r&s®efa78 test receiver (d/k or i analog tv) | 概览 -九游官网下载

the analog r&s efa models provide high-precision demodulated baseband signals (vision and sound) for measurements in various applications (tv transmitters, cable headends, coverage measurements, r&d). at the same time, all relevant rf parameters are monitored at high speed and represented in a logical manner (fig. 13). user-configurable alarm messages permit unattended monitoring of the received signals as well as switchover to alternative links in the event of a failure.

the high-end demodulator version is used for on-site measurements on tv transmitters. this version offers particularly lowdistortion demodulation of the broadcast signal. it is perfectly suited for these types of measurements; its low measurement uncertainty permits optimal alignment as well as permanent quality control of transmitters.

all parameters for the demodulated standard b/g tv channel are displayed on a single screen and can be checked at a glance:

• vision carrier level
• video modulation depth
• sound intercarrier measurements
• vision/sound level ratio
• sound 1 & 2 fm deviation
• pilot decoding

in-channel distortion is determined by means of a modulated tv signal with a vision carrier (fvc), a colour subcarrier (fsb) and a sound carrier (fsc). modulation is chosen such that the vision carrier is lowered by 6 db, the colour subcarrier by 14 db and the sound carrier by 10 db relative to the sync pulse level. the level of the intermodulation product is measured at the video output relative to the black-to-white transition of the video signal. fig. 26 shows the signals involved and the reference level at the rf.

the effect of signals outside the received channel is described by the 3rd-order intercept point (toi). for the efa family, this parameter is specified on the basis of a three-tone measurement with the following signals: a wanted carrier at the receive frequency f vc and two unwanted carriers 14 mhz and 15 mhz above the receive frequency.

the unwanted frequencies are chosen to be within the bandwidth of the rf preselection but outside the bandwidth of the first if filter. the effect of out-of-channel interference on the receiver can thus reliably be determined. it is assumed that each of the three signals has a level p = -33 dbm. the level of the intermodulation product δim 1 mhz relative to the wanted carrier is measured (see fig. 27, measurement at the rf). the 3rd-order intercept point is: