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I have a multiband vertical antenna mounted onto the railings of my balcony apartment high up on the 6th floor of an apartment building. The antenna is not grounded. This antenna comes without radials.

I can see at the side of my building, a ground wire coming down from the roof of the building from other antennas from the roof to ground. Would it make sense if I attached the outer coax of my feeder to this ground wire, for better antenna performance.

Feel free to correct me and tell me if this is a nonsense idea and why. I am still learning here:) Thanks

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  • $\begingroup$ What bands is your antenna designed for? $\endgroup$
    – rclocher3
    Aug 5 at 18:04
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Engineer999.

While it might seem like a good idea to connect your antenna to the building ground wire, my experience has been that for those vertical antennas which are designed to operate without radials it makes little or no difference what the ground is connected to.

You also should consider that if you are in a multi-tenanted building where you aren't the owner, there may be legal reasons not to connect to that wire, it may be there for lightning protection for example.

Also, how it's wired into the building grounding system is unknown and you may run into problems with grounding currents which can cause damage to electronic equipment.

For example, imagine this : your mains supply ground is connected to an earth at one point in the building and that ground wire is connected to a different earth somewhere else. If you connect your antenna to the ground wire, then the ground of the radio and the ground of the power supply for the radio will be different, and if there is a voltage difference between the two grounds, which is a distinct possibility, then there will be AC current flowing in your equipment, the result can be burnt out ground tracks in the radio or the radio power supply.

One other side effect may be the increased risk of RFI interference to your neighbors' TVs and radios when you transmit, because the building ground wire will become part of your antenna system.

My suggestion is that it's a bad idea.

Hope that helps !

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    $\begingroup$ Even TX in an apartment block that’s completely isolated can and most likely will interfere with something. Been there, done that. Entry systems in particular are very prone to interference $\endgroup$
    – Dan K
    Jul 26 at 11:00
  • $\begingroup$ @DanK By "entry systems" do you mean burglar alarms? $\endgroup$
    – rclocher3
    Aug 5 at 20:15
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It may be great, it may not... that's definitely an empirical question due to the many factors:

  • how much of the xmit current on the ground leg will be parallel and next to your vertical? this could cause destructive interference and make the antenna pattern more directional.
  • are there other currents on the ground that will make their way into your antenna system as RFI?
  • prob more.

If this is primarily for 10/20m, you might first experiment with dropping a simple 1/4 wave wire attached to the coax shield at the feed point to create a place for the "ground leg" of your RF current to operate. I would expect to find an improvement in SWR as well as both xmit and receive capability.

I should add: since the goal is to provide a low impedance path for the shield current, it can really be any multiple of 1/4 wave... so if 20m is your lowest frequency, cut to that wavelength which is 2/4 waves at 10m and still good.

There are some GREAT Q&A here on the topic of grounding, I've learned a ton by perusing.

Especially relevant, this answer to a closely related question. In part, Phil notes:

"RF ground" usually means "something that is at the same potential as the soil". This is important because if you have a wire (such as your feedline, for example) which is not at ground potential, then there exists a non-zero electromagnetic field between that wire and the soil. That means the feedline is radiating/receiving, which is usually undesirable.

It's worth checking out the entire answer.

Unrelated: if you haven't already installed an RF choke on the feedline at the feed point, you should consider doing so to keep RF off your coax and keep it going thru your antenna. Likewise, you should consider another RF choke on the feed line at the receiver to keep any environmental RFI that enters your feed line out of your receiver. I've found this to be very helpful in some of the dense living situations I've encountered :-)

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    $\begingroup$ Thanks alot for your reply. I appreciate it. Yes, I have ordered some HF RF chokes online and still waiting for them. Somebody recently told me that the chokes won't do much in my case, because I am using an unbalanced antenna with no common mode currents. That doesn't sound right though? Do you think the chokes would even help me on TX aswell as RX ? $\endgroup$ Jul 23 at 12:49
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    $\begingroup$ The shield current has to go somewhere, and when there isn't a lower-impedance path available, it will certainly run on the outside of your coax shield (yes, common-mode). Dropping a 1/4 wire AND adding an RF choke at the feed point will present a lower-impedance path for that current to run and greatly reduce the common-mode current. $\endgroup$
    – webmarc
    Jul 23 at 12:52
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    $\begingroup$ The choke + 1/4 wire at the feed point WILL (perhaps better to say SHOULD?) improve both RX and TX, and the choke at the radio MAY improve RX if there is environmental RFI/Noise that the external shield picks up by acting as an antenna. I expect any apartment building will have plenty of RFI though, and strongly recommend a choke at your transceiver! :-) $\endgroup$
    – webmarc
    Jul 23 at 12:53
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    $\begingroup$ Sorry for my imprecise language! I mean a 1/4 wave connected to the shield of the coax at the feed point (not the outside jacket/rubber), I edited the answer. $\endgroup$
    – webmarc
    Jul 23 at 14:17
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    $\begingroup$ Re coiling the coax on the metal railing, ugly baluns are a thing, but that linked answer indicates prob not appropriate for multi band. $\endgroup$
    – webmarc
    Jul 23 at 14:20
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Would it make sense if I attached the outer coax of my feeder to this ground wire, for better antenna performance.

Probably not, at least because you will gather the noise from the entire building.

I had a similar antenna (OPEK HVT-400B) for some time. What it actually needs, as a vertical, are radials, more is better. I had space for two radials 5 meters long each (they can be folded if there is not enough space). This worked OK, I could use the antenna on 20m and 40m. Although after I learned a little more about antennas I realized that 10 meters of the RG-58 coax were probably working as a radial for 40m, HI HI. To prevent this from happening you need a balun at the feed point of the antenna.

