Telamon wrote:
In article . com,
wrote:

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...%20Of%20Some%2
0Antenna s %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.

That's why even if I know the model number of the spectrum analyzer I
can not easily know the instrument noise floor in the sweep. The sweep
settings will modify the noise floor.

I took another look at the measurement pdf and I think it likely that
the analyzer noise floor at those settings is lower than the
measurement noise in the sweeps and so at least in the last pair of
comparison photos on page 3 clearly show that the ALA-100 has a poorer
signal to noise than the vertical he is comparing it with.

I still don't know about the other sweeps as I don't know what is a
radio station and what is the local noise in the sweep. When I did work
on a range I would turn the DUT on and off to see what actually popped
up on the sweep when the DUT is turned on. You had to do this on a
range where you can't have a large enough screen room due to cost. I'm
sure the author knows what is being generated by the stuff in his house
and what is a radio station.

It looks to me that although the Wellbrook amplifiers have very good
intermodulation numbers but that the noise floor may be high. You would
have to put in a larger signal into the Wellbrook to measure the
intermodulation products relative to the other antenna amplifiers in
the pdf document.

Wellbrook does not appear to give a noise figure for the amplifier. The
author of the pdf could easily make that measurement since he has an
analyzer. Maybe noise is coming in through the power supply connection
for the amplifier, the amplifier has a poor noise floor, or the antenna
is picking it up.

--
Telamon
Ventura, California

The difficulty in making measurements on the ALA 100 with test
instruments is you need a differential drive. I don't know if grounding
one side is kosher.