RadioBanter - Phone line as SW antenna [12-Jul-06]

On Aug 1, 3:00*am, (William Mcfadden) wrote:
[Last modified 12-Jul-06]

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 preceded 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. *Phone lines carrying DSL service may be unsuitable because
| DSL operates over a wide spectrum. *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 found that it outperformed the
| telescopic whip antennas built into many 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
* lightning arrestors may pass enough energy during a lightning 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. *The capacitor should
| be rated 250 volts or higher.

* *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 terminal, 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 shortwave dealers (see below for recommendations).

* A high-pass 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 low-pass 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.

* 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

| RECOMMENDED FILTERS
|
| If you don't want to make your own filters, the following have good
| performance, are well-built and affordable:
|
| * Model 400 BCB interference filter (3.5 MHz highpass)
| *http://www.iceradioproducts.com/filtersrf.html#bcb
|
| * Model 420 HF lowpass filter (30 MHz lowpass)
| *http://www.iceradioproducts.com/filtersrf.html#3
| * (scroll down a bit to see the model 420)
|
| If you have a random-wire antenna, the following unit will provide
| impedance matching and lightning protection (connect antenna to 450-ohm
| terminal):
|
| * Model 182A beverage matching unit
| *http://www.iceradioproducts.com/reco...verageMatching

* FILTER PLANS

* The original credit for the high-pass and low-pass filters goes to Paul
* Blumstein and John Shalamskas, respectively. *Edited versions of their
* articles are included he

* * Date: * *09 Jan 91 00:54:08 GMT
* * From: * (Paul Blumstein)
* * 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
* * From: * (William K. McFadden)
* * Subject: 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 long-wire
* * antennas.

* * Date: * *22 Apr 92 08:59:33 GMT
* * From: * (John Shalamskas)
* * 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

* Parts for the filters can be obtained from the following source:
*http://www.digi-key.com/

--- end ---

--
Bill McFadden * * * *http://www.rdrop.com/users/billmc
CAUTION: Don't look into laser beam with remaining eye.

I have to ask. Why is this same thread always posted? Is it setup to
post every so often? I wonder if anyone really has no choice (meaning
they can't clip 10ft. of wire for an antenna) but to use their
personal phone line as a SW antenna. shaking my head Just curious-
if it has helped someone in here then I apologize. :-)