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Re: (meteorobs) (Radio) Meteor Observation Project
At 06:43 PM 2000-02-27 EST, JWink38223@aol.com wrote:
>In a message dated 2/27/00 11:11:39 AM Central Standard Time, ko0u@os.com
>writes:
>
><< http://www.bnv-bambergdot de/home/ba0249 >>
>This time I managed to copy all. I have found the problem with using an FM
>radio for meteor detection is very difficult in the city (Houston, Texas my
>home) because there are so many stations. If there are any VHF stations
that
>could be used from Houston I would like to know about them. I do have a
>number of shortwave radios and a scanner that covers most all to 1300 MHz.
How about TV video carriers? The larger metropolitan areas have TV
transmitters on channels 2, 4, 5, 7, 9, 11 and 13. The smaller areas have
transmitters on channels 3, 6, 8, 10, and 12. Those suitable for meteor
detection are channels 6 on down since they are between 54 and 88 MHz
(channels 7 through 13 are in the high VHF range from 172 through 216 MHz,
too high for consistently-good sporadic meteor detection).
Alternatively, some are able to use airport VOR transmitters which are
located between 108 and 116 MHz but are also much lower power and perhaps
with fairly-directional antenna systems.
One would want to use the TV video carriers in lieu of audio carriers
because the video carriers are amplitude-modulated, meaning the frequency
does not shift with modulation. The aural carriers, however, are
frequency-modulated in addition to being transmitter with 8 to 16 dB less
power than the video carriers.
The last resort would be to listen for amateur radio beacon stations
between 50.0 and 50.080 MHz. These are an excellent possibility although
they transmit with relatively-slow-speed morse code, which means that their
signal is much less than 100% duty cycle and one can easily miss a meteor
reflection that might occur when the transmitter happens to not be
transmitting. But the good side is that with the ability to copy morse
code, one can easily identify which station is being heard from where, and
the beacons are spread out around the world. Those on the same frequency
are normally spread out geographically so that a particular meteor
reflection would likely not reflect more than one beacon at a time. Their
effective radiated power is far below that of a TV transmitter but because
their whole reason for existing is to act as a beacon, they are erected and
built so that they show a very high radiation efficiency. A simple 3
element yagi antenna will do a great job picking up reflected beacon
signals while discriminating against other beacons on the same frequency
from other antenna headings.
SteveH
Shrewsbury MA
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