Frank wrote:

In the BPL report at
http://www.ofcom.org.uk/research/tec...line/ascom.pdf
I noticed the system noise floor at about 10 dBuV/m (in 9 kHz). For the
tests they used an active bi-conical antenna. (By my calculations 10 dBuV/m
is about 9 uV(2.5 kHz BW) from a 40 m dipole at 7 MHz.) In the previously

Yes, Fig 8 shows about 10dBuV/m in 9KHz which interpolates to 5dBuV/m in
3KHz, and their measurements used a peak detector. On white noise, the
QP value would probably be 2 to 3dB lower.

I have made a large number of measurements at my home QTH (in a
residential neighbourhoos) using a half wave dipole and assuming an
average gain of -1.2dBi or an AF of -11.6dB/m and I regularly get
ambient noise readings down to around 0 to 3dBuV/m QP in 3KHz or
extrapolated to 9KHz BW, 5 to 8dBuV/m QP. Ambient noise is probably
lower than indicated by ITU P372-8!

mentioned report most of the BPL signals -- even at 1 meter from the
source -- is 60 dBuV/m. It seems your system with the loop will be much
less sensitive at about 100 uV/m (+40 dBuV/m).


See my response to Reg re the noise floor for the setup, I make it
around 8dbuV/m or 2.5uV/m. I don't pretend it can measure ambient noise,
but it can and has measured BPL interference at 40dBuV/m to 70dBuV/m.

Incidentally, when I attempted to save your web page of math, it was saved
as an ".mcd" document. Obviously I was not able to open it with Mathcad,
but will have to type it in by hand.

No you won't, I have posted a later version of the mathcad file to
http://www.vk1od.net/bpl/loop02.mcd .

The file you downloaded is an image (.gif) called loop.mcd.gif, and it
looks like your download process dropped the extension, or you hide the
extension on your machine. (Some software thinks that the first dot
begins the file extension, whereas it is the last dot that does so.)


Might be interesting to replicate your results with NEC2.

I have modeled the loop in EZNEC and get very similar inductance and
resistances.

Thanks Fred, appreciate the review.

Owen

No you won't, I have posted a later version of the mathcad file to
http://www.vk1od.net/bpl/loop02.mcd .

Yes, got it ok, thanks.

The file you downloaded is an image (.gif) called loop.mcd.gif, and it
looks like your download process dropped the extension, or you hide the
extension on your machine. (Some software thinks that the first dot begins
the file extension, whereas it is the last dot that does so.)

Guessed it was something like that.

Might be interesting to replicate your results with NEC2.

I have modeled the loop in EZNEC and get very similar inductance and
resistances.

Now this is where it gets interesting, and hope I can learn something from
it, as I am sure I have made a mistake someplace. I have not directly
attempted to verify your math, so don't know if you developed it from first
principals or got it from a book. I have a number of references including
Kraus' "Antennas", and also a text by Stutzman and Thiel, etc., so may try
to replicate your methods later.

Using NEC2 I set up a 40 m dipole in free space, and fed it with 1 kW (for
nice large current values in the loop). I placed a square loop, 0.5 m per
side and 40 m distance. with the plane of the loop parallel to the axis of
the dipole, also two sides parallel to the dipole. The dipole uses perfect
conductors, and copper for the loop, with 0.7 mm radius conductors. The
segmentation of the loop is significantly different than the dipole, but
thought it not important because of the large separation of the two
antennas. In the loop I am very close to the minimum segmentation allowed
in NEC at 0.001 wavelengths per segment -- i.e. 11 segments per side. One
segment, near a corner, has a 50 ohm load.

As is easily verified, the field strength from the dipole, at 40 m, is
5.5V/m (RMS). According to NEC the current in the loop varies from segment
to segment, ranging from 0.1 mA (peak), to 0.3 mA (peak). I took the
average (0.191 mA peak), and computed the RMS average current in the loop.
Multiplying by 50 ohms, gives me an output voltage 6.76 mV RMS.

The antenna factor is therefore 58 dB. Wonder if anybody has any idea where
the error lies. I have copied the code below.

