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Old April 10th 14, 10:55 PM posted to rec.radio.shortwave
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Default Phone line as SW antenna [12-Jul-06]

On 04/01/2014 03:00 AM, William Mcfadden wrote:

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.


Illegal. Hazardous. What more is there to say?

I suppose it works, after a fashion. If you have _any_ way of doing it,
though, I would suggest even a short length of ordinary wire, even
magnet wire, suspended outside somewhere instead. You can use an
antenna tuner with if you like. I assume they make one for SWL purposes;
no point getting a beefy one designed for, say, ham radio transmitters.

[...]

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.


There are protective circuits on the line as it arrives at the home.
If you want you can parallel them with something designed for SWL
use if you want extra peace of mind.

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


The phone wiring I am familiar with is strictly two-wire. Typically
there are four wires coming to a wall jack, but the other two amount
to a second pair, say for a second phone line if you were to have one.
I have also seen a pair (the 2nd one as well?) used to feed power
from a wall transformer for the old lighted dial phones such as
were used in the "Princess Phone" era.

So I don't think of there being any ground wire at all.

But if you do have a ground running in the cabling along with
the active pair, you still have, effectively, a transmission
line. But likely the line impedence is far from the effective
antenna impedence, and you'll have losses that way. Instead,
use a local ground, from a ground rod or cold water pipe, at
your receiver.

Again, it might help to put an antenna tuner in the mix.

[...]

You mention that a .01 capacitor blocks "voltages". You mean
DC voltages, of course, because the whole idea is to have it
pass high frequency voltages through. A quick calculation is
that if this is a 600 ohm circuit the time constant is
..01 uf x 600 ohms or 6 microseconds. So switching transients -
like going off-hook, pulse dialing, etc., especially with older
relay-based telco equipment, could still pass through as
relavitely tall spikes - spikes that are ballpark of, say, 2-
20 micro-second duration.

If the spikes are 50-100V (wild guess based on old data).
Then your receiver must be capable of absorbing these without
damage. I suppose a well designed receiver can do this, but
who knows with the cheaper stuff.


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Old April 11th 14, 03:28 PM posted to rec.radio.shortwave
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Default Phone line as SW antenna [12-Jul-06]

On 04/10/2014 02:55 PM, George Cornelius wrote:
On 04/01/2014 03:00 AM, William Mcfadden wrote:


You mention that a .01 capacitor blocks "voltages". You mean
DC voltages, of course, because the whole idea is to have it
pass high frequency voltages through. A quick calculation is
that if this is a 600 ohm circuit the time constant is
.01 uf x 600 ohms or 6 microseconds. So switching transients -
like going off-hook, pulse dialing, etc., especially with older
relay-based telco equipment, could still pass through as
relavitely tall spikes - spikes that are ballpark of, say, 2-
20 micro-second duration.

If the spikes are 50-100V (wild guess based on old data).
Then your receiver must be capable of absorbing these without
damage. I suppose a well designed receiver can do this, but
who knows with the cheaper stuff.


Haha. Somebody replied to the the Billbot.
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Old April 11th 14, 05:32 PM posted to rec.radio.shortwave
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Posts: 3,217
Default Phone line as SW antenna [12-Jul-06]

///Choie yi ka oie. WOOO WOOO WOOF!/// What's that you say, doggy? ///You said it. WOOF!///
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Old April 14th 14, 12:51 AM posted to rec.radio.shortwave
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Default Phone line as SW antenna [12-Jul-06]

On 04/11/2014 10:28 AM, dave wrote:
On 04/10/2014 02:55 PM, George Cornelius wrote:
On 04/01/2014 03:00 AM, William Mcfadden wrote:


[...]


Haha. Somebody replied to the the Billbot.


I already bit on the power line as antenna post
from someone else, so it's in for a penny, in
for a pound.

Of course there's a reason the newest stuff he's
got is from 2006.


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