john@anasaz.UUCP (John Moore) (09/26/89)
I am interested in building a system to receive WEFAX APT pictures from at least the polar orbiting weather satellites and maybe also from the geosynchronous ones. One question I have is: what is a good receiver to use? I have a scanner that can receive 137.5MHz but it's bandwidth is either 6kHz or 200kHz. I understand that the appropriate bandwidth would be about 50kHz. What do other experimenters do in this regard? P.S. - I would expect to receive the GOES satellites with a down-converter to the 137 MHz range, so the same receiver could be used for both. -- John Moore (NJ7E) mcdphx!anasaz!john asuvax!anasaz!john (602) 861-7607 (day or eve) long palladium, short petroleum 7525 Clearwater Pkwy, Scottsdale, AZ 85253 The 2nd amendment is about military weapons, NOT JUST hunting weapons!
paul@hpldola.HP.COM (Paul Bame) (09/28/89)
>I am interested in building a system to receive WEFAX APT >pictures from at least the polar orbiting weather satellites >and maybe also from the geosynchronous ones. One question >I have is: what is a good receiver to use? I have a scanner >that can receive 137.5MHz but it's bandwidth is either 6kHz or 200kHz. >I understand that the appropriate bandwidth would be about 50kHz. I'm curious about this bandwidth thing too. I have trouble believing the FM signal actually has a short-term deviation of 50kHz - but I *can* believe this might be wide enough to copy the signal during the doppler shift from AOS to LOS (I haven't calculated this though, or looked it up). Would a NBFM (6kHz mentioned above) receiver work just as well as one with a 50kHz bandwidth as long as the center frequency was periodically changed to account for the doppler shift? -Paul Bame paul@hpldola.hp.com hplabs!hpldola!paul
magore@watdcsu.waterloo.edu (Mike Gore, Institute Computer Research - ICR) (09/28/89)
Hi John, You wrote: > what is a good receiver to use? I have a scanner >that can receive 137.5MHz but it's bandwidth is either 6kHz or 200kHz. >I understand that the appropriate bandwidth would be about 50kHz. >What do other experimenters do in this regard? I replaced the filters in my unit with a MuRata 10.7MA and a muRata CFM455A. My dual band IF uses 10.7MHZ and 455KHZ. The CFM455A gives +/- 17.5 KHZ or 35KHZ total bandwidth. This filter works for me... I have a list that muRata sent me with the filter docs of authorized distributors. For your area they have: Phoenix: Future Electronics 602-968-7140 Sterling Electronics 602-268-2121 Tempe: Acacia/Deanco 602-894-2874 602-882-9054 Time Electronics 602-967-2000 muRata Erie North America Regional Sales Office Southwest: 714-832-9972 >P.S. - I would expect to receive the GOES satellites with a down-converter >to the 137 MHz range, so the same receiver could be used for both. Yes this works and is in fact what many people do. You might look into a reprint for "An S-Band Receiving System for Weather Satellites; Emilini, G. and Righini, M.: QST, August 1980". This can be obtianed from Mono Smith @ NOAA/NESDIS (1-301-763-8447). I just ordered my copy. Good Luck, PS. For others looking for muRata parts you might try asking asking someone at their main number for a distributor nearer your area. Otherwise you may try Future Electronics as they seem to have stores all over North America. muRata Erie 2200 Lake Park Drive Smyma, Georgia 30080 404-433-7820 [ No I don't work for them :-) ] PPS. Many receivers use an mc3259 or mc3261 FM IF chip. You might have to reduce the resistor across the quad. coil to about 22k or so. This resistor controls the output transfer for a given frequency swing. The higher the resistor one has will increase the output voltage from the quad. detector for a given frequency shift. So the idea is to reduce this value such that one gets the max. output swing for a given signal bandwidth *but* without clipping. # Mike Gore, Technical Support, Institute for Computer Research # Internet: magore@watdcsu.waterloo.edu or magore@watdcsu.uwaterloo.ca # Bitnet: magore@watdcsu.bitnet UUCP: uunet!watmath!watdcsu!magore # These ideas/concepts do *not* imply views held by the University of Waterloo.
kenny@m.cs.uiuc.edu (09/29/89)
/* Written 2:51 pm Sep 27, 1989 by paul@hpldola.HP.COM in m.cs.uiuc.edu:sci.electronics */ I'm curious about this bandwidth thing too. I have trouble believing the FM signal actually has a short-term deviation of 50kHz - but I *can* believe this might be wide enough to copy the signal during the doppler shift from AOS to LOS (I haven't calculated this though, or looked it up). Would a NBFM (6kHz mentioned above) receiver work just as well as one with a 50kHz bandwidth as long as the center frequency was periodically changed to account for the doppler shift? /* End of text from m.cs.uiuc.edu:sci.electronics */ No. Short-term deviation of 30KHz is common in metsat signals. It's still not as wide as commercial FM broadcast, but it's lots wider than NBFM. A-T