Mast question

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by SAMDAWSON92, Jun 8, 2021.

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  1. SAMDAWSON92

    SAMDAWSON92 QRZ Member

    Hi folks,

    I'm looking to put a lightweight 5.8dbi Antenna on the top of a 12 metre mast. I'm looking to attach it to the side of a building. See attached for diagram.

    Which of these two masts would anyone recommend? One is Steel, and the other is Aluminium. People online generally say Steel is better because it's stronger, but is it a little OTT for this use case?

    Aluminium Mast here
    Steel Mast here

    Another question... should I use Guy ropes here? I'd rather avoid if possible, alternatively, may be able to install 2 ropes to attach to the wall.

    Thanks for any help in advance!

    Cheers,
    Sam

    PS. If you're someone who does consultation on Antenna/Mast installation, would be great to connect !
     

    Attached Files:

  2. W4PG

    W4PG Super Moderator Lifetime Member 279 Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    What is the weight of the antenna and the wind load??
     
    SAMDAWSON92 likes this.
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Both those mast products are designed to be guyed. If you intend to extend one 30 feet above the highest bracket at about ten feet, either mast would need to be guyed.
     
    WB5YUZ and SAMDAWSON92 like this.
  4. SAMDAWSON92

    SAMDAWSON92 QRZ Member

    Thanks for your responses both,

    Weight of the steel mast: 21kg
    Not sure on the weight of the aluminium, can't seem to find manufacture info online, must be quite old, little concerning.
    No mention of wind load on either.

    Would I need to use guy ropes in all 4 directions? There's a road immediately on one side of the antenna. See attached for my reference.

    I could always not fully extend, and go to 30ft total height - would that still require guy ropes?

    All ears for better solutions too,
    Cheers,
    Sam
     

    Attached Files:

  5. SAMDAWSON92

    SAMDAWSON92 QRZ Member

    Infact there's a 30 foot version of the steel mast here. Would that need to be guyed too?
     
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Guying in three directions, angled 120 degrees apart per guy and anchor point, is sufficient.

    It seems you could guy in two directions 120 degrees apart using the roof, and add a third guy towards the "road" side using a cantilever guy and an earth anchor directly below it where it looks like trees (or bushes) are:
    [​IMG]

    The 30 degree angle shown in the sketch is the minimum, but this can be 45 or 60 degrees just as well. The cantilever might be 8 feet long or so, whatever space is available, and clamped securely to the mast down low where the brackets are.
     
    AK5B and WB5YUZ like this.
  7. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Yes, the mast you linked to must be guyed. You can see some of the guy hardware in the photo if you know what you are looking for.

    Any 30 ft. mast (as opposed to a tower) will either need to be bracketed in two places, with the top bracket pretty close to the top of the mast, or guyed. The strength of most masts comes mostly from the guying system, not the mast itself! The only "stand alone" masts that tall are "flagpole" masts, and those are not rated to support any kind of antenna, just themselves, the flagpole either serving as the radiator itself or having a wire fixed inside somehow. These are intended for HF operations. You haven't said what kind of antenna you are installing, just the gain figure and the weight. People need to know exactly what you have to help you properly!

    I looked at your photo. If I interpret it correctly, all three guy lines would be on the same side of the mast. This is worse than no guying at all in that any attempt to even slightly tension the guys will pull the mast right over.

    All three guys must be spaced approximately 120 degrees apart. There is no work around for this!

    I know this is discouraging, but you are encountering what I call the 30 ft. conundrum. It is easy to get an antenna 20 ft. in the air; getting it significantly higher than 40 ft. in the air almost always requires a tower. 30 ft. is right around the height where we start to encounter difficulties.

    If you have room to install a tower, you might be able to get to 30 ft. unguyed, but again, that depends very much on the wind load of the antenna, which we don't know and can't even guess at because you haven't told us what kind of antenna you are installing yet!

    Pay special attention to any advice from WIK. He has been a professional installer and has the experience.

    Good luck! There is a solution; but you may have to think outside the box to get there.
     
    Last edited: Jun 8, 2021
    AK5B likes this.
  8. SAMDAWSON92

    SAMDAWSON92 QRZ Member

    That's great, thanks guys.

    WIK - Thanks for your info here - great stuff. I hadn't thought of using a cantilever guy. That gives me hope - will mock this up this week.

    YUZ - Thanks for your info here too, all very useful. Sorry I didn't mention the antenna - it's one of these.

    It's for the Helium mining a lot of people have started doing this year - helping support the "internet of things" using radio frequencies. Become very popular - and meant a lot of people who have no experience with Antenna's are suddenly ending up on forums like this! :)

    Cheers,
    Sam
     
  9. AK5B

    AK5B Ham Member QRZ Page

    Helium mining? o_O Does one go around with a bunch of empty balloons and say, "Here helium. here helium, HERE HELIUM, C'MON HELIUM, NICE HELIUM, GOT BALLOONS FOR YA!"
     
    2E0CIT and SAMDAWSON92 like this.
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

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