|
IEEE
MEMBERS RESEARCH COMMUNICATIONS, ELECTROMAGNETISM, POWER AMPLIFICATION
AND RADIO TRANSMISSION IEEE
Students braved a tempestuous blizzard in February to work with Ron Gnadinger (EET, MTU, 1992) on his regular monthly rounds to the most powerful
radio station transmitter in the Upper Peninsula.
Two other cars of researchers were grounded by the blizzard,
making the demonstration a bit more exhilarating than normal.
With
a maximum transmitter output of 21,000 Watts, the WGLI tower in
For
clarification, www.reference.com is quoted here…“In radio
telecommunications, effective radiated power or ERP is
determined by subtracting system losses from system gains. ERP is typically
applied to antenna systems. For example, if an antenna system has +9
dB gain and −6 dB loss, its ERP is +3 dB over the transmitter
power output (TPO). For example,
an FM radio station which advertises that it has 100,000 watts of power
actually has 100,000 watts ERP, and not a 100,000-watt transmitter.
The transmitter power output (TPO) of such a station is most likely
around 10,000-20,000 watts, with a gain of +7 to +10 dB (5× to 10×).
In addition, if the antenna is directional, the ERP figure is usually
the maximum in any one direction, rather than the average.”
We
know from our EMAG class that this power varies downward exponentially
by distance and yet again by rain, buildings, humidity, clouds, people,
trees, etc.
Ron
is the sole individual responsible for many of the Houghton and Baraga
county radio transmitting towers. “It
really is an (increasingly rare) kind of engineering job”, he says.
He performs regular maintenance on a range of equipment, including
the radio stations themselves in addition to the towers. “This is the nicest set-up I work with; some
of the stuff at the other stations is a lot older. It all still works, though, which is great”.
Ron
shows IEEE member Josh Dorn (EE) how much reflected power is coming
back to the transmitter. In this
case, it was around 3%
The
last few basic connections are the coax that runs up the tower from
the transmitter. The connector is shown here…
Additionally,
a tank of Nitrogen sits next to the transmitter, its hose winding up
to the 21,000 watt transmitter cable, filling the space between the
actual coax and the outer protective sheathing.
The dielectric strength (ability of the insulation to keep the
power on the inside from breaking out, called “breakdown voltage”) is
held ‘near-invariable’ by constantly keeping Nitrogen in the cable in
addition to the cable’s already strong dielectric insulation near the
core. To picture this in your
head, it’s just like a garden hose inside a larger fire hose with the
space between the outside of the garden hose and the inside of the fire
hose filled with plastic strengthening filler (that is porous) in an
environment made completely out of Nitrogen.
The Amplification equipment was studied next.
From
the top down, the IPA (Intermediate Power Amplifier), Microwave transceiver
and filter. An intermediate power amplifier is needed
because the gain of one amplifier is not enough to take a few watts
to 21,000 watts all at once. It
is done in two stages.
The
microwave transceiver also demodulates and re-modulates the signal from
the free microwave spectrum to FM frequencies as purchased by the license
contract through the FCC.
The
FCC License info has to be in plain sight
At
the time of this study, the transmitting equipment was only handling
one station frequency. The combiners shown below will be brought
into service as the AM and other FM stations, also owned by the KBIC,
are brought online. The combiners,
as their name implies, allow the transmission of other frequencies on
the same tower at the same time. Their
physical size is also indicative of their high power handling capability.
A
Svetlana Power Amplification Tube
About
11” tall and aerated on the sides to keep it cool, vacuum tubes are
still used throughout the world in transmitting equipment because of
their high voltage/high power handling capability.
“They haven’t made anything that behaves like a tube.
They do wear out, which is why I check them once a month, but
nothing solid state can compare to the vacuum tubes ability to not brake
down when driven really hard”, like in going from 1000 Watts to 21,000
Watts.
The
Power Amp, just above the red button, must be kept cool with high-velocity
fans. Even in the frigid storm
they are running 24/7 to keep the amp operating efficiently.
This experience was one of the many activities IEEE had during the 2005-2006 school year. (For more info, see our site, www.sos.mtu.edu/ieee, and click on 2005 – 2006 activities). Our purpose is not only to connect what we do in school with how things work in real life, but to do so in a way that inspires our curiosity and creativity. Being an all-student run group and also not being a part of any one branch of the ECE department at Tech, allows us to excel in the core area of what Electrical Engineering is all about in the world. Respect for the expertise of our teachers, commitment to excellence and above all genuine inspiration accentuates our understanding for our field. In this research trip, our branch was exposed to communications, electromagnetism, power amplification and radio transmission. This we recognize is not something you get in a Business/Engineering hybrid program that gets sidetracked on Entrepreneurship. Our commitment to sustainability and engineering ethics is unshaken in this regard. We all look to our futures as engineers in the sense of service to mankind through the application of the sciences. We are proud that there is still a part of that here at MTU.
Another IEEE Project Story: IEEE Students Perform Research on Renewable Energy System |
