In message , Bob
writes


If the Sangean external antenna input were designed for 50 ohm coax,
it would probably have a coax jack, not the 2.1 mm jack.

The 'type' of connector - especially on something like a small portable
radio - is absolutely NO guide to the input impedance (which, actually
could be almost anything). It's often determined by the need to keep it
small. I have a small VHF/UHF TV set which use a 3.5mm audio jack.
--
Ian

Bob wrote in
:

The Sangean external antenna input is a 2.1mm jack which would
acommodate a high impedance long wire, as per the instructions:


3.5mm, not 2.1mm

"ANT-60 PORTABLE SW ANTENNA
Included with the ATS-909 is the Sangean ANT-60 Portable SW Antenna.
The antenna is plugged into
jack (26) labeled EXT AM ANT. When fully extended this antenna should
improve SW reception. For
maximum performance this antenna should be placed as high as possible
above the ground and in an
unobstructed area if possible."


I know that, it was the first thing I found, but it doesn't answer any
questions about impedance, especially if the radio you buy is second hand and
doesn't have the antenna wire with it.

Your idea of attaching the antenna via 50 ohm coax would probably be
below the impedance range of the jack, tho' I'm not sure you would
really hear much difference.

If the Sangean external antenna input were designed for 50 ohm coax,
it would probably have a coax jack, not the 2.1 mm jack.


Agreed, which is why I don't assume it's 50 ohms, and I start looking for
answers. I think you're likely right that it might not make enough difference
to worry about though. If using coax can get the SNR higher I'm in business
so long as the signal is strong enough for the input's gain to use.

Gaius wrote in
:

Lostgallifreyan wrote:
Gaius wrote in
:

Lostgallifreyan wrote:

Also, I see that pot now, (and noticed that it also affects the
telescopic inbuilt antenna's pickup on SW (not FM as far as I know)),
but I also see a lot of other parts associated with that part of the
circuit. I don't know enough to be sure but it seems they might
complicate the picture. If not, I don't know why the impedance seems to
be a mystery. If it were well established I know my searches would
found it so in triplicate by now...

I've just found a schematic JPG - 475Kb. It claims to be a "RK777", but
I think that's one of the 909's aliases. I can send it - mail me at john
at aultmore dot net.


Thanks, but I'm ok, I got a schematic.. It just appears that those links
became forbidden access in the week or so since I found them. Might even be a
local error, thogh as I no longer do HTML or User-Agent filtering or similar
things I can't see what the cause might be.

"IanT" wrote in
:

Ok, so that's two people saying that could work, and sure, I won't be
relying
on a single narrow range, I want to see what's out there and
detectable. I might want to limit peaks and troughs in sensitivity by
using a 9:1 transformer though, as I read several times that it is a
useful way to do that for general SW listening via a long wire. That
alone means I probably DO
need to care about impedance matching.

You need an impedance matching device otherwise incorrectly called
"antenna tuning unit". It doesn't tune the antenna, it only matches the
impedance
for a given frequency. The main loss will be with the aerial NOT being
resonant at your chosen frequency.
The only way you are going to find out is try what people have
suggested, then compare the results for yourself.


Thanks, that could be useful. I've heard of them, wasn't sure if I'd need
something beyond a means to reduce peaks and troughs in resonance or
sensitivity across bands while trying to match impedance though. I read some
old posts by John Doty (archived on web sites) that suggested that a single
device could be set and placed at the end of the antenna wire and grounded
there too, and then weatherproofed and ignored. It's an attractive idea.

"Lostgallifreyan" wrote in message
. ..
Bob wrote in
:

The Sangean external antenna input is a 2.1mm jack which would
acommodate a high impedance long wire, as per the instructions:


3.5mm, not 2.1mm

"ANT-60 PORTABLE SW ANTENNA
Included with the ATS-909 is the Sangean ANT-60 Portable SW Antenna.
The antenna is plugged into
jack (26) labeled EXT AM ANT. When fully extended this antenna should
improve SW reception. For
maximum performance this antenna should be placed as high as possible
above the ground and in an
unobstructed area if possible."


I know that, it was the first thing I found, but it doesn't answer any
questions about impedance, especially if the radio you buy is second hand
and
doesn't have the antenna wire with it.

Your idea of attaching the antenna via 50 ohm coax would probably be
below the impedance range of the jack, tho' I'm not sure you would
really hear much difference.

If the Sangean external antenna input were designed for 50 ohm coax,
it would probably have a coax jack, not the 2.1 mm jack.


Agreed, which is why I don't assume it's 50 ohms, and I start looking for
answers. I think you're likely right that it might not make enough
difference
to worry about though. If using coax can get the SNR higher I'm in
business
so long as the signal is strong enough for the input's gain to use.

Hey Lost,
This page has lots of good info,
http://www.hard-core-dx.com/nordicdx.../magbalun.html
Sounds like the N8KDV Transformer would work for you, but you
still don't know the input impedance of your radio. You could try
getting that info from Sangean.
The problem you have is whatever antenna you have the impedance changes
with frequency. If you find a band that interests you, build an antenna for
that band.
Here's another that shows how impedance changes with frequency, it's put
in
mismatch loss rather than resistance and reactance, but it gives the general
idea.
www.iw5edi.com/ham-radio/?swl-longwires,47
Mike

3.5mm, not 2.1mm

"ANT-60 PORTABLE SW ANTENNA
Included with the ATS-909 is the Sangean ANT-60 Portable SW Antenna.
The antenna is plugged into
jack (26) labeled EXT AM ANT. When fully extended this antenna should
improve SW reception. For
maximum performance this antenna should be placed as high as possible
above the ground and in an
unobstructed area if possible."


