== Crystal NOAA Weather Radio (NWR) == --- //[[honeypot@handbasket.org|David Wagner]] 2007/11/21 16:37// * [[crystal_nwr-notes]] In the US, the National Oceanic and Atmospheric Administration (NOAA) broadcasts FM(( "...voice program audio is transmitted over the NWR transmitter network using standard pre-emphasis for narrow band VHF FM of 6 dB per octave increasing slope from 300 Hz to 3,000 Hz applied to the modulator."--[[http://www.weather.gov/nwr/resources/same.pdf|NATIONAL WEATHER SERVICE NOAA WEATHER RADIO (NWR) TRANSMITTERS NWR SPECIFIC AREA MESSAGE ENCODING NWR SAME]])) weather information in the VHF range. | 162.400| 162.425| 162.450| 162.475| 162.500| 162.525| 162.550|MHz| | 1.84601| 1.84573| 1.84544| 1.84516| 1.84488| 1.84459| 1.84431|m| | 72.6777| 72.6665| 72.6553| 72.6441| 72.6329| 72.6218| 72.6106|in| San Antonio weather is broadcast at 162.550 MHz, WXK-67, 1000 Watts.(([[http://www.srh.noaa.gov/nwr/wxk671.html|San Antonio's NOAA Weather Radio Coverage]], NOAA)) * [[http://www.pollenpurge.com/]] has a webcast of WXK-67. Station Transmitter location Call Frq. Power Latitude Longitude Antenna Elev. San Antonio San Antonio WXK-67 550 1000 29 30 25 98 34 29 1168 / 356.1 {{electronics:loadpfmap.adp.jpg?320|Map of Transmitter Location (May be out of date.)}} --[[http://www.weatherradio.info/usa/techlist.html]]: //This page is archaic.[...]The National Weather Service has discontinued giving out the latitude/longitude information for NWR transmitters[...]// ====== Antenna ====== An AM broadcast band crystal radio is a high-impedance ((FIXME: //calculate tank impedance//))and seems to work best with a high-impedance antenna, usually a simple random wire antenna for the AM broadcast band. A //[FIXME even multiple of?]// one-half wavelength end-fed wire should provide the highest impedance, and this is practical for the FM broadcast and weather radio bands. * A [[http://members.tripod.com/AMN92/antenna.htm|collinear J-pole]] looks promising. Perhaps eliminating the hook will leave a high-impedance collinear random wire. * [[http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=13084| The Twinlead J-pole]] is popular for operation at two meters (150 MHz). ([[http://www.bbtel.com/~hbennett/jpole.htm|Also described here.]]) It seems odd that NOAA recommends using a folded dipole, an antenna with a wide bandwidth(( [[http://www.crh.noaa.gov/mqt/nwr/nwrwebpg/antenna.php|Radio Receivers and Methods to Improve Reception of Weather Radio Broadcasts]])). Also, the dimensions given do not seem to account for the velocity factor of twinlead. The standard formula, 468/MHz for the length (in feet) for a specific frequency(([[http://kgnu.org/ht/helpfm.html#makeantenna]])) gives, and 34.5" for weather radio frequencies. The standard AM crystal radio operates from an unbalanced (one-wire) feedline/antenna. See [[http://www.ham-radio.com/k6sti/balun.htm|A Simple 75-ohm Coax Balun for 88-108 MHz]] for how to make an FM balun. ===== Yagis ===== Perhaps a better solution is a directional yagi antenna. * [[http://bfn.org/~bn589/antenna.html]] * [[http://www.csgnetwork.com/antennae3ycalc.html]] * [[http://www.csgnetwork.com/antennae7ycalc.html ]] ====== Tuning ====== It should be possible to make a crystal set to tune these stations, though the Q necessary is 162.550/0.025=6502, and the frequency seems to be beyond what an LC circuit can do. * Consider using a VHF resonant cavity, as used successfully for some crystal radio designs. * Consider using a quartz or ceramic filter. * Design a PCB with the FIXME" antenna, coil, and half the capacitor printed on it. * Use FIXME/FIXME Litz wire (size for frequency). * Micrometals Materials: 17, 12, 0 Start with a basic [[http://solomonsmusic.net/FM_CrystalRadio.html|FM crystal radio circuit]], and add output impedance improvements. The basic circuit appears to have something like these coil and capacitor combinations. * 0.12 μH coil/50 pf air variable capacitor, tapped in the middle at 0.03 μH * 0.15 μH coil/80 pf air variable capacitor, tapped in the middle at 0.04 μH \|/ \ / | +--[]---||--+ | | S1 C3 | L1 | / | / | +----UU+UU--+--|<---VV---UU--+-------VV--+ | | | /R1 L2 | /R2 | | / | | | | +--||--+-||-+ +-------||--+ | /C1 C2 C4 | | | +----------------------------------------+ Or, try an even more basic circuit. o----------------+ A | o--+-----UU------+ | 220n | | / | +-----||------+ | /5-30p | | | +--|<--+--||--+---o | 100p ) +----------o * 0.22 uH: 1 turn, d=4" * How a [[http://www.somerset.net/arm/fm_only_lowtech.html|crystal radio decodes FM signals]] Antenna 299 792 458 m / s / 162475000 = 1.845 m 7" x 98000000/162475000 = 4.22" FIXME should decrease by the square root? Coil Tuning Capacitor Other Capacitor Choke //The LCRA also rebroadcasts our weather radio information an the AM Dial 1610, for a radius of 10 to 20 miles. Their transmitters are located at Lakes Buchanan, Marble Falls, Travis, Bastrop, and Fayette.//--[[http://www.srh.noaa.gov/ewx/html/radio.htm|WFO, Austin/San Antonio]]