Antenna reception theory
 

Richard Clark wrote:
"You make a loop."

There is a difference. The small whip has a high capacitive reactance.
The small loop has a high inductive reacvtance. Both have low radiation
resistance. But, the loop is more often used to determine EM field
strength. You just need the right "fudge factor" to convert antenna
voltage tto field strength or vice versa.

Best regards, Richard Harrison, KB5WZI

Antenna reception theory
 

"Richard Harrison" wrote in message
...
Richard Clark wrote:
"You make a loop."

There is a difference. The small whip has a high capacitive
reactance.
The small loop has a high inductive reacvtance. Both have low
radiation
resistance. But, the loop is more often used to determine EM field
strength. You just need the right "fudge factor" to convert antenna
voltage tto field strength or vice versa.

Best regards, Richard Harrison, KB5WZI
=====================================

For the very last time I will repeat my question :-

"What is the voltage measured between the bottom end of a 1 metre
vertical antenna and ground when the field strength is 1 volt per
metre.

The height (length) of the antenna is much less than 1/4-wavelength.
The bottom end of the antenna is immediately above the ground. The
ground is assumed perfect. The field is vertically polarised.

Frequency, loops, reactance, radiation resistance do not enter into
the argument. No other information is needed.

Terman, Kraus and Balanis' bibles provide answers to a different
question in which I am not interested. Mere mention of these learned
gentlemen only confuses the issue.

The answer is entirely fundamental to e.m. radiation and reception.

All I need is a number of volts. What is it please?
----
Reg, G4FGQ.

Antenna reception theory
 

"Reg Edwards" wrote
For the very last time I will repeat my question :-

Pray it so...

"What is the voltage measured between the bottom end of a 1 metre
vertical antenna and ground when the field strength is 1 volt per
metre."

Of what relevance is this to anyone but (apparently) you? Please elaborate.

RF

Antenna reception theory
 

On Tue, 20 Dec 2005 22:06:56 +0000 (UTC), "Reg Edwards"
wrote:

I normally reply, if I reply at all to your idiotic statements, with
"Phooey".

Ah yes, Punchinello,

As gracious as ever.

it should be said
Well, you generally fill the gap the
that the voltage induced in a circular loop is altogether different
which is redundant to the following:
and very much smaller from that induced in a straight wire of the same
length.

Notably you say nothing of how much.

For the sake of novices for whom you have such paternal feelings (but
absolutely no answers) I would offer that the solution in the loop
(that same wire bent over to touch ground) and loaded with 200 Ohms
(not an open) reveals a voltage that need only be multiplied by 20 to
obtain the correct value. Trivial! And what is more, far simpler to
measure across 200 Ohms than an open at 20MHz.

Thus in response to the question:
On Tue, 20 Dec 2005 14:40:14 GMT, Andy Cowley
wrote:
And just how are you going to measure that voltage without getting an
opposite voltage in your voltmeter leads.
has been responded to fully, with a realizable design (barring this
folderol of perfect ground) and removing the objection for meter
leads. It takes no more software than the free version of EZNEC
(zipped up, but it works).

Have a miserable Christmas!
That will be all too true with a visit to and through several of our
nation's airports here soon. ;-(

XOXOXOXOX,
Richard Clark, KB7QHC

Antenna reception theory
 

Richard Harrison wrote:
Reg, G4FGQ wrote:
"Terman, Kraus, and Balanis and some computer programs are of no help!"

My dictionary defines "field strength" as:
"3. The strength of radio waves at a distance from the transmitting
antenna, usually expressed in microvolts-per-meter. This is not the same
as the strength of a radio signal at the antenna terminals of the
receiver."

The definition looks OK to me. The reason the signal is not the same as
the microvolts-per-meter even when the antenna is a 1-meter length of
wire with just the right slant is because the induced voltage gets
divided between the antenna and its load (the receiver).


No, that's not why. The terminal voltage of an open circuited 1 meter
(electrically short) dipole is 1/2 the field strength in volts/meter.
The terminal voltage when terminated with a conjugately matched load can
be well over a thousand volts (in the theoretical lossless case).

But it's pointless to keep repeating this. Reg keeps asking the same
question, and you keep responding with the same incorrect answers. I
believe I've gotten through to everyone who really wants to know the
answers, so I'll let this be my last repetition.

Roy Lewallen, W7EL

Antenna reception theory
 

"Richard Fry" wrote in message
...
"Reg Edwards" wrote
For the very last time I will repeat my question :-

Pray it so...

"What is the voltage measured between the bottom end of a 1 metre
vertical antenna and ground when the field strength is 1 volt per
metre."

Of what relevance is this to anyone but (apparently) you? Please
elaborate.

RF
=========================================

For starters, Have you never heard of field strength measurements?

Have you ever designed the input stage of a radio receiver?

