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                                 HIDDEN ANTENNAS
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Windows, (the clear stuff made out of glass) don't conduct rf very well, but a
lot of people have them in their homes, or apartments on the upper floors.
Using lead burglar foil as radiators is one possibility, and most part stores
stock it, but for those who don't want to play with pb, Stained glass window
supply houses also stock copper foil with adhesive in various widths (like
1/8th in. and up) which I've used to quick fix or design printed circut
boards. I can't see why if hard pressed, such material couldn't be pressed
in and on for service at 2, 440, or even 10 meters if the window was large
enuf. Let's see, what would a folded dipole for 20m be? I know someone is
selling such things for $30 for use in cars, but the material is cheap enough
to experiment with on your own.  After all its going to be a hard winter.
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 >    I went to K Mart and spent $19 on some TV rabbit ears.  I took off
 > the bottom and removed the UHF loop, since i have two scanners.  I wired
 > the lead-ins so they each had an "ear" and plugged them into my
 > scanners.  It doesn't work quite as well as connecting both ears to a
 > single scanner, and I may try connecting both ears to both scanners.

 >    How does it work?  When I first tried it, I got cordless phone calls
 > from all over the neighborhood.  The McDonald's over a mile away came
 > booming in, and the 30-32 MHz range was filled with skip and harmonics
 > from SW stations.
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 Or U could use a piece of 5 wire rotor wire. Build a multi length dipole
(vertical) buy cutting each length for a certain band. UHF,VHF,LB etc. Makes
for a cheap antenna. Add a length of coax and away you go. I saw in a book,
just cannot find it right now. I'll try to find it.
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When I lived in an apartment(rented condo) I used an antenna tuner to load the
aluminum balcony for HF use.  It worked on10 to 80.  One night in the rain
while on 40 cw I developed an RF short.  Never worked after that. Used an
'invisible' wire thereafter.  Didn't win DXCC but still had lots of fun.
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This article describes how to use a phone line as a shortwave antenna.
Performance will vary depending on the kind of line you have.  Overhead
lines make fairly good antennas, while underground lines generally
don't.

A highpass filter is used to remove signals below the shortwave bands.
This improves rejection from local AM stations.  In addition, a lowpass
filter can be used to reject interference from FM stations.

The original credit for the highpass and lowpass filters goes to Paul
Blumstein and John Shalamskas, respectively.  I have included edited
versions of their articles below.

The filter(s) should be connected to the phone line in this manner:

 Phone line                                       RF plug
    red         --------    center cond.            / \
     or   o----|        |--------------------------|-o |  To receiver
   green       |        |                           \ /
               | FILTER |  50 ohm coax               |
               |        |                            |
    N.C.  o----|        |----------------------------+
                --------      shield

N.C. = no connect.  Alternatively, you could connect this to a ground.
I tried the phone line ground (yellow wire) and it worked more poorly
than no ground at all.  I haven't tried any other ground, because that
would defeat the purpose of a portable antenna.

If the highpass filter is used, all phone line voltages, including
ringing, are eliminated and thus will not harm the receiver.  I should
also mention that this filter works very well with random wire
antennas.

Someone who wrote asked about lightning protection.  I haven't thought
much about this because thunderstorms are rare in my area.  However, I
believe most phone lines have lightning arrestors on them where they
enter the house.  Anyway, my suggestion would be to unplug the antenna
when not in use if you experience frequent thunderstorms.

Okay, here are the articles on the filter designs:

=========================================================================
                        BC Band Hi-Pass Filter
=========================================================================

The following ascii-schematic diagram is a high pass filter that will
filter out Broadcast Band (MW) stations.  I found it a great boon to my
shortwave listening since local MW stations overload my ATS-803A front
end & appear in SW, especially with a long antenna.

If you remember my antenna saga, I went from 50 feet to 150 feet & had
overload problems causing me to cut back to 50 feet.  (Even at 50 feet,
I still have some MW interference).  I took the advice of Gary Coffman
and looked up filters in the ARRL Handbook.  With the filter in place,
I intend to try to increase my antenna length again.

Anywho, here is the filter, for interested parties.