Regards,

Frank

NEC Code:

CM Dipole antenna
CE
GW 1 41 0 0 0 20.25 0 0 0.0026706
GW 2 11 10 40 0.25 10.5 40 0.25 0.0007
GW 3 11 10.5 40 0.25 10.5 40 -0.25 0.0007
GW 4 11 10.5 40 -0.25 10 40 -0.25 0.0007
GW 5 11 10 40 -0.25 10 40 0.25 0.0007
GS 0 0 1
GE 0
EX 0 1 21 0 379.63 0.00000
LD 4 5 1 1 50 0
LD 5 2 1 11 5.8001E7
LD 5 3 1 11 5.8001E7
LD 5 4 1 11 5.8001E7
LD 5 5 1 11 5.8001E7
FR 0 12 0 0 7.15 0.0025
RP 0 181 1 1000 -90 90 1 1
EN

"Owen" wrote in message
...
Frank wrote:

In the BPL report at
http://www.ofcom.org.uk/research/tec...line/ascom.pdf
I noticed the system noise floor at about 10 dBuV/m (in 9 kHz). For the
tests they used an active bi-conical antenna. (By my calculations 10
dBuV/m is about 9 uV(2.5 kHz BW) from a 40 m dipole at 7 MHz.) In the
previously

Yes, Fig 8 shows about 10dBuV/m in 9KHz which interpolates to 5dBuV/m in
3KHz, and their measurements used a peak detector. On white noise, the QP
value would probably be 2 to 3dB lower.

I have made a large number of measurements at my home QTH (in a
residential neighbourhoos) using a half wave dipole and assuming an
average gain of -1.2dBi or an AF of -11.6dB/m and I regularly get ambient
noise readings down to around 0 to 3dBuV/m QP in 3KHz or extrapolated to
9KHz BW, 5 to 8dBuV/m QP. Ambient noise is probably lower than indicated
by ITU P372-8!

mentioned report most of the BPL signals -- even at 1 meter from the
source -- is 60 dBuV/m. It seems your system with the loop will be
much less sensitive at about 100 uV/m (+40 dBuV/m).


See my response to Reg re the noise floor for the setup, I make it around
8dbuV/m or 2.5uV/m. I don't pretend it can measure ambient noise, but it
can and has measured BPL interference at 40dBuV/m to 70dBuV/m.


What detector do you think should be used to evaluate the interference
potential of BPL?

I had thought that the QP detector was designed to the "annoyance" effect to
AM or SSB modulation. CISPR has standardized this detector, and it's been
adopted for many legal compliance standards world-wide. Yet the USA &
British military insist on use of a Peak detector. Perhaps a dual level is
needed, with a QP value for comparison of harm to the older analog
modulation techniques, and a Peak value, for comparison of harm to digital
modulation techniques.

--
Ed
WB6WSN
El Cajon, CA USA

Ed Price wrote:
....
What detector do you think should be used to evaluate the interference
potential of BPL?

I had thought that the QP detector was designed to the "annoyance" effect to
AM or SSB modulation. CISPR has standardized this detector, and it's been
adopted for many legal compliance standards world-wide. Yet the USA &
British military insist on use of a Peak detector. Perhaps a dual level is
needed, with a QP value for comparison of harm to the older analog
modulation techniques, and a Peak value, for comparison of harm to digital
modulation techniques.


I understand that the CISPR 16-1 QP detector and 9KHz bandwidth are
rooted in a series of subjective listening tests done somewhere around
the 1930s.

(cue storyteller here...)

Firstly, the bandwidth survives, and you are right that it is embedded
in all sorts of EM standards.

I understand that part of the tests I referred to was to discover a
instrument response that fitted well with subjective assessment of the
impact of interference (I presume on an AM broadcast transmission).

I think EMC measurement equipment often contains some of Average, RMS,
QP and Peak detectors.

I have seen several recent reports on BPL radiation that have not used
the QP detector and the reasons have IIRC been that on a scan in xyz
planes over a wide range of frequencies, the EMC receiver is too slow
using the QP detectors.

Ed Hare suggests that the AGC on a receiver acts similarly to the QP
detector, and he is probably right. So the effect being that in an
impulse noise scenario, your receiver will reduce gain roughly in line
with the QP value (rather than say the RMS or the Peak), so it may be a
good measure of gain reduction due to interference. As to interference
with the detection process, the subjective tests to arrive at the QP
detector did not assess impact on digital modulation. It seems to me
that the impact on digital modulation / encoding systems would depend on
the peak value / repetition scenario in concert with the encoding
system's capacity for error detection / correction, but that is just me
thinking aloud.

Measurement bandwidth and extrapolation / interpolation is an issue, and
possibly a bigger one than the detector response. Again there is a
disconnect between 9KHz MBW (below 30MHz) for the standards and the 2KHz
wide receivers in use for SSB. In my opinion, there is no better way to
demonstrate the impact of interference in a 2KHz wide receiver than to
measure it on a 2KHz wide receiver, so I suggest that (for us amateurs)
there may be value in measuring both where possible.

Owen