On Tue, 17 Aug 2004 14:01:06 -0700, Roy Lewallen
wrote:

The method you propose seems workable, except I didn't see any mention
of heat leaving the box via thermal conduction along the wires.
Depending on the box's insulating property and the wires, this could be
a significant contributor to the total heat loss from the box. Therefore
it's very important to either insure that this loss is negligible
compared to the loss through the styrofoam, or else to manage it (most
easily by using exactly the same wires and wire orientation during
calibration and test).

In my original post I suggested using the same container and the same
cable to feed either the antenna or the dummy load. Thus the power
escaping through the feedline is the same in both cases and thus,
cancels out.

My suggestion of using a cold liquid and measuring how long it takes
until it gets warmer just helps to give a ballpark value of the
thermal conductivity, which will help to set the appropriate power
levels for the actual antenna/dymmy load tests, i.e. not too cold or
too warm.

Paul OH3LWR

"Yuri Blanarovich" wrote in message
...
So, when you tell me to "forget the igloo", you seem to have placed
yourself in a position where you think you know how to evaluate antenna
efficiency and that I dont. I dont think you are *that* smart.

Jerry


You win, I ain't so smart as I thought. :-)
I thought that antenna is supposed to radiate RF in the direction and with
pattern one desires. That's what I want to measure, how effective radiator
it
is, how much RF it produces at the point of interest.
If you want to know how well it works as a heater, more power to you.
I am not in a ****ing contest who is "smarter", I was trying to convey
some
practicality and what I do and what I am interested in.
Over and out!

Back to DR1 (www.computeradio.us)

Yuri, K3BU

I was under the impression that radiation efficency was pretty much a"
no-brainer".If the antenna is built of quality materials with good
workmanship the antenna would be an efficent radiator with little ohmic or
dielectric losses. The exception to this of course would be antennas that
use an earth ground. I just found I was losing at least 3 db to heating up
the ground.

Jimmie

I was under the impression that radiation efficency was pretty much a"
no-brainer".If the antenna is built of quality materials with good
workmanship the antenna would be an efficent radiator with little ohmic or
dielectric losses. The exception to this of course would be antennas that
use an earth ground. I just found I was losing at least 3 db to heating up
the ground.

Jimmie




Keep digging, you will find more lost dBs. Things get aggravated in loaded
antennas when you start inserting coils, loading elements, folding them back,
etc. Efficiency is roughly proportional to the area under the current
distribution curve along the radiator. That can be affected by any of the
shortening "miraculous" gizmos, like Vincent DLM antenna. It is not just heat
loses in resistances. You can't have "perfectly" conducting piece of 1 ft
copper tubing be as effcient as 130 ft full size radiator on 160m.
Getting smarter, Eh ? :-)

Yuri, K3BU

On Mon, 23 Aug 2004 03:01:53 GMT, "Jimmie"
wrote:

I was under the impression that radiation efficency was pretty much a"
no-brainer".If the antenna is built of quality materials with good
workmanship the antenna would be an efficent radiator with little ohmic or
dielectric losses. The exception to this of course would be antennas that
use an earth ground. I just found I was losing at least 3 db to heating up
the ground.

Hi Jimmie,

3dB heating up the ground with an antenna that has 5dBi gain in the
preferred direction and launch angle compared to an antenna that has
no ground and 0dBi gain in the same preferred direction and launch
angle may give you pause and allow the worms some comfort on a cold
day.

Workmanship and quality materials tests those reputations vastly more
for smaller antennas than standard sized ones. Those 1 meter loops
used for HF are not rated for the lower bands for very good reasons,
and they claim (and I believe them) high standards for their product.
However, if you could resonate them in the 160M band, you'd be lucky
to see 1% efficiency.

Small antennas carry a lot of baggage, and any claims of efficiency
superior to the standard antennas they replace are suspect. When they
qualify that efficiency in creative terms like "more efficient per
unit length" you would do well to skip that and ask for field
strengths out 10 miles. A model called the eh had an FCC style site
survey performed to which they crowed it proved their design was equal
or better to a full size antenna. The data revealed results 10 and 20
miles out were 15-17dB down below that same standard they were so much
more efficient than.

73's
Richard Clark, KB7QHC

On Mon, 23 Aug 2004 04:24:52 GMT, Richard Clark
wrote:

Workmanship and quality materials tests those reputations vastly more
for smaller antennas than standard sized ones. Those 1 meter loops
used for HF are not rated for the lower bands for very good reasons,
and they claim (and I believe them) high standards for their product.
However, if you could resonate them in the 160M band, you'd be lucky
to see 1% efficiency.

You would be lucky if you could get 10 % efficiency at 40 m for these
1 m loops. Since the radiation resistance is inversely proportional of
the fourth power of frequency and the skin effect losses proportional
to the square root frequency, one could expect to get nearly 1 %
efficiency at 80 m and well below 0.1 % efficiency at 160 m.

On the European 135 kHz LF band, the practical vertical antennas are
usually less than 0.01 .. 0.02 WL, the estimated efficiency is less
than 0.1 %, so more than 1 kW has to be driven into the antenna to
even get 1 W of ERP. This 1 W ERP limit is used by many countries and
still narrow band contacts of several thousand kilometers are made.

Unfortunately, trying to compensate the low efficiency in a small
magnetic loop with a high transmitter power is not very practical,
since the voltages would be huge.