           --------||---+----||-----+----||-----------
                        }           }
                        {           {
                        }           }
           -------------+-----------+-----------------

The outer capacitors are 1500 pf ceramic disks.
The inner capacitor is 820 pf ceramic disk.
The squiggly things are coils (two total).  Each one is 2.7 uh.
  (a close value will do).

=========================================================================
                         BC Band Hi-Pass Filter
=========================================================================

I built the filter that Paul Blumstein posted recently and measured it
on a gain-phase analyzer.  Here are its characteristics:

 100 KHz -120dB
 500 KHz  -68dB
1000 KHz  -38dB
1600 KHz  -15dB
2100 KHz   -3dB

The source and load impedances were 50 ohms.  Because the filter
has five elements, the attenuation is 30dB per octave.  The
measurements confirmed this.

This filter seems to be a pretty good compromise between interference
attenuation and passband response.  There is very little attenuation
in the 120m band and above.  It could use a little more attenuation
at the upper end of MW, which could be done with more stages or a
higher cutoff frequency.  Alternatively, you could build two of
these filters and put them in series.  (Since two 1500pF capacitors
in series are really 750pF, you could eliminate one cap.)

Just for fun, I decided to put 470 ohms in series with the input
to see how the filter performs with an antenna mismatch.  The
characteristics were:

 100 KHz -105dB
 500 KHz  -60dB
1000 KHz  -35dB
1600 KHz  -15dB
2300 KHz   -3dB

These figures are normalized to the passband response of -15dB,
which is due to the impedance mismatch between the source and load
and would have been there without the filter.  Hence, the filter
works almost as well in spite of the mismatch, which is good news
to those who use longwire antennas.

===========================================================================
               Construction of filters for SW reception
===========================================================================
        Several people have asked for construction details of the filters
        I built for my DX-440.

        The high-pass filter helped some, but in my location the VHF/UHF
        broadcasters are also causing problems.  So, I dug out the
        ARRL handbook and chose a 7-element Chebyshev low-pass design
        that is -3 dB at 35 MHz, -20 dB at 43 MHz, and -50 dB at 64 MHz
        (all calculated; it works well in practice!)

                LOW-PASS FILTER  (Rejects FM, TV, etc.)

                        0.36 uH  0.42 uH   0.36 uH
       signal  -------+--UUU--+--UUUUU--+--UUU--+-------  signal
                      |       |         |       |
                 82  ___  180___    180___     ___  82
                 pF  ---   pF---     pF---     ---  pF
       shield         |       |         |       |         shield
        braid  -------+-------+----+----+-------+-------  braid
                                   |
                             chassis ground

        I had to do a little more improvising at this point.
        I used .33 uH instead of .36, and .66 uH instead of .42,
        but it works fine.

        The 5-lug terminal strips were perfect for these circuits,
        since there are 4 lugs plus a grounded lug.  All "ground"
        connections go to the lug that is mounted to the chassis,
        and the other 4 lugs are used for each of the connections
        on the signal line.  One terminal strip is used per filter.
        Since both filters were necessary to clean up the hash,
        I am going to put them both into one box when I get the time.

        The proper way to connect them is in series, i.e.

        signal in ------- filter 1 -------- filter 2 -------- signal out


        There is no difference between ends.  They are "bilateral"
        which means you can't possibly hook them up backwards.
        (In the above schematics, left and right ends are interchangeable.)

=============================================================================

 > OK, the wire antenna sounds just like what I need.  However, you left out
 > 1 small detail for us who are not very technical.  How do you connect the
 > two wires to your scanner?

Sorry if there was confusion concerning my antenna. The wire antenna
is for a shortwave receiver. For a scanner I used a magnetic mobile
antenna mounted on the outside of a window air conditioner.

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                             Hidden antennas
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Several methods of hiding antennas exist.  Aluminum balcony railings,
flagpoles, "electric fences", aluminum clotheslines, and similar structures
can be made to camoflage the function of ordinary looking objects.  The type
of foil used for burglar alarms on windows allows dipoles to be set up.
Beams can be mouted inside an attic.  Dipoles, or quarter-wave verticals can
de disguised as leaded and/or stained-glass windows.  Dowels or 2x2's can be
bored and have antennnas concealed inside them.
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