RadioReference Wiki:Ka3jjz

After you get your radio, you're next question is likely to be 'what else do I need to hear something on shortwave'. The answer is greatly dependent on many factors. If you are using a portable, the whip antenna will get you started, but generally speaking, that's about it. On HF, these small whips are very inefficient, and would likely capture the stronger signals, but not anything much weaker. Using a desktop, you will need some sort of antenna to hear anything at all.

Portables and Multi Band Handhelds

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These radios are designed to work with the relatively small input that a whip antenna would supply; in many cases, putting a substantial antenna on them would cause more grief in the form of overloading than it's worth. Sometimes an extendable whip will help, but you may find you will need to fiddle a bit with the length to get it right.

In most cases, a small hunk of wire - 20 or 30 foot or so - attached to an appropriate plug into the antenna jack on the side of the radio (if it has one) will do. Try to avoid clipping anything directly to the whip (although that will do in a pinch). Any static charges that might build up would likely damage the radio if discharged into the whip. To avoid that same issue with the antenna jack, you can build a small box with some inexpensive diodes which would blow in the case a static charge were encountered. The diagram shown on the right includes a small variable resistor (potentiometer) that would serve as a crude RF gain control so you can reduce the level of the signal if needed.

If you live in an urban area with lots of MW, TV or FM stations nearby, you may find that this circuit actually causes hash, overloading and other issues. The problem is the diodes - under certain conditions, they may rectify a large RF signal and cause issues. You may substitute something else in their place, such as a small gas discharge tube, or even an old flashlight bulb will work. See the Static Drain for Outside Long Wire Thread for additional ideas.

Portatops, Desktops SDRs and Amateur Radio Transceivers

People using a desktop radio (Drake, JRC, etc.), a portatop (like the Tecsun H501X) or a modern ham transceiver (which often has a general coverage radio built in) have a somewhat better time of it because their front ends tend to be more robust. But make no mistake, they can be overloaded, too.

If there’s only one range that is giving you issues, then a filter will very likely solve the problem. If you have multiple ranges that are affecting you (MW and FM, for example) , adding some passive preselection to help protect your front end is almost a must. Our Improving HF Reception article has several links for these. If you have added filtering and still have issues, it’s very likely the offending RF is either being picked up and re-radiated by something (long leads from power cubes are a good possibility) or is forcing its way through the casing of the radio (many cheaper radios use plastic which is invisible to RF). Choking and grounding may help in these instances, but overload issues like this tend to be a very tough nut to crack. With that out of the way, let’s start with...

A Couple of Basic Rules

Before you erect anything, survey your property carefully. If the antenna should get knocked down in a storm, will it fall over a power or telephone line? If it would, then find another spot. Remember, safety first.

Every home has appliances in it that generates noise; noise is the bane of the HFer. Ideally, you would want to mount your antenna far enough away from the house to avoid this problem.

Proper grounding is often an essential concept that is very often overlooked. There are numerous sources of information on this, and it's beyond the scope of this article to cover them all. If you live in the US, the NEC code should be followed as closely as possible. There's no easy way to make an existing structure lightning proof- the best you can do is to try to mitigate its effects.

The Most Popular Antennas (if you have the room)

The most basic form of the antenna is the inverted L or random length (many folks would call this a 'long wire' - that term should be avoided, as that describes a very different type of antenna). See the article from MT here for a description. This antenna is very broad banded, and easy to construct. Some folks have used coaxial cable as the lead in to help shield against noise pickup.

A very popular antenna for folks just getting started is the Vibroplex Par EF-SWL end fed. This antenna comes pre assembled - all you need to do is to supply the coax (and waterproofing for the feedline connection), and you're good to go. The wire can be mounted in numerous different configurations, and the included transformer will help with noise reduction. The transformer has several connections - you must experiment with them to see which one works the best for your environment. The reviews on this antenna are all superb - just don't try transmitting with one! This antenna is available from numerous suppliers.

If you are interested in certain bands, the basic dipole will work well. Be sure to mount it at a height at least 1/4 wavelength from the ground for best results. To find this height, use the standard formula 234/f(mhz) where f(mhz) is the desired frequency in megahertz. Dipoles will also work well on their odd harmonics - so a 3 mhz dipole would work very well on 9 mhz, a 4 mhz dipole would work well on 12, and so on. It is described here.

Verticals have a nasty rap against them. They are (generally) very prone to receiving lots of noise. This is not to say that they don't have their place; If you can get them away from the home (and other people's homes) they are good DX performers. You do have to deal with proper grounding of these antennas (including installing radials, if you are using it for transmitting) but if you put it in the right place, they can be hard to spot. See this section from our HF Antennas wiki for some examples.

