"Owen" wrote in message
...
Ed Price wrote:

So practically, since the average ham has a receiver with a sensitivity
in the order of a microvolt, then your antenna limits your minimum
discernable signal level to around 65 uV/m. Maybe 100 uV/m to be on the
safe side.

In fact, the technique calls for measuring signals on the rx from the
noise floor to about 20dB above it. The noise floor for receivers today is
typically -135dBm.

No, the technique does not use an S-meter. In a nutshell, it uses Ed
Hare's (W1RFI) technique for calibrating the noise floor of the receiver,
using an external attenuator to keep the rx input below the AGC threshold,
and measuring the audio output with signal and the audio output from rx
internal noise as inputs to a calculation of the input signal power.
Applying external attenuator losses, feedline losses and antenna factor
allows calculation of field strength.

Owen

IS Hare's technique published somewhere on the web?

--
Ed
WB6WSN
El Cajon, CA USA

Ed Price wrote:
"Owen" wrote in message
...

Ed Price wrote:


So practically, since the average ham has a receiver with a sensitivity
in the order of a microvolt, then your antenna limits your minimum
discernable signal level to around 65 uV/m. Maybe 100 uV/m to be on the
safe side.

In fact, the technique calls for measuring signals on the rx from the
noise floor to about 20dB above it. The noise floor for receivers today is
typically -135dBm.


No, the technique does not use an S-meter. In a nutshell, it uses Ed
Hare's (W1RFI) technique for calibrating the noise floor of the receiver,
using an external attenuator to keep the rx input below the AGC threshold,
and measuring the audio output with signal and the audio output from rx
internal noise as inputs to a calculation of the input signal power.
Applying external attenuator losses, feedline losses and antenna factor
allows calculation of field strength.


Owen


IS Hare's technique published somewhere on the web?


Yes it is, see http://www.arrl.org/~ehare/aria/ARIA_MANUAL_TESTING.pdf .

That paper outlines the principle of using the known rx noise floor as a
baseline for measurements. I have developed a piece of software for
making the associated audio power measurements and automating the
calculation / documentation process.

Thanks for taking the time to review the loop model, it is appreciated.

Owen

PS: I saw your other response and Richard's suggestion that I use the
units capability of Mathcad. Sometimes the unit capability gets in the
way of readability, for instance I think you could not take the log of E
in volts / meter divided by V in volts and get dBV/m, I think you would
need to split E into two variables (say E' and l) and say
AF=20*log(E'/V)/l. Additionally, you can spend more time trying to get
the units to work, so that they don't collapse to fundamental units of
MLT etc, than solving the numerical side of the problem.

"Owen" wrote in message
...
Ed Price wrote:
"Owen" wrote in message
...

Ed Price wrote:


So practically, since the average ham has a receiver with a sensitivity
in the order of a microvolt, then your antenna limits your minimum
discernable signal level to around 65 uV/m. Maybe 100 uV/m to be on the
safe side.

In fact, the technique calls for measuring signals on the rx from the
noise floor to about 20dB above it. The noise floor for receivers today
is typically -135dBm.


No, the technique does not use an S-meter. In a nutshell, it uses Ed
Hare's (W1RFI) technique for calibrating the noise floor of the receiver,
using an external attenuator to keep the rx input below the AGC
threshold, and measuring the audio output with signal and the audio
output from rx internal noise as inputs to a calculation of the input
signal power. Applying external attenuator losses, feedline losses and
antenna factor allows calculation of field strength.


Owen


IS Hare's technique published somewhere on the web?


Yes it is, see http://www.arrl.org/~ehare/aria/ARIA_MANUAL_TESTING.pdf .

That paper outlines the principle of using the known rx noise floor as a
baseline for measurements. I have developed a piece of software for making
the associated audio power measurements and automating the calculation /
documentation process.

Thanks for taking the time to review the loop model, it is appreciated.

Owen


Thanks; looks like I have a lot of reading to do!

--
Ed
WB6WSN
El Cajon, CA USA

Looks pretty decent, until the very end. Antenna Factor (AF) is the ratio
of the field strength voltage to the output VOLTAGE, not power, although
you did get the numbers right.

So practically, since the average ham has a receiver with a sensitivity in
the order of a microvolt, then your antenna limits your minimum
discernable signal level to around 65 uV/m. Maybe 100 uV/m to be on the
safe side. That's likely quite adequate for detecting BPL noise, but the
real problem is having the average ham get an anywhere near reasonably
accurate measurement of 100 uV. Your S meter just isn't good enough, so
now you're moving beyond the "average" ham's capability. Accurizing your
receiver into an RF microvoltmeter is a tough task, so maybe the best
route is to use a signal generator as a comparison standard. Old
boatanchor signal generators in the 7 MHz region are reasonably available,
and their attenuators are a lot better than their frequency stability and
portability. g

I applaud your goals, but getting data accurate enough to toss into an
intelligent argument about BPL is a tough task. Good luck.

