Phone line as SW antenna [04-Apr-00]

Phone line as SW antenna [04-Apr-00]

Post by William Mcfadd » Tue, 02 Mar 2004 17:00:03

[Last modified 04-Apr-00]

The latest version of this file can be accessed via my web page at:
http://www.rdrop.com/users/billmc

Phone line as SW antenna
Bill McFadden

Changes preceeded by "|".

  WARNINGS AND DISCLAIMERS

  Connecting unapproved devices to phone lines may be illegal in your
  area.  Telephone lines present a potential shock hazard.  Do not use this
  antenna for transmitting.  Use at your own risk.

  INTRODUCTION

  This article describes how to use a phone line as a shortwave receiving
  antenna.  Performance will vary depending on the kind of phone line you
  have.  Overhead lines usually make okay antennas, while underground lines
  usually don't.  A phone line antenna will generally pick up more power
  line noise than a dedicated antenna, so don't expect to use it for DX
  work.  Nevertheless, I find that it outperforms the telescopic whip
  antennas built into most portables.

  A reader sent in this suggestion:  If you're concerned about connecting
  the phone line directly to the receiver, try wrapping the phone cord
  several times around the receiver's telescopic whip antenna instead.
  Performance may not be as good as a direct connection, but it will
  probably be better than the whip antenna by itself.

  Someone else wrote asking about lightning protection.  I haven't thought
  much about it because thunderstorms are rare in my area.  Most phone lines
| have lightning arrestors on them where they enter the house, but the
| lightening arrestors may pass enough energy during a lightening strike
| damage a receiver.  My suggestion is to disconnect the antenna when not in
  use if you experience frequent thunderstorms.

  HOW TO DO IT

  The simplest connection is a single capacitor between the phone line and
  receiver.  The capacitor eliminates all phone line voltages, including
  ringing, so that they will not harm the receiver.

   Phone line                                    RF connector
      red          .01 uF     center cond.            / \
       or   o--------||------------------------------|-o |  To receiver
     green                                            \ /
                             50 ohm coax               |
     ground                                            |
       or   o------------------------------------------+
      N.C.                      shield

  N.C. = no connect.  I originally connected the phone line ground (yellow
  wire) to this teminal, but reception was better without it (if you do
  this, play it safe and put a .01 uF capacitor in series).  If another
  ground is available, you can connect it to this terminal.

  If you are picking up local AM or FM radio stations on the shortwave
  bands, it is likely that your receiver is overloaded.  Inexpensive and
  portable receivers usually lack the filtering needed to eliminate this
  interference, but you can make your own filters.  Filters can also be
  purchased from some shortwave dealers.

  A highpass filter can be used to remove signals below the shortwave bands.
  It rejects interference from local AM stations and presents a high
  impedance to the phone line at audio frequencies so that the phone line
  remains balanced.

  A lowpass filter can be used to remove signals above the shortwave
  bands.  It rejects interference from FM and TV stations, as well as VHF
  2-way radio transmitters.  If you use both filters, connect the output of
  the first filter to the input of the second (don't forget to connect
  their ground terminals together).  It doesn't matter which filter is
  connected first.

  By the way, these filters also work well with random wire antennas.  Just
  connect the antenna in place of the phone line.

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

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

  FILTER PLANS

  The original credit for the highpass and lowpass filters goes to Paul
  Blumstein and John Shalamskas, respectively.  Edited versions of their
  articles are included here:

    Date:    09 Jan 91 00:54:08 GMT

    Subject: 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).

    Date:    12 Jan 91 00:44:25 GMT

    Subject: Re: 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 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 put 470 ohms in series with the input to see how the
    filter performed with an antenna mismatch.  The response was:

     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.

    Date:    22 Apr 92 08:59:33 GMT

    Subject: 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.)

  COIL WINDING

  You can make the coils yourself using this formula:

  L = 0.2 * B^2 * N^2 / (3B + 9A + 10C)

  L is the inductance, in uH
  A is the length of the coil, in inches
  B is the mean diameter of the coil, in inches
  C is the diameter of the wire, in inches
  N is the number of turns

  For small wire, you can assume C = 0.

