What Antenna for Short Wave

For general 'short wave' reception, any random length of wire is appropriate. General rules of thumb are make it as long as is practical in the space available, as high as you can get the whole thing, or any part of it, keep any part of it as far away from any high voltage cables as possible, use good insulators at any physical suspension points. It needn't face in any particular direction, but a good compromise is to 'bend it at some convenyient point along its length if you can, so you might be able to run it say from a point on the eaves of your roof to the top of the fence at the bottom of the garden, and then turn it 90 deg to run along the top of the fence across the bottom of the garden. Anything you can come up with that fits the space, really ...

You might not need (or in fact want) to make a direct physical connection to the telescopic antenna. Experiment with just wrapping a few turns of the (still insulated) end of the wire around the telescopic. You can also try grounding the end of the wire, and then wrapping a few turns around the telescopic. If you do use an external antenna with the radio, I would not recommend leaving it connected - or even just wrapped around - the telescopic, on a permanent basis. When there are thunderstorms about, very significant static voltages can build up on external antennas, and if there is an actual lightning ground-strike within a couple of miles of your house, large 'real' pulse voltages can be induced in long-wire antennas.

Arfa

A Short Wave antenna that is longer, higher and more clear of any obstructions such as the side of your house will work best.

It has been my experience that you do not need to actually go to these extreme lengths to get more than enough signal pickup. For a simple effective not to ugly omni-directional outdoor Short Wave antenna all you have to do is make a helical vertical antenna and mount it on the roof. Just take any plastic or non conductive form like a 2" - 4" PVC pipe and wind wire helically, similar to the threads on a bolt. As little as a three foot plastic pipe with only 15 foot of wire will work great.

If the house is metal (a Quonset hut?), why not just attach the radio to the house?

To paraphrase Stan Freberg -- "Your whole house becomes a giant antenna. It's settled."

It's worth a try for sure, but depending on the frequencies of interest, you might find that the performance is sometimes not as good as you might expect, due to the fact that this type of antenna will have a fundamentally vertical response pattern. This is great for say CB transmissions which are normally vertically polarised from both base stations and mobiles, but not so great for ham transmissions in similar bands, which are more likely to be (at least initially) horizontally polarised as horizontal wire antennas or horizontal beams are often what are used for transmitting on. A 'sloper' is often a good compromise, as it has a roughly equal response to both vertically and horizontally polarized signals. The best suggestion really, is to just arm yourself with a roll of wire and a few long bamboo poles, pick a nice warm Saturday when you've got nothing else to do, and have a little experiment. If you had a sloper passing over the top of your rear electric fence, provided that it was ten feet or so above the 'active' strand, you might be surprised at how little interference it actually caused.

Arfa

An end fed, horizontally oriented random length of wire should do just fine. The longer the better and the height isn't too important.

(snip)

to

(snip)

No, don't ground anything. Any coil around the metal telescopic antenna is effectively shorted by the metal "core" (a single shorted turn - read transformer theory.) If you ground the end you short out all the antenna signal. If you leave it ungrounded you have decent capacitive coupling that works. But if you take a few turns around a true antenna coil (to make a primary coil) you will couple some signal into the radio - but this is generally too much trouble. Better, connect the antenna via a 100 pF capacitor to the telescopic antenna. Cheers, Roger

(snip)

(snip)

No, don't ground anything. Any coil around the metal telescopic antenna is effectively shorted by the metal "core" (a single shorted turn - read transformer theory.) If you ground the end you short out all the antenna signal. If you leave it ungrounded you have decent capacitive coupling that works. But if you take a few turns around a true antenna coil (to make a primary coil) you will couple some signal into the radio - but this is generally too much trouble. Better, connect the antenna via a 100 pF capacitor to the telescopic antenna. Cheers, Roger

There are many references on the 'net to 'inductively' coupling an external long wire antenna to a telescopic, by either wrapping turns directly around the telescopic, and grounding the 'free' end, or by wrapping the turns around a tube, also with the free end grounded, and then sliding the tube over the telescopic, the latter method claiming to allow a certain amount of 'adjustment' to the degree of coupling, to prevent strong signals overloading the front end, and giving rise to all manner of intermod products.

Arfa

wrote in message news: snipped-for-privacy@4ax.com...

I personally have a (roughly) 110 foot random wire antenna hiding under the edges of the ridgevent on my house, and it is only grounded in the sense that the shield of the coax between it and my radio is attached to a couple of 10 foot copper-plated ground rods driven into the ground. The "signal" line (wire antenna and center conductor of the coax) are not attached to ground anywhere, as this would indeed kill any signal intended for the input of the radio. And the coax comes in my wndow and terminates in a "male" plug, to which I attach an alligator clip that goes to a foot or so of (insulated) wire that I coil around my (closed) whip antenna. And this works great. Note that I only use the coax to shield the signal line against EMI from the A/C that all of this has to go past to get to my window. The shield to that coax is grounded where line comes off of the roof, and again where it comes in my window. At the random-wire end, the shield is unconnected, and the center conductor of the coax is soldered to the 110 feet of wire. Also, if you directy connect the wire antenna to your whip, I believe you may eventually have trouble from static discharge building up from wind blowing across the wire. Note that I said "I believe", as I do not actually *know* this to be a fact. But that is why I put a static discharge circuit into the RF amplifier that I built to enhance weak signals.

My $.02. Hope that perhaps it helps...

Shortwave Dave

In any case a static discharge device would be very NICE to have. We used to use Blitz Bugs on antennas. I don't know what the rating was. There are probably other low capcitance devices that can be used to drain a charge, even a high value resistor will drain a charge to ground without affecting the antenna. Having an outside "spark plug" to ground would make me happier.

greg

news:rec.radio.amateur.antenna would be the right newsgroup for your questions.

--

aioe.org, Goggle Groups, and Web TV users must request to be white listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in your account:

There are two kinds of people on this earth: The crazy, and the insane. The first sign of insanity is denying that you're crazy.

"Arfa Daily" wrote in news:FqNhl.1$ snipped-for-privacy@newsfe30.ams:

IF you were to ground one end of the coil AND ground the top end of the whip antenna, you would turn the whip into a single turn of wire and have inductive coupling.

Otherwise, regardless of what it says 'on the net' most of the coupling is capacitive, from the 'hot end' of the coil to the whip.

If you tight wrap a few turns of insulated wire around the whip antenna, you probably have half a dozen or so pF of capacitance, which should be sufficient for many purposes.

I don't agree. Its a Ham newsgroup.

How about rec.radio.shortwave

greg

The last time I went there it was >90% trolls but if that's where you want to go, I don't care.

Check out alt.binaries.schematics.electronic for my recent posting of the static-discharge circuit I use on my RF amplifier for shortwave. Also protects against nearby lightening strikes (see previous post on 1/31/09 on the topic of single wire shortave antennas."

Dave