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)… UEP protection Bit rate kb/s Sampling rate kb/s DAB Rx #1 DAB Rx #2 DAB Rx #3 DAB Rx #4 3482444.7431.1544.8041.74 3642443.7430.1539.8041.74 3964845.7431.1546.8040.74 31124845.7432.1548.8041.74 31284844.7431.1544.8042.74 31604845.7431.1546.8041.74 31924845.7433.1544.8042.74

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