| + + + - D L 4 X A V - jo 43 xn - h a m b u r g , g e r m a n y , e u r o p e , e a r t h + + + |
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Realistic PRO-2005 quick and dirty WFM filter modification |
| i dont use the scanner in the WFM-bordcast band. but i like to lisen to radio feeder signals on satellites. these sigals are week and have less bandwith than normal WFM transmisions. |
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| 1 - 2nd original ceramic filter removed 2 - 1st original ceramic filter left in place 3 - WFM chip KA2243 4 - a 3 pin socket is soldered to KA2243 pins 4, 5 and 6 5 - new cristal filter pluged in |
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| KA2243 pins 4, 5, 6 and the filter - for reference KA2243 datasheet |
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| i choosed this filter out of a bunch i had in the junkbox. it has 35KHz -3dB bandwith. and 100 KHz bandwith at -20dB. the center frequency is a little off frequency (10.706 MHz), so i have to tune 5 (6) KHz up in WFM and also NFM mode. |
NFM-discriminator out modification for pocsac or 9k6 packet decoding |
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| 1 - 0 ohm resistor near the NFM demod IC 2 - red wire 3 - 10 K ohm resistor 4 - 22 K ohm trimpot 5 - cinch socket |
discriminator out is taped at the zero ohms resistor near the NFM demod chip. the red wire goes to the back. than comes a 10K ohm resistor in series. the trimmpot is soldered direct to the new cinch socket on the back wall. here is the schematic. |
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| DL4XAV - 2012 |
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