On Monday, September 1, 2014 10:00:05 AM UTC+3, 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/reconly.html#Beverage Matching





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.

What about phone line voltage in case the cap opens up? No risks there, William?