(Dave Platt) wrote in
:

In article ,
Lostgallifreyan wrote:

I'll pass. I think the reason no-one knows is that as you (and
others) say, it's not important enough. What does seem important is to
try to reduce localised noise, and to break the current link to protect
the radio input from static discharges. Whether I use coax or a balanced
loop made from speaker wire, it loooks like my next step is to get
Amidon FT-114-75 ferrite cores to play with, and in Britain I can't
easily do that, but if anyone knows a local direct equivalent to them I
can try that. I'll Google for things that fit the description (AL about
3000, permeability u=5000, about 1.14 inch outside diameter) but I think
it's wise to ask here to try to save time.

You can probably at least start your experimentation using the common
sort of interference-suppression ferrites that are found in many
computer accessories - e.g. molded onto DC cords, VGA cables, USB
cables, and so forth. Here in the U.S. these are easily available at
electronics surplus stores, ham-fest flea markets, and other such
sources.

In my experience, these tend to be a ferrite mix such as type 43,
which is optimized for use at somewhat higher frequencies than
HF/SWL... so they will probably not be optimal for your purposes.
However, they can be made to work.


A complete ring is better, air gaps might make it harder to assess how good
it is unless you know enough (or have equipment) to make comparisons. I
don't. But I did find an appropriately sized type 43 ferrite ring on eBay
and put it on my watch list a few hours ago, so I guess this is what I'll buy
if I don't find better quickly. The seller has a few, I think.

A few years ago I constructed a common-mode feedline choke for our
local ARES/RACES ham station, to try to keep 40- and 80-meter signals
from being carried back down the outside of the coax and into the
building (our signal was audible on phones in the city's "911"
emergency dispatch center... *not* good). I took several tubular
computer-interference-suppression ferrite cores (large inner
diameter), glued them end-to-end with cyanoacrylate, let them dry, and
then ran some RG-8X coax through the center and back around the
outside and through the center again. The coax looped through the
tube of ferrites three times.

This resulted in an extremely effective common-mode choke. According
to my MFJ antenna analyzer, the impedance looking up through the coax
in the usual way (standard hookup, into a 50-ohm dummy load) was 50
ohms... the ferrites had no effect at all on the differential-mode
signal in the coax.

But, when I measured the impedance along the braid (i.e. from the
ground shell at one end of the coax, to the ground shell at the other...
a DC short circuit), I couldn't get a reading at any frequency... the
meter just said " 1500 ohms". Even at the lowest frequency of
interest, these non-optimal ferrites added so much inductance to the
common-mode signal path that they were blocking the feedline current
flow very effectively.

[Unfortunately, we determined that the phone interference was caused by
direct RF pickup by the phone wiring, which was in the "near field" of
the antenna above the roof. It occurred even if we completely
disconnected the building feedline, and fed the antenna directly from
a radio located up on the roof. The feedline choke couldn't help us.]

In your situation, I'd guess that you could probably make an efficient
feedline choke by using almost any surplus ferrite toroid which is
sufficiently large to wind your feedline (coax or speaker wire)
through it a few times. Or, use several surplus ferrite cores,
end-to-end, and if they're large enough in diameter, loop the feedline
down through the center more than once.


I hadn't thought of this for common mode noise suppression but I will try it,
sounds like a good idea. The rings I'm after are for the coupling at each end
of the line though, 9:1 or 10:1 at far end, 1:1 at receiver end. But I guess
that the clamp-on ferrite slug could be useful on the balanced line loop
that runs between the rings. I've also wondered if that balanced line might
better be a twisted pair with each twist perhaps 10 cm or so long to be sure
that common mode really is common, but I have no idea if that's wise or
required. Haven't seen anything to suggest I need to do it.

It won't be perfect (nor as good as if you used a ferrite optimized
for use at lower frequencies) but it will probably help matters, and
will give you some sense as to whether it makes sense to go to the
trouble and expense of buying ferrites that are better for your purpose.


80 turns.. plus another 8 for the secondary.. I read they should be close
turns, and the ring size was probably specified mainly to accomodate them
all. I will try other ferrites and carbonyl iron power type cores and
whatever else comes my way perhaps, I found four small toroids in a broken
computer SMPU that might be fun to try. Ultimately though, I'm aiming for
best shots because it's like plotting an unknown graph curve with only a few
samples, so the better the accuracy of each move, the better I can understand
any discrepancy in any one of those moves.

