HF Ham Radio Antennas For Apartments

HF Ham Radio Antennas For Apartments

by AG4DG 

 

The Issues

 

A full-size antenna for HF (except for the 10m band) is not feasible for apartments due to the space required. An apartment antenna should have the following characteristics:
  • Compact Size: This is the most obvious requirement of apartment antennas. As an apartment dwelling amateur radio operator, you want to keep a relatively low profile in order to minimize complaints from neighbors and the landlord/management. Except for the very highest HF bands like 10m, a full-size antenna would be conspicuous and even intrude into common areas and other people's property.
  • Multiband: Due to limitations in storage space and an aversion to overloading my home with stuff, I prefer multiband antennas. Of course, if your only transceiver is a singleband transceiver, then a singleband antenna would make more sense.
  • Easy to set up and take down: If you are on the ground floor or neighbors can easily see your balcony/patio, you want to remove your antenna when you are not operating. If your antenna is always visible, this presents a security risk (on the ground floor) AND increases the chances that neighbors and/or the landlord/management will object.
  • Cost: I want to operate HF that offers the most bands for the least cost. In other words, I want the most bang for the buck.

Popular Apartment Antenna Ideas That Didn't Work For Me

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    • There may not be trees in the right locations.
    • You need two wires, not one, because a random wire antenna needs a ground plane to act as the second half of the antenna. And no, the two wires cannot be taped together. (Have you seen a dipole with the two halves taped together?)
    • Too difficult to set up and take down: Setting up a wire antenna requires shooting it into the air with a slingshot or other device. This can take several minutes. Likewise, it also takes too long to take the antenna down.
    • Too conspicuous: The process of setting up the antenna and taking it down could attract the attention of people. Also, the antenna isn't confined to your own property; it likely would intrude into common areas. If you live on the ground floor, the antenna could also get in the way of people walking by.
    • Coax Length: You might need VERY long coax to try this idea. Since my apartment points away from the parking lot, I would need a few HUNDRED feet of coax.
    • Conspicuous: This would also be a VERY conspicuous setup. The coax would likely get in the way of people walking by (unless you are parked directly in front of your apartment and there is no sidewalk between your car and the apartment). Also, your antenna and the coax would be easy to spot. In some cases, the coax would cross part of the parking lot, and people would have to drive over it.
    • In most apartments, no room is big enough to accomodate a full-size wire antenna (except perhaps for the highest HF bands) without making it double back on itself (which makes it less effective).
    • Parts of the antenna will be TOO FAR from the exterior of the apartment and thus reduce the signal received from outside while increasing the noise received from inside. This effect would be particularly pronounced in a stucco building or other metal structure.
    • Finally, THIS IS THE PERFECT RECIPE FOR RFI. Think about this. If you use a small antenna that is confined to just one part of one room, most of the RF field will be confined to that one place, and the rest of the apartment will be relatively free from RFI problems. But if you string the wire antenna all over the apartment, MANY PLACES are close to the antenna, and there will be RFI galore. When I tried this solution, I kept tripping the circuit breaker even at the lowest power levels. At least the RFI from the indoor slinky dipole antenna that was confined to just part of my bedroom was more controllable. In this case, all I had to do was unplug the lamp in my bedroom or plug it into an RFI filter.
    • It didn't perform adequately unless it is stretched almost all the way out.
    • Fragility: The slinky coils do NOT lend themselves to being thrown onto a tree.
    • Supports: This antenna requires MANY supports. You need a support (1) on which to hang the center of the antenna, a rope inside both coils (1+2=3) to support them, and supports at both ends of the antenna (4). Then you have to stretch out both slinky coils and secure the ends of the coils (4+2=6) to hold them in the stretched position.
  • However, I can't completely dismiss these ideas, as one of them may work for you.

    Outdoor Wire Antenna

    This would be an excellent setup for an apartment on the top floor with a tall tree brushing the balcony. Just use trees for supports and wires. An outdoor wire antenna would also be good for a house or townhouse. The problems:

    Mobile Antenna On Car With Long Coax To The Shack

    This could be a good solution for hams living in a house or townhouse. It wouldn't be optimal considering that you would likely have the space for something better, but it might be a good temporary home setup for those who already operate HF mobile. For apartment dwellers, this usually will NOT be feasible for the following reasons:

    Indoor Wire Antenna

    I would recommend against an indoor wire antenna, but since it has worked for a few people (particularly on the higher HF bands), you should experiment with this idea anyway. For the following reasons, I don't think an indoor wire antenna will work:

    Cliffdweller II

    This is a slinky dipole antenna intended for 10m through 80m. It collapses for easy transport and stretches out to 50 feet in length for respectable performance. This could work in a high-rise apartment or hotel room (where it would be over 1/2 wavelength above the ground), and it may work at a lower elevation for NVIS. However, it didn't work for me for the following reasons:

Methods of Shortening Antennas

A full-size antenna (1/4 to 1/2 wavelength long/tall) is not feasible for most apartment dwellers on HF. The antenna must be this size in order for it to be near resonance. However, there are ways to achieve resonance with smaller antennas by using loading methods that electrically lengthen an antenna while keeping it physically short. This is NOT a free lunch. Smaller antennas, although resonant, are less efficient and have a narrower bandwidth than full-size antennas. So if you have the room for a larger antenna, you should take advantage of this.
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      • There MUST be good conductive contact between the capacitance hat and the top of the antenna.
      • Capacitance hats can use spokes, a single wire, and/or a metal disc. I prefer a metal disc, as this provides more capacitance for a given amount of space.
      • The capacitance hat MUST be at the top of the antenna. Mounting the capacitance hat lower makes the portion of the antenna above inactive and has the same effect as chopping off the part of the antenna above the capacitance hat. SO PLEASE KEEP THE HAT AT THE TOP!
    • Inductive Loading

      Adding inductance will compensate for the high capacitive reactance of a shortened vertical antenna. Inductance is usually added in the form of a loading coil. It should be noted that the more inductance you need, the greater the resistive losses in the inductor. This diminishes your antenna's efficiency. Inductance losses can be minimized by using a loading coil with a high Q value. In general, increasing the coil diameter and the thickness of the wires increases the Q value.

