Here's an idea: Instead of alligator clipping the wire to the antenna,
loosely wrap about 6 - 8 turns of the wire around the whip so it
inductively couples to the antenna. If the radio is indeed
overloading this could solve the problem; not as much signal is
transferred to the whip as with a direct connection. I've done this
with portables and have had success, your mileage may vary.
HK

The above idea has worked for me in the past.
These radios are very sensitive so they can be used with the whip, I might
be wrong but I dont think it has anything to do with the resonance frequency
of the wire, I would say its more the length of the wire that is the problem
when it comes to the smaller portable radios.

"Dave" wrote in message ...
I recently hooked up a thirty-six foot (plus or minus a couple of feet)
piece of four-stranded wire with alligator clip to the internal "whip"
antenna of my portable shortwave receiver, for the extra performance such a
device offered. It works so well that I now cannot usually use my "DX"
setting because of all the background noise (sounds like hundreds of other
broadcasts vying for attention.) I don't know the frequency source of all
this background noise, but would like to filter out as much of it as I can.
One manufacturer of a similar "wind-up" antenna adds a capacitor to the wire
in order to lower the resonance frequency of the wire. If I were going to
try something similar (adding a capacitor, in series) in an attempt to bring
the resonance of the wire down into the 30 MHz range, what size (roughly)
capacitor should I use? Should I just try a few with different ranges, or
does anyone here have any suggestions?

TIA

Cross-posted between sci.electronics.basics and rec.radio.shortwave


Dave


Antenna basics with formulas

http://www.electronics-tutorials.com...nna-basics.htm

you may also want to do a search on "antenna tuners"

"Dave" wrote in message
...
One manufacturer of a similar "wind-up" antenna adds a capacitor to the
wire
in order to lower the resonance frequency of the wire. If I were going to
try something similar (adding a capacitor, in series) in an attempt to
bring
the resonance of the wire down into the 30 MHz range, what size (roughly)
capacitor should I use? Should I just try a few with different ranges, or
does anyone here have any suggestions?

This isn't likely to help your basic problem, which appears
to be a lack of selectivity in the radio (in other words, it
is accepting signals over too wide a bandwidth, so you hear
not only the station you're interested in, but those "to either
side" as well. Having the passband too wide also makes
for more noise in general. There are filters that can be
added (within the receiver) to improve this, but your best
bet may be to simply look for a better receiver.

Bob M.

"Bob Myers" wrote in message news:M7Dcc.2397
"Dave" wrote in message

One manufacturer of a similar "wind-up" antenna adds a capacitor to the
wire
in order to lower the resonance frequency of the wire. If I were going
to
try something similar (adding a capacitor, in series) in an attempt to
bring
the resonance of the wire down into the 30 MHz range, what size
(roughly)
capacitor should I use? Should I just try a few with different ranges,
or
does anyone here have any suggestions?

This isn't likely to help your basic problem, which appears
to be a lack of selectivity in the radio (in other words, it
is accepting signals over too wide a bandwidth, so you hear
not only the station you're interested in, but those "to either
side" as well. Having the passband too wide also makes
for more noise in general. There are filters that can be
added (within the receiver) to improve this, but your best
bet may be to simply look for a better receiver.


Not necessary at all. With a little studying of how antennas work,
Dave could build an antenna tuner and preselector all rolled into
one, with only a few parts.

For specifics, that's a homework problem and I'm personally
currently engaged in a project much like this; I'll post when
I have something a little more concrete.

Cheers!
Rich

"-=jd=-" wrote in message
On Wed 07 Apr 2004 07:18:56a, "Dave" wrote in message
:
"Rich Grise" wrote in message

Thank you, Rich. That is just what I have decided I need. Where are
you finding your information on building such a device?
I've no interest re-inventing the wheel, so if you come up with a design
or have links to the design(s) you've settled on - and if you are
agreeable to it - please share.

Well, I was just basically thinking of an ordinary antenna tuner,
which can be as simple as one capacitor or one inductor, or various
combinations, depending on what kind of impedance you're seeing
at the feed point.

The seat-of-the-pants way to do it is get a variable cap and
variable inductor in a range appropriate for the freq, and just
stick them in various arrangements and play with the tuning
until you get the best signal.

If you want to be scientific aboutg it, you might find something he
http://www.google.com/search?hl=en&l...tenna+tuner%22

Have Fun!
Rich

Dave,

I have been in a very similar situation. I used almost an identical
antenna and had fantastic results. The radio likely does not have
sufficent filtering in this case (Antenna is likely working great). I
would start by ensuring the antenna has a good ground connection to
the radio.

