What Would You Do?

[kk4hg]

You live on the 8th floor of a 10 story apartment building. The facilities manager has given you permission to install an HF antenna on the roof. Excluding a beam, which multiband (10-80 mtrs) antenna would you select?

Comments?

 

[Wire Weasel]

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[mackmobile43]

I would use what I do now and have used for the last 15 years. A Loop made for 80M. Depending on the shape and area you have to work with, either a square or rectangle. A square would be around 75 feet per side. The loop will work on all bands 80 and above up to 6 meters with a decent tuner. 10 stories should be 100 feet up plus the height of 4 support poles which could be short....simple 10' sticks of PVC pipe. It will be only wire which will be very unobtrusive and will be invisible from the ground. It should work like gangbusters.

Don't forget the warning about voltages present with these antennas and be sure not to allow anyone near it while txing.

 

[W5LZ]

I like loops too. But I think the style/type of antenna used will depend on the shape/size and what's already there on the proposed roof. Some types of antennas probably won't 'fit' (at least without a lot of work).
As far as those high voltages go, those 10 feet support poles should take care of keeping people far enough away from them.
- 'Doc

 

[Radioman1]

Which antenna for roof top

Wireweasel is spot on.

I've been using exact same lashup for years,

Good:
Easy to erect
Inexpensive
Works well very very well
All bands with good tuner (manual or auto)

Bad:
None that I am aware of.

.....Mac

 

[mackmobile43]

I like loops too. But I think the style/type of antenna used will depend on the shape/size and what's already there on the proposed roof. Some types of antennas probably won't 'fit' (at least without a lot of work).
As far as those high voltages go, those 10 feet support poles should take care of keeping people far enough away from them.
- 'Doc

Remember as a child we would use a long stick to poke at things we did not understand or could not reach? same applies here and high voltage practices should be followed at all cost.

 

[Wire Weasel]

...........................

 

[wavrider]

Loop if you have the area to put it in, at 100 feet in the air ir will scream. Added benifit it is quiet on recieve also.

If you are feeding it with ladder line make sure it is protected from people. The ladder line also carries current on it.

You may want to run coax up to the roof top and then feed it with ladderline and a 1:1 balun to convert from coax to feedline, yes an unun will work and is probaly better but 1:1 are easier to come by and serve the purpose of transitioniing from coax to ladderline.

You will have great impedance mismatches on that coax if you use the loop multiband and a 20 feet run may cause some issues if you run an amplifier.

Coax is designed to connect to a 50 ohm load if the load is different than 50 ohms coax says that Sh#T is not my job so there will be some loss due to impedance mis match.

Any antenna you decide on will scream at that height.

You may want to look at some of the multiband trapped verticals available, small footprint, light weight, direct feed with coax. some verts are no radial, so many choices out there and your advantage is the height factor.

 

[hookedon6]

well, everyone is jumping on the loop,.... and i don't disagree with that, but, you asked for options, soooooooo, how about a vertical stepIR?

 

[W5LZ]

A loop does seem to get a few votes, but it's certainly not always the best option. I'd recommend taking a good look at the area you have to work with and then deciding what may be your 'better' options.
'Simple' is a very good idea unless there's some particular reason for it to be 'complicated'. One of those 'complications' is what's already there. And/or who else that landlord may give permission to put up an antenna?
Another option with that loop, or other types of antennas, isn't just "up", but "out" (away from the top edge of the building?). Big loops are nice because they allow you to use them on other bands, with a tuner of course (in most cases). And depending on the 'shape' of that building, they can get directional to varying degrees, that may be nice.
And then, along with that "StepIr" antenna, how about a screwdriver type? Same basic principal, vary the height of the thing to change bands. It's still involve running control cables like the "StepIr".
Lots of options!
- 'Doc

 

[KB1TPX]

Flat roof, gable, gambrel, hip, or...? At that height, be careful.

 

[CDX-007]

Since it's not really in the interest of best performance to tune the radio end of the coax instead of the antenna end...

I'd go for one of these

- Plus one of these

- Plus one of these

(If there's a safe location on the roof to place them)

...into a ~250' loop with, if possible, a set of high voltage vacuum relays, ~12" apart & 180° from the feed point so you may open / close it for incredible 160m performance when open (differing patterns / gain / bands, plus will act as a ½ wave HALO for 160m).

73