
On The Air!

 
On The Air! 
A Guide to Setting Up Your Own FM Station 

INTRODUCTION

MICROBROADCASTER'S RESPONSIBILITY 

Version 0.9, Preliminary
(This document is under development and as yet incomplete, however
I think the need for expediency in disseminating this information
outweighs the concern about completeness at this time.) 
"To sound legitimate -- even if you aren't."   
BACKGROUND:

I've prepared this document for public distribution for the public
well-being and in the interest of promoting responsible, professional
operations of LPFM (micropower) radio stations. There are a great
many people who feel that radio is a toy and that "getting on the
air" is a game to be taken lightly. It is not. Many "pirate" broadcasters
have made a bad name for the micro community broadcasters because
of reckless, irresponsible operation and cause of much interference
  
as well. This document will help all concerned to better understand
the issues, the equipment and the procedures required to build and
maintain a small FM station. 

ETHICS:


  
The airwaves are a community property. One must always treat it as
such, respecting the space of other stations, both commercial and
micro. In addition, there are many other services that use radio
frequencies which may be disturbed unintentionally by micropower
stations if care is not taken to evaluate each step of the process
of constructing your station. A "Do not do unto others..." attitude
is a good start. Acquiring knowledge needed to operate responsibly
and with awareness of what is going on with the signals in your area
is the next step.

LOOKING FOR OPENINGS:


  
Admittedly, some parts of the country have no empty channels. Places
like south Florida, California, New York and Chicago are virtually
crammed full of stations. For the rest of us, if we look hard, we
can locate one or more unused channels. There is MUCH more to this
than simply turning on a cheap radio in ONE LOCATION and tuning around
the dial. I recommend a 4-pronged approach: 

ONE

STATIONARY TESTING


  
Use a high-quality receiver connected to a high-gain beam antenna
mounted on a tall mast. If you're on a mountaintop location, this
works well at ferreting out the weakest signals that may exist on
the prospect channel. Find a channel where you hear nothing. Rotate
the antenna 360 degrees and see if it remains empty from all directions.
Remember, the next adjacent channel should be at least 75 miles away
for a 3000-watt station, and the second adjacent should be at least
50 miles away. Once the prospect passes phase one of your testing,
move on to the next step:

TWO

MOBILE TESTING


  
Choose an automobile with a very sensitive FM receiver (if you don't
have one, ask a friend to help you and offer to buy him lunch for
his time). Next, monitor the empty channel prospect and drive out
to the farthest extents of your station's proposed coverage contour.
Better yet, drive another 15-20 miles out and make a huge arc around
the station site so you get a feeling for any signals that are on
the channel that were too weak to pulling at your home site. If you
hear a consistent, weak signal on that channel for any substantial
leg of the journey, do not use that channel.

THREE

CHECK THE OFFICIAL RECORDS


  
Elliot Broadcasting Services provides a good online reference which
will help you determine what stations are using your frequency and
where they're located. The FCC publishes the M Street Directory,
a printed publication which lists the current stations that are on
the air, but it costs more to obtain.
Take a few weeks and recheck the prospect channel periodically. Conditions
may change due to weather, varied operations of co-channel stations,
etc.

FOUR

FIND OUT WHAT'S ON MULTIPLES OF THE CHANNEL


  
It may not be obvious, but it's a very good idea to find out what
service is using TWICE the frequency of your broadcast channel. Usually,
this will be a TV station. The Radio Amateur's Handbook will have
data on this. Get a book that lists all the frequencies from AM to
microwaves and multiply your channel by 2, 3, 4, 5 and 6 times the
frequency and then look up what service is using that frequency.
You may need to buy a scanner radio to monitor those frequencies
to determine if you are causing any interference. 

ONCE YOU DECIDE:


  
You've located a channel that's clear and has no strong nearby adjacents
broadcasting. Fine. Now it's time to look into what you'll need to
do this project right.
I should point out that most pirates work completely blind. Not a
good idea. Get the right lab equipment or get out of broadcasting.
The fines are too great if you screw up some vital service and you
make a nuisance of yourself regardless this way. Let's do it right.
Here's what you'll need:

WISDOM


  
Educate yourself about radio theory. Buy the Radio Amateur's Handbook
and study it. Learn the theories and some of the formulae. Read every
book you can find on the subject of radio and if you can obtain books
on commercial FM theory of operation, read those especially.

