white catch you in a large-handled net will be sincere.
“May” is the Correct Description?
This May Be Why Submitted by Carl Blare on September 21, 2012 – 18:16. I suspect that large fire trucks act as great inductors that attract radio signals, which is obviously what happened in your experiment, FLEA 88.3. etc
While some might chuckle at such an evaluation and disregard its reality — that might not be true of some other readers.
Say More Please
Dear Mister Rich:
Please give more explanation of what you are saying. It was so subtle that I cannot guess at its meaning.
Are you telling us that fire trucks are in fact large signal gathering inductors?
Awww Geeesh…
You mean I have to sweep all this dirt up and put it back outside.