parnass@ihu1h.UUCP (Bob Parnass, AJ9S) (05/05/85)
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HOW DO YOU FIND THESE FREQUENCIES?
PART II - SLEUTHING
Bob Parnass, AJ9S
Part I of this series discussed how scanner enthusiasts
can obtain frequency information from books, government
microfiche records, or other listeners. This install-
ment discusses digging up new frequencies on your own.
Do Your Own Sleuthing
There is a challenge in deriving new spectrum usage
information on your own. Sometimes it requires several
days of listening, taping, and compiling fragments of
information. Other times, the frequency information is
there for the taking - without hassle.
You can approach from two directions:
1. Listen first: Monitor a frequency or frequen-
cies, and determine who's transmitting and what
purpose the channel serves. Once you identify
the user, log the information.
2. Compile first: Take advantage of opportunities,
such as examining the frequency label on a
guard's radio, or reading the FCC license hanging
on the "radio room" wall1, to compile frequency
lists, then monitor the listed frequencies to
confirm that they are really in use.
Most listeners use a combination of both approaches.
What Makes Station Identification Difficult?
In most instances, FCC rules require radio users to
identify their operations with FCC assigned call
letters. Police and fire departments, especially those
with trained radio dispatchers, seem particularly con-
scientious about station identification. Like commer-
cial broadcasters, many of these stations identify on
the hour and the half hour.
Some repeater stations have Morse code identification
circuits which transmit call letters on a periodic
basis, insuring compliance with FCC rules.
On the other hand, about half the industrial radio sta-
tions monitored within the last year ignore the FCC
regulation, making it difficult for a listener to know
who he's listening to. Some stations may operate for
years using the undescriptive "base to mobile 2" or
"Joe to base" protocol. One rung up the hierarchy are
stations that identify using something like "Acme base
to 107", giving the listener a clue for his log. If
call letters are given, they are often rendered unin-
telligible by operators who fail to enunciate. The
failure to identify is more likely due to sloppiness,
rather than any attempt to hide station identity.
While not regulated by the FCC, federal government
radio stations vary in the extent to which they iden-
tify their transmissions. Some federal stations do not
have call letters. A nearby paging transmitter period-
ically transmits a voice recording announcing, "This is
the Army Joliet Ammunition Plant." What more could a
listener ask for?
The following examples illustrate techniques I've used
to derive new frequency information.
Examine the Labels on Radio Equipment
Frequency information is engraved on labels on the back
of many walkie-talkies, or inside the battery compart-
ment, like in the Motorola HT220 model. Most pagers
have labels on the bottom or inside. Like passwords
taped onto terminals, it's not uncommon to find Dymo
tape labels embossed with frequencies or call letters
glued to the front of base stations.
You can make your own opportunities for eyeing the
equipment or take advantage of "open house" events. If
information is displayed publicly, then a reasonable
person could assume it's not government secret.
- At the annual Glenview Naval Air Station open
house, I examined a military manpack radio being
used by dispensary paramedics. The radio's tuning
dial was set at 34.15 MHz.
- The Illinois Army National Guard proudly displayed
two armored personnel carriers at the local county
fair, each equipped with VHF-FM and HF-SSB tran-
sceivers.
In addition to a tuning control (VFO), the VHF-FM
radio had a set of channel select pushbuttons,
much like those in a car radio. I asked a guards-
man a few questions about the radio, and he gladly
demonstrated the channel preset feature. A panel
above the channel pushbuttons was labeled with the
frequencies: 32.055, 34.45, 35.35, 40.55, and
40.60 MHz.
Hobbyists are urged to exercise a modicum of restraint
and good judgement. In New Jersey, a radio
technician/hobbyist called to service a transmitter in
a county building, noticed a new unattended repeater
installation in the same room. Being curious about
what frequency this repeater was on, he opened the
access door to copy the frequencies from the radio's
crystals. It turns out that this radio belonged to the
US Secret Service, and opening the access door had
activated a "tamper alarm"!
The tech was skating on thin ice. He had nobody's per-
mission to tamper with that equipment.
Equipment to Determine Frequency Usage
If you don't know the exact frequency, but have a gen-
eral idea of the range (e.g. 150 - 152 MHz), use your
scanner's "search" mode. Most programmable scanners
afford the ability to search between two frequency lim-
its set by the user. Two older models, the Bearcat 250
and Regency K500, have the ability to automatically
store active frequencies found during an unattended
search operation.
To find the frequency of a hotel communications system,
one fellow installed his Bearcat 250 in his car and
parked in the hotel lot, leaving the scanner in the
"search and store" mode. He left the antenna discon-
nected so the scanner would only respond to a
transmitter in the immediate vicinity.
Test equipment can aid in the quest for new frequency
information. I've used a spectrum analyzer connected
to an outside antenna, and a frequency counter for
close-in work.
How Can I Determine To Whom I'm
Listening? - An Example
While scanning the industrial frequencies in the 150
MHz range, a van driver was overheard communicating
with "base" while driving around my town. The stations
involved never used FCC call signs - this would have
made life a lot easier for me, and legal for them!2
Transmissions were short and infrequent, so it was
decided to tape record all transmissions on this fre-
quency for several days to determine the station's
identity.
During daylight hours, a modified Regency K500 scanner
was left tuned to the target frequency, connected to a
cheap tape recorder through a home built interface.
Using a carrier operated relay, the tape interface sup-
plied power to the recorder only during radio transmis-
sions, so a day's worth of traffic could be compressed
into a 45 minute tape.
Each day, the tape was played back and notes on names,
locations, and activities mentioned during the day's
transmissions were taken. The van driver appeared to
be making daily stops at a local bank and two shopping
malls. A Walgreen's store seemed to be the only stop
at one mall. A few times, "base" ordered the van "back
to the Training Center." There were frequent references
to "guests checking out", "dropping a guest off", and
"instructor[s] missing a class". At times, "base"
spoke with "security", who must have been using a
walkie-talkie as his signals weren't strong enough to
hear.
Was this a hotel? Calls to the three local hotels
revealed that none provides shuttle bus service to the
shopping malls. A call to the Walgreen's, inquiring
about bus service to the store, drew another blank.
During my shopping trips, I began to pay closer atten-
tion to vans with antennas driving through the parking
lots.
I was leaving the mall one day, when a week's effort
paid off. A maroon and white van, equipped with a
VHF-Hi antenna, was dropping shoppers off at
Walgreen's. A sign on the van's door read:
XYZ Central Training Center3
Lisle, Illinois
I watched the driver pick up a microphone, and listened
to him on my portable scanner checking back with his
"base".
All the pieces fit: the "guests", the "classes", the
"instructors". Mystery solved; I had been monitoring
the customer training center for a large computer
manufacturer. The training center has hotel rooms and
dining facilities to accommodate students from out of
state. As a convenience, shuttle van service is pro-
vided to local shopping malls.
Summary
Through books, government records, and radio clubs,
scanner listeners can make use of frequency information
compiled by others. Since two-way radio users some-
times fail to identify their transmissions properly,
making it more difficult for listeners to know who they
are monitoring. By examining radio equipment labeling,
and monitoring and taping transmissions, scanner
enthusiasts can unearth new information.
__________
1. Readers are urged to abide by the rules of good taste
and local laws in the quest for frequency information.
Don't trespass, wait for an invitation.
2. One may use FCC license microfiche, described in Part I
of this article, to identify stations using call
letters.
3. XYZ is a pseudonym for the actual licensee name.
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Bob Parnass, Bell Telephone Laboratories - ihnp4!ihu1h!parnass - (312)979-5414