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First HF antenna (on roof)?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KM6LYW, Nov 8, 2018.

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  1. KM6LYW

    KM6LYW Ham Member QRZ Page

    Please be gentle, I still don't have an HF radio yet, so I'm looking into antenna ideas for the fateful day I have enough saved up.

    Having done maybe 15 hours of research, given HOA and wife constraints. I'd like to install a permanent windom on the roof. I have acreage and trees out back for an 160m dipole, but that'd be temporary, on the weekends.

    So, for the permanent wife-approved scenario, I've chosen a 40m Windom off-center-fed dipole with 4:1 balun.

    Installation will be on one side of a roof with about 2-foot offsets at ends and peak. Peak (feedpoint) will be 17' above ground, and ends suspended at 12' above ground.

    What can I expect? worth the effort? will a 3:1 balun be a better match for this height?


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  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    It will work and any antenna is worth the effort compared to not getting on the air.

    That said, it would work a lot better if you could raise that center support a bit to get the antenna higher above your roof.
     
    WB5YUZ, KM6LYW and NH7RO like this.
  3. NH7RO

    NH7RO Ham Member QRZ Page

    The above should be fine for SWLing strong stations, but if I was serious about my hobby (especially if working dx is an objective) I'd opt for a vertical any day of the week. Horizontal antennas so close to ground mostly radiate straight up and straight down; verticals (which can be tilted over or hidden fairly easily) radiate out towards the horizon which is where you want your signals to go.

    We do learn by our mistakes, though, so have at it.

    Antennas so close to house wiring and RFI generating devices seldom are something to write home about. Your wife may not complain about the above installation but I doubt you'll be happy over the long run.

    One other tip: don't try to work every ham band right out of the gate; at this point of the dismal solar cycle the main bands for real fun are going to be 20-40 and 80m. Since you don't have near the height for the last two I'll suggest a 16.5' tall 20m ground plane with a few radials (if elevated above ground---otherwise you'll need LOTS of radials laid out on the ground)
     
    KK5JY, WB5YUZ, KC8VWM and 1 other person like this.
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I think a vertical in the yard is probably a better choice, also, and a good one with traps or separate resonating sections for all the bands will provide a better match than you can achieve (on more bands) than a 40m OCF fed with a 4:1 balun, which is likely usable only on four bands.
     
    WA8FOZ, KK5JY, WB5YUZ and 1 other person like this.
  5. N7WR

    N7WR Subscriber QRZ Page

    I agree with WIK that a vertical would probably be a better choice given your height restrictions on the OCFD. As we recently moved I did not have time to put up a tower before winter. So I went with a ground mounted vertical and I am pleased with the results
     
    KM6LYW and NH7RO like this.
  6. NH7RO

    NH7RO Ham Member QRZ Page

    With your roof peak at 17' no one would really notice a 16.5' vertical in the back yard somewhere (somewhere=far away from the house as possible, ideally). For best results mount at least 4 feet above the ground---you could get by with only two tuned radials that way and still end up with a simple, inexpensive, and well-performing 20m antenna that won't be finicky to tune. Simple to homebrew with wire or tubing that can be painted flat green or camo color to match your surroundings.

    73.

    Jeff
     
    WA8FOZ, KK5JY, KM6LYW and 1 other person like this.
  7. KV4JW

    KV4JW Ham Member QRZ Page

    Check out my many threads on putting a G5RV on a rooftop tripod. WB2WIK and NH7RO among others have provided excellent advice, and a rendition of what I'm doing may work well for you.

    Listen to those guys, they know thier stuff. :)
     
    NH7RO and KM6LYW like this.
  8. AI3V

    AI3V Ham Member QRZ Page

    By installing a deliberately unbalanced antenna next to your house you can expect everything in the house to be "hot" with rf.

    This will manifest itself with high levels of noise on receive, and interference issues on tx.

    A similar situation will happen with a vertical ground mounted next to your house.

    I usually recommend a new station start on a single band, :) with a simple, center fed, half wavelength dipole (Hertz antenna), cut for 40 meters.

    Install it as far away from the house as possible, as high and straight as you can.

    Feed it with coax.

    If you need 200 feet of coax because your 40 meter dipole is up 90 feet in some trees, a hundred feet from your house, that's a very, very good thing:)


    Adjust it so that you have a vswr under 1.5:1 or so somewhere in the 40 meter band.

    Use either a radios built in "tuner", or if your rig lacks same, some sort of desktop tuner to "flatten out" the vswr across the 40 meter band.

    You only need one vswr meter, the one built into your rig.

    The simple "all band wire antenna" is pretty much a myth, as a inexperienced operator they will cause you much grief.

    Rege
     
    NH7RO, N5AVF and KM6LYW like this.
  9. KM6LYW

    KM6LYW Ham Member QRZ Page

    Wow - spectacular amount of advise here, thank you!

    Okay, so OCF dipole is likely a bad choice on the roof, unless I want an NVIS setup, which isn't a bad thing either, just local contacts.

    So, looking again at the G5RV, could I run one along the roof ridge line, and then run the twinlead into the attic, or down the slope of a roof? Picture a big T on my drawing instead of a falling over inverted V. What would I expect with this? same? better?

    I see there is a "G5Rv Jr" which is ~60 feet in length with 14 feet of twinlead, potentially giving me 40/20 meters. Is this better or worse than the Windom/off-center?
    https://www.gigaparts.com/radiowavz-g5rv-jr.html

    Again, I'm looking for a "permanent" installation, in addition to some simple dipoles I can deploy temporarily on the weekends back into the oaks on my acreage. I realize I'm just cutting losses with my constraints, but my requirements would include North America, and slim possibility of trans-oceanic when conditions improve.

    As for verticals, I'd need to put them on the roof, as that was a requirement. I'll seriously look into this when it's time to re-roof the house. Backyard is a visual no-go-zone for the wife, at least for a permanent installation, and I have no way to feed it except for overhead/suspended coax (patio/concrete). I could possibly string something 20' from the house to the shed, but it would parallel power/phone/cable lines.


    Thanks a zillion, again!

    -craig
     
  10. KV4JW

    KV4JW Ham Member QRZ Page

    Any kind of G5RV is going to be a compromise antenna. A lot of people hate them, a lot of people like them, and a lot of people say that optimized versions are better. I'll guarantee you that a resonant monoband dipole will outperform any variant of a G5RV. A fan dipole (multi-band) will as well, however they're more intuitive than a single wire G5RV.

    I've personally used a G5RV Jr in the past, and it worked fine for 10-40. Was it an awesome DX machine? No. But it got me on the air. Is a fullsize G5RV better? Slightly? Not at all? I don't know, I've personally never used one (still haven't got mine installed just yet, working on it) I guarantee it will get me on the air though.

    For simplicity and performance, I'd recommend choosing ONE band, say 40, or 20, or 80, whatever and building yourself a simple resonant dipole. Play with it, try it out, and if you like it, perhaps turn it into a fan, or add different lengths of wire for whatever bands you happen to be interested in at the time.
     

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