On 2007-09-26, Richard Clark (67.168.144.41) wrote in
message


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).


Hi Richard,

I forgot to mention that I have also done the test with both windings
grounded. It didn't make any audible quality/QRM difference. ( at least
not with the present weather/soil conditions)




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."


I guess so too... :0)


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


The noise level drops when the antenna is disconnected from the
receiver. ( I'm using a Lowe HF-225 btw)

This is how the receiver sounds:
http://users.pandora.be/dirk.claessens2/div/LoweHF225BGNoise.wav

With the antenna connected, tuned on 518 KHz, no signal, it sounds like
this:
http://users.pandora.be/dirk.claessens2/div/antenna_noise.wav

Note that recordings were taken during daytime. At night, more static
is present usually.


I 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?

[ long snip - but thanks for the thorough explanation, Richard]

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).

I guess I have an old antenna tuner lying around somewhere on the
attic. I'm unsure if it will go as low as 518KHz. I'll have to check...

73's and thanks for the many tips - Dirk