SHORTWAVE ANTENNA

[flybynight]

In a grid down scenario  . Could un powered, powerlines be used as a shortwave antenna ?

[Blast]

For best results, an antenna's length is determined by the particular wavelength that one is trying to pick up. This is particularly important when trying to transmit because if the antenna's length is too far off from the length (or specific fraction) of the wavelength the transmitting energy bounces back into the radio, damaging or destroying it. That being said, adding an antenna tuner between the radio and the powerline allows electronic magic to be done which lets you use pretty much any chunk of conductive metal as your antenna. Antenna tuners range from $40 DIY kits to $250 units on Amazon.

Using the powerlines as a receiving antenna might work, mainly due to the improved height off the ground. I'm thinking I need to attach the antenna of a cheap transistor radio the the mega-powerline tower in my neighborhood, and also the metal streetlights to see if I get an improved signal.

One last bit: The Random Wire Antenna https://w6fsb.org/DIY/Random%20Wire%20Antennas%20-%20Best%20Lengths.pdf
-Blast (KI5BOG)

[Crosscut]

Interesting, no idea but have to believe it'd be better than the telescoping antenna many SW receivers have.  As Blast said, paraphrasing, receive antennas are pretty forgiving unlike those for transmit.

Maybe instead of using the power lines themselves, attach an alligator clip to the steel cable that provides the support for the power line from the pole to your house, and run a wire in a window to the radio instead?  The AC on the line would likely cause a lot of noise when the grid is up, but might work fairly well when the grid is down.  (Checks the junk drawer...), else you're looking at something like this.



Uhhhh, no. 

[Raptor]

It is common for sailboats to use the mast backstay as an antenna for marine SSB. There are specialty backstay insulators that isolate a section of the standing rigging. That section is in turn hooked up to an antenna tuner that in turn is connected to a marine SSB. The tuner adjusts the antenna
to match frequency.

It is complex but is sensible if you already have a mast and standing rigging to use with little extra space for other antennas.

[NT2C]

I would encourage anyone contemplating this sort of antenna hookup to give very careful thought to lightning arresting.  Power lines are common lightning targets and the last thing you want is to give lightning a path inside your house.

[Crosscut]

Another long/random wire receive antenna option is making a dipole antenna from coax wire.  This can be real inexpensive if you already have a reasonably long length of coax (any type), and best if it's already a broken one with a connector (any type) on only one end. 

Just strip the outer insulation from a long section of the coax, and then separate the shield and center conductor to be the two sides/legs of the dipole.  Basically this:



but carefully pull many feet of the center conductor out instead of just a few inches so the separated legs of the dipole will be as long as possible.  I used a 16' or so section of coax that had been attached to a mobile mag mount antenna before it broke near the antenna end.  The cut made in the shield to pull the conductor out is the weak point, I wrapped electrical tape over that section afterwards so there wouldn't be any strain there that might break the shield. 

I installed mine permanently in the attic, stapling the two sides/legs of the dipole to the rafters in an "L" design, and leaving only a short section of the undamaged coax with the connector down into the living space - or it'd roll up easily for storage and just hang it for temporary or field use when needed too.  I use this with a couple diiferent radios so I bought/built adapters to mate the PL-259 connector on the coax/antenna to each radio; PL-259 to BNC for the scanner, to 3.5 millimeter plug for the SW radio, and to bare wires for an AM/FM component receiver.  Not gonna say it "works great", but it does improve reception over the stock antennas that came with the radios.

[albert]

Power lines can make decent antennas, if and only if, both ends are disconnected.  Power lines are typically fairly high in the air, and are supported by high voltage insulators, which offer low capacitance to ground.  Sadly, most are not of resonant length, so you'll typically need a very good "antenna tuner" to get them to work very well. 

Now, having said that, the limiting factor for the AM broadcast band, and even for the low shortwave band tends to be atmospheric noise.  Adding a larger antenna will tend to pick up more atmospheric noise, as well as signal, thus not improving the reception as much as it would first appear.  Obviously, if the limiting factor is receiver noise, due to insufficient signal, then a larger antenna will help.

Additionally, the point about lightning arrestors, and even static discharge devices, can become exceptionally important.  A long piece of wire, suspended in inclement weather (rain, snow, dusty wind, etc.) can develop a rather incredible static charge, one strong enough to knock a person on their butt, cause an arc, or blow the front end right out of a receiver.  Many will even cause a Neon bulb to fire (which requires about 90 Volts or so)!  So, make sure you have those static discharge devices in place, and make sure you ground the line before you grab ahold of it.

Most power lines are constructed from seven-cored cable, where the center strand is a steel conductor, with six Aluminum conductors around it.  That's not too bad, given that the electrical energy travels on the outer, Aluminum conductors.  Aluminum isn't as good of a conductor as Copper (or as Silver), but it's not bad.  What you do not want to do is to use only a steel conductor, which has absolutely lousy conductivity.  Additionally, the high permeability of steel causes the skin effect to be much higher than for Copper/Aluminum, resulting in the resistivity losses being even greater than they might first appear.  The exception to this is with something called Copperweld (TM), or Copper-covered-steel (CCS).  This is a steel wire, with a thick layer of Copper plated on it, which offers the RF (radio frequency) conductivity of Copper, but with the strength of steel.  Be warned, though, that Copperweld/CCS wire is exceedingly springy, and seems to have a mind of it's own; Don't let it get away from you as you're trying to string it.  A lot of the old telephone system wiring, which went from pole-to-pole, or pole-to-house, was Copperweld/CCS.

As for Copper wire, the biggest problem is that Copper is relatively soft, and will stretch under tension, usually to the point where a resonant antenna becomes non-resonant, or even to the point where it will break.  Copper, when it's stretched, undergoes "work hardening", which makes it brittle, and prone to breaking if there's any flexing of the wire.

The other thing to consider is directionality.  Resonant antennas are typically most sensitive perpendicular to their orientation.  However, as the length of an antenna increases, the directionality tends to change, resulting in maximum sensitivity nearly parallel to the antenna.  Most antennas have a bidirectional pattern, but it is possible to make a really long antenna unidirection, such as is done with the Beverage Antenna, or Rhombic Antenna.

That's probably more than y'all wanted to know about antennas, though.