You also need a static bleeder to protect the transceiver from static electricity. I used 90 turns of 0.9 mm insulated solid copper wire on a ferrite rod with μ = 400, which gave 313.7 uH, between the shield and inner conductor of the coax for several years now. This arrangement works flawlessly.

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Grounding of window-mounted antennas on apartments is a topic I must admit I don't fully understand. It's tricky because there's some controversy, even among hams well known for their technical competence. And, to make things a bit more challenging, it seems that the more experienced, technical and "professional" hams seldom operate from apartments.

I'm going to share here what I learned from reading blogs and from and experience:

  • antennas on apartments are hard to model and their performances are hard to predict because there is a variety of unpredictable factors affecting them. What works on one location may not be great for another; and it's not uncommon for a setup to work really well but for reasons you can't properly explain (like those "miracle antennas" that work decently but due to unbalances that make the coax to irradiate);

  • you must be aware of the difference between DC/mains ground and RF ground. Both are important, but for different reasons. Connecting the antenna to the DC ground may hinder its performance due to reasons like 1) DC ground shows higher impedances under RF frequencies and 2) after all, you don't actually want to short circuit any of your antenna's arms to 0V.

  • about DC grounding: ground your power supply; ground the casing of your auxiliary equipment, like SWR meters, the casing of your radio etc; connect them all together to your DC ground (I'm assuming you have a working ground terminal on your power outlet). Besides safety, that will guarantee that all your equipment will operate using the same ground potential, and that will help to decrease your noise floor. I've operated without a DC ground, but it should be avoided if possible.

  • RF grounding: lay a wire over your shack's floor. Some sources say this wire must be as long as possible; some others say it must be resonant (around 1/4 wavelength in your case). The latter ones sound to be right for me, but I may be wrong. This type of grounding means that there'll be RF on your shack, so you may wish to operate on QRP levels. Keep the wire as close to the floor as possible, maybe under a carpet. That will reduce the RF irradiated inside your shack, since there will be more power going into the floor. That will also increase the capacitance between the wire and the floor, therefore decreasing the impedance to common-mode currents on your coax, which will, by its turn, reduce the amount of noise collected by the coax and captured by the antenna -- and that will probably also help to reduce your noise floor.

  • I must confess I still can't visualize the "operating mechanism" between RF groundings and common-mode currents on coax.

  • I see some sources making no distinction between "RF ground" and "counterpoise". Just remember that your transmitter needs somewhere to draw/insert RF currents from/into whenever it needs to insert/draw current into/from your irradiating "wire". If you fail to provide it to your transmitter, the feed point's impedance will be too high. Even antenna designs with very high feed point impedances (also called "voltage driven" antennas by some) needs some amount of counterpoise, as the currents needed to operate the antenna may be low, but not zero.

  • consider using a balun. It's going to reduce common mode currents on your coax (helping to prevent it from irradiate) and will also reduce common-mode, noise currents collected by the coax getting into the antenna -- which will also reduce your noise floor.

  • consider using a ground tuner. It will help to make the counterpoise to resonate on the desired frequency -- and all the advantages related to properly managing common-mode currents on the coax cable will follow.

I hope it helps. By using this info, I could build a shortened monopole for 40 meters and made some contacts on CW with stations ~ 1000 miles far from me, using 60 BRL worth on parts or so. But I'm still learning too and at least some of the explanations I've presented here might not be exactly right, so everybody feel free to disagree with me.

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There's lots of engineering precedent for operating vertical antennas from the top of tall buildings: nearly every skyscraper that dominates its local skyline has a roof crowded with radio and TV antennas. But those antennas are on roofs, not on balconies.

Here are a few things to consider:

  • That wire on the side of the building may be a ground for AC and DC power, but it's not an RF ground. An RF ground connection has to be a small fraction of a wavelength long to be a low-impedance connection to ground. Connecting to that wire probably won't help your antenna.
  • @Andrew is right when he says that connecting to that wire on the side of the building is a bad idea, because it could bring noise to your antenna and send RF into other devices connected to the wire.
  • If the antenna really doesn't need radials, then some part of the antenna is designed to be almost exactly λ/4 long to be a low-impedance path, a simulated ground (a "counterpoise"), for another part of the antenna to "push against". If that's true, then the antenna is probably meant to be operated with no conductive objects within a wavelength or two of it. If the antenna is on a balcony, then you probably have wires or pipes in the walls that are within a wavelength or two of the antenna, unless you only operate at UHF or higher frequencies. These nearby conductors may "de-tune" the antenna and change the pattern and/or the SWR.
  • You should use a balun. A common-mode choke makes a good balun at HF.
  • Connecting a wire λ/4 long (a "counterpoise") to the coax shield at the feed point might help, but that's easier said than done. Such a wire would radiate RF. If anything is near such a wire, if the wire is not by itself in the air, then the wire will be detuned. In other words, a simple wire that is λ/4 long in the air won't be λ/4 long when it is near other objects. There is such a thing as an artificial ground such as the MFJ 931 that uses a tuned circuit to adjust the impedance of such a wire to make it λ/4 long electrically. (I have no connection with MFJ. I'm not recommending that product, I'm just mentioning that such a thing exists.)

In summary, I wouldn't recommend connecting the wire on the side of a building to your antenna, because bad things could happen. You should use a balun if you aren't already. If your antenna isn't working well or if the SWR is high, it could be because the antenna is too close to other objects, especially conductive objects like electrical cables or pipes. If you have those problems you could try a λ/4 long wire connected to the coax shield at the feed point, possibly with the help of an "artificial ground" tuning device, but it's probably not worth the trouble.

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