NECESSARY EQUIPMENT


  
You'll need some essential tools to avoid working blind.
   
You should have an oscilloscope with at least a 100Mhz         bandwidth
so you can see what your carrier looks like and         if the device
is operating incorrectly, causing parasitic         oscillation.
            
You should have a good stable frequency counter that has        
at least a 10 ppm accuracy and resolution to 1hz at         100Mhz.
            
A good Volt-Ohmmeter for general measurements of voltages       
and resistance.      
A SWR impedance analyzer bridge (MFJ Enterprises makes an       
affordable unit, model MFJ259, which combines a frequency      
 counter, R.F. signal generator, SWR meter and resistance      
 meter in one versatile unit).
            
An SWR/Power meter for monitoring your transmitter's         output
power and monitoring antenna matching conditions.
            
Several good FM receivers, some mobile, some stationary,        
connected to a high-gain FM receiving antenna.
            
A dummy load for testing RF amplifiers.
          
OPTIONAL EQUIPMENT

   
A scanner radio
            
A spectrum analyzer
            
A modulation analyzer such as QEI model 691
          
CONSTRUCTION PRACTICES


  
No circuit that operates above 20Mhz operates independently of its
environment. Shielding and all-metal chassis construction is a necessary
part of circuit design. Forget about that audio amp kit you built
on a wooden box. Different physical laws are at work in the VHF spectrum.
Every RF unit MUST be encased in metal boxes. AC mains MUST be RFI/EMI
filtered. These are two essential keys to hum-free unmodulated carriers
and to spurious signal elimination.
Build all RF circuits on PC boards. Don't use perf board or project
breadboard circuit evaluators. You'll need to etch your own circuit
layouts on double-sided copper-clad PC board material, for reliable
operation. A lot of groundplane is necessary in these designs. A
well-constructed transmitter uses "airline" inductors and "stripline"
interconnection methods, keeping distances short between components.
All DC voltage supply leads should have .001uf bypass capacitors
shunting RF to ground so it doesn't enter the power supply. Mica
capacitors work well for this. Do not use electrolytic! They will
overheat and explode in some cases.
Keep all leads as short as possible and install components close
to the PC board to reduce stray coupling effects.
Use components that are designed for the application. Don't use an
audio transistor for your RF oscillator, for instance. Motorola makes
many suitable transistors for this kind of application. Consult their
RF Data Manual for specifics.
Mount sensitive circuits like VCO modules in sub-chassis within your
main chassis for extra shielding and isolation from other circuits.
Good design practice will pay off. Instead of a sloppy, interference
"hog" with 25db of signal-to-noise ratio, you could achieve 80-90db
of signal-to-noise and spectral purity so good you might not need
a filter to suppress harmonic radiation. Such a transmitter will
sound like any other commercial transmitter, if you've paid the same
attention to other aspects of circuit design as well as packaging.

SPECIAL HARMONIC REDUCTION MEASURES: 


  
Harmonic interference is a major problem for any FM station that
operates on a sub-multiple of a TV channel that is important to the
community. This second harmonic interference can destroy television
reception over several blocks radius of the transmitter in the case
of a micro station and over several miles in the case of a full-power
FM station. I'm going to share with you an effective, yet simple
solution to second harmonic interference that will make your transmitter
so clean that TV reception in the same house as the transmitter can
be unharmed. It's a 1/4-wave tuning stub. Here's how it works:
Transmission line has a particular characteristic at multiples of
a wavelength. At 1/2-wave multiples, if a short is at the far end
of the line, a short appears at the opposite end too. If it's open,
then the other end is nearly infinite resistance too. However, at
1/4-wave intervals, the OPPOSITE is true. A short at halfwave interval
appears like an infinite resistance at half the frequency where that
distance is only a quarter wavelength. For example, a second harmonic
filter stub for a station operating at 100Mhz would be approximately
two feet long. At 100Mhz the shorted far end would be only 1/4 wavelength
away from the generator, hence appear unshorted. But at the second
harmonic, 200Mhz, that distance is 1/2 wavelength and characteristically,
the short at the far end appears at the generator end too. It's a
frequency selective short, in other words.
This stub gets inserted into your antenna transmission line by adding
a Tee connector in series with the line and hanging the stub off
the tee. It doesn't look like it can do anything, but it's darned
effective and when two or more are cascaded 1 wavelength apart, even
the most severe second harmonic interference can be banished.
This is one good reason why you'll need an SWR Analyzer / Resistance
Bridge, because you'll need to fine-trim the stub by measuring its
resistance at fundamental and second harmonic frequencies. Tuning
is critical and cannot be guessed at.

