Measuring the fieldstrenght nearby is not reliable.
 

When matching a very short whip one gets a big reading but
further down the road is could all be dissapeared.

Can a closeby fieldstrenght measurement be done ?
The magnetic field is also great with a short whip.

Measuring the fieldstrenght nearby is not reliable.
 

If you are changing nothing except the impedance matching, you can put
the field strength meter anywhere, and the highest reading will mean
you've adjusted it for the strongest signal at any distance.

Roy Lewallen, W7EL

Norbert M. wrote:
When matching a very short whip one gets a big reading but
further down the road is could all be dissapeared.

Can a closeby fieldstrenght measurement be done ?
The magnetic field is also great with a short whip.

Measuring the fieldstrenght nearby is not reliable.
 

On 6 ene, 09:55, "Norbert M." wrote:
When matching a very short whip one gets a big reading but
further down the road is could all be dissapeared.

Can a closeby fieldstrenght measurement be done ?
The magnetic field is also great with a short whip.
Hello Norbert

A similar question appeared some days ago in a Dutch amateur radio
newsgroup.

As Roy also mentioned, when you do not change the antenna (inclusive
any ground system) and also not change the E-field meter position and
orientation, but only change the matching, every dB increase in the
near field, will give the same dB increase over distance. Assuming
that your matching network does not produce significant E-field.

Determining the radiated power from near field measurements is
theoretically possible, but not easy in real world for most
amateurs.

You might measure the field strength at a certain (near field)
distance. Run an EM simulation for your antenna construction
(inclusive ground system if present). Compare the simulated (near
field) E-field with the measured value. From the radiated power (in
the simulation) you can calculate the radiated power from your
antenna.

Best regards,

Wim
PA3DJS
www.tetech.nl

Measuring the fieldstrenght nearby is not reliable.
 

Wim, PA3DJS wrote:
"Determining the radiated power from near field measurements is
theoretically possible, but not easy in the real world for most
amateurs."

My experience in tuning commercial 2-way HF radios for maximum power
radiated. It could be obtained by placing my multimeter (using crystal
rectifiers for a.c. scale rectification) with its test leads attached on
the hood of the vehicle containing the radio and tuning for maximum. The
measured performance proved as good as any other tuning method.

Best regards, Richard Harrison, KB5WZI

Measuring the fieldstrenght nearby is not reliable.
 

On 6 Jan, 16:06, (Richard Harrison) wrote:
Wim, PA3DJS wrote:

"Determining the radiated power from near field measurements is
theoretically possible, but not easy in the real world for most
amateurs."

My experience in tuning commercial 2-way HF radios for maximum power
radiated. It could be obtained by placing my multimeter (using crystal
rectifiers for a.c. scale rectification) with its test leads attached on
the hood of the vehicle containing the radio and tuning for maximum. The
measured performance proved as good as any other tuning method.

Best regards, Richard Harrison, KB5WZI

But that doesn't change anything that Wim stated which is entirely
correct.
You did not "determine" radiated power.......period
Art

Measuring the fieldstrenght nearby is not reliable.
 

art wrote:
"You did not 'determine" radiated power.....period"

Exactly right. Power in the near field is largely reactive. To determine
radiated power you measure the in-phase volt-amperes with a wattmeter.
The multimeter on the hood maximizes output same as a Bird wattmeter for
practical results, but you hanen`t quantified watts out.

Best regards, Richard Harrison, KB5WZI

Measuring the fieldstrenght nearby is not reliable.
 

On 7 ene, 04:25, (Richard Harrison) wrote:
art wrote:

"You did not 'determine" radiated power.....period"

Exactly right. Power in the near field is largely reactive. To determine
radiated power you measure the in-phase volt-amperes with a wattmeter.
The multimeter on the hood maximizes output same as a Bird wattmeter for
practical results, but you hanen`t quantified watts out.

Best regards, Richard Harrison, KB5WZI

Hi Richard,

You can determine radiated power and radiation pattern by near field
measurements (theoretically). Please search for "poynting theorem"
and "Huygens principle", "Huygens Source" or "Fresnel diffraction
theory". Most texts require differential vector calculus.

Because determining radiated power based on E- and H-Field measurement
is generally not feasible for amateurs (and even for many
professionals), I suggested another approach based on E-field
measurements and EM simulation.

As absolute E-field measurement and EM simulation are within the reach
of amateur radio operators, one can both tune for maximum field and
determine absolute radiated power.

Of course you don't know how much power is dissipated in nearby
structures (buildings, etc).

Best regards,

Wim
PA3DJS
www.tetech.nl

Measuring the fieldstrenght nearby is not reliable.
 

Wim, PA3DJS wrote:
"Of course you don`t know how much power is dissipated in nearby
structures (buildings, etc)."

Yes. Standard broadcast field strengths are measured at distances along
radial paths begining at one mile from the station to ensure far field
determination. Conductivity of the earth affects received signal
strength. Over sea water, the millivolts per meter decline inversely
with distance. Over the earth, decline is more rapid depending on
conductivity. Some sites along the radials are unacceptable due to
proximity of conducting structures. The more measurements along a
radial, the better. 25 sites per radial is about the minimum. In the
USA, the FCC has published Groundwave Field vs Distance Charts, and made
them a part of its rules. One can try to fit his measured data to the
FCC curves. Groundwaves is what broadcasting is all about at these
frequencies.

Best regards, Richard Harrison, KB5WZI

Measuring the fieldstrenght nearby is not reliable.
 

To add to what PA3DJS has observed:

I have seen the use of near-field measurements to determine directivity and
gain at the (then) NBS in Bolder, Col. A huge x-y table was used to move a
probe over the face of an energized microwave antenna. Lasers (with cycle
counters and mirrors) were used to measure the actual coordinates of the
probe! A staggering amount of data was collected over a long period of time
and then digested over another long period of time. This was done inside of
a very large building where reflections were minimal.

To use this technique at, say, 10 MHz with a yagi would be improbable, but
not impossible.

73, Mac N8TT

--
J. McLaughlin; Michigan, USA
Home:
"Wimpie" wrote in message
...
On 7 ene, 04:25, (Richard Harrison) wrote:

snip
Hi Richard,

You can determine radiated power and radiation pattern by near field
measurements (theoretically). Please search for "poynting theorem"
and "Huygens principle", "Huygens Source" or "Fresnel diffraction
theory". Most texts require differential vector calculus.

Because determining radiated power based on E- and H-Field measurement
is generally not feasible for amateurs (and even for many
professionals), I suggested another approach based on E-field
measurements and EM simulation.

As absolute E-field measurement and EM simulation are within the reach
of amateur radio operators, one can both tune for maximum field and
determine absolute radiated power.

Of course you don't know how much power is dissipated in nearby
structures (buildings, etc).

Best regards,

Wim
PA3DJS
www.tetech.nl

Measuring the fieldstrenght nearby is not reliable.
 

J. Mc Laughlin wrote:

...
To use this technique at, say, 10 MHz with a yagi would be improbable, but
not impossible.

73, Mac N8TT


It would be interesting to hear ideas of those on "probes", methods,
etc., on how to do such, would be attempted--implemented-imployed ...
never say never.

I think it would be interesting to hear on endeavors along these lines,
brave hearted individuals may be willing to share their experiences,
findings, guesses, etc. ... the bark is often much more dangerous
sounding than the the "bite." :-)

Frankly, "re-inventing the wheel" is welcomed here!

Regards,
JS