You Dont Have a Lot of Room

• You don't have enough space for the PAR? Then try this one. Coverage is good down to 3.5 Mhz, and doesn't take quite as much space
• The EWE antenna is another possibility. The plus to this antenna is that it also works down on the tropical bands below 6 Mhz.
• If you have a wood fence adjoining your property, would be to run a wire using the fence as a support. Don't let the wood touch the wire; in some cases when it gets wet, the antenna might crudely couple with the wood. Some small standoffs will work well here. A transmatch will be needed for this one.
• Some have used gutters as antennas. One issue here is that the bonding between joints might not be very solid; some work will need to be done here to insure that there is a good mechanical and electrical bond. This is another antenna where a transmatch will be very helpful

Transmatch, not Antenna Tuner

This is a term that is frequently misued, and is in part a ploy for marketing to make it easier for people to understand. First let's define an antenna tuner; this is a unit that when placed at the antenna feedpoint, attempts to tune the antenna to make sure the maximum amount of energy is delivered down the feedline. To do this, a small amount of RF is employed to trigger the tuner (SGC is one well known manufacturer). Obviously this isn't something a listener is going to be able to do.

The term that should be used would be a transmatch. What we want to do is to create a resonant path for the antenna and feedline (notice I said both here) to deliver energy (RF) to the receiver. You certainly don't need a 1 kw version to do the job; there are many versions, some very complex, others quite simple. The classic Pi network is one that's easy to find plans for on the net - a variation of one is shown here. For some commercial units, see the Improving HF Reception article.

Active (E Field) Antennas

These antennas are attractive because, in some cases, their receiving element is relatively small and use a broadbanded amplifier to supply the gain. But it's that gain that might get you into trouble. Too much gain, and you will hear all sorts of stations appearing as distorted spurs all over the place. The higher gain can also introduce issues with noise. Even reviewers of the well known PA0RDT Mini Whip will tell you that keeping the antenna as far away from your home as possible is essential, as is proper grounding. Height is also important – the higher you can get it away from your home, the better. By the way, this is the same antenna that is used at the popular University of Twente online SDR. You can find some examples of these in this section of the HF Antennas wiki.

Loops

This kind of antenna has literally been around since the beginning of broadcasting. Did you ever notice that weird looking contraption on top of those old radios? Yep, that's a loop. While Loops are typically used on MW and lower, they work just fine on HF too. Up to about 2 Mhz or so, they can be directed to enhance or null out an offending station. And speaking of noise, loops are also resistant to it, which is very helpful in an urban situation.

A couple of other characteristics deserve a mention; while the word on wire antennas is that you have to get them up high, loops are better off no more than a few meters off the ground. Putting them up too high will make them overly sensitive to skywave propagation. There are many variations on a loop - a skyloop is usually quite large (depending on the frequency desired), but there are smaller options that will perform very well.

Many newcomers expect that a loop will produce a signal that rivals a good outdoor wire. This is incorrect; keep in mind that a loop rejects noise, and works very differently from a wire antenna. When you compare a loop to another antenna, compare the quality of the signal, rather than the signal strength.

Passive loops are probably the ones you would identify most easily, especially if you are into restoring vintage radios.. Those loops on those old classic radios from the 1900s were passive in nature. They didn't have, nor need, an amplifier as the radio did more of the work to amplify the signal.

Today, passive loops should be used on radios that are very sensitive, such as a SDR or a good portable. There are a great many plans for passive loops on the net - recently a very inexpensive one known as the YouLoop came on the market. You can certainly buy one from the links below…

• AirSpy US
• RTL-SDR.com announcement

But you can build one if you have a good junkbox handy. Here are some ideas and plans from the SWLing.com blog;

• How to Build a Noise Cancelling Passive Loop (NCPL) Antenna
• Hack a Broken VGA Cable to Make a Binocular Ferrite Core for your NCPL Antenna
• More About Hacking VGA Cables to Make Binocular Ferrite Cores

We have plans for many more such passive loops in the Loops wiki. If you find your loop to be lacking a good signal, then perhaps an amplifier is in order. The wiki article above has plans (and kits) for that as well. Some kits provide the amp and power supply - you supply the loop. These experimenter's kits are great for the tinkerer as you can build various passive loops to try out. Again, as with other antennas, if one design doesn't work well, there's no damage to the radio - just maybe to your budget...

Active loops have rapidly gained favor with SWLs, hams and DXers for their small size, noise rejection and (below about 2-3 Mhz) the ability to discriminate one signal over another. It should be noted that like Active Antennas, you might get some headaches from overloading if you are in a heavy RF environment, particularly with cheaper portables and SDRs. In these cases, additional filtering will be required.

Loops can be hidden in the most unlikely of places. Take this loop shown in a recent SWLing.com article - can you spot it? And how about this one? It resembles a volleyball net.

There's even a loop known as the Loop on the Ground (or LoG for short). There was an extensive discussion on RadioReference regarding the LoG. There's even a Facebook group and a website for it. If you have a small plot and want to have something that's invisible, this might be a way to go. Ground losses may be something of an issue here; you may end up using an amp to overcome the loss, or even one of the experimenter's kits found in the Loops article.

But I cant put anything outdoors

Anything you put indoors on HF is a compromise. You will have trouble trying to keep from hearing noise sources in the home, you may be constrained as to how much antenna you can put up, home covenants prevent you from putting anything outside - these are just some of the issues.

Using the attic or crawlspace is a very good idea. It doesn't remove the antenna from the noise sources, but it is sometimes more convenient. You won't have to contend with moving furniture or carpeting, and you might be able to bend the antenna around corners to make it work. Bending a receive antenna generally doesn't adversely effect it all that much; try to avoid bending the antenna back on itself, as that can sometimes cancel a signal out.