I have a basic philosophy that is similar to Jeff Liebermann's 'Learn By
Destroying' thing, as I also used to take stuff apart as a kid, and destroyed
plenty, but actually apart from seeing what sort of build quality was
acceptable and how discrete components were built, I didn't learn much
beyond tool handling, the thing that taught me most was when I took apart
something I had to put together again for fear of punishment if I failed and
got found out. So the closer I get to starting with something like an ideal
working part or whole, the faster I can figure out the meaning of significant
excursions from that ideal. It's kind of like the argument of whether a kid
should get his first bike new and working, or self-built from bits. I think
the first way is right because it's the fastest way to know what working
(and safety) really is, then start changing things, knowing what path was
taken and how to get back without help. Works great with computers too...

On Dec 19, 10:14*am, Lostgallifreyan wrote:
Does anyone know what the Sangean ATS-909's external antenna input impedance
is?

I searched for days for documentation on that radio and found plenty, mods,
schematics, service manuals, reviews, but no straight word on the impedance
of that input! (Not even in the service manual specs). The only reference I
found was a from a guy on a 7-page set of ham reviews, and all he said was
that it was a mystery!

Maybe the only way to know is to start from the schematic but I don't know
how, but here's the best schematic I could find:http://eric.horsemensociety.info/TEC...chematic_A.gif
(Antenna input is near top right).
(Link appears to be dead, 403, forbidden. I'm sure it worked last week..)

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.

Ive measured the input impedance of a few SW receivers and found them
to be in the 1Kohm ballpark for the most part. I did this by applying
a voltage through a series resistor to the frontend of the radio and
adjusting the value of the resistor until the voltage dropped by 50%.
If you have a schematic an analysis of the front end circuit might
give you and idea.

Jimmie

JIMMIE wrote in news:a189b33a-452f-4dd7-8f82-
:

Ive measured the input impedance of a few SW receivers and found them
to be in the 1Kohm ballpark for the most part. I did this by applying
a voltage through a series resistor to the frontend of the radio and
adjusting the value of the resistor until the voltage dropped by 50%.
If you have a schematic an analysis of the front end circuit might
give you and idea.


Ok. That fits with the 1K pot for RF attenuation in that radio, someone
mentioned this and I wasn't sure if other parts might alter the picture, but
I guess not by anything that matters. I'll be using a ferrite at the radio
end of a balanced line so I guess I can experiment with turns count and watch
the signal strength meter. Might not even need a preamp if that works.

If I'm thinking wrong, please stop me before I crash into something.

On Dec 19, 3:14*pm, 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.

lets go back to the beginning... this is what i would do.
1. hook up whatever coax you have to the radio and run it as far
outside away from the house as it will go.
2. hook up a wire directly to it as long as you can go in whatever
random direction you may be able to go
3. enjoy.

if in the future there are signals that just aren't strong enough, but
still above the local noise, then start playing around with either a
matching network or a preamp. but until you know how well the
receiver by itself works with the plain wire/coax you are wasting time
over designing something you probably won't need.

On Dec 24, 5:15*pm, Dave wrote:
On Dec 19, 3:14*pm, 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.

lets go back to the beginning... this is what i would do.
1. hook up whatever coax you have to the radio and run it as far
outside away from the house as it will go.
2. hook up a wire directly to it as long as you can go in whatever
random direction you may be able to go
3. enjoy.

if in the future there are signals that just aren't strong enough, but
still above the local noise, then start playing around with either a
matching network or a preamp. *but until you know how well the
receiver by itself works with the plain wire/coax you are wasting time
over designing something you probably won't need.

You may find that a good RF ground more benificial than any particular
antenna. I discovered this while in the military and had a chance to
hook my little cheap portable Setico rx to an antenna made of 20ft of
emt conduit and the ground system on an abandoned comm unit. Lots of
good info arounf on RF grounds on the web and this group.


Jimmie

Jimmie

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

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.

On Sat, 02 Jan 2010 13:21:03 -0600, Lostgallifreyan
wrote:

Well, my plan is to use a ground at the antenna end, right
underneath it.

This bodes ill if you do not tie that ground directly to the service
ground. Further, a "ground" as you describe it (incompletely) sounds
suspiciously like a ground rod. This is NOT the same thing as RF
ground - not even close unless you live within several meters of low
tide along a major ocean shore.

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.

Suspicions confirmed....

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.

This does not acknowledge the significance of INTERMOD problems.
Experience may have to teach that (when you make all these
improvements and have poor results for your effort).

My first attempt at the line between
antenna and receiver will be a balanced line with a toroid at each end for
current isolation

This is a very, very curious novelty. You do not describe a
"balanced" system with a ground rod and vertical, so any effort at
"balanced" lines is window dressing only. The reason for placing
"balanced" within quotes is due to the inordinate care and skill
required in obtaining a balanced design. It is more often achieved
with coax. Too often, "balanced line" is approached with the
mysticism of universal relief for whatever ails a listener.

and possibly the suggested Norton preamp on the receiver
input,

I must have missed that posting. Sounds like another elaboration.