  PARTS SOURCE

  All of the parts for the filters can be obtained from the following
  source:

  Digi-Key
  http://www.digi-key.com/
  701 Brooks Av S
  P.O. Box 677
  Thief River Falls, MN  56701-0677  USA
  Voice: 800-344-4539
  FAX: 218-681-3380

  PART                    DIGI-KEY PART NO.
  82 pF capacitor         P4023
...

read more »

 
 
 

Phone line as SW antenna [04-Apr-00]

Post by Jim Dougla » Tue, 02 Mar 2004 21:26:51


Has anyone tried one of these, how did it work? I'm looking at lot's of
vodoo, black magic and some snake oil to make my reception better?


> [Last modified 04-Apr-00]

> The latest version of this file can be accessed via my web page at:
> http://www.rdrop.com/users/billmc

> Phone line as SW antenna
> Bill McFadden

> Changes preceeded by "|".

>   WARNINGS AND DISCLAIMERS

>   Connecting unapproved devices to phone lines may be illegal in your
>   area.  Telephone lines present a potential shock hazard.  Do not use
this
>   antenna for transmitting.  Use at your own risk.

>   INTRODUCTION

>   This article describes how to use a phone line as a shortwave receiving
>   antenna.  Performance will vary depending on the kind of phone line you
>   have.  Overhead lines usually make okay antennas, while underground
lines
>   usually don't.  A phone line antenna will generally pick up more power
>   line noise than a dedicated antenna, so don't expect to use it for DX
>   work.  Nevertheless, I find that it outperforms the telescopic whip
>   antennas built into most portables.

>   A reader sent in this suggestion:  If you're concerned about connecting
>   the phone line directly to the receiver, try wrapping the phone cord
>   several times around the receiver's telescopic whip antenna instead.
>   Performance may not be as good as a direct connection, but it will
>   probably be better than the whip antenna by itself.

>   Someone else wrote asking about lightning protection.  I haven't thought
>   much about it because thunderstorms are rare in my area.  Most phone
lines
> | have lightning arrestors on them where they enter the house, but the
> | lightening arrestors may pass enough energy during a lightening strike
> | damage a receiver.  My suggestion is to disconnect the antenna when not
in
>   use if you experience frequent thunderstorms.

>   HOW TO DO IT

>   The simplest connection is a single capacitor between the phone line and
>   receiver.  The capacitor eliminates all phone line voltages, including
>   ringing, so that they will not harm the receiver.

>    Phone line                                    RF connector
>       red          .01 uF     center cond.            / \
>        or   o--------||------------------------------|-o |  To receiver
>      green                                            \ /
>                              50 ohm coax               |
>      ground                                            |
>        or   o------------------------------------------+
>       N.C.                      shield

>   N.C. = no connect.  I originally connected the phone line ground (yellow
>   wire) to this teminal, but reception was better without it (if you do
>   this, play it safe and put a .01 uF capacitor in series).  If another
>   ground is available, you can connect it to this terminal.

>   If you are picking up local AM or FM radio stations on the shortwave
>   bands, it is likely that your receiver is overloaded.  Inexpensive and
>   portable receivers usually lack the filtering needed to eliminate this
>   interference, but you can make your own filters.  Filters can also be
>   purchased from some shortwave dealers.

>   A highpass filter can be used to remove signals below the shortwave
bands.
>   It rejects interference from local AM stations and presents a high
>   impedance to the phone line at audio frequencies so that the phone line
>   remains balanced.

>   A lowpass filter can be used to remove signals above the shortwave
>   bands.  It rejects interference from FM and TV stations, as well as VHF
>   2-way radio transmitters.  If you use both filters, connect the output
of
>   the first filter to the input of the second (don't forget to connect
>   their ground terminals together).  It doesn't matter which filter is
>   connected first.

>   By the way, these filters also work well with random wire antennas.
Just
>   connect the antenna in place of the phone line.

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

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

>   FILTER PLANS

>   The original credit for the highpass and lowpass filters goes to Paul
>   Blumstein and John Shalamskas, respectively.  Edited versions of their
>   articles are included here:

>     Date:    09 Jan 91 00:54:08 GMT

>     Subject: 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).

>     Date:    12 Jan 91 00:44:25 GMT

>     Subject: Re: 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 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 put 470 ohms in series with the input to see how the
>     filter performed with an antenna mismatch.  The response was:

>      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.

>     Date:    22 Apr 92 08:59:33 GMT

>     Subject: 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.)

>   COIL WINDING

>   You can make the coils

...

read more »