Telamon wrote:
In article .com,
"R390A" wrote:
Telamon wrote:
In article .com,
"R390A" wrote:
To Whom It May Concern: Additions and revisions have been made to two
of my articles about vertical antennas and the ALA 100 on the
www.kongsfjord.com web site. The articles are (1) "Measurements Of
Some Antennas Signal To Man Made Noise Ratios In The Daytime MW And LW
Bands," and (2) "Some Of My Favorite Small Antennas For MW And LW." In
the first article an additional comparison of the ALA 100 was made with
an active whip antenna. The ALA 100 and active whip had about the same
signal to man made noise ratio. In the second article some information
was added about reducing noise in active whip antennas due to what are
believed to be ground loops in the DC feed.
The link is dead.
http://www.kongsfjord.no/dl/Antennas...ome%20Antennas
%20Signal%20To%20Man%20Made%20Noise%20Ratio.pdf
Try www.kongsfjord.no and then click on The Dallas Files.
That link worked.
Looking at your data I'm at a disadvantage not knowing which are radio
stations and which are computer noise other than KNOE 540 kHz you
specifically pointed out. Another problem for me is the loop antenna
gain looks to be about 10 dB less than the other antennas. While
actually not a problem for signal to noise measurements it does make the
sweep look different to a person that did not make the measurement.
Antennas in different locations around your house is not exactly apples
to apples comparison.
If your spectrum analyzer has a max hold on the trace that would be a
help in measuring the top of the noise floor.
A clear difference in S/N would be the last pair on page three 1500 to
2000 KHz where the ALA-100 looks to be 22 dB (-42 S to -60 N) compared
to the vertical 33 dB (-32 S to -65 N). One problem for me here is I
don't know what the analyzer noise floor itself is at this point and I
can see that the loop has 10 dB less gain than the other antennas.
Assuming that the analyzer noise floor is -70 dBm and lower would make
this comparison valid. A simple check of just disconnecting the cable
from the analyzer at those settings would show the instrument noise
floor. Using max hold would make the noise floor less ambiguous.
Due to my disadvantages noted I can't draw any firm conclusions based on
the analyzer pictures.
I'm an audio person, but noise should be measured in terms of root
hertz. Thus the noise floor you see is a function of the bandwidth of
the tracking filter. As you go narrower, the noise floor should drop.
*************
I have to take exception to the wording you ascribe to other people such
as myself about a "belief in magnetic field sensitive antennas". I rely
on belief only when I have no other choice as a fall back to no being
able to test a thesis empirically.
An electrically small shielded loop antenna will respond very poorly to
a local electric induction field and very well to a magnetic one. An
electrically small dipole would be just the opposite in response to
induction fields. This is theoretically and empirically correct. I have
much experience using these types of antennas monitoring for induction
fields and they behaved as theory predicted.
When poorly designed electronic devices generate induction fields the
electric fields have the tendency to spread farther from the source than
the magnetic fields. This is a generalization but knowing this leads to
the conclusion that a loop would pick up less of the locally generated
noise most of the time or in other words it would be an advantage to use
over a dipole.
Most people that have local noise problems and purchase a loop antenna
such as the Wellbrook find that their listening situation is greatly
improved.
I use a non-amplified folded dipole and non-amplified shielded loop. The
loop picks up much less of the local noise and picks up as much signal
as the folded dipole depending on the band.
Notice that belief is not required for any of the foregoing.
************
You have the right idea about field impedance vs distance but that
relationship is appropriate for transmitting antennas that are
efficient. Here the subject is inefficient noise sources. Here the
induction fields fall off rapidly compared to an efficient antenna.
*************
I just noticed that your ALA 100 is pretty big and not electrically
small at SW frequencies. This means it will also respond to electric
fields and being broadband will raise the noise floor. Your 60 foot
amplified loop is 10 feet bigger than my passive loop. Why do you need
an amplifier with a 60 foot loop? Normally when I consider an amplified
loop it more like 1 to 3 foot in diameter.
Here again, I believe being broadband increases the integrated noise,
but not necessarily the noise measured per root Hz. The final bandwidth
of the filter of the radio determines the integrated noise.
Say the noise was 1nV/root Hz. Say the filter bandwidth was 6Khz.
Multiply the square root of 6Khz times 1nV/Root Hz to get 77.5nV.
--
Telamon
Ventura, California