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.

This is the doohickey I spoke of. It is basically the refuge
accessory of the lowfers where the span of frequencies is, maybe,
three to one and not like the ten to one of HF SWLing.

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.

This is at cross purposes. You don't have many realistic options of
changing antenna length (height) as you do with a simple tuner when it
comes to matching.

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.

Traps don't work very well for adjacent AM/SSB stations, you need
cascade XTAL ladders to do that. Tuners, also, can only operate
within the combination of number of reactive elements and Q.

Please respond to your perception of the problem of INTERMOD as it is,
as I said, the silent killer of reception.

73's
Richard Clark, KB7QHC

Richard Clark wrote in
:

On Sat, 02 Jan 2010 13:21:03 -0600, Lostgallifreyan
wrote:

Well, my plan is to use a ground at the antenna end, right
underneath it.

This bodes ill if you do not tie that ground directly to the service
ground. Further, a "ground" as you describe it (incompletely) sounds
suspiciously like a ground rod. This is NOT the same thing as RF
ground - not even close unless you live within several meters of low
tide along a major ocean shore.

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.

Suspicions confirmed....

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.

This does not acknowledge the significance of INTERMOD problems.
Experience may have to teach that (when you make all these
improvements and have poor results for your effort).

My first attempt at the line between
antenna and receiver will be a balanced line with a toroid at each end
for current isolation

This is a very, very curious novelty. You do not describe a
"balanced" system with a ground rod and vertical, so any effort at
"balanced" lines is window dressing only. The reason for placing
"balanced" within quotes is due to the inordinate care and skill
required in obtaining a balanced design. It is more often achieved
with coax. Too often, "balanced line" is approached with the
mysticism of universal relief for whatever ails a listener.

and possibly the suggested Norton preamp on the receiver
input,

I must have missed that posting. Sounds like another elaboration.

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.

This is the doohickey I spoke of. It is basically the refuge
accessory of the lowfers where the span of frequencies is, maybe,
three to one and not like the ten to one of HF SWLing.

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.

This is at cross purposes. You don't have many realistic options of
changing antenna length (height) as you do with a simple tuner when it
comes to matching.

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.

Traps don't work very well for adjacent AM/SSB stations, you need
cascade XTAL ladders to do that. Tuners, also, can only operate
within the combination of number of reactive elements and Q.

Please respond to your perception of the problem of INTERMOD as it is,
as I said, the silent killer of reception.

73's
Richard Clark, KB7QHC


I haven't a clue about intermod, yet. One thing at a time. Right now I see at
least three contradictions (re ground rods, transformers, and feedlines) with
advice from several people, one of which (the guy who wrote the description
of the antenna and balanced line I mentioned) is part of a group of hams who
is turned to for advice by the others. No guarantee of correctness, perhaps,
but if I keep on being told I'm wrong when my stuff is coming as directly as
I can get it from others with experience, then as far as I'm concerned I'll
do what I think best and get out of the crossfire. Specifically, many times
I've seen advice that service grounds are not adequate because of common mode
noise and local currents, hence the ground rod you vehemently negate. I can
ground to service ground at near end but if the receiver is on batteries, not
connected to anything except a transformer coupling RF from the antenna, then
the ground only needs to be at the antenna end, according to advice I've seen
in several places. Even if I do ground to a water pipe or other local ground,
all advice I see until now insists on having a ground rod as close to the
antenna as possible, no matter what else I do, yet now you urge against this.
I will stop asking for advice if all I see is vigorous contradiction between
people who claim knowledge I do not have. Diverting that disagreement to one
with me doesn't alter this, I did not originate the info behind the choices I
am considering. Even if all the various contributors come here and duke it
out between them it appears I'll be none the wiser.

Lostgallifreyan wrote in
:

...several people, one of which (the guy who wrote the description
of the antenna and balanced line I mentioned) is part of a group of hams
who is turned to for advice by the others.

To save time:
"http://www.kongsfjord.no/dl/Antennas/The%20Best%20Small%20Antennas%20For%20M
W,%20LW,%20And%20SW%20rev%202.pdf

The start page for that link is here;
http://www.kongsfjord.no/dl/dl.htm"

(Copied from a post by 'amdx' earlier in this thread). The line IS balanced,
as it carries only its own internal current, driven by an isolated coupling
with the antenna circuit. Anyway, if he's wrong, there's not much point in
taking it up with me, for obvious reasons. He wrote that. I didn't.