HFU HF Underground
General Category => Huh? => Topic started by: ThaDood on July 30, 2023, 1748 UTC
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So, how many teeth fillings and fluorescent lights will this light-up? https://www.radio.gov.pk/30-07-2023/marriyum-aurangzeb-performs-groundbreaking-of-pbcs-digital-transmitter-in-rawat Yeah... Another SWL'ing rip. Interesting, that it's going to be DRM. I wouldn't mind seeing a VID tour of this station.
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That is the problem with these digital transmissions. Just like the conversion to over-the-air HDTV, what a few 100 kW and a good antenna previously accomplished in the analog world now requires a 1 Mega Watt emitter in digital / DRM to achieve comparable coverage.
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Actually, TV ERP's went down with the conversion to digital. What used to be a 3-4MW ERP UHF is now about 1MW. There is one caveat; analog TV power was measured in PEP essentially (sync tip power) whereas DTV is measured in average power. When factoring in the crest factor of the DTV waveform, ERP's are still about 2x what they once were. The power limits are dependent on frequency range, as the equivalent service contour on a UHF TV station requires more power than VHF low and VHF high. People used to put up with the noise in the picture to watch TV. I remember sitting on the floor of my grandparent's farm in the midwest and watching snowy TV from far away, because there was nothing else. Digital of course has the cliff effect. The SNR required for the receiver to decode the datastream is much higher than what we would tolerate in the analog days.
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I get TV over the air. I have some channels with marginal reception at my house and generally they are better in the day than at night.
Because I'm a geek, I will go into the settings of my TV to get the SNR values and compare 1) when I can receive certain channels well, 2) when it is indicating "no reception" at all and 3) when it's marginal (cycling between displaying a screen image and not). In general, the threshold where my TV stops showing a consistent image is around 19 +/- 1 dB SNR. Not really knowing much about digital TV, I assumed that it would need a better SNR than that, but apparently not.