Testing DAB Receiver Performance: Challenges and Recommendations for Improved Reception
This report by Richard Drinkwater from the Radiocommunications Agency investigates complaints from DAB listeners regarding poor reception quality. The study examines whether these issues stem from inadequate service coverage or ineffective receivers. It details sensitivity tests of various domestic DAB receivers, the complexities of DAB technology, and the challenges listeners face due to higher costs of equipment. Recommendations for enhancing reception include deploying low-power transmitters and improving receiver antennas to overcome interference caused by shielding.
Testing DAB Receiver Performance: Challenges and Recommendations for Improved Reception
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Presentation Transcript
T-DAB Receiver testing Richard Drinkwater Radiocommunications Agency
Introduction • Complaints received from DAB listeners about poor reception • Is this due to poor service coverage or poorly performing receivers? • Receiver tests performed to establish the sensitivity of a selection of current domestic receivers
Technology • DAB technology • Benefits • More rugged transmission format • Much less spectrum usage – capable of carrying 6 quality audio stereo programmes in 1.5MHz against 2.2MHz per programme for complete mainland UK FM coverage • Drawbacks • More complicated (= expensive) receivers for the listeners
BS 50248:2001 test criteria • BS EN 50248:2001, “Characteristics of DAB receivers” • Minimum power of -81dB(mW) for a BER of 10-4 at the convolutional decoder output of the receiver (VHF and L-band)
Methodology • Objective tests were not possible without connections to internal circuitry • Subjective tests were performed which established the minimum field-strength at which audio impairments (more than 1 click in 5 seconds) were heard
Test set-up Measuring voltage V and height X enables a known field strength (V/m) to be established at the receiver under test
which means… For a field strength of 45dBµV/m, the receiver input power at 222MHz would be-77dBm if the receiver had a 50Ω input impedance, and a dipole antenna Tested receivers did not, and the standard is written in antenna port power terms, so it is impossible to equate the tests with the standard
Receivers tested • DAB #1 • Miniature personal receiver using earphone lead as antenna • DAB #2 • Portable receiver with rod antenna • DAB #3 • Portable stereo unit with rod antenna • DAB #4 • Miniature personal receiver using rod antenna
Service planning criteria • National DAB services • Edge of service area is considered to be when field strength is 58dB(µV/m) at 10m above ground level for 99% locations, 99% of the time • Field strength at 1.5m agl is very approximately 10dB lower than at 10m agl in open terrain • In a single frequency network, other transmitters within about 70km (246us) add to the signal available to the receiver
Portable equipment • Inefficient antennas • Low antenna height • Body shielding • Building shielding and reflections • Shielding attenuates the signal • Local reflections tend to add to the signal received
Analysis of test method • Strengths • Straightforward, repeatable method using GTEM! cell • Weaknesses • Subjective assessment • No multipath reception distortion • Incomparable with BS test method
Some thoughts Assuming a field strength at the edge of the service area of approximately 48dBµV/m at 1.5m agl, it would appear that the tested receivers would work in free space conditions. Due to shielding effects there is probably inadequate margin in sensitivity (in 3 out of the 4 tested receivers) for satisfactory reception under everyday usage conditions.
Possible solutions • Very low power fill in transmitters • Relatively inexpensive solution • No international clearance required • Improve receiver antenna performance • Particularly the match to input circuitry
Contacts • richard.drinkwater@ra.gsi.gov.uk • richard.drinkwater@ofcom.org.uk RTCG Radiocommunications Agency Whyteleafe Hill Whyteleafe Surrey CR3 0YY +44 (0)20 8655 8300
