Best discreet multi-band antenna for NYC rooftop?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KD2VTZ, Apr 1, 2021.

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  1. KD2VTZ

    KD2VTZ Premium Subscriber QRZ Page

    Hi there,

    I think there's a decent chance I can convince my building super and/or condo board to let me install a vertical antenna on our rooftop, if it's not too tall (ideally 10' or less, but really anything fairly discreet that won't make neighbors in the building complain). Our building is just 6 or so stories tall, so anything too large would stand out and cause trouble. I'm OK with compromise antennas.

    If you could install just one multi-band antenna that's discreet and appropriate for an NYC rooftop, what would you recommend?

    Access to an HF ground from the roof won't be an option. So something self-contained.

    I mostly work 20m and 40m.

    Right now I'm using a portable mag loop that works pretty well, but I'd really like the ease of operating from home when I don't feel like loading things in a backpack to set them up outside. But I can't find something that's both discreet and doesn't require a good HF ground.

    Thanks,
    Vance

    KD2VTZ
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Looks like you're in Queens, which is likely better than many parts of Manhattan where so many buildings are a lot higher than six stories.

    Why not a remotely-tuned loop? They're on the market (can be homebrewed, but the ones available commercially may be easier since they've worked out so many kinks) and can often handle 100-150W transmitter power on HF.

    In my experience, having owned one for 20+ years, they work better "vertically" than horizontally; but the drawback to using them vertically is they have two deep nulls and two fairly broad peaks and it would be best to mount one on a rotator to take advantage of that. Still, a 3-foot (or so) diameter "mag loop" with remote tuning, and a rotator to steer it, can be a pretty viable antenna that nobody would really see if it's up six stories.

    You'd need a cable for the rotator and of course coax for the antenna, but some designs allow "tuning" the antenna with DC current that shares the coax as a conductor so doesn't necessarily need a separate "tuning control" line.

    I'd think getting the two cables from rooftop into abode may be the challenge, if you have to hide them.
     
    AK5B likes this.
  3. N8TGQ

    N8TGQ Ham Member QRZ Page

    Maybe the EARCHI end fed antenna? Only 1 coax cable to the roof at least 15' long(I think), coax acts as the counterpoise and tunes 40 to 6 meters. The wire is 30' long but you can run it as a vertical, sloper or inverted v. It does require a tuner though. If your rig has one built-in, you're set! You can build it or buy it. They give you instructions on their page:

    http://www.earchi.org/proj_homebrew.html
     
    Last edited: Apr 1, 2021
  4. KD2VTZ

    KD2VTZ Premium Subscriber QRZ Page

    Thank you both!

    WB2WIK: is there a remotely-tuned loop you recommend, or at least one with the characteristics you described so I can dig in deeper and see if it might work for me? I'm not too worried about getting the wires into the apartment, as our building already has numerous external wires (like people running their satellite TV coax down the side into their apartment). I can certainly pull off one wire, maybe two, but any more than that wouldn't look great. If I understand the setup you're suggesting, it would require 2 wires even if the loop supports DC via coax for tuning, because the rotator would need a 2nd wire, right? Would it be absurd to just fix the rotation of the loop to point a lobe westward (for full U.S. coverage) or something, and do away with a wire? I understand I'd have nulls covering a swath of states, but maybe I can point them at the ocean.

    N8TGQ: This is an interesting idea! I love the simplicity. My only concern, if I understand this antenna -- is that the entire coax itself is used for transmit. Since it will be running along not just my wall but my neighbor's walls, I wouldn't want to have ~100watts of transmit right behind their wall for safety reasons. But do let me know if I misunderstand this one!

    If anyone else has other ideas I'm all ears, this is a good start. Thanks.
     
  5. AK5B

    AK5B Ham Member QRZ Page

    I like WIK's idea of a STL, too, and have built a few over the last several years---surprisingly good dx antennas IF built well. Pix on my QRZ page if curious.

    What I was going to suggest instead was a Scorpion screwdriver (SA-680 or the "Shorty" model) with a cap hat (and maybe a taller radiator than the 3' stock "mast" it comes with since you are primarily interested in 20/40 meters.

    You would need at least the coax plus a two-wire control cable for remote tuning; I use 18 gauge doorbell/alarm wire from Lowe's for mine which is currently mounted at roof level (instead of on my car as it makes a great home antenna for 10-80 meters.

    Here's a link to Ron's site: https://www.scorpionantennas.com/

    73,

    Jeff
     
  6. W9XMT

    W9XMT Ham Member QRZ Page

    A "ground plane" antenna needs no connection to an r-f ground reference, and might be worth considering for this application. Below is a NEC analysis of one on the 40m band, meeting the OP dimensions.

    That basic antenna would perform better on 20m, but of course the other numbers shown in this graphic would be different. Its radiation efficiency on 20 meters could be better than 70%.

    A caveat: these parameters are for free space. The presence of the building and other structures on top of the building, and CM radiation from the transmision line could have a significant affect on them (as well as those of any other antenna).

    [​IMG]
     
  7. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hi Vance

    I have pretty much the same constraints as you: living in an metropolitan area, managed to get to an agreement with the superintendent and the condo - and part of the agreement is a low visual impact antenna.

    I ended with a T2FD antenna; far from awesome but enabled me to work nearly all the bands from 60m-10m reasonably fine. 80m is busted due to elevators noise.

    There are pictures in my zed profile and a buried link somewhere of my review of the antenna.
     
  8. WA7ARK

    WA7ARK Ham Member QRZ Page

    Does the building have a lightning protection system on its roof? If so, you should be proposing an antenna that is electrically bonded to the "down-conductors" that are part of the existing lightning protection system.

    The last thing you want to do is erect something that sticks up higher than the existing "terminals" without being electrically tied to one of them...

    The bonus is that a lightning protection system will provide a "ground plane" for your antenna...
     
    Last edited: Apr 1, 2021
    AK5B likes this.
  9. RW4HFN

    RW4HFN Ham Member QRZ Page

    PYRAMIX 40\30\20ΠΌ. 24' hight.

    imgonline-com-ua-2to1-RAcQD9E4vD.jpg
     
    Last edited: Apr 1, 2021
    N3OX likes this.
  10. VE7BPB

    VE7BPB Ham Member QRZ Page

    In your case, I would be inclined to not use a vertical antenna due to their likelihood of picking up more local noise than a horizontal antenna.

    Instead, I would try to put up full wavelength horizontal loops. Your available height above ground makes that a very attractive proposition.

    A 20m loop is only 16 feet square, assuming a rectangular loop. A 40m antenna would be about 33 feet square.

    You don't have to mount them very high above the roof top, just enough to clear any roof top mounted obstacles. Four short poles of any type, or light ropes at the loop corners off to existing structures would do the job.

    The best part, the loops would already be resonant, so good swr is easy and no tuner is required, though of course you could still do some tuning from the radio end of the coax if required.

    I recently put up a full wavelength 20m loop strung around the ceiling of my top floor apartment(wood building). The antenna is a little over one-half wavelength above ground, so getting up into the sweet spot for a horizontal antenna. Best antenna I've ever used here, without doubt. The greater height of your building would make it even better.

    It occurs to me that if you had two horizontal loops, a 40m and a 20m , mounted with the 20m loop inside the 40m loop, it might be possible to feed both with one feedline. Let's call that a "fan loop" design, hi. Perhaps our antenna modeling contingent can comment on that idea.

    regards, Roy
     
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