Shortwave Antennas Page 8

Copyright © 1999-2016 by Harold Melton KV5R. All Rights Reserved.

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Understanding Shortwave Antennas: Page 8

Simple Antennas

Now that we know our antennas should be resonant, let’s see how to make them resonant.

First, are we transmitting or receiving? Transmitting antennas are much more critical than receiving antennas, although a receiving antenna can transmit if it is resonant (or otherwise matched) and if it can handle the transmitter’s output power. A transmitting antenna can also receive, and will do so particularly well on the frequency for which it was designed.

If you are running a CB or HAM station, you already know something about transmitting antennas. Amateur operators, in particular, must pass exam questions on antenna design and theory.

If we are operating a shortwave radio, we want it to quit fading out in the middle of our favorite shows.

Now that you are ready to get brilliant, learn rule #1 of antenna design: All antenna designs are a mixture of compromises. Just like boat hulls and airplane wings.

What we need to do, therefore, is identify our particular need and design an antenna which is optimized to fulfill that particular characteristic - whether it be directionality, gain, or bandwidth, or just all-around good performance.

I have been an antenna experimenter for over 35 years. My goal has always been to build cheap, simple antennas that work well. It’s all in the numbers. I once had a $25 multiband shortwave antenna in the attic that performed as well as any $150 manufactured SW antenna. I had a discone scanner antenna made of brazing rods and a PL-259 that I built for about $10. I once built a 10-element 2-meter yagi from scrap TV antenna parts. Some of my other antennas are shown in articles on this site.

You can string up a wire just about anywhere and get a good signal on shortwave. Fifty feet of very fine wire, strung along the ceiling on thumbtacks, will give you much more signal than the telescopic whip that comes with portable radios. Telescopic antennas are way too short for shortwave frequencies!

There is one fundamental rule for receiving antennas: It must be at least ¼-wave long at the lowest frequency you plan to use. Thus, if your lowest regular listening is on 3315 kHz, your wire should be 70 feet long - minimum. Obviously, the 5-foot whip antenna on your shortwave is just a bit too short. For much better performance, it shoud be ½ wave long on your lowerst frequency (a Zepp). Multiwire fan dipoles are best of all.

Let’s design a decent longwire antenna for general shortwave listening. We will want to listen down to 2500 kHz (2.5 MHz), then analyze its performance.

The formula for determining the ½ wave length of wire is: 468 ÷ f (MHz) = feet.

In our example, 2.5 MHz is our lowest frequency, therefore: 468 ÷ 2.5 = 187.2 feet of wire. That’s a lot more than most city lots can handle!

Okay, let’s say we’ll design it for 5 MHz, and be willing to accept slightly reduced performance down to 2.5: 468 ÷ 5 = 93.6 feet of wire. We can handle that.

Longwires are usually strung up something like this:

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This arrangement keeps constant tension on the wire while allowing the tree to sway without breaking the wire.

Electrical suppliers carry 500-foot rolls of #14 stranded THHN wire (about $50). Electricians frequently have scraps and partial rolls. Farm supply stores carry #17 aluminum fence wire (about $15 for ¼-mile roll). Any wire will do — but some will last longer than others. Stranded, insulated wire (#14 THHN) works well.

Classic Longwire Installation

This page details the installation of a relatively safe, good-performing, long-lasting shortwave antenna. The #1 rule is: Where you scrimp on quality is where it will eventually break!

Yes, you can simply hang a wire out the window. But experience shows that a properly installed antenna that is mechanically and electrically sound, and a properly grounded radio, will consistently yield better performance and reliability. It really is worth the extra effort to use good materials, solder, and weather-proofing.

Wires should be insulated, stranded #18 - #14. A jack may be soldered on to plug into your radio. If the radio has no external antenna jack, solder an alligator clip to the antenna wire and clip it to the telescopic whip.

Which Direction Is Best?

Usually, directly away from overhead power lines.

If the lines run across the back of your property, go up the back of the house, over the roof, to a tree in the front yard. If the lines run across the front of your property, go up the front (or side) of the house, over the roof, to a tree in the back yard. You can also run a wire along eaves and/or the top rail of a wooden privacy fence.

Run the longwire as far from, and as perpendicular to, the power lines as possible. This will help reduce noise. If you have buried power lines, run your antenna any way you like. In the USA, pointing your longwire northeast will help bring in European stations in the daytime, on the higher shortwave bands.

