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

Owen wrote:

I hate replying to my own posts... but...

I should have reminded you that if you are having trouble viewing the
fig file because it has been zoomed to fit in the browser window, most
modern browsers allow you to zoom it up to 100% size.

In Windows Exploder, hold your cursor over the image until a little
"Expand" control appears, click the "Expand" control and there you go.

In Firefox, just click on the image.

Owen

Owen wrote:

I hate replying to my own posts... but...

I should have reminded you that if you are having trouble viewing the
gif file because it has been zoomed to fit in the browser window, most
modern browsers allow you to zoom it up to 100% size.

In Windows Exploder, hold your cursor over the image until a little
"Expand" control appears, click the "Expand" control and there you go.

In Firefox, just click on the image.

Owen

Doesn't the receiver input impedance come into it somewhere? Where is
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

Doesn't the receiver input impedance come into it somewhere? Where
is
it?
----
Reg.

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

Sorry! Looked through it again and found load impedance = 50 ohms.
----
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


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

Ed Price wrote:

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.

I have looked at it and I can't see that I said "power" in relation to
Antenna Factor. Perhaps I am blind. (You didn't confuse the units dB/m
(dB per meter) with dBm (db wrt 1mW) did you?)

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.

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

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.

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


I have gotten sidetracked here, my real interest is the completeness /
accuracy of the loop model.

Owen

A well thought out approach, nice job!

"Owen" wrote in message
...

I have gotten sidetracked here, my real interest is the completeness /
accuracy of the loop model.

Owen

On Sun, 19 Jun 2005 01:59:51 GMT, Owen wrote:

Hi Owen,

Between:

I have looked at it and I can't see that I said "power" in relation to
Antenna Factor. Perhaps I am blind. (You didn't confuse the units dB/m
(dB per meter) with dBm (db wrt 1mW) did you?)

and:

I have gotten sidetracked here, my real interest is the completeness /
accuracy of the loop model.

I have observed that your Mathcad design is short of providing
something of a self-check feature. No where in any of your formulas
do you use Units.

Yes, you label them as notes, but this is risky and has been revealed
in your first comments in response to Ed's comment:
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.

Folks who follow your math work, will be skimming it, and perhaps a
few will be transcribing it while others will have picked up your MCD
file. This is to say, very few will actually go the whole distance
for a sanity check.

That sanity check is to include the Units within the formulaic Mathcad
expression; that is, after all, one of the boons of using this
package, otherwise any spread sheet would do as well. This inclusion
would enforce a strict compliance with keeping every transformation
accurate, and you would not end up mixing terms which is very simple
to do - and later suffer from. Cecil's work with Photonics suffers
from this problem horribly such that expressions of power end up in
terms so bizarre and thoroughly out of whack that anything could be
proven, except the proof.

73's
Richard Clark, KB7QHC

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

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.

I have looked at it and I can't see that I said "power" in relation to
Antenna Factor. Perhaps I am blind. (You didn't confuse the units dB/m (dB
per meter) with dBm (db wrt 1mW) did you?)

Owen


Yep, that's exactly what I did. Maybe I was looking at your units too fast
and didn't see that "/" in there.

--
Ed
WB6WSN
El Cajon, CA USA