An antenna tuner/preselector would defantely help. Purchasing a new
or used amateur radio tuner (i.e. MFJ) 1.8Mhz-30Mhz would be the
easiest option. Adding capacitors separetely could work, but from
experience is a challenge to achive an workable solution for all
frequencies.

Homac


"Dave" wrote in message ...
I recently hooked up a thirty-six foot (plus or minus a couple of feet)
piece of four-stranded wire with alligator clip to the internal "whip"
antenna of my portable shortwave receiver, for the extra performance such a
device offered. It works so well that I now cannot usually use my "DX"
setting because of all the background noise (sounds like hundreds of other
broadcasts vying for attention.) I don't know the frequency source of all
this background noise, but would like to filter out as much of it as I can.
One manufacturer of a similar "wind-up" antenna adds a capacitor to the wire
in order to lower the resonance frequency of the wire. If I were going to
try something similar (adding a capacitor, in series) in an attempt to bring
the resonance of the wire down into the 30 MHz range, what size (roughly)
capacitor should I use? Should I just try a few with different ranges, or
does anyone here have any suggestions?

TIA

Cross-posted between sci.electronics.basics and rec.radio.shortwave


Dave

The antenna does indeed seem to be working great, and the radio is not
operating too shabily either as it is only the "background noise" I am
trying to reduce. I hooked a 100 mH RF choke up to it with good results,
and am planning on adding another one or two similar devices in an effort to
cut down on higher frequency interference. Question: how would I ground
this antenna? I have a grounding rod right outside the window, but don't
know what to hook it too. The negative battery terminal? This radio does
have an external antenna input, but that has a plastic ring around the
outside. Open to suggestions. And thanks for the input RE purchasing a
new/used tuner.

dave


"Private" wrote in message
om...
Dave,

I have been in a very similar situation. I used almost an identical
antenna and had fantastic results. The radio likely does not have
sufficent filtering in this case (Antenna is likely working great). I
would start by ensuring the antenna has a good ground connection to
the radio.

An antenna tuner/preselector would defantely help. Purchasing a new
or used amateur radio tuner (i.e. MFJ) 1.8Mhz-30Mhz would be the
easiest option. Adding capacitors separetely could work, but from
experience is a challenge to achive an workable solution for all
frequencies.

Homac


"Dave" wrote in message
...
I recently hooked up a thirty-six foot (plus or minus a couple of feet)
piece of four-stranded wire with alligator clip to the internal "whip"
antenna of my portable shortwave receiver, for the extra performance
such a
device offered. It works so well that I now cannot usually use my "DX"
setting because of all the background noise (sounds like hundreds of
other
broadcasts vying for attention.) I don't know the frequency source of
all
this background noise, but would like to filter out as much of it as I
can.
One manufacturer of a similar "wind-up" antenna adds a capacitor to the
wire
in order to lower the resonance frequency of the wire. If I were going
to
try something similar (adding a capacitor, in series) in an attempt to
bring
the resonance of the wire down into the 30 MHz range, what size
(roughly)
capacitor should I use? Should I just try a few with different ranges,
or
does anyone here have any suggestions?

TIA

Cross-posted between sci.electronics.basics and rec.radio.shortwave


Dave

"Bob Myers" wrote in message
...

"Dave" wrote in message
...
One manufacturer of a similar "wind-up" antenna adds a capacitor to the
wire
in order to lower the resonance frequency of the wire. If I were going
to
try something similar (adding a capacitor, in series) in an attempt to
bring
the resonance of the wire down into the 30 MHz range, what size
(roughly)
capacitor should I use? Should I just try a few with different ranges,
or
does anyone here have any suggestions?

This isn't likely to help your basic problem, which appears
to be a lack of selectivity in the radio (in other words, it
is accepting signals over too wide a bandwidth, so you hear
not only the station you're interested in, but those "to either
side" as well. Having the passband too wide also makes
for more noise in general. There are filters that can be
added (within the receiver) to improve this, but your best
bet may be to simply look for a better receiver.

Bob M.




Hello Bob,

The selectivity doesn't actually seem to be too bad, as it is only the
weaker signals that I have trouble digging out of the hash and trash. It
does seem to be picking up some out-of-band signals, but they are very, very
weak. As I posted in another message, a 100 microhenry RF choke cut that
stuff out considerably, and I am planning on adding another 100 or 200
microhenry RF choke to see if that helps make the slightly stronger signals
a little more discernable. Next on the worksheet is an antenna tuner of
some sort.