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Continued…

20 thoughts on “Shortwave Antennas Page 8
  1. I have just purchased my first portable shortwave radio, it is a tecson PL-880. I am wanting to install a point gap lightning arrester on a random length long wire antenna, I am concerned about the grounding there does not seem to be anywhere to ground the radio how would you suggest that this be done? Thanks for your help.

    • I looked at the manual and it doesn’t say anything about grounding it. However, if the ext. ant. jack is a 2 conductor type, the “shell” side could be grounded (with the jack’s “tip” connected to your long-wire antenna).
      In any case, always disconnect the external antenna when you first hear thunder, as a point-gap arrestor will not arc until several thousand volts.
      73, –kv5r

  2. Hi Harold,
    I’ve spent many hours reading your posts and I appreciate the knowledge and effort you’ve spent blogging.

    I’m a bit confused about the “twisted coat hanger” you suggest for the antenna support on p8 of SW antennas. It seems that the antenna wire would slide right through the twists. So what is it accomplishing? Where is the strain relief?

    This just tells you what I’ve accomplished so far:
    I’ve got WSPR running and receiving stations across the country. But only after I set up an outdoor wire antenna that is 2 stories high and about 60 ft long to a tree. Used a fishing pole to cast a small weight and pulled an intermediate twine before pulling rope up through the tree. But strain relief at the near(house) end is temporary that needs to be addressed. So far I haven’t wired up any grounds or used a counterpoise. Before this antenna I tried 2 different indoor antennas that were not very successful.

    I’m using a 9:1 unun at the end of the wire right before it attaches to sdr (SDRplay RP2) after coming into the house. I’m contemplating moving the unun up to the near end support and then running coax down (~25 ft) into the house.

    Thanks,
    Pete.

    • The twisted wire strain relief is just stiff wire. You wind it around a drill bit or something about the size of your antenna wire, clamped in a vise, 10 turns or so. Then remove the bit, clamp one end of the coil in vise, grab other end with vise-grips, and stretch it way out, until it’s like a very elongated corkscrew. Then put a loop in one end for lag-bolting to house. You then wind the antenna wire into that long corkscrew and it will grip the wire over its entire length (a foot or two), thus providing strain-relief.

      If it slips, stretch out the corkscrew longer, or start over and make another one with a smaller I.D. The I.D., after stretching, needs to be much smaller than the wire for it to grip. As the wire pulls on, it further stretches it, gripping the wire tighter, sorta like a Chinese-finger toy.

      They work really well for coax (and extension cords) but I’m not so sure about small single-conductor wire. You might need to make the corkscrew out of smaller wire like maybe #17 electric fence wire, or even picture-hanger wire.

      Your SDR setup sounds nice. I run a cheapo RTL-SDR dongle here sometimes; they work pretty well if you filter out the FM broadcast band with a 30-40dB notch.

      73, –kv5r

  3. Making a shortwave antenna was a lot of fun for me as a kid! I use to tie the end of my copper wire to a heavy rock and throw the wire over a tree branch of an old oak tree! The antenna worked well everytime!

    • Same here. My first SW antenna went out the window, over the roof, to a Cottonwood tree. About 75 feet total length, of which 50′ or so was ~12 feet high. Got all the strong stations (VOA, RM, HCJB etc) on old Hallicrafters. SW was so much better in those days.

  4. I am new to Short Wave, just received a Grundig Satellit 750 for Christmas and was looking for guidance on antenna design. This is good advice for a novice. Thank you!

  5. You mention here running the antenna line along the top of a wooden fence. I presume insulators would be used to hold the line parallel to the top of the fence. But here’s my thought: What if the fence is a metal chain-link type? Could it act as a counterpoise, or would the metal just muck up reception?

  6. I have almost exactly 100′ from the 2nd floor window I want the antenna to go in, out to a pole in the back yard, So I’d like to make the 94′ longwire antenna as a reception antenna, not for transmission. At the point the antenna reaches the house at the 2nd floor, it will need to go down 20′ to the lightning arrestor near the ground rod, and back up the house 20′ and into the room. Does that 40′- 50′ length down and up help or hinder the antenna for reception? What if it *were* used for transmitting? Then what?

