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T-DAB Receiver testing

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?

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T-DAB Receiver testing

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  1. T-DAB Receiver testing Richard Drinkwater Radiocommunications Agency

  2. 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

  3. 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

  4. UK Spectrum Occupancy FM v DAB

  5. 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)

  6. 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

  7. Test set-up Measuring voltage V and height X enables a known field strength (V/m) to be established at the receiver under test

  8. GTEM! cell

  9. Results on channel 12D (229.075 MHz)…

  10. …graphically

  11. 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

  12. 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

  13. 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

  14. 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

  15. Analysis of test method • Strengths • Straightforward, repeatable method using GTEM! cell • Weaknesses • Subjective assessment • No multipath reception distortion • Incomparable with BS test method

  16. 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.

  17. 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

  18. 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

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