💾 Archived View for gemini.spam.works › mirrors › textfiles › hamradio › MODIFICATIONS › bc210.txt captured on 2022-07-17 at 02:13:46.
⬅️ Previous capture (2022-06-12)
-=-=-=-=-=-=-
Weather Satellite Reception on a BEARCAT 210 Scanner
Steve Warley / K1LJL
63 Moore Drive
Burlington, Vermont 05401
Modifications to the 210 will provide the following:
1) Reception of 137 Mhz Range.
2) Increased bandwidth of the IF.
Modification to the Bearcat 210 scanner for reception of 137
mHz FM is a fairly simple process. These receivers operate
from 146 to 170 mHz using low side oscillator injection, with
a non-standard (10.8) mHz Intermediate Frequency. By
utilizing high side injection with the oscillator above the
input frequency we can receive 137 mHz simply by inputing a
frequency 21.6 mHz above 137.xx mHz. Examples below are
frequencies for NOAA / METEOR satellites.
BC210 Weather Sat Freqs (F+21.6)
Channel Freq Satellite Freq
--------------------------------
1 158.9 MET 2-17 137.3 (137.3+21.6=158.9)
1 158.9 MET 2-18 137.3
1 158.9 MET 2-18 137.3
1/4 158.9 MET 3-3 137.3/137.85
2 159.1 NOAA 10 137.5
3 159.22 NOAA 9 137.62
3 159.22 NOAA 11 137.62
4 159.45 MET 2-16 137.85
4 159.45 MET 2-19 137.85
4 159.45 MET 2-20 137.85
5 159.395 FEN-YUN 137.795
----------------------------------
Of course the rf amplifier is now tuned to 158 mHz and needs
to be re-tuned to 137 mHz. The Bearcat receiver design
utilizes "track-tuning" using varactor diodes on the rf
amplifier stages. At 158 mHz the voltage on the diodes is
approximately 9 V. At 137 mHz the voltage needs to be about
3 V. This voltage isn't critical since the rf stages are
fairly broad. Make a simple voltage divider using a 100k pot
in series with a 10k resistor connected to the internal 10 V
power supply. The CT of the pot is tied to the control
diodes after cutting the circuit land on the circuit board
going to the VCO tuning voltage.
Where to cut the circuit land and install the CT wire? Look
at the component side of the circuit board near the antenna
input to the scanner. Locate coil labeled L9. Just to the
right of this label is a 470 kohm resistor connected to a
land connection with two traces. The CT of the pot is
soldered to the resistor at the land. The trace going to the
IC is cut. The 10 V can be obtained from regulator Q8.
L9 470 Kohm
10K 100K POT () / 0--/\/\/\/\-
10 V 0-\/\/\/--/\/\/\/-Gnd / |^\Cut
^CT------------/ | \ TO IC
The Receiver is now modified for tuning the 137 mHz range.
The receiver should be sensitive enough to hear satellites
once the pot is adjusted to 3V. Once a satellite is heard,
fine tuning of the pot for the strongest signal is
recommended, however stay as close to 3 V as possible to
detune the rf amps away from the 158-159 mHz range.
The IF on the scanner is +/-5 kHz for narrow band FM
reception This will give marginal APT pictures. To increase
the bandwidth to +/-40 kHz the 10.8 mHz filter must be
replaced with a .01 ufd capacitor. This crystal filter is
located between Y1 and Y2 next to R3 labeled on the board.
Cut the traces going to the filter and install a .01 ufd
capacitor in place of the filter. The filter can be left in
place soldered to the board. This completes the conversion
to the scanner.
The scanner should have a GASFET preamp installed in order to
get "state of the art" low noise figure performance. I am
using a Hamtronics $24 preamp with excellent results. I use
a linearly polarized 7 Element 2 Mtr Beam AZ/EL and get noise
free APT pictures with the satellites 2-4 degrees above the
horizon. The only possible problem that will be encountered
is reception of commercial signals on the 158-159 mHz
frequencies since the receiver is tuned to the image freq. I
am planning to install a filter at the antenna input to
attenuate the 1 local signal I have on NOAA 9 (159.22) freq.
I would like to acknowledge the "Weather Satellite Handbook"
by Taggart for the ideas in this conversion. Have fun and
good APT reception. 73 K1LJL@W1KOO