On Tue, 29 Jun 2004 22:41:44 -0600, John Doty
wrote:
Consider a lamp dimmer that generates 10 mW of RFI, which rides out in
common mode on the mains, finds its way to the power cord of your
transceiver, rides out on the feedline to the antenna, and then couples
back through differential mode to your receiver input. That's not a very
efficient coupling path, so suppose it has a loss of 60 dB. You'll still
get 10 nW to the receiver. This is a lot: even if it's spread over 30
MHz, it's still 10 uV in a 6 kHz channel. That's S6 on my Drake R-8, a
very serious quantity of noise.

10 uV into 50 ohms is 2 pW, not 10 nW (E^2/R). 2 pW = -117 dBW = -87
dBm. Multiplying by 30000/6 = 5000 buckets makes 10 nW or -50 dBm.
Cancel the assumed 60 dB loss and I get +10 dBm, or 10 mW. The numbers
add up fine.

As I said, one of the two of us was being pencil-whipped. This does
nothing to change the fact that the original term has no basis in
fact. It could as easily be laid to the effects of a nuclear EMP 2000
miles away. There will always be something to blame, and that is NOT
a solution nor is it differentiable between Ham and SWL antennas.

However, if I return to the original "problem" of noise derived from
household sources; then that is also something I have closely
measured.

Across time, frequency, antennas, and known noise sources I have found
it as low as S1 for my longwire (an antenna supposedly unused by Hams)
to as high as S7 (for that same longwire). My loops, dipoles and
verticals hardly fell outside of this range to present any gilt-edge
design.

Just because you couldn't doesn't mean others can't.

Can't WHAT? The numbers I offer are shown of direct experience
correlatable to real world conditions and conform to 3 Sigma of SWL
conditions. Being correlatable they were also resolved and reduced to
that same unpowered baseline without forcing me off the grid into
darkness. My station sits with a noise flicker based upon
atmospherics and radiation borne products, not the usual household
pollution that I both describe above and eliminated through techniques
described as commonplaces in this group.

There are no magic antennas and no magic rituals equal to these
commonplace practices that are offered here.

Look at the rest of
the articles on the BADX site. Taking steps to minimize common mode
coupling has worked very well for me, and many people tell me it works
for them too.

This material is NOT novel by any stretch of the imagination.
However, it is hardly fully encompassing and falls short of the entire
treatment. The notion that a spike in the ground solves common mode
reveals a very limited experience in the matter, and simply devolves
to the misty eyed sentimentality of "it works for me, so there is no
better way for you." Testimonial is a poor substitute for how and why
- especially when the suggested solution inevitably fails for someone.
The common response in that situation is to sneer them away as somehow
deserving their predicament - again, with no one knowing the basis of
the problem, they can hardly help but repeat the same nostrum now
shown to fail somewhere (an anathema in religion).

You might also find the articles at http://www.qsl.net/wa1ion/

These suggestions grow more bizarre by the posting where the
correspondent offers that SWLers ignore Amateur advice as poor quality
(a remark from a noted Yahoo), and then offer proof of their own
beguiling theories through quotes from - Amateur references.

interesting, especially the one entitled "Another Look at Noise Reducing
Antennas". Mark's antenna designs are generally useless for
transmitting, but they make superb MWDX receiving antennas.

I cannot see how injecting the notion of uselessness is a boon for an
argument upon a physicist who can understand the notion of symmetry or
what is called in this field of study, reciprocity. If it is useless
as a transmit antenna, is it useless as a receive antenna? Of course
not, as such the injection of this comment serves no purpose other
than rhetorical noise.

The problem with such a degraded S/N in the correspondence of ideas is
that the larger body of uninitiated SWLers come to the conclusion that
this "uselessness" is a positive boon to be sought in every antenna
design. Our eminent Yahoo wears this badge of anti-intellectualism as
a patronizing populist.

This discussion also reveals a poverty of alternative designs that
have equal or superior merits, even if devoid of transmitting
application. Those designs are widely discussed here and their merits
are weighed not in prejudicial terms but rather in technical
comparisons and their correlation to application. That is to say,
anyone can make an informed decision on the basis of these evaluations
offered here where we typical discard "testimonials" to the rubbish
heap.

A narrow null takes little power from the pattern:
you get little gain by putting that in a broad lobe. For example, an
elementary dipole has, theoretically, infinitely deep nulls yet it only
has about 2 dBi gain. Now consider a phased array: small phasing errors
have little effect on the gain, but they can have a large effect on the
null depth.