--
Ed
WB6WSN
El Cajon, CA USA

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
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).

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.

Might be interesting to replicate your results with NEC2.

Frank

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

If you find yourself short of sensitivity, try a tuned loop in the
style of a magloop and match the antenna to the receiver.

But whatever you adopt, accuracy will be limited by the uncertainty in
the amateur's receiver input impedance. This will change from band to
band and its actual value will be a matter of guesswork.

A receiver's input impedance can be masked with an attenuator. But
this further reduces sensitivity.

With amateur grade equipment, facilities and environment, expect a
measuring uncertainty in the region of 4 to 7 dB at 7 MHz. Which is
good enough for most amateur purposes and makes your precision
calculations, including conductor diameter and conductivity, not worth
the trouble.

All you need for calculation is enclosed loop area, loop inductance,
receiver impedance and a pocket calculator.

The uncertainty of a measurement is just as important as the value
itself. The only way to assess uncertainty is to compare with
professional-grade equipment. In which case, if professional grade is
obtainable, you can dump the amateur stuff.

I do like the way your calculations appeared on my screen with one
mouse click.
How do you do it?

----
Reg.

==================================

"Owen" wrote in message
...

I have been working on the BPL Interference issue.

One of my projects has been exploring ways by which ordinary (well,
competent anyway,) amateurs can make reasonably reliable
measurements of
noise / interference using existing amateur station equipment or
equipment that is easy for amateurs to construct.

This has led me to search for a portable antenna of reasonably
predictable gain that can be used with a known HF SSB receiver.

I have had a hack at predicting the gain and antenna factor of a
small
square untuned loop driving a 50 ohm load. The model is in a Mathcad
worksheet, but I have copied it to a gif file which you can view on
my
website at http://www.vk1od.net/bpl/loop.mcd.gif . (The worksheet is
entirely in metric units.)

I would appreciate any comments / review on the model and calcs.

Owen

Reg Edwards wrote:
If you find yourself short of sensitivity, try a tuned loop in the
style of a magloop and match the antenna to the receiver.


In concert with an SSB rx of noise floor -135dBm in 2KHz Effective noise
bandwidth (they are realistic figures for an IC706IIG for example), the
rx noise in 2KHz BW is 0.04uV. With an antenna with AF=36dB, the rx
noise floor translates to field strength of 2.5uV/m or 8dBuV/m.

Clearly, the "instrument" is not going to be suitable for measurements
below 11dBuV/m. However, measurements of the BPL systems on "trial" here
(Mitusbishi based on DS/2 45Mbps chipsets) showed field strengths of 45
to 65dBuV/m in 2Hz and a rx with this loop needs 20+dB of RF attenuation
to keep the interference below the AGC threshold (with the benefit of
stabilising the rx input Z somewhat).

But whatever you adopt, accuracy will be limited by the uncertainty in
the amateur's receiver input impedance. This will change from band to
band and its actual value will be a matter of guesswork.

Yes, I have been measuring the rx noise floor with 20dB of attenuation
to simulate the common measurement configuration.


A receiver's input impedance can be masked with an attenuator. But
this further reduces sensitivity.


As discussed.

With amateur grade equipment, facilities and environment, expect a
measuring uncertainty in the region of 4 to 7 dB at 7 MHz. Which is
good enough for most amateur purposes and makes your precision
calculations, including conductor diameter and conductivity, not worth
the trouble.

Given that the interference is 70dB above the ambient noise floor, we
don't need 1/10dB accuracy to demonstrate to regulators that there is a
problem


All you need for calculation is enclosed loop area, loop inductance,
receiver impedance and a pocket calculator.

The uncertainty of a measurement is just as important as the value
itself. The only way to assess uncertainty is to compare with
professional-grade equipment. In which case, if professional grade is
obtainable, you can dump the amateur stuff.

Understood. My view is that if professional grade EMC measurement kit is
available, we can use it to do a lower grade calibration of the amateur kit.


I do like the way your calculations appeared on my screen with one
mouse click.
How do you do it?

The model is in Mathcad, I copied it to the clipboard and pasted it into
Frontpage (my web editor) which finds only a useful format in the
clipboard and saves it as a GIF file (ie a graphics image).

Thanks for checking the model Reg, I think you are telling me it is more
precise than needs to be, but you haven't faulted it for accuracy.

Owen