THE HAM‘S WIRELESS WORKBENCH n BY WARD SILVER N0AX
The goal of this column is to give you an idea of what options you have and point you to resources
where you can learn the details of doing things right. Along the way, I’ll introduce some terms and
techniques to get you started.
A Higher Calling
Most places are not very good “radio locations,”
particularly on the VHF, UHF, and microwave bands.
Nearby buildings and trees block most paths. The closer
you are to buildings, the stronger the RF noise from all
the electronics inside them becomes, too. A time-tested
solution is elevation. Getting away from the ground pays
many benefits for wireless data and point-to-point voice or
data communications.
Let’s start with the most obvious benefit: increased
range. VHF+ wireless is pretty much a line-of-sight
proposition, so the higher the antenna, the farther
it can “see.” It’s that simple. You can calculate the
distance to the radio horizon with the equation:
3. 57
1.23
km meters
miles feet
Radio horizon height
Radio horizon height
=
=
Or, use an online calculator like the one at www.
rfwireless-world.com/calculators/radio-horizon-calculator.html.
Unless you live on a wide-open plain, you also have
to take into account any hills or valleys along the desired
path. There are good tools online such as Radio Mobile
( radiomobileonline.pe1mew.nl) to help you find out
whether you have a clear shot or not. Higher antennas give
you more options.
Obstructions (whether caused by the local topography
or buildings) can bend, block, or reflect your signals. You
might find that your signal can get from Point A to Point B
in a number of ways by reflecting from buildings and hills;
this is called multipath.
The reflections can cause signals to cancel or add
at a receive antenna. (Reflections alternately canceling
and reinforcing is the cause of mobile flutter you hear in
fringe-coverage areas while driving around.) By placing
your antenna higher, you can pick from more directions to
either use a direct path or find the best reflecting path.
hwardsil@gmail.com
The Prime Directive
As techies, we like to improvise and tend to not read the directions. This can lead to
problems when putting things in the air. My friend and professional tower worker, K7LXC
often cites his “prime directive:” First, do what the manufacturer tells you to do. Second,
don’t do what the manufacturer doesn’t tell you to do or tells you not to do. Simple, no?
or short-range and in-the-home wireless, you don’t need much more
antenna than what is supplied with your router, dongle, or laptop.
Handheld FRS (Family Radio Service) radios are great for inside a
warehouse or around a campus. Once you start thinking about a longer
link such as to supply Internet connectivity at a temporary site, improve
marginal mobile phone service, or set up your company’s new repeater
system, you’ll need outdoor antennas. And something to put them on.
That may not be a workbench topic but it’s certainly a part of wireless!
Antenna Supports
What You Need to Know Aloft F
18 May/June 2018
