The orbital period of a satellite is the time it takes for a satellite to complete one revolution around the Earth. The direction of an ascending pass for an amateur satellite is from south to north. A descending pass is from north to south. Due to the Doppler Effect, a satellite's transmitted signal appears to shift lower as the satellite passes overhead. One way to predict the location of a satellite at a given time is by calculations using the Keplerian elements for the specified satellite. A geosynchronous satellite appears to stay in one position in the sky. The received signal from an amateur satellite exhibit a rapidly repeating fading effect is because the satellite is rotating. The type of antenna that can be used to minimize the effects of spin modulation and Faraday rotation is a circularly polarized antenna. The primary reason for satellite users to limit their transmit ERP is because the satellite transmitter output power is limited. All these answers are correct. The following types of signals that can be relayed through a linear transponder include
The term “mode” as applied to an amateur radio satellite is the satellite's uplink and downlink frequency bands. The letters in a satellite's mode designator specify the uplink and downlink frequencies. A satellite receives signals in the 432 MHz band is operating in mode U/V. The terms L band and S band with regard to satellite communications specify the 23 centimeter and 13 centimeter bands, respectively. A new frame is transmitted 30 per second in a fast-scan (NTSC) television system. A fast-scan (NTSC) television frame is made up of 525 horizontal lines. An interlace scanning pattern generated in a fast-scan (NTSC) television system is made by scanning odd numbered lines in one field and even numbered ones in the next. Vestigial sideband modulation is amplitude modulation in which one complete sideband and a portion of the other sideband is transmitted. An advantage of using vestigial sideband for standard fast scan TV transmissions is that it reduces bandwidth while allowing for simple video detector circuitry. The name of the video signal component that carries color information is the Chroma. Blanking in a video signal is the turning off the scanning beam while it is traveling from right to left or from bottom to top. All of these choices are correct. The following are all common methods of transmitting accompanying audio with amateur fast-scan television.
Other than a transceiver with SSB capability and a suitable computer no other hardware is needed to decode SSTV based on Digital Radio Mondiale (DRM). An acceptable bandwidth for Digital Radio Mondiale (DRM) based voice or SSTV digital transmissions made on the HF amateur bands is 3 KHz. Analog slow-scan television images are typically transmitted on the HF bands by varying tone frequencies representing the video using single sideband. The function of the Vertical Interval Signaling (VIS) code transmitted as part of an SSTV transmission is to identify the SSTV mode being used. The tone frequency of an amateur slow-scan television signal encodes the brightness of the picture. Specific tone frequencies are used in SSTV receiving equipment to signal the beginning of a new picture line. The number of lines commonly used in each frame on an amateur slow-scan color television picture is 128 or 256. Special operating frequency restrictions imposed on slow scan TV transmissions are they are restricted to phone band segments and their bandwidth can be no greater than that of a voice signal of the same modulation type. The approximate bandwidth of a slow-scan TV signal is 3 kHz.
The video standard used by North American Fast Scan ATV stations is NTSC.
If 100 IRE units correspond to the most-white level in the NTSC standard video format,
the level of the most-black signal is 7.5 IRE units.
Immunity from fading due to limiting is NOT a characteristic of FMTV (Frequency-Modulated Amateur Television) as compared to vestigial sideband AM television. One is likely to find FMTV transmissions on 1255 MHz. The frequency 14.310 MHz would generally be acceptable for U.S. stations to work other U.S. stations in a phone contest. The amateur radio 30 meter band is generally excluded in contesting. The frequency 146.52 MHz is generally discouraged for contacts in an amateur radio contest. (it is the national simplex calling frequency). During a VHF/UHF contest, you expect to find the highest level of activity in the weak signal segment of the band, with most of the activity near the calling frequency. One true fact in about contest operating is that operators are permitted to make contacts even if they do not submit a log. “Self spotting” in regards to contest operating is the generally prohibited practice of posting one's own call sign and frequency on a call sign spotting network. When attempting to contact a DX station working a “pileup” or in a contest you should generally sign your call by sending your full call sign once or twice. The Cabrillo format is a standard for organizing information in contest log files. All of these choices are correct. A phone DX station may state that he is listening on another frequency
In North America during low sunspot activity, when signals from Europe become weak and fluttery across an entire HF band two to three hours after sunset, to contact other European DX stations you might switch to a lower frequency HF band. Received spread-spectrum signals are resistant to interference because signals not using the spectrum-spreading algorithm are suppressed in the receiver. The spread-spectrum technique of frequency hopping (FH) works well because the frequency of the transmitted signal is changed very rapidly according to a particular sequence also used by the receiving station. Store-and-forward is a techniques normally used by low-earth orbiting digital satellites to relay messages around the world. The purpose of digital store-and-forward functions on an Amateur satellite is to store digital messages in the satellite for later download by other stations. “Command mode” in packet operations is the state where the TNC is ready to receive instructions via the keyboard. The definition of the term “baud” is the number of data symbols transmitted per second. When comparing HF and 2-meter packet operations, HF packet typically uses FSK with a data rate of 300 baud; 2-meter packet uses AFSK with a data rate of 1200 baud. Under clear communications conditions, the digital communications mode that has the fastest data throughput is 300-baud packet (compared to AMTOR, 170-Hz shift 45 baud RTTY or PSK31, which are all much slower). An APRS station can be used to help support a public service communications activity because an APRS station with a GPS unit can automatically transmit information to show a mobile station's position during the event. The digital protocol is used by APRS is AX.25. A commonly used 2-meter APRS frequency is 144.39 MHz. Unnumbered Information frames are used to transmit APRS beacon data. Any of these choices is correct. The following data sources can accurately transmit your geographical location over the APRS network
A common method of transmitting data emissions below 30 MHz is FSK/AFSK. When one of the ellipses in an FSK crossed-ellipse display suddenly disappears it indicates that selective fading has occurred.
The letters FEC, as they relate to digital operation, mean Forward Error Correction.
Forward Error Correction is implemented
by transmitting extra data that may be used to detect and
correct transmission errors.
If errors are detected, ARQ accomplishes error correction by requesting a retransmission. The most common data rate used for HF packet communications is 300 baud. The typical bandwidth of a properly modulated MFSK16 signal is 316 Hz. The HF digital mode PACTOR can be used to transfer binary files. The digital communication mode that has the narrowest bandwidth is PSK31. The HF digital mode PSK31 uses variable-length coding for bandwidth efficiency. The Baudot code is the International Telegraph Alphabet Number 2 (ITA2) which uses five data bits. |