On Wed, 26 Sep 2007 19:13:44 GMT, Navtex-Fan wrote:
Not really - it may cast the problem into a different coupling
mechanism. You still have capacitive coupling and you want to ground
the smallest signal end (the antenna), not the load end (the
receiver).


Ehrm... that's exactly what I did. For a SWL, the antenna end is the
primary end :0)

Hi Dirk,

But you lifted the secondary ground and use the ground at the receiver
end (if I understand your description). This creates a capacitive
link into the front end through that long path. By the designation of
UnUn, both sides (Pri/Sec) of the transformer go to ground. For low
noise, this grounding should be at the antenna end of the transmission
line (which re-introduces the possibility of ground loops if the
receiver is also grounded). You also lose choking action (an UnUn or
BalUn does not necessarily choke common mode currents).

However, it sounds like it didn't make a substantial difference, or
any difference (seeing as you would have mentioned performance).

QRM levels were the same, very low to totally absent. Signal quality/
performance seems to be the same.

Then, as the song from Oklahoma suggests, "you've gone about as far as
you can go."

A simple test is to tune off frequency to background noise (absolutely
no signals). Remove the antenna, what happened to the noise level?

There is indeed a lot of confusing stuff about baluns circulating in
magazines and on the internet. Is thought it was only possible to use a
antenna tuner at the receiver end when the antenna wire is directly
connected to the tuner, ( that is: without using a coax line)
Right or wrong?

Yes (for the simple answer).

Depends (for the complex answer).

It is far easier to try and see. The issue is one of mismatch and
fully coupling ALL of the available power in the signal into your
front end. You want a transmission line instead of a drop wire so
that you cut down on QRM from devices in the home near you. Hence the
choking of the line to cut down on nearby home noise that
conducts/inducts onto the exterior of the shield traveling down to the
antenna connection and coming back into the front-end. If you float
that far end at the antenna, the noise will simply leap the choke and
capacitively couple to the antenna and then travel back into the front
end with your desired signal (what a bitch).

The conventional usage of BalUns or UnUns for SWL is for matching, not
noise control. However, through careful selection of those BalUns and
UnUns by their construction methods, you can get both. Unfortunately,
most SWL BalUn UnUn designs are built backwards with the thought that
the typical home SWL antenna represents a Hi-Z transmission line with
respect to earth. By and large that is true, but as a signal source,
most home SWL antennas are Low-Res, Hi-Imp sources. Yes, a Hi-Z
results, but it is the R that counts and the step-down is discarding
power.

I am well aware that testimonials abound to "prove" nothing is lost. I
am equally aware that there are negative testimonials too. As such,
this contradiction gives the lie to the credited theory of "magnetic
baluns" (the term being a dead giveaway to a con job). I've also read
the apology that SWLers don't have time to tune up with every
frequency change - sounds like whining slackers to me. Tuners come
with knobs and numbered scales. It takes very little effort to log
settings once for a band, and use them forever after with slight
adjustments to pull in DX.

Power matching involves equalizing the source R to the load R and
eliminating the source/load I through conjugation. This requires a
tuner which supplies the necessary L for the excess C, or versa-vice
(it is, of course, more complex that this, but this convenient short
hand is sufficient to explore the topic).

Just to cover all bases, there will be problem tunes for certain
frequency/line-length/antenna-length combinations. There is no
universal fix. You can anticipate this by building a fan antenna, or
using cage construction techniques. Something tells me that this is
probably not an option or even within the scope of your interest.

73's
Richard Clark, KB7QHC