The AM Window: Tech: General: Small Antenna Ideas for 160 Meters

It’s that time of year again. Winter is on the way and fall is here, depending where you live. The lower frequency HF bands are much quieter, now that the static from the summer thunderstorms is gone. Do you feel left out when you hear other AMers talk about getting on 160 meters because you don’t have room for an antenna? Well, you may have room after all.

It’s true, a full-sized, half-wave dipole for 160 meters is rather big - around 250 feet long. If you’re like me, you don’t have enough real estate for that amount of wire! However, you DO NOT need a full sized antenna to produce a respectable, if not good signal on 160 meters.

First, let’s assume you already have a 75 meter dipole up. If it is coax fed, you could connect the appropriate antenna tuner, tune it up on 160 meters, and see what happens. This arrangement will work, but at will require a pretty hefty tuner, especially of you’re plan to run higher power AM. I haven’t heard to many people with real good signals using this setup, but it is probably the easiest way to get on 160 meters.

Another option is to short the center conductor and shield of the coax together and use the tuner, once again, to to the system up on 160 meter. This approach often works better than the first approach but it does require a ground system. This means radials. There is tons of information on radial systems in numerous antenna books. In short, the more the better. If you don’t feel like messing with radials, then stick with a balanced antenna. [You’re less likely to have RFI problems with a balanced antenna too.]

The most common balanced antenna in amateur radio is the dipole. Let’s go back to your 75 meter dipole. If you are already feeding it with ladder line or open-wire line, or are willing to change to the feed line from your existing coax, many possibilities open up. The most simple is a 75 meter dipole fed with open wire or ladder line, tuned up on 160 meters, as shown in Figure 1.

Standard 75 Meter Dipole

Figure 1 - Basic 75 Meter Dipole

For best results on 160 meters, the tuner must be low loss. I recommend using a link coupled, balanced tuner, as shown in Figure 2. This tuner isn’t something you can buy, so you’ll have to build one. Fear not, it is easy to build. I built mine on a piece of plywood, and made a simple cabinet from masonite. Simple hand tools and a drill was all I needed. I’ll leave the construction details to your own tastes and abilities.

Parallel-Fed

Figure 2 - Link Coupled Tuner, Parellel-Fed

It very likely that since you are using a short antenna, the link tuner will work better (tune more easily and have higher efficiency - less heating) if it is configued for series-fed tuning, as shown in Figure 3.

Series Connections

Figure 3 - Link Coupled Tuner, Series-Fed

Notice that Figure 2 and Figure 3 are nearly identical, just the position of the various jumpers is changed. Once again, there are numerous mechanical options for switching between the two feed methods, so use your ingenuity. Figure 4 shows one option if you have a big knife switch (it could be done with jumpers too) and a split stator cap or two caps on a common shaft (ganged).

Switchable

Figure 4 - Link Coupled Tuner, Switchable

You can also use a commercially made, unbalanced (generally a T-type circuit) tuner, with a balun to tune this system. Be aware, many commercially made tuners are able to tune the antenna system to resonance (you’ll see a low SWR) but they won’t do it in a low loss manner. In other words, they’ll get hot. Some will get so hot, damage will occur. So, if you plan to use a commercial tuner, make some test transmissions and then check the tuner and the balun for heating. Any heat, means loss is occurring and your signal is not as good as it could be. However, a slight amount of heating is probably okay, especially if you are getting good signal reports.

We can make it easier on our tuner by increasing the length of the dipole. Right, you say. Except, I don’t have room. Probably not in a straight line. But additional wire can be added by dangling some vertically from the ends of your existing dipole, as shown in Figure 3. Add as much as you can, at least till the ends are within 15-20 feet from the ground. If the ends of your existing dipole are at 50 feet, you can add 30 feet to each end with no problem. Your 120 foot dipole is now 180 feet . This length is a lot closer to the full half-wavelngth size of 250 feet. It is much easier to tune, and much less likely to cause your tuner to get hot. So, it should put out a better signal.

Vertical Sections Added

Figure 5 - 75 Meter Dipole with Vertical Sections Added

You can also add length to the dipole by horizontally zig-zagging the wire, as shown in Figure 4. This can be done by itself, or in conjunction with the vertical sections on the ends. By combining the two, you can add a significant amount of wire in your existing space. You could easily have 200-240 feet of wire up in the air. As you can see, these lengths are getting very close to the half-wave size.

Zig-Zag

Figure 6 - Added Length with Horizontal Zig Zag

Another approach is to zig-zag vertically. I used this method on the antenna system at my previous QTH. See Figure 5. I used sections of ladder line to do this because, it’s light, cheap and easy to install. On my antenna system, these ladder line sections were 30 feet long. That means a total of 60 feet of wire is added (30 down and 30 back up) to each leg of the dipole. I also had 30 foot vertical sections on the ends as shown. The flattop portion was 120 feet long. So adding up all the wire, I had 300 feet in total. All this fit on a lot that was about 120 feet deep and 70 feet wide!

Ladder Sections Added

Figure 7 - Added Length with Ladder Line Sections

If you have room for a separate antenna for 160, but not a full-sized one, AND you really want or need to use coax and no tuner, there is hope. A variation of the ladder line section approach as shown on Figure 6 can be fed directly with coax and have a SWR of about 2:1. Since the coax loss on 160 is so low, and the SWR is relatively low, this arrangement will work just fine. No tuner is needed. The tank circtuits in most vintage AM rigs will tune and load just fine into such a small SWR.

Shortie

Figure 8 - Coax Fed Shortie

If you just HAVE to have a lower SWR, there are two things you can do. One is to put a tuner in line. Since the impedance is very close to 50 Ohms anyway, the tuner shouldn’t have to “work too hard” and most of the heating warnings of above probably won’t apply. But check anyway. Some commercial tuners weren’t made to handle much AM power in any situation. The second option is to put a 2:1 or 4:1 Balun at the feedpoint. This will provide an almost perfect match to 50 Ohm coax. Joe, N2YR proposed this idea to me about a while ago and I tweaked the design on an antenna modeling program. He then built and erected one with the help of Paul-K2ORC. The antenna worked very well. He’s used it over the past two years on 160 with excellent results. So, it’s not a theoretical fantasy. It works in the real world.

So, there you have it - some options for getting on 160 meters. There are many more that we won’t delve into at this time - Inverted-Ls, short verticals, various types of loops, and numerous other loading schemes for shortened dipoles. The bottom line is not to feel left out on the 160 meter fun this winter. Read, research, test and experiment. You probably can get on 160. It will just take a little extra work, but will be very much worth it.

There are numerous stations on 160 meters using one of these antennas (or a variation) with great success. They work and are proven.

Catch you on 160 meters.