At 02:44 PM 5/10/2006, Kevin der Kinderen wrote:
>I knew I came to the right place with my questions. I've already received
>some good answers that have made me sit back and think a little more about
>my situation. Some of the points that were made I probably should have
>thought through before - but I've never had anything other than wire
>antennas and was pretty excited when the landlord said a beam would be OK.
>Here's a quick summary of what I heard:
>* The tin roof is going to be a problem with any beam. I can't get far
>enough above it or away from it to make it a non-issue.
Sure.. but just because your beam isn't operating in idealized free space
doesn't mean that it will be terrible. A lot of the advantage of a beam is
in the front/back ratio, and while the tin roof will perturb it some,
it's better than a dipole.
People run beams sitting 10 feet off the roof with adequate results.
Here's an experiment to try (if you have some modeling code).. simulate a 3
element beam in free space. Now simulate the same beam sitting over a
highly conductive ground (or a grid of wires) and see how bad it actually
is (might not be all that bad). Now try running an optimizer in the new
environment. You might be able to get just as good f/b as you had with the
beam in free space.
Seriously consider something like a SteppIR (hey, someone just offered one,
with rotator, on this list for pretty close to your budget). Why? Because
you can adjust the element lengths to compensate for the effects of the
roof. Figuring it out isn't trivial, but it is doable.
>* Liability issues - I have to be more concerned with protecting my landlord
>and myself from any damages caused by the installation. I didn't even think
>about adding this expense into the cost.
I wouldn't think there's much additional cost, unless there's some
regulatory requirement. What it means is that you can't just do some sort
of temporary lashup.
>* I'll have to investigate if there's anything I need to do with the town
>before putting an antenna on the roof. I knew it would be an issue with a
>tower, but I guess it might also be an issue with a roof mounted antenna.
Often, if you're within 12 ft of the rooftop, the regulatory requirements
are much lower (in terms of structures, etc.).
>* The tin roof (it is peaked, not flat) may make a better platform for a
>vertical - the tin actually being an advantage. I guess the advantages here
>would include 1) a choice of antennas vertical vs. doublet 2) lower angle of
>radiation for DX (I'll have to check the book to see how the sloped roof
>will affect this). Disadvantages are 1) verticals are more susceptible to
>man made noise 2) no directional discrimination and 3) I only had one
>vertical in the past and I never made a contact on it! Bad install - again,
>compromised by small space at an apartment.
with regard to radiation angles, the low angle or not of the vertical is
more likely influenced by things out of your control and way past the tin
roof. It's more about what are the EM properties of your neighbors.
The noise thing is a canard. The polarization sense of manmade noise is
pretty random. It's more a matter of comparing an antenna sitting on the
ground (and being close to the noise) vs an antenna way up in the air.
There's all sorts of other confounding factors that make the noise issue
one that you cannot legitimately make any sort of general statement, other
than "higher is better".
As for directionality.. what about an array of two verticals. One of those
little adjustable phasing boxes would let you phase them easily on receive,
and you could just transmit on one. At least you'd be able to place a null.
>* Length of time in the apartment. A beam installation is probably more
>suited to a long-term use based on the installation requirements. Living
>in apartments, I don't expect to be in one place more than 3-5 years.
>There were also a number of recommendations on alternatives to the MA5B.
>That Hexbeam has always looked interesting to me but is beyond my means at
>So, back to the drawing board. I'll do a little research on vertical
>options, read some reviews and installation practices and see if this might
>make a better choice for my situation.
>Thanks to all for your comments and suggestions. Half the fun of any project
>is the search for the solution.
>Kevin - K4VD
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