I know that, it was the first thing I found, but it doesn't answer any
questions about impedance, especially if the radio you buy is second hand
and
doesn't have the antenna wire with it.

Your idea of attaching the antenna via 50 ohm coax would probably be
below the impedance range of the jack, tho' I'm not sure you would
really hear much difference.

If the Sangean external antenna input were designed for 50 ohm coax,
it would probably have a coax jack, not the 2.1 mm jack.


Agreed, which is why I don't assume it's 50 ohms, and I start looking for
answers. I think you're likely right that it might not make enough
difference
to worry about though. If using coax can get the SNR higher I'm in
business
so long as the signal is strong enough for the input's gain to use.

Hey Lost,
This page has lots of good info,
http://www.hard-core-dx.com/nordicdx.../magbalun.html
Sounds like the N8KDV Transformer would work for you, but you
still don't know the input impedance of your radio. You could try
getting that info from Sangean.
The problem you have is whatever antenna you have the impedance changes
with frequency. If you find a band that interests you, build an antenna
for
that band.
Here's another that shows how impedance changes with frequency, it's put
in
mismatch loss rather than resistance and reactance, but it gives the
general idea.
www.iw5edi.com/ham-radio/?swl-longwires,47
Mike

You might try posting on rec.radio.shortwave, someone there may know
about the Sangean.
Mike

On Sun, 20 Dec 2009 04:01:16 -0600, Lostgallifreyan
wrote:

Bob wrote in
:

The Sangean external antenna input is a 2.1mm jack which would
acommodate a high impedance long wire, as per the instructions:


3.5mm, not 2.1mm

"ANT-60 PORTABLE SW ANTENNA
Included with the ATS-909 is the Sangean ANT-60 Portable SW Antenna.
The antenna is plugged into
jack (26) labeled EXT AM ANT. When fully extended this antenna should
improve SW reception. For
maximum performance this antenna should be placed as high as possible
above the ground and in an
unobstructed area if possible."


I know that, it was the first thing I found, but it doesn't answer any
questions about impedance, especially if the radio you buy is second hand and
doesn't have the antenna wire with it.

Your idea of attaching the antenna via 50 ohm coax would probably be
below the impedance range of the jack, tho' I'm not sure you would
really hear much difference.

If the Sangean external antenna input were designed for 50 ohm coax,
it would probably have a coax jack, not the 2.1 mm jack.


Agreed, which is why I don't assume it's 50 ohms, and I start looking for
answers. I think you're likely right that it might not make enough difference
to worry about though. If using coax can get the SNR higher I'm in business
so long as the signal is strong enough for the input's gain to use.

You might shoot an email to tech at C.Crane Co. -- a lot of their
branded radios are actually customized Sangeans...they might be able
to tell you the most effective antenna and/or the impedance of the
thing.

bob
k5qwg

Bob wrote in
:

You might shoot an email to tech at C.Crane Co. -- a lot of their
branded radios are actually customized Sangeans...they might be able
to tell you the most effective antenna and/or the impedance of the
thing.

bob
k5qwg


Nice, I saw their page, didn't check that far though, and it is worth a try.

"amdx" wrote in
:

www.iw5edi.com/ham-radio/?swl-longwires,47

Oh yeah.. Saw that one. That was what I had in mind. It irons the bumps
out. That guy mentions John Doty, his page was one of many I found while
looking for John Doty's DIY transformer plans. (Still not found those).

The way I see it (hopefully this is right) is that those deep level
variations really DO need smoothing out as described there, because they
represent signal loss greater than is likely to be caused by other errors
like basic mismatches, and possible overload at peaks as Europe has many
strong SW stations. Again, if I can use coax to increase SNR by reducing
noise out of nearby buildings, it reduces the problem to one of loss/gain.

As Anthony Alouitius StJohn Hancock pronounced: "Stone me, you've got to have
something to start with!". Not that I'd trust his judgement as a radio ham.


That's my plan for the other end of the wire though, the question is whether
I'll have trouble at the ATS-909 radio end if I use it. Though I guess the
antenna matcher (misnamed 'tuner' as IanT mentioned in his post) can help,
and probably further assist the business.

I'll probably try longwire straight to coax first just to see what results,
then an earth rod to ground the coax far end, and then the 9:1 transformer,
before considering the more complex adjustable impedance matcher though. Got
other problems like money and dodgy neighbour problems to solve first too,
which is why I'm saying more than doing right now (and gathering info). Once
I start doing, I need to minimise the actions so I don't have more than
reception issues to worry about.

"amdx" wrote in
:

Well most tuner/antenna matcher are designed to take the impedance that
the
antenna cable presents and transformer it to 50 ohms. Your problem is the
Sangean is probably not 50 ohms.

Ah, but in reverse? I don't know if this is good thinking, but if the coax
IS 50 ohms, could I not put the 50 ohm connection onto the coax and tweak the
other end (on the input instead of the coax) impedance by watching the signal
strength meter on the receiver?

(Might be undeed according to posts people made earlier that suggest that
losses here might matter less than what happens on the longwire end of the
coax).