      Capacitive Loading

      Adding capacitance to the antenna will raise the antenna's overall capacitance value, reduce the capacitive reactance, reduce the inductance loading needed for resonance, and thus raise the efficiency of your antenna. Although a capacitance loaded antenna is not as efficient as a full-size antenna, it is more efficient than an antenna of the same size that uses only inductance loading. As you might imagine, operating the lower bands will require the use of BOTH inductive and capacitive loading. Capacitance is added by simply by attaching a capacitance hat (conductor) to the top of the antenna. Some additional notes:
  • Vertical Antennas

    A vertical antenna much shorter than 1/4 wavelength long has capacitance. The shorter the antenna is relative to the wavelength of the RF, the lower the capacitance value and the higher the capacitive (negative) reactance.

    Loop Antennas

Popular Apartment Antennas

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      • Unless your antenna is at least 1/2 wavelength above the ground, it will transmit most of the RF straight up instead of at low angles above the ground. While this may work well for local contacts, this will handicap your DX capability.
      • If your dipole is made of wire, it must be 1/2 wavelength long. Unless you make a dipole out of Hamstick mobile antennas (there is an adapter you can buy to do this), a shortened dipole may be difficult to find or make.
    • Pros

      Dipole antennas require no ground plane. This makes them more efficient than 1/4 wavelength monopole antennas.

      Cons

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      • The loop antennas sold by vendors are VERY expensive ($300 to $500) and only transmit on the higher bands. NONE of the compact loop antennas is designed for 80m. Only one is designed for 40m, and this is one of the priciest ones.
      • Homebrewing a loop antenna is difficult. Good variable capacitors are hard to come by, and having VERY low conductor losses is VERY important due to the VERY low radiation efficiency. Thus, building a loop antenna requires using a blowtorch or other large and dangerous gadgets to bend a copper pipe and weld things together. An apartment wouldn't be an appropiate place to try to build a good loop antenna.
    • Pros

      Like dipoles, loop antennas are balanced antennas and thus require no ground plane. Unlike dipoles, they can transmit RF at low angles from any height. Thus, loop antennas can be quite efficient.

      Cons

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        Pros
        CHEAP! They are only about $25 apiece. Their light weight also makes them popular for mobile antennas.
        Cons
        They are singleband antennas and have low efficiencies (as demonstrated by the mobile antenna shoot-outs) on the low bands.
        Pros
        These are RUGGED AND multiband (10m through 160m). If you want to operate mobile from an SUV and drive off-road, this is your antenna.
        Cons
        Outbackers are very expensive, and mobile antenna shoot-outs show them to be no more efficient than Hamsticks.
        Pros
        The Texas Bugcatcher antenna performs the best in the mobile antenna shooutouts. It is also multi-band (10m through 80m).
        Cons
        The version sold by GLA Systems is quite expensive (over $300). Although Texas Radio Products sells a version for only $150, I have heard that it isn't as good.
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        • Even on 80m, the Screwdriver antennas are almost as efficient as the Texas Bugcatcher. (Note that both have large coils for better Q.)
        • The main selling point is the REMOTE tuning. A screwdriver motor (hence the name of the antenna) that you control with a switch moves the coil up and down in order to adjust the inductance loading. This gives you flexibility in the height of your antenna and makes the antenna CONTINUOUSLY tunable FOR RESONANCE.
        • NO tuner is needed, because the Z-match built into the bottom of the antenna matches your antenna to provide a 50 ohm impedance at the coax feedpoint.
        • Best of all, this antenna allows you to use every band from 10m through 80m and is priced at only $160. If you use a tall enough antenna and a large enough capacitance hat, you can probably even work 160m as well.
      • Pros
        Cons
        It's not plug-and-play.
    • Hamsticks

      Outbackers

      Texas Bugcatcher

      DK3 Screwdriver

      The DK3 Screwdriver antenna from Don Johnson (W6AAQ) himself is the antenna I finally decided on. IT ROCKS! The DK3 Screwdriver is so popular that there are several knock-offs. There are many variations of the Screwdriver antenna, but the DK3 is the cheapest.
  • Dipole Antennas

    Loop Antennas

    1/4 Wavelength Monopole Antennas

    The advantages of these antennas are that they do NOT need to be 1/2 wavelength above the ground and are more widely available and cheaper than loop antennas. The drawback is that a ground plane is required, and this lowers efficiency. However, a respectable ground plane is possible with a modest amount of space. PLEASE NOTE also that the performance differences among these antennas are greatest on the lower bands, as ALL of the antennas have high efficiencies on the high bands due to the fact that less inductive and capacitive loading are needed. Performance differences will only be slight on 10m through 20m.