Again, this exposes a lack of experience in the matter. Those nulls
are balanced against the theoretical radiator called an isotropic
source. This is the i of the 2dBi (and in fact is actual;y higher
than that value).

Worse yet, this lack of experience further pollutes the uninitiated
SWLer's notion of this balance of ledger because no one on this earth
is ever going to experience that 2dB gain (nor the supposed sharp
nulls) - and simply due to earth being nearby (an irreconcilable fact
of life that extends out beyond 6 Sigma for the population of
listeners). A simple dipole one quarterwave above earth exhibits an
additional 3dB gain above and beyond your cited number. This goes to
show how your casually abandoned 4dB for an inverted L is so simply
recovered - through real comparisons rather than xeroxed theories.

The level of discussion is so unbalanced with myth, superstition and
hearsay that the casual SWLer seeking advice faces the problem of
sorting out the **** from the shinola. If I were to hike the dipole a
little more, it shows 8dB gain after allowing a real world loss of
1dB. To tell that same casual SWLer 4dB is no great loss gives a
spread of 10dB.

The consequence of this challenging this poor coverage of intellectual
offering is that the casual SWLer having the facts known, can in fact
choose to build a less optimal antenna, one that suits his real world
limitations, and enjoy a design that does not simply discard signal
with abandon. Alternatively, a simpler receiver can perform with an
excellent antenna as well as a box full of expensive knobs can with an
air cooled resistor.

When transmitting, you're generally interested in putting the power in
the right place, but when receiving you're often more interested in
avoiding picking up power from the wrong place. These considerations are
only weakly related.

This has been spoken too, the limitation is found in the signal and
noise being aligned along the same meridian. If there is any weak
relation it is found in the chance of distribution. The laws of
reciprocity are not violated by chance, and both Ham operator and
SWLer suffer the same odds. There is NOTHING separable here.

Who needs an efficient MW antenna?

People who transmit, of course!

And SWLers are not transmitting are they? Really, these specious
arguments do not advance any notion of this being separate issues.
There is nothing in the circularity of logic that demands poorer
transmit antenna designs are better receive antenna designs. Nearly
every beneficial description from your sources cited above lie outside
of the antenna and reside in the coupling or in the receiver. Such
commonplaces are not novel; they are not unique and special knowledge;
and they are certainly not universally applicable.

How would you undo that 4 dB loss without loss of bandwidth?

That has been responded to above. Loss of bandwidth is a chimera
suited for argument rather than operation. To say it is frequency
agile is the crowning claim for someone who is fain to turn a switch
and set a capacitor in 5 seconds. This isn't rocket surgery, children
learn such techniques within minutes of explanation and faithfully
demonstrate far less loss consistently for ever after.

Further, the usage of a tuner solves many other ills related to noise
and front end overload. The argument of the 9:1 transformer to ease
operation comes at the expense of simple cheap solutions - to no great
benefit, and further, to 4 dB additional loss as you describe. What
boon is to be found in that combination?

I find it laughable that one web site offered claims that a resonant
system is bad for your reception. What a crock! This has all the
logic of buying square wheels to increase your gas mileage.

I'm hardly
boasting of martyrdom anyway: a broadband inverted L is a fine general
purpose receiving antenna.

And what distinguishes it as a poor transmitting antenna? The
inclusion of the engineering decoration of the 9:1 transformer? This
logic is destroyed by a conventional tube transmitter (the original
application suited to this design).

Once again, every issue in relation to even this point is discussed as
a commonplace in this group with simple and cheap solutions that
perform without the concurrent 4dB loss. Such a cavalier attitude of
discarding signal is evidence of purchasing power, not technical
competence.

I've never seen mention of this efficiency/bandwidth tradeoff in the ham
literature,


You haven't looked. Either contrived, wholly fictional, or accurately
represented, it is part of the stock in trade for selling antennas.
In this group, I would wager its discussion consumes more bandwidth
than bragging about how many QSL cards have been pasted to the wall.

Examples?

As I offered, you need to look rather than claim. They are so common
that if they escape your attention, no work on my part is going to
satisfy you.

So, the question remains:
Do you or others have any actual differentiable discussion, or is this
simply an outlet for appoligia for why it isn't worth the strain to
lift a soldering iron when you can bench press a credit card?

73's
Richard Clark, KB7QHC