Thanks all,

Dave

"Michael Black" wrote in message
...
"Dave" ) writes:
I recently hooked up a thirty-six foot (plus or minus a couple of feet)
piece of four-stranded wire with alligator clip to the internal "whip"
antenna of my portable shortwave receiver, for the extra performance
such a
device offered. It works so well that I now cannot usually use my "DX"
setting because of all the background noise (sounds like hundreds of
other
broadcasts vying for attention.) I don't know the frequency source of
all
this background noise, but would like to filter out as much of it as I
can.
One manufacturer of a similar "wind-up" antenna adds a capacitor to the
wire
in order to lower the resonance frequency of the wire. If I were going
to
try something similar (adding a capacitor, in series) in an attempt to
bring
the resonance of the wire down into the 30 MHz range, what size
(roughly)
capacitor should I use? Should I just try a few with different ranges,
or
does anyone here have any suggestions?

TIA

Cross-posted between sci.electronics.basics and rec.radio.shortwave


Dave




It's probably designed for use with the whip, note the absence of
an antenna jack. It needs to be sensitive because it's using that
small whip, and when you add something longer, it overloads.

In other words, it's not one single signal, but all the strong local
signals, that are overloading it. TV and AM and FM broadcast stations
can put out pretty strong signals locally, and they can get around any
filtering in the radio, and still be strong, and then overload the active
stages in the receiver.

Michael


Just a quick note: it actually does have an external antenna input, I just
don't know what type of plug to stick into it. Plastic ring with metal
contact inside, looks like 1/8" mono would do it, but how would I ground it?
Negative battery term?

Thanks,

Dave

DAVE : Wind yer coil of at least a hundred turns of magnet "war"
around a 1" PVC pipe segment (when I was a KID I used a lacquered
toilet paper core) and take taps off it every 2-5 turns (arbitrary)
and use the selector switch to derive signal from the taps that give you
the best performance (it will vary per band) The capacitors are from
old garage sale radios and may not even be needed

This accomlishes what you have already proven with your work, that
certain frequencies can be canceled out by selection of signal
inductor-load.in series with your antenna The capacitors merely
help you tune it in more making a tank circuit that resonates with the
frequency you're "working"

I did perhaps the same thing by winding 100 turns of magnet war on a
salvaice ring torid core from a ttransistor powwer supply off a dead
computer...The antenna went to 1 end of this 100 turns and the other end
was grounded. On top this hundred turns I wound 25-40 turns and ran on
end of THAT winding to my radio's antenna IN connector and the other end
to the radio's ground

You have just made a 4:1 balun...which all in one almost does what the
couple above does...no adjustment tho

Or you can do the quick and dirty trick with a TV 300 ohm to 75 ohm
coupler, connecting the 300 ohm end to the antenna and ground as above,
and the 75 ohm connectors to your radio's antenna and ground

You wont notice the difference

Yodar





Dave wrote:
The antenna does indeed seem to be working great, and the radio is not
operating too shabily either as it is only the "background noise" I am
trying to reduce. I hooked a 100 mH RF choke up to it with good results,
and am planning on adding another one or two similar devices in an
effort to
cut down on higher frequency interference. Question: how would I ground
this antenna? I have a grounding rod right outside the window, but don't
know what to hook it too. The negative battery terminal? This radio
does
have an external antenna input, but that has a plastic ring around the
outside. Open to suggestions. And thanks for the input RE purchasing a
new/used tuner.

dave

...






Private wrote:
Dave,

I have been in a very similar situation. I used almost an identical
antenna and had fantastic results. The radio likely does not have
sufficent filtering in this case (Antenna is likely working great). I
would start by ensuring the antenna has a good ground connection to
the radio.

An antenna tuner/preselector would defantely help. Purchasing a new
or used amateur radio tuner (i.e. MFJ) 1.8Mhz-30Mhz would be the
easiest option. Adding capacitors separetely could work, but from
experience is a challenge to achive an workable solution for all
frequencies.

Homac


"Dave" wrote in message ...

I recently hooked up a thirty-six foot (plus or minus a couple of feet)
piece of four-stranded wire with alligator clip to the internal "whip"
antenna of my portable shortwave receiver, for the extra performance such a
device offered. It works so well that I now cannot usually use my "DX"
setting because of all the background noise (sounds like hundreds of other
broadcasts vying for attention.) I don't know the frequency source of all
this background noise, but would like to filter out as much of it as I can.
One manufacturer of a similar "wind-up" antenna adds a capacitor to the wire
in order to lower the resonance frequency of the wire. If I were going to
try something similar (adding a capacitor, in series) in an attempt to bring
the resonance of the wire down into the 30 MHz range, what size (roughly)
capacitor should I use? Should I just try a few with different ranges, or
does anyone here have any suggestions?

TIA

Cross-posted between sci.electronics.basics and rec.radio.shortwave


Dave