Thus, if some exotic small antenna with inevitably low efficiency is
to be used, I would first check that it can constantly handle the full
legal limit power, so that it would be possible to compensate for the
lower efficiency.

The low antenna efficiency is not much of a problem in receiving on
LF, MF and lower HF frequencies, since the band noise is still well
above the receiver front end noise. However, on upper HF and above, a
low efficiency will degrade the reception, especially if the receiver
noise figure is high (which it often is in HF receivers that try to
maximise the intermodulation performance).

Paul OH3LWR

"Richard Clark" wrote in message
...
On Mon, 23 Aug 2004 03:01:53 GMT, "Jimmie"
wrote:

I was under the impression that radiation efficency was pretty much a"
no-brainer".If the antenna is built of quality materials with good
workmanship the antenna would be an efficent radiator with little ohmic
or
dielectric losses. The exception to this of course would be antennas that
use an earth ground. I just found I was losing at least 3 db to heating
up
the ground.

Hi Jimmie,

3dB heating up the ground with an antenna that has 5dBi gain in the
preferred direction and launch angle compared to an antenna that has
no ground and 0dBi gain in the same preferred direction and launch
angle may give you pause and allow the worms some comfort on a cold
day.

Workmanship and quality materials tests those reputations vastly more
for smaller antennas than standard sized ones. Those 1 meter loops
used for HF are not rated for the lower bands for very good reasons,
and they claim (and I believe them) high standards for their product.
However, if you could resonate them in the 160M band, you'd be lucky
to see 1% efficiency.

Small antennas carry a lot of baggage, and any claims of efficiency
superior to the standard antennas they replace are suspect. When they
qualify that efficiency in creative terms like "more efficient per
unit length" you would do well to skip that and ask for field
strengths out 10 miles. A model called the eh had an FCC style site
survey performed to which they crowed it proved their design was equal
or better to a full size antenna. The data revealed results 10 and 20
miles out were 15-17dB down below that same standard they were so much
more efficient than.

73's
Richard Clark, KB7QHC


Certain products that include antennas may have to be tested for emissions
on a standardized site called an OATS, but that is a very bad choice for
antenna measurements (distance is 10 meters at most, and there is a
perfectly conducting ground plane).

As an engineer, I prefer to see performance data obtained in as simple an
environment as possible. But as a ham, I also have to admit that most people
don't use antennas under "test range" conditions. I can easily imagine an
antenna that looks good in "test range" conditions, but is badly influenced
by real-life items like proximity to ground, chimneys and trees.

Does the FCC (or anyone else) define any standard site for measurement of
antennas? Could the closest thing be NIST's antenna calibration ranges?

Ed
wb6wsn

"Ed Price" wrote
I can easily imagine an antenna that looks good in
"test range" conditions, but is badly influenced by
real-life items like proximity to ground, chimneys and trees.
Does the FCC (or anyone else) define any standard site
for measurement of antennas? Could the closest thing be
NIST's antenna calibration ranges?
_________________

Most test ranges are designed to measure (as accurately as practical) the
radiation pattern of the antenna hardware alone, and normally in relative
field only -- not in absolute gain.

The affect of the installation environment on the free-space patterns of an
antenna vary widely. The azimuth patterns of FM broadcast transmit antennas
are sometimes measured at the OEM's test range while mounted on a section of
tower, and in the mounting configuration to be used for the final
installation. That will show how the signal will be "launched," but gives
no final data about how well the antenna will perform after installation.
That will depend on its height above ground and propagation conditions along
the path from the transmit site to the receiver.

RF

Visit http://rfry.org for FM broadcast RF system papers.

On Mon, 23 Aug 2004 02:04:23 -0700, "Ed Price"
wrote:

Does the FCC (or anyone else) define any standard site for measurement of
antennas?

Hi Ed,

It is called in situ. A field survey is required in the process of
licensing.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote
Does the FCC (or anyone else) define any standard site for measurement of
antennas?

Hi Ed,

It is called in situ. A field survey is required in the process of
licensing.
_______________

However the FCC does *not* require in situ measurements for the
proof/operation of ANY transmit antenna used for FM or television
broadcast -- whether required to be directional or not. If directional, the
required pattern is defined in the license application/grant, and is
demonstrated only via relative field measurements by the antenna OEM on his
test range.

The reason is that the measured value on VHF/UHF can depend at least as much
on the propagation paths to the measured points as the true radiation
pattern from the antenna hardware itself.

In situ measurements are required for certain qualified bearings on the
calculated radiation patterns of MW broadcast directional arrays, to ensure
that co-channel interference is controlled. There really isn't another
choice in this case -- the array is purpose-built on site. Erecting and
testing it off site would not be practical, and the terrain likely would be
different anyway. MW directional arrays also have means of adjusting the
phase and power in each radiator to adjust the pattern values as shown
needed by the monitoring point measurements.

RF

Visit http://rfry.org for FM broadcast RF system papers.

On Mon, 23 Aug 2004 10:59:54 -0500, "Richard Fry"
wrote:

However the FCC does *not* require in situ measurements for the
proof/operation of ANY transmit antenna used for FM or television
broadcast --
¿ does not clash with
The reason is that the measured value on VHF/UHF can depend at least as much
on the propagation paths
?

73's
Richard Clark, KB7QHC