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Quarter wave 40m vertical plans - Need some input

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KE0CPH, Jan 19, 2020.

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  1. KE0CPH

    KE0CPH Ham Member QRZ Page

    I live in a two story apartment building and I've gotten permission from my landlord to put in place an antenna.

    I'm thinking about running ~30ft of copper cable vertically alongside the apartment, which has a brick exterior. Mostly concrete or cement construction as well.

    The vertical would run at the corner of the building. I would run two, 40m quarter wavelength counterpoises, one running North, the other running West.

    The three wires and coax would meet at an outdoor rated PVC box. Box would be properly labeled as messing around with the box could cause RF burns.

    Coax would be looped around sufficiently to create an air choke. This would be right before it enters the PVC box.

    I'd have my radio, a FT-101ZD plugged into a tuner as well.

    I do plan to get the ARRL antenna theory book as well as I think that's my (and probably mostly everyone's) weakest point.

    Anyone have any suggestions or recommendations as to what I could do differently?
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Is there any way to put something above the roof instead? Anything (not necessarily a vertical)?
     
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Stranger things have been done and anything can work in a pinch but I'd expect that antenna to be an RFI nightmare both on transmit and receive. I'd also expect some serious detuning of the antenna running right up against a brick and concrete (which means rebar) building. Concrete really isn't a great insulator for low frequency AC or RF, the use of concrete encased electrodes as a code approved grounding technique known as Ufer grounds is a pretty good example of how concrete is NOT a good insulator even at low frequencies.

    But assuming you get the antenna tuned and it radiates well you'll be running a transmit antenna right up the outside of other people's apartments which is a recipe for both transmit and receive RFI issues. Remember in a vertical like this the radials (especially a single radial pair) are also carrying substantial RF current and running right outside of other apartments.

    Hams have loaded up their transmitters into and made QSOs on bed springs and light bulb dummy loads so just about anything conductive can work as some kind of antenna in a pinch but in terms of planning a new antenna system I'd look at other options. As Steve posted above getting anything up on or above the roof, even a shortened loaded antenna (e.g. a mobile screwdriver or Bugcatcher antenna with some kind of ground screening or radials) would probably yield better results than a wire vertical running up along the outside of the building.

    If this really is your only option, then give it a go but I'd keep a lid on transmit power and don't be surprised if you have a lot of RF receive noise issues to contend with.
     
    AJ5J likes this.
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    And with a current-fed antenna such as a 1/4-wave vertical with radials ("counterpoises"), if the tips (ends) of the radials can be contacted, that's where the most danger is -- not at the feedpoint, where the RF voltage is low. The RF voltage is highest right at the tips of the radiator and the radials, farthest away from the feedpoint.

    I agree with the above about bricks and cement being rather terrible for RF and would surely recommend keeping away from both if at all possible. A low dipole above the roof may be more "invisible" (impossible for anyone to see) as well as safer since nobody would be able to touch any part of it -- if that's possible, probably a better choice.
     
  5. KE0CPH

    KE0CPH Ham Member QRZ Page

    I will not be able to put anything up on the roof as it's some kind of fragile rubbery material (flat roof).

    Come to think of it, I should have considered an end fed instead. I just need to read up on how to properly RF ground that kind of antenna. Apparently I can run a grounded (and grounded to my radio/tuner) wire parallel to the radiator. At least that's the gist of what I understand. Unless the parking lot could be the ground system? I'm in north central Iowa and I'm not too sure on the conductivity of the soil. I live in a river valley.

    I'm thinking that would do the job much better. I can attach it to the side of the building near roof level, run it across the apartment garages/parking lot and tie the other end from some trees.
    I think the only main issue is if/when the line comes down but at least it wouldn't be near any power lines.
     
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Sure, you can try different stuff and see what works best.

    But those flat "rubbery" roofs are very, very walkable (the installers walked all over it) and waterproof. That's exactly the kind of roofing I had at my town house back in 1989 (it was a 3-1/2 story building, and each townhouse wall all 3-1/2 levels, with a garage at the bottom and bedrooms and two bathrooms at the top, with living room, family room, kitchen and dining room on the intervening levels, plus a powder room (1/2 bath) on the lower floor near the living room). While I owned that (22020 Strathern Street, in Canoga Park) the roofing was replaced with the new rubbery stuff and it was great! Better insulation to keep heat in when it's cold and keep cold in when it's hot, plus helped reduce outside sounds from above and was extremely "walkable." It was also "white" in color so you could see the footprints of others who had previously walked on it, which was a lot of footsteps.:p

    To access the roof, I leaned a 24' extension ladder against a permanently attached service/fire ladder on the far side of the building and just climbed up. Installed two dipoles and two verticals (the verticals supported by my own rooftop A/C unit, which was huge and heavy and not going anywhere -- and I owned that) up there, and because the building was ~40' high and the roof flat, by locating the antennas pretty far back from any "edge," you absolutely couldn't see them from anywhere unless you were blocks away, using binoculars -- or flying overhead in a helicopter.

    I brought coax down two different ways over a year's time, but the easiest way was running it through a rain downspout (completely invisible) and pulling it out the bottom end, then running it behind existing bushes to the garage, where it entered at floor level and one corner. The garage door closed on it thousands of times, no damage (a rubbery weather seal at the bottom of the door did a great job for this). Once the cables were "inside," of course I could run them anywhere I wanted to.

    That was a great situation, all allowed because of the "rubbery" roof, which made it really easy to work on.
     
  7. AJ5J

    AJ5J Ham Member QRZ Page

    Sounds good to me; I'd put a wooden pallet up there and a tripod/quadpod atop it and install a rotatable beam instead. Hexbeam, Moxon or whatever has decent gain yet is not unreasonable with your landlord.

    When I lived in Albuquerque we had a big flat roof and a few pallet/tripod or foldover mounts enabled me to install a 5 el. Yagi for 6m, a 10-20 cobweb and a 10m Moxon and all were around 25-30-35 feet in the air. I tied the guy lines to various secure points well below the roofline/vigas which pleased the landlord since he wanted to keep his sprawling 1947 adobe intact.

    A 40m vertical using the same method would be a cakewalk. Run the radials out and have a ball chasing dx!
     
  8. W9GB

    W9GB Ham Member QRZ Page

    AJ5J likes this.
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    There are "non-penetrating roof mounts" all over. To support stuff with higher wind loads, they not only spread out the load over the roof but add weights like sandbags or whatever.

    They work.

    Although almost nobody uses 10-12' dish antennas for TV reception anymore since the DBS system that works with 18-36" dishes works fine, at one time there was a ~12' dish for satellite reception on the roof of the Federal Building on Wilshire Blvd. in L.A.

    I was up there to service an LMR antenna system (the building has a flat roof and is 30 stories high or something) about 20 years ago and noticed whoever installed the big dish used a non-penetrating mount. A bunch of aluminum and about 40 sandbags that probably weighed 60 lbs each or so. It was up there for years, in high winds.

    I don't know who installed that, but they did a great job.
     
  10. K0UO

    K0UO Platinum Subscriber Platinum Subscriber QRZ Page

    It is great that they are going to let you put up a antenna
     
    AJ5J likes this.

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