99 lines
4.8 KiB
Plaintext
99 lines
4.8 KiB
Plaintext
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Weather Satellite Reception on a BEARCAT 210 Scanner
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Steve Warley / K1LJL
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63 Moore Drive
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Burlington, Vermont 05401
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Modifications to the 210 will provide the following:
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1) Reception of 137 Mhz Range.
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2) Increased bandwidth of the IF.
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Modification to the Bearcat 210 scanner for reception of 137
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mHz FM is a fairly simple process. These receivers operate
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from 146 to 170 mHz using low side oscillator injection, with
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a non-standard (10.8) mHz Intermediate Frequency. By
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utilizing high side injection with the oscillator above the
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input frequency we can receive 137 mHz simply by inputing a
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frequency 21.6 mHz above 137.xx mHz. Examples below are
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frequencies for NOAA / METEOR satellites.
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BC210 Weather Sat Freqs (F+21.6)
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Channel Freq Satellite Freq
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--------------------------------
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1 158.9 MET 2-17 137.3 (137.3+21.6=158.9)
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1 158.9 MET 2-18 137.3
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1 158.9 MET 2-18 137.3
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1/4 158.9 MET 3-3 137.3/137.85
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2 159.1 NOAA 10 137.5
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3 159.22 NOAA 9 137.62
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3 159.22 NOAA 11 137.62
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4 159.45 MET 2-16 137.85
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4 159.45 MET 2-19 137.85
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4 159.45 MET 2-20 137.85
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5 159.395 FEN-YUN 137.795
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----------------------------------
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Of course the rf amplifier is now tuned to 158 mHz and needs
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to be re-tuned to 137 mHz. The Bearcat receiver design
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utilizes "track-tuning" using varactor diodes on the rf
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amplifier stages. At 158 mHz the voltage on the diodes is
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approximately 9 V. At 137 mHz the voltage needs to be about
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3 V. This voltage isn't critical since the rf stages are
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fairly broad. Make a simple voltage divider using a 100k pot
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in series with a 10k resistor connected to the internal 10 V
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power supply. The CT of the pot is tied to the control
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diodes after cutting the circuit land on the circuit board
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going to the VCO tuning voltage.
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Where to cut the circuit land and install the CT wire? Look
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at the component side of the circuit board near the antenna
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input to the scanner. Locate coil labeled L9. Just to the
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right of this label is a 470 kohm resistor connected to a
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land connection with two traces. The CT of the pot is
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soldered to the resistor at the land. The trace going to the
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IC is cut. The 10 V can be obtained from regulator Q8.
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L9 470 Kohm
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10K 100K POT () / 0--/\/\/\/\-
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10 V 0-\/\/\/--/\/\/\/-Gnd / |^\Cut
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^CT------------/ | \ TO IC
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The Receiver is now modified for tuning the 137 mHz range.
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The receiver should be sensitive enough to hear satellites
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once the pot is adjusted to 3V. Once a satellite is heard,
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fine tuning of the pot for the strongest signal is
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recommended, however stay as close to 3 V as possible to
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detune the rf amps away from the 158-159 mHz range.
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The IF on the scanner is +/-5 kHz for narrow band FM
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reception This will give marginal APT pictures. To increase
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the bandwidth to +/-40 kHz the 10.8 mHz filter must be
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replaced with a .01 ufd capacitor. This crystal filter is
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located between Y1 and Y2 next to R3 labeled on the board.
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Cut the traces going to the filter and install a .01 ufd
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capacitor in place of the filter. The filter can be left in
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place soldered to the board. This completes the conversion
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to the scanner.
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The scanner should have a GASFET preamp installed in order to
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get "state of the art" low noise figure performance. I am
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using a Hamtronics $24 preamp with excellent results. I use
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a linearly polarized 7 Element 2 Mtr Beam AZ/EL and get noise
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free APT pictures with the satellites 2-4 degrees above the
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horizon. The only possible problem that will be encountered
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is reception of commercial signals on the 158-159 mHz
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frequencies since the receiver is tuned to the image freq. I
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am planning to install a filter at the antenna input to
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attenuate the 1 local signal I have on NOAA 9 (159.22) freq.
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I would like to acknowledge the "Weather Satellite Handbook"
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by Taggart for the ideas in this conversion. Have fun and
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good APT reception. 73 K1LJL@W1KOO
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