It can be observed, with a radio receiver, in the form of a combination of white noise ( coming from distant thunderstorms ) and impulse noise ( coming from a near thunderstorm ).
12.
While this error correction can work well in the UHF band where the interference consist largely of white noise, it has largely proven inadequate on lower VHF channels where bursts of impulse noise disrupt the entire channel for short lengths of time.
13.
The terrestrial ATSC system ( unofficially ATSC-T ) uses a proprietary impulse noise which is especially present on the VHF bands that other countries have discontinued from TV use, but are still used in the U . S . There is also no hierarchical modulation.
14.
Thus it's quite common, in order to get better performing impulse noise filters, to use model-based systems that know the properties of the noise and source signal ( in time or frequency ), in order to remove only impulse obliterated samples.
15.
The FCC proposed to scrap the " UHF discount " in 2013; digital transition ( aggravated by everything from impulse noise problems to restrictively-low licensed power levels ) did so much damage to low-VHF broadcasting that the original rationale of UHF inferiority to VHF for TV is no longer valid from a technology standpoint.
16.
On April 10, 2012, Shaw Media applied for permission to change CIII-DT-6's allocation from VHF channel 6 to UHF channel 14, switching from circular to elliptical polarization, citing the VHF-Low band's impulse noise ( compared to the VHF-High and UHF bands ) causing reception issues, which would be mostly resolved with a higher frequency.
17.
For WABW and WCES, this makes them one of the few television stations in the country to operate on low-band VHF channels ( 2 to 6 ), which require larger receiving antennas, are prone to tropospheric ducting ( weather ) and impulse noise, make mobile TV ( ATSC-M / H ) difficult, and for 5 and 6 are also an obstacle to expanding the FM broadcast band.
