Hi STC830,

Good article ....

however, I think that Para 2, sentence 2 should read ....
......"If the earth connection is omitted, the aerial can only function through the effect of the capacitance between the aerial and the chassis .."

I am sure that the circuit being discussed is ..... vertical aerial with its bottom being connected to the top of Aerial inductor ..... with the lower or 'earthy' end of the L being connected to the chassis ...... which can be connected to natural Earth.

If the natural Earth connection is missing, then the signal can only be developed between the aerial and chassis.

I have quoted accurately. I am no expert in aerials so that is why I have quoted verbatim between the quotation marks (the bits in brackets are my additions to make things clearer, in my interpretation). Out of quotes are what I thought were useful points of understanding.

In regard to your concern, I think that it is necessary to make a connection between the reflected aerial referred to and the wire aerial, through the aerial coil. This is best made by a wire connection to earth, but can also be made with capacitance, between chassis and earth. This is what it seems to me that the long earth wire mentioned in the post that started the thread is doing.

The trouble with all this theory is that it doesn't matter much if you have a strong signal and low electrical noise. But as regulations are not controlling electrical noise as they used to, and with the increase in such noise-makers as switch mode power supplies, the right theory applied correctly can help control noise.

The section on Broadcast Receiving Aerials has the following subheadings:

Preamble

Aerial System Fundamentals
Effective Height

Aerial-Earth Systems
Vertical Rod Aerials
Inverted "L" Aerials
Loop Aerials\

Noise Reducing Systems
Matching Transformer Systems

Short-wave Aerials
Half-wave dipoles
Folded dipoles
Angle of Radiation and Reception
Ground Plane Aerials

I can pdf this and make available if anyone is interested (14 pages).

Thanks STC830, I would like to read the article. My email address should be visible.

OK, got that address so can take down if you want to.
Might take a day or to to get around to the job.

"but can also be made with capacitance, between chassis and earth"
I imagine the chassis is doing next to nothing as a counterpoise
until connected to wire that is approaching 1/4 wavelength.

If you can get a long wire outside, it's worth a try leading the antenna
out to it with coax and connecting it up high with the antenna.
It works wonders here, and I think it's because it keeps the long wire
away from objects on the way out the window (such as the window frame).

Thanks for that description STC830. I have always understood that it was the vertical section of a long wire that did most of the work but never understood why. I too would appreciate a PDF copy when you get around to it. My address should be visible.

Cheers,

Warren

Warren, if you put up your email address, will send the pdf in the next day or so.

Done! I thought it was visible but I must have changed it at some time.

Hi STC830,
Got aerial article and readable. Will get to read it over next few days.
Thanks,
Ian

Hello Ian & Warren. Should be in your in-boxes now.
Graham

I'd be very interested to read the full article too, please STC. Address uncovered.

The other day I tried to replicate the effect and did not get nearly as strong a result. Then I realised that the first time, when I noticed the affect, there was an extension reel with a circuit-breaker and about 20metres of coiled cable on the remote end of the horizontal power cable. Perhaps more capacitance tuning effects.

I will try to grasp the fundamentals of the antenna issue. How amazing that reception is possible with an elementary crystal set or, sometimes, a length of farm fence wire that happens to resonate at some multiple of wavelength with no electronics at all.

Maven

"sometimes, a length of farm fence wire that happens to resonate at some multiple of wavelength with no electronics at all"

Any old ham radio book you might find will dedicate entire chapters to HF antennas
which is still very applicable for AM broadcast.
The same length of wire can act as a full wave antenna on one band,
1/2 wave on another, and 1/4 wave on yet another band.
Not so much for AM broadcast because the wavelength across the band is all very long,
but there are actually also lengths of wire to avoid.

It would take a 50 metre wire to truly resonate on any AM broadcast frequency,
but a shorter wire can get there through additional (perhaps accidental) tuning.

The reason a wire can resonate at 1/4 wavelength
(remembering that one complete wave has a positive and negative peak)
is because a quarter wave length of wire is enough to see a peak.

Also the benefit of a vertical wire over horizontal is not so clear cut.
Interference in your area may also come in stronger on one polarity over the other.
No use improving a stations signal if you also bring in much stronger noise.
A horizontal straight wire is also directional, where a vertical wire is not.
Back in the day, it might have been of benefit to receive directionally
from your one local station.

"sometimes, a length of farm fence wire that happens to resonate at some multiple of wavelength with no electronics at all"

There is an antenna called the Beverage or wave antenna that consists of a wire ranging from one half to several wavelengths long, pointed in the direction of the desired transmitter and mounted usually 10-20 feet above the earth. The end towards the transmitting station is grounded through a resistor equal to the impedance of the antenna and the other end is connected to the radio. Another advantage of this antenna is that is non-resonant.

It works with vertically polarised signals because the earth is neither a perfect reflector nor a perfect conductor and this effectively tilts the vertically polarised wave giving it a component of horizontal polarisation.

Supposed to be used for long-wave reception but may work for medium wave broadcast signals. If so maybe this is what happens with the fence wire.