    • Hi,
      Good question! The 20′ down and back up would not help reception, and would pick up a lot of household electronics noise.
      I’d just put the spark-plug right outside the window, in an L-bracket, then run a ground wire down to a rod. That way, the “down” part isn’t part of the antenna until the plug arcs.
      Remember that “lightning arrestor” is a misnomer — it’s really an “impulse shunt,” grounding high-voltage impulses from nearby lightening strikes, and offering no protection from direct strikes. Also, always disconnect from radio when not using it.
      For transmitting, a 20′ down-up would complicate matching. Again, I’d just put the spark-gap at the entrance point.
      73, –kv5r

  7. Hi. Thank you for your very clear and helpful site. I am a novice swl, and wanting to put up a non-obtrusive long line. Question:How much does having the wire go around corners, (not one straight line) effect performance? Thanks.

  8. “I had a $25 multiband shortwave antenna in the attic which would outperform any commercially-made $150 antenna”.

    I’ve seen many youtube videos with similar claims. Not that I don’t believe you, but just curious, are those professional electrical engineers that work for these companies not good enough to design a good cheap antenna? You’d think that the antenna industry is highly competitive so they wouldn’t intentionally overprice their stuff too much? If you made it for $25 buying retail parts, they would probably have access to cheaper wholesale prices for mass production and could make it much cheaper and still sell for $25 at a profit, no?

    • No. There’s a lot of overhead in any small manufacturing business besides sourcing parts. Commercial facility, utilities, insurance, accounting, taxes, order processing, packaging, shipping, customer service, returns, and most of all, employees’ labor, insurance, taxes, and benefits. All that overhead, and more, comes before making any profit.
      That’s why the DIYer can make a $150-something for $25, on relatively simple things like antennas.

      • Thank you, that is a very interesting topic for me that applies to any diy project. What you said may be true for the U.S. businesses. But what about China! Many of the overhead factors may not apply to them since they just copy ready made designs and manufacture them cheaply in a sweat shop. Not sure about antennas but I did various microcontroller projects etc. and very often buying individual parts at retail prices is more expensive, since ready made products are so dirt cheap on Ebay! So it is really hard to motivate yourself. Of course there is a fun factor and that seems to be the main (only?) driving force behind most of the electronics diy projects… I am glad that this may not be the case with antennas!

        • Yeah, that’s why I said “”on simple things like antennas.” For any SMT-PCB device, the big automated factory is certainly appropriate.
          A while back I wanted a good 5V 2.5A regulator for my Raspberry Pi. I could have rounded up the parts and built a very simple (and ugly) buck regulator, but hey– $12 delivered one complete with LED readout, heatsink, and even a microcontroller and two tiny buttons for calibration! I couldn’t have built one so small, or with those features.
          Manufacturing always wins on high-volume and complex products, but SWL antennas are low-volume and simple, usually just wire and feed-line. And they are fun DIY projects!

  9. Hi! 🙂

    Regarding soldering the jack to the antenna, could you briefly tell me which parts of the jack are soldered to which parts of the electrical wire? The wire I own is 14ga insulated copper electrical wire.

    Also should I get a TS or TRS jack (2 or 3 contacts) ?

    Thanks a lot for your work.

    • Most portable SW radios will have a 1/8th-inch (3.5mm) TS plug. The antenna wire connects to the tip of the jack, the ground wire (or coax shield, if used) connects to the sleeve.

  10. Hi,
    The insulation on the wire should be enough, as long as it is unbroken where it touches wet wood. It should work fine, but even better if you can get it up 20 feet or more.
    I put one in for someone many years ago that was about 50 feet of #28 (very fine) green enameled magnet wire stapled under the eave (backside of fascia board). The antenna was almost invisible, and it worked fine for the domestic US stations like wwcr etc.
    73,
    –kv5r

  11. I have purchased a Grundig Satellit 750 shortwave radio. My first attempt at an outdoor antenna was to tie one end of 18ga insulated copper wire around a piece of wood, string the wire 60 feet, 8 feet of the ground. The other end of the wire also wraps around a piece of wood and then comes into the house and is connected to the external antenna connection on the radio. I can’t judge if the antenna is working well, since this is my first antenna.
    Question
    Wrapping the wire around wood, is this acceptable, or should the ends of the wire outside be insulated?

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