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

Dave wrote:

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?

What receiver? It sounds like it's being overloaded.

"N8KDV" wrote in message
...


Dave wrote:

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?

What receiver? It sounds like it's being overloaded.



Sorry, forgot to include that information. I am using a DX-402 (aka Sangean
ATS-505). I honestly wondered about that, but hesitated to shorten the wire
because I would (obvioiusly) lose some sensitivity, and really like being
able to pick up VOK's English broadcasts to Central America. Only problem
is the noise that makes it difficult to single out.

Thanks,

Dave

Is it ALL frequencies that have the " overload" or just a few??

- try Unclipping the antenna wire & moving it 1/4 inch away from the antenna
( use a string to move it around)

& see if that helps..

Dan


In article , "Dave"
writes:

Subject: Shortwave random-wire antenna question
From: "Dave"
Date: Sat, 3 Apr 2004 13:41:21 -0600

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

"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

Do you have some filtering built in to your radio? Some of the better rigs
have noise blanking, AGC, extra RF amplification (which can be bypassed),
frequency shift/width, etc.

"Dave" wrote in message 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?

Bring it down? You mean bring it up. It's resonant about 6 mhz or so.
To tune it for 30 mhz, you would need to cut about 28 ft or so off of
it. If you are severely overloading, cutting off a few ft would be a
good place to start anyway.. You probably can't handle more than 5-10
ft by the sound of it... MK


TIA

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

Not no mo... I dumped s.e.b. ...MK

In article ,
"Dave" wrote:

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?

Since you have cross posted to sci.electronics.basics lets try to look
at this logically and as non technically as possible.

The are two things that you need to accomplish to hear a station on your
radio in the way of signal strength.

1. The signal must large enough for the radio to amplify it and
reproduce it at the speaker.

2. The signal must be stronger than the noise floor of the radio and any
external noise the antenna picks up by some margin over the station you
want to hear. Usually this is something like 10 dB.

You can't do anything about the noise floor of the radio unless you want
to modify it. The basic sensitivity of the radio is a decision you made
when you bought it.

That leaves the antenna. What you did was to put up the most basic type,
which is called a Marconi or common mode antenna. For a simple antenna
it is about as non-selective as you can make hence the noise level is
high on the radio. Worse you might be over loading the radio and the
radio itself may be generating some of the noise. Portables are designed
to be sensitive and simple so they can't handle much signal. A strong
signal out or in band could be causing you additional trouble.

Whether 36 feet of wire is to much or not depends on where you live but
for most radios generally won't cause the overload problem it's just
that it is picking up everything well including lots of locally
generated noise.

That is the basically where you are at.

What can you do about this. You want to pick up more of the signals
(stations) you want to hear without hearing noise from other electrical
appliances or stuff out of band.

You need a more complex antenna design that will not pick up as much
noise as the signal you want to hear. Noise is on all frequencies and
comes from all directions.

A more complex antenna design can do things like:

1. Limit the direction it picks up signal or noise. You can benefit from
this by pointing the antenna at the signal you want or conversely
attenuating a noise source.

2. Changing the type of energy the antenna picks up. The antenna type
determines whether it picks up common mode or differential mode.

3. The antenna type also determines whether it is sensitive to the
electric, magnetic fields or both.

4. The antenna type also determines the band or bands of frequencies it
will pick up well.

All the above will limit the total amount of noise energy it will
present to the radio so it has less to deal with. Basically you use the
antenna design to preselect the signals you want to pick up. The
downside of this is short wave covers a wide range of frequencies so you
will need more than one antenna. For some type of resonant antenna the
smallest number of antennas you need are two and better would be three.

To get started with a more complex antenna and to see if you are really
improving your reception start with a weak signal using just the radios
whip antenna. Use a station on a high band (smaller antenna) during the
daytime.

Make a simple resonant antenna like a dipole cut for that frequency
connected to a coax and determine how to connect the coax to your radio.
If it is a portable radio try operating on the batteries as some of the
wall wart power supplies are noisy or noise on the house wiring is being
conducted to your radio through the power cord.

Now to test the antenna to see if it really helping you can disconnect
it from the radio and extend the radios whip antenna and collapse it
again reconnecting the external antenna to see which works the best.

You can put the external antenna outside away from noise generating
electrical equipment or switch them off.

Once you have a dipole making an improvement on weak signals you can
make other antenna types and antennas for other frequencies.

There are plenty of antenna sites on the web and ideas on finding local
noise sources.

--
Telamon
Ventura, California

On 3 Apr 2004 21:11:32 -0800, (Mark Keith) wrote:

"Dave" wrote in message 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?

Bring it down? You mean bring it up. It's resonant about 6 mhz or so.
To tune it for 30 mhz, you would need to cut about 28 ft or so off of
it. If you are severely overloading, cutting off a few ft would be a
good place to start anyway.. You probably can't handle more than 5-10
ft by the sound of it... MK


TIA

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

Not no mo... I dumped s.e.b. ...MK
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

Howard wrote:

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

Good idea. You can adjust the number of turns of the coil which are over
the whip by slowly moving it up or down to see how much signal the radio
can handle. Do this with the whip fully down. The coil must have
insulation on the wire. One of the symptoms of overloading is hearing
many strong stations *outside* the international bands where they don't
belong. Tune to a frequency range that is not an international band and
see if you can still hear those stations.


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