The topic is fundamental to an understanding of e.m. radiation and
reception.

Can YOU answer the simple question? Or are you entirely dependent on
your gospel faith in 'Bibles'.

On this occasion at least, the Bibles are letting dependent people
down.

The immediate relevance to me is that I have a program which has been
reported to have a calculating error. It was reported by a person who
is not dependent on bibles. He stated that the
conventional/traditional calculating method used in my program was
incorrect. I was not entirely convinced so I posed a related question
on this newsgroup to which only one person has replied with a number.
And he was wrong first time.

Other persons who replied, after consulting their bibles, were unable
even to answer the question, either rightly or wrongly. They just
generated more confusion.

The program concerned is GRNDWAV4 which I think, but not absolutely
certain, has now been corrected. Why not download it, input a very few
standard values, and tell me whether or not it provides the correct
answer to receiver power input? You may, of course, prefer not to
commit yourself.

Is that enough elaboration for you?
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Antenna reception theory
 

Reg, G4FGQ wrote:
"All I need is a number of volts."

I`ll guess, because Reg asked, not because I know aanything. I`ve now
discovered Kraus` effective antenna height which may be related to an
Icelandic connection. Reg hasn`t told us everything he knows. One reason
we don`t know is because the effective antenna height is related to the
antenna`s length in terms of wavelength according to Kraus. One of the
examples given by Kraus is a dipole of 1/10 of a wavelength. Kraus tells
us the effective height of this length gives a factor of 0.5. According
to Equation (1) on page 30 of the 3rd edition of "Antennas", Voltage at
the terminals of the antenna = effective height X field strength.

If we guess that a short whip might have the same effective height as a
short dipole, then with a 1 volt per meter field strength X 0.5 as an
effective height factor, their product would be 0.5 volts. I`ll assume
rms because that`s the convention for expression.

I don`t have much confidence in the number because I think you must
determine the effective height experimentally. Terman says on page 991
of his 1943 "Radio Enginneers` Handbook: "If an antenna other than a
loop is used, the effective height must be determined experimentally.
Maybe someone has worked this out since 1943.

Best regards, Richard Harrison, KB5WZI

Antenna reception theory
 

"Richard Harrison" bravely wrote to "All" (20 Dec 05 09:38:02)
--- on the heady topic of " Antenna reception theory"

RH From: (Richard Harrison)
RH Xref: core-easynews rec.radio.amateur.antenna:221565

RH Reg, G4FGQ wrote:
RH "Terman, Kraus, and Balanis and some computer programs are of no
RH help!"
RH My dictionary defines "field strength" as:
RH "3. The strength of radio waves at a distance from the transmitting
RH antenna, usually expressed in microvolts-per-meter. This is not the
RH same as the strength of a radio signal at the antenna terminals of the
RH receiver."

RH The definition looks OK to me. The reason the signal is not the same
RH as the microvolts-per-meter even when the antenna is a 1-meter length
RH of wire with just the right slant is because the induced voltage gets
RH divided between the antenna and its load (the receiver).


Not only that, but also this: the antenna rebroadcasts half of the
intercepted energy.

A*s*i*m*o*v

Antenna reception theory
 

Asimov wrote:
. . .
RH The definition looks OK to me. The reason the signal is not the same
RH as the microvolts-per-meter even when the antenna is a 1-meter length
RH of wire with just the right slant is because the induced voltage gets
RH divided between the antenna and its load (the receiver).


Not only that, but also this: the antenna rebroadcasts half of the
intercepted energy.

But voltage isn't energy. Or power.

Roy Lewallen, W7EL

Antenna reception theory
 

On Tue, 20 Dec 2005 22:08:44 -0600, (Richard
Harrison) wrote:

Reg, G4FGQ wrote:
"All I need is a number of volts."

Hi Richard,

You forgot to quote Reggie's promise this would be the last time he
asked....

I don`t have much confidence in the number because I think you must
determine the effective height experimentally. Terman says on page 991
of his 1943 "Radio Enginneers` Handbook: "If an antenna other than a
loop is used, the effective height must be determined experimentally.
Maybe someone has worked this out since 1943.

Well, in fact it had been known for at least 3 or 4 decades before
that. From the "Standard Handbook for Electrical Engineers,"
1907-1917:

"284. Receiving Antenna. ... When an electric field of intensity
E is produced on the antenna, there is an electromotive force in
the antenna equal to Eh2, where h2 is the height of the receiving
antenna from the earth to the centre of capacity."

As to the term "centre of capacity," this has a variable meaning
according to the structure (top hats were common back then for obvious
reason of the predominance of LF work) and ground conditions:

"In land stations the actual effective height is from 50 to
90% of the measured height. That the height may be made
as high as possible, it is desirable to increase the capacity
of the upper portion...."

73's
Richard Clark, KB7QHC