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Description
Various strategies for improving the signal to noise ratios of t.v. and radio receivers are examined as well as an application of white noise in testing the noise performance of a distribution amplifier.
Various strategies for improving the signal to noise ratios of t.v. and radio receivers are examined as well as an application of white noise in testing the noise performance of a distribution amplifier.
| Module code and title: | T321, Telecommunication systems |
|---|---|
| Item code: | T321; 05 |
| First transmission date: | 10-04-1976 |
| Published: | 1976 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:25:00 |
| + Show more... | |
| Producer: | Tony Jolly |
| Contributors: | Gary Alexander; David Crecraft |
| Publisher: | BBC Open University |
| Keyword(s): | Distribution amplifier; Intermodulation distortion; Radio receivers; Signal-noise ratio; Television; White noise testing |
| Footage description: | David Crecraft demonstrates the effect, on a t.v. test card, of interposing a low-noise pre-amplifier in the aerial circuit of a t.v. receiver. He simulates a weak signal by feeding the camera signal to a u.h.f. modoilator. The output is fed to the t.v. receiver along a coaxial cable which simulates the down cable from a roof top aerial to a ground floor receiver. Crecraft uses a block diagram of an AM receiver to introduce a sequence on the effect of random noise on demodulators. Crecraft demonstrates how signal to noise ratio, particularly intermodulation distortion, is affected by the type of modulation system. He begins by demonstrating ordinary envelope modulation with 50% modulation by a 1 kHz- sine wave. Crecraft next looks at double sideband suppressed carrier modulation. Crecraft goes on to simulate single side band modulation and then sums up by comparing, briefly, the three methods outlined above. Crecraft uses an F.M. tuner to demonstrate the signal to noise ratio of this type of modulation. With the aid of a block diagram he explains how the system works and then carries out a demonstration. Crecraft reduces the frequency deviation to quite low levels which approach that of the noise. A clearly recognisable signal output is still seen at output. Crecraft sums up the discussion on amplitude and frequency modulation by pointing out and comparing the features of each system. Gary Alexander with a white noise test set. He explains how the apparatus works and then demonstrates how the set up is used to analyse the noise performance of an amplifier. Alexander explains why this particular method is used to analyse noise performance and goes on to demonstrate at higher power levels where intermodulation and harmonic distortions occur. Credits. |
| Master spool number: | 6HT/72028 |
| Production number: | 00525_5224 |
| Videofinder number: | 1346 |
| Available to public: | no |