ESSENTIAL COMPONENTS OF A STATION 

   
The main transmitter. A unit that is crystal-controlled         and/or
PLL synthesized, using varactor diode tuning and         modulation
methods. See Tech Note         BC-02 regarding bandwidth requirements
for optimum audio         performance. 
            
A broadcast limiter. Stereo, if you have a stereo         generator.
This is essential to insure non-interference         to adjacent
channels and maintain maximum volume without         overmodulating.
See Tech Note         BC-01 regarding filtering and pre-emphasis.
   
Setting your modulation levels. See         Tech Note BC-04 regarding
setting modulation levels.
            
An SWR/Power Meter to monitor the condition of your         antenna
system.
            
A mixing board to act as your program control center.
            
Audio sources to provide program material.
            
A good microphone.
          
  
Optionally, if you broadcast in stereo, you'll need to add the following:
   
A multiplex "stereo" generator.  See Tech Note BC-03 regarding stereo
       generator adjustments and theory of operation. 
       
            
Two-channel broadcast limiter.
            
All components back to the studio should be stereo         capable.

          
YOU'RE ON THE AIR!


  
Once the engineering work is done, and the field testing is done
and you're satisfied with your coverage, the sound of your transmitted
signal, etc., it's time to focus on professionalism as a key part
of your broadcast operation.
Before you go on the air, practice reading the news and weather into
a taperecorder. Study professional announcers by listening to how
they use the pitch and intensity of their voices -- how they add
emphasis and excitement to a phrase or sentence -- and try to emulate
a style you find that fits your way of speaking. Practice and listen
to the recordings, noting the things that need work, yet recognizing
the things you did well. After a few months of practice, you'll find
that your reading skills have improved and your voice is becoming
trained.
Plan ahead what your programming is going to focus on and develop
a schedule. Decide what services you want to provide, such as news,
weather, community calendar, local events coverage and formulate
a plan for carrying out these activities.
Work on your station's "theme". This could include station ID, a
jingle, etc. Try to produce it as professionally as you can manage.
You'll need good audio equipment to insure the quality of everything
you produce.
Think about the equipment you'll need. Here's a list of suggestions:

   
Two cassette tapedecks
            
Two CD players
            
A turntable, if you play older recordings
            
A PC with a high-end sound card like Turtle Beach or         Card-D.

            
A decent mixing board with enough stereo inputs to handle       
all of your sources without the need to unplug things and      
 swap cables.
          
  
IMPORTANT: an EXCELLENT quality microphone with a cardioid directional
pattern and a wide frequency response. This will make or break a
station, because "pirates" usually give themselves away just by the
tonal quality of the audio pickup. A broadcast-quality mic will make
you sound like a pro station, even if you don't sound perfect.
Every day before going on the air, prepare your program schedule.
Obtain the materials and information you will need for that day's
broadcast BEFORE you turn on the Big Switch. Line up your music selections,
if you run a music program, think about what you're going to say.
Try to be creative and knowledgeable about the program content. If
you're announcing a song title, sometimes it makes for more interesting
listening if you can mention some interesting fact about the song
or the band that performed it. Learn to improvise and think on your
feet.
Theme is up to you, but I make this statement: I have noticed a definite
pattern between FCC busts and politically-dangerous commentary. I
suspect that such content is dimly looked upon by the feds and hence
made a priority second only to interference complaints. If this is
a fun hobby, and political change is not your main reason for broadcasting,
you will be safer leaving the political talk to Rush and others who
have to defense budget to back them.
When you make a conscious effort to follow these suggestions and
operate more like a pro than a pirate, you'll enjoy the possibility
of increased positive notoriety and less chance of a negative experience
such as a complaint, or a visit from the FCC.
Authored by your friendly "Peg-legged" Bass Pig


  
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