We
at the Del City Amateur Radio Club are very much aware of a
radio frequency interference problem on our repeater frequency.
The coordinated frequency pair that we are using just happens
to share the same frequency with the video signal of Cable television
channel 18. Any time there is a leak in the cable television
lines, some of their signal escapes and can be heard as a low
level dead carrier on 145.25 MHz. As you drive around the Oklahoma
City metro area, you will no doubt get a fluctuating signal
as you pass businesses and residential neighborhoods.
The
signal comes from leaking cable lines around town and are weak
until you approach the leak. Below is an article taken from
the ARRL RFI handbook to explain the Cable channel 18 source
of noise.
We
also suffer from a signal from computers. With the new fast
processors in the computers today, they emit signals that can
be heard all across the 2 meter band. At the IRLP node site,
this interference is full scale on the node link radio.
One
more problem that we have is the location of our repeater in
proximity to industrial paging services. Anyone that has driven
around the Oklahoma City metro area surely has noticed that
Del City is right in the middle of many new towers and industrial
facilities. We receive paging interference on both VHF and UHF
in our area nearly 24 hours a day. The strongest is on a 600
foot tower on the North side of Crossroads mall. There is a
powerfull paging system on 152.24 MHz that sends pulses of data
all day. Here at the repeater site, we receive these pulse anywhere
from an S-4 to an S-9 signal.
In
addition to all the above noises, we also share this frequency
with another repeater in Harrah, OK, just to the East side of
the metro. The Harrah repeater uses a CTCSS tone. With all these
sources of potential interference in the Del City area we had
to put a CTCSS tone on the repeater and simplex IRLP nodes.
The repeater and IRLP simplex node also encode a tone so users
can squelch out all this noise by simply adding a tone squelch
to their radio.
Our
repeater has a CTCSS tone of 103.5 Hz and also encodes a tone
of 103.5 Hz. Our simplex node on 145.670 has a CTCSS tone of
162.2 as well as encodes a tone. The Harrah repeater has a CTCSS
tone of 114.8 Hz. If all users will set their radios up to both
send and receive a tone of 103.5 Hz for the repeater and 162.2
for the simplex node, the interference can be eliminated.
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