# How far does an antenna need to be from metal to avoid problems?

Living in an apartment, I'm struggling to get good antennas set up, especially for HF. Worse yet, I'm not allowed external antennas (but am willing to try something low profile on the balcony), my apartment is built with stucco (with the "chicken wire" embedded in it), and my window frames are all aluminum. I have a balcony, but it's got a low (3') wall made of stucco inside and out (2 layers of mesh!) topped with a metal railing.

I tried a dual-hamstick dipole for 20M, but was placing it only 24" over the balcony floor, and this is below the edge of the wall. Tuning it was basically impossible, though I eventually could get 2:1 at one frequency. The balcony is about 4 feet deep and 10 feet long, and there is another floor above mine (so no roof access, and there's poured concrete above).

So how far away does metal have a significant impact on my antennas? I'm assuming it's design- and frequency-dependent, but I'm looking for resources that can help me figure out approximate clearances that are needed. Mostly I'd like to work at 20M, 10M, and 2M. (My balcony is way too small to think about 40M and lower.)

• You may wish to clarify your question: When you say you are not allowed external antennas, does that include that you need to be discreet on your balcony? Jan 18, 2015 at 5:00
• Also, I don't have an answer but I can say that whatever clearance you need will be proportional to wavelength. Jan 18, 2015 at 5:10
• I've clarified a bit about the balcony. And while I do guess it will be proportional to the wavelength, I suspect it will also be distance^2 (if the metal is parallel?) or distance^3 (as in field strength). Jan 18, 2015 at 5:11
• You might consider an antenna something like offered by Buddipole Antennas (buddipole.com). I have the buddstick antenna and I am very impressed with its operation. I operate QRP mostly on 20 but also some on 10. I plan to get the Buddipole antenna (Buddipole Deluxe) this coming summer for my various portable ops out at spots where my wife and I go on birding trips. A friend of mine operates his Buddipole Antenna of the back deck of his apartment and he has made many DX contacts with it. Jan 19, 2015 at 5:29
• Design of apartment-based antennas may be something better relegated to a forum-type environment, like QRZ. There are a lot of individual factors that are mostly only manageable on each case and with a lot of use of an antenna tuner+SWR meter. I'm going to have fun dealing with the constrained antenna situation of an apartment shortly. Jul 12, 2016 at 23:23

It sounds like any antenna you can build in this situation is going to be a compromise.

Distances are going to be relative to wavelength, so an HF antenna will be more difficult than VHF or UHF. For the antenna to be really in the clear, two wavelengths is a good rule of thumb. You can probably get as close as a quarter wavelength and still make things work with some adjustments to the tuning.

You can use the metal parts of your structure as part of the antenna, if that makes things easier. For example, I bet a 2m whip on the corner of the balcony could work well enough, with the metal railing being the ground "plane". It's far from ideal of course.

HF is going to be tricky, no way around it.

• What dimensions and gaps would be required to turn his entire balcony opening: railing, walls and ceiling into a slot antenna? Jan 23, 2015 at 6:57
• @hotpaw2 that's such a broad question I don't even know how to begin answering it. Jan 23, 2015 at 9:50

The region around the antenna where metallic objects will have the most impact is within the "near field". This distance is directly proportional to wavelength, and varies depending on if the antenna is electrically short or long. The energy reflections in the near field will have a direct impact on the source, impacting the impedance seen and the loss experienced.

There is a good description of Near Field vs. Far Field here: https://en.wikipedia.org/wiki/Near_and_far_field

Reflection from a grounded surface can cause an issue; but who knows if the chicken wire is grounded and how good a ground it is? The more probable cause of your high VSWR is common-mode current finding it's way back to your radio on your coax shield unless you've put choke on the coax near the antenna feed-point. To address your desire to work 2M, that is easily done with a J-Pole antenna that you can build out of some old 300 Ohm twin lead, or any number of plans online; here's one: J-Pole Example 1 J-Pole Example 2

A J-Pole is a 1/4 wave (λ) parallel transmission line, shorted on on end, with the other end feeding a 1/2λ radiating element, with the transmission line (coax) feeding the 1/4λ wave transmission line at the 50 Ohm point; so the overall antenna is 3/4 of a wave length, with only the 1/2λ element at the top, radiating, and allowing the bottom of the U part of the antenna, to be grounded if desired. You do want to form a choke out of your coax as near to your feed-point as possible, without letting the coil touch the parallel transmission line.

For 10M, and 20M if you dare, you can build this balcony antenna out of PVC and coax. Basically, everything left of the coax choke hangs outside your balcony, and the coax choke, along with some creativity, keeps the antenna vertical and stable on your balcony (that part of the design is up to you). The design uses 1/2" PVC outside the balcony for weight savings, and 3/4" PVC for strength and counterbalancing, inside the balcony. If you're ambitious, you can use threaded fittings here and there so you can take it apart and keep your better half happy when you're not using it.