"Joel Koltner" wrote in
:

....
But the loss resistance of the antenna itself is still contributing
kTB, right?

Yes... but summing the contributions isn't trivial.

An alternative view is to consider the contribution of conductor loss and
other losses in the antenna structure and feed, and treat the system as
an ideal (lossless antenna) with a specified 'feed loss'.

My observation is that convention is the use the antenna connector or w/g
flange as a reference point for such calcs. It may even be laid down in
standards... but I am not sure. Someone else may know?

Notwithstanding that convention, I note the VK3UM tools seem to make
their reference point a point on the space side of the antenna. That
would give rise to a slighly different G/T figure.


If I take a small loop of wire that has, say, a 100 milliohms of
resistance, it still generates kTB watts of thermal noise power. Why
isn't this a "problem?"

I don't know what you mean by "problem". I have explained above that it
should be accounted for, and a method.
....
A discussion of noise sounds like a good topic for a ham fair...
technically there's little more complex than algebra (i.e., it's
accessible to pretty much everyone), but plenty of room for
misapplication.

I haven't been to ham fairs in your country, but here there are mostly
focussed on exhanging junk (selling the junk bought at the last fair, and
buying some different junk to sell at the next fair).

Noise is dealt with pretty well in text books, but text books aren't as
popular as mags.

Complicating this in the real world is that receivers aren't perfectly
linear, and measurements in a shielded room often have limited relevance
to real life performance where the 'noise' due to intermodulation
distortion is a significant issue... especially with a trend to avoiding
front end loss (noise) by ditching front end selectivity.

Noise is an interesting topic.

I have just discovered an Agilent AN which discusses uncertainty in noise
measurement. I am about to compare it to my proposition of a statistical
estimate of noise measurement (sampling) uncertainty, see
http://www.vk1od.net/measurement/noise/nmu.htm .

Owen

Hi Owen,

"Owen Duffy" wrote in message
...
Yes... but summing the contributions isn't trivial.

OK.

I don't know what you mean by "problem". I have explained above that it
should be accounted for, and a method.

By "problem" I mean "the noise contribution from the loss resistance of the
antenna is routinely ignored." -- Presumably because the background EM noise
(coming in through the antenna's radiation resistance) often far exceeds it.

I haven't been to ham fairs in your country, but here there are mostly
focussed on exhanging junk (selling the junk bought at the last fair, and
buying some different junk to sell at the next fair).

:-)

The larger ham fairs often have some reasonably "meaty" technical seminars
(antenna design and modeling in, e.g., EZNEC is popular). Somewhat more
focused conventions (e.g., Microwave Update) often end up with a fair amount
of technical information as well.

But yes, there's always plenty of junk to be exchanged and junk food to be
consumed.

eBay has diminished the number of true "deals" left at ham fairs, but they do
still exist... including such relevant items as phase noise meters, LNAs, RF
generators.

---Joel

Ha... look at this: http://www.microwaveupdate.org/prgmactivities.php

"Noise figure testing w/probable network analysis"

There you go. Come on over from Oz, Owen, we'd love to have you!

:-)

---Joel

On Mon, 23 Mar 2009 23:39:42 GMT, Owen Duffy wrote:

My observation is that convention is the use the antenna connector or w/g
flange as a reference point for such calcs. It may even be laid down in
standards... but I am not sure. Someone else may know?

Hi Owen,

What you describe is typically called the "reference plane" in
metrology. This is a term that is found in many standard methods of
RF measurement. Most often it is a point that is neutral to the
introduction of new variables (and concommittant error). To achieve
this neutrality, it must be an access point that is reproducible -
hence the association with the connector or flange as these are
controlled points of access. Connectors can be measured separately to
validate their contribution to error and variability as they can
typically be mated to instrumentation whose own connectors have been
validated by more rigorous means.

There are other issues with the reference plane, one of which is heat
transfer through it which should ring bells here.

73's
Richard Clark, KB7QHC