Richard Clark wrote in
:

On Sat, 19 Dec 2009 09:14:46 -0600, Lostgallifreyan
wrote:

What I really want to know is whether the ATS-909 will work ok with a
long(ish) wire outside feeding a 50 ohm coax via a 9:1 transformer, or if
that would cause more bother than connecting a wire directly to it and
putting up with local noise picked up from nearby buildings.

Hello Dr,

Well, I've been on the East Coast for several weeks and am just
catching up with your particular problem (which is not too uncommon
for SWL'ers who post here).

Many suggestions have been useful, but some contra-indicate others,
while some merely rely on lore and superstition.

One of the last suggestions, from JIMMIE, is probably the single
greatest boon for signal strength: Ground. Ground is always the least
appreciated component, and is always the single most important one.
Ground for RF is not always the same as the ground for safety. Worse
yet is that mixing them can sometimes introduce grief (AKA ground
loops). ALL grounds should eventually find their way to the service
ground. This advice serves both safety and engineering. More can be
said - but we move on.

One antenna does not always work for all bands (not without a lot of
work and the ability to change its polarization). As such, two or
more antennas are necessary for SWL'ing. They don't need to be
isolated to one band, but if any antenna is resonant for one, it will
probably be difficult on another band that is twice or half that
frequency. Thus you add another antenna that is half or twice the
first's dimension. The benefit here is that they can be wired to the
same feed point with little interaction between them. More can be
said here too.

Matching with a one-size-fits-all doohickey is pabulum for the masses.
When it is tossed into the mix, it usually forces the user to add the
components already described above that are responsible for most of
the benefit attributed to the doohickey. Hosanna's are misplaced.
More can be said here, to not good outcome.

Matching with an antenna tuner (yes, I am aware of the irony in its
name) satisfies all issues (except for the transmission line loss - if
it matters) of matching. The tuner's responsibility is to see to it
that an unknown source is matched to an unknown load (that is why it
has so many adjustments). You can use any Ham grade tuner, get one
without a meter to save the big bucks. Whatever product that is
designed for the ham bands is satisfactory for the SWL bands. Of
course, you could build your own (what a concept!).

Matching with a preselector takes the antenna tuner one step further,
and protects your receiver from the scourge of these "modern" designs:
intermod. The SWL-monkeys who demand the ability to "quickly" tune up
different bands/frequencies usually whine and squeel about the
difficulty of tuners and preselectors (and in the same breath praise
the doohickey's font of blessings). I let them indulge in their
illusions and say no more.

INTERMOD is the silent killer (as they used to say about high blood
pressure). A strong station (a nearby AM transmitter in town) can
easily close down your 31M listening experience by simply driving the
AGC into overload without you being aware of it. Preselectors and
Tuners will drive down that off-band signal, peak the selected
frequency, and give you what you tuned for in that band. Beware of
imitations that suggest they do the same without tuning (what a
crock).

As for that antenna impedance. Others have suggested a myriad of
possibilities. The first active component's shunt reactance (often
the base-emitter capacitance) is the limiting factor even when
humongous resistance bridges those same points. Resistance is for
bias folks. More can be said, but enough has been said here.

Feel free to ask for more to be said.

73's
Richard Clark, KB7QHC


Thanks. Well, my plan is to use a ground at the antenna end, right
underneath it. My neighbourhood problems recently were solved when a guy on
the first floor ****ed off someone enough that said someone blew their flat
door in with a shotgun! So the whole problem ended with a neat flameout a
few days ago. I couldn't go out there rigging antennae while paranoid
criminals were still active, it's seriously asking for BAD trouble. Right now
I have the lesser problems of dental and other bills imminent, but I'll get a
good 4' ground rod and rig up an 18' vertical whip as I learned of in details
I posted about earlier. I understand that good reception depends on a good
compromise between selectivity and sensitivity, and no doubt the antenna
'tuner' helps with that, though I'll mainly be concerned with good ground and
local common mode noise rejection. My first attempt at the line between
antenna and receiver will be a balanced line with a toroid at each end for
current isolation and possibly the suggested Norton preamp on the receiver
input, but I'll try without it first as I suspect I'll get enough signal
strength to satisfy me for a while. If I have to use coax I will but I'll try
the easier options first. This basic plan does involve a 10:1 ratio in
windings on the far end toroid which should help smooth out peaks of
resonance as described by John Doty and others as mentioned before, and if
nothing else, drives a stronger current in the balanced line part of the
system. I'm no longer much concerned about matching impedances, but I will be
watching for results of changing antenna length if resonance seems to be an
issue. My interest in the 'doohickey' or any other widget was mainly in what
appeared to be a means of reducing the difference in signal strength extremes
due to resonance. I understand that if I subsequently have to select the
weaker of two close stations I'll either have to add some 'trap' for a
specific offender, such as a trimmed lengh of unterminated coax (though as
far as I know, that trick is usually reserved for much higher frequencies),
or use a manually tuned system which I'll explore if it becomes a dominant
concern.