Similcast Distortion on Metrocrest Quad Cities Public Safety Radio System
I agree that this sounds like simulcast distortion. To me it sounds somewhat similar to what happens when you simulcast audio from one digital system through another digital system. I've seen similar problems on the SAUA P25 system, which is a simulcast of the San Antonio/Bexar County EDACS system. By the time the audio has been encoded as EDACS ProVoice, decoded by the ProVoice radio, and re-encoded by the P25 radio, it gets pretty nasty and difficult to understand. This may be oversimplifying the situation a bit, but that does appear to at least partially explain the issue.
EDIT: Also, having those interop frequencies is not only convenient for working with other agencies - it could be a matter of life or death in the event that one of these large, complicated systems goes down. Having them and knowing how to switch to them should be a safety requirement. As I recall, those Harris portables should be capable of VHF as well, so it would probably be helpful to have the old VHF interop channels as well. A vast majority of departments still have those programmed into at least some of their radios.
I am the feed provider for the Broadcastify audio service, providing audio of the Metrocrest Quad Cities Public Safety Radio System using both the Uniden Bearcat BCT536HP and BCD996XYP2 radios. I have struggled to adequately receive and properly decode the digital voice of this system for months.
Despite very strong received signal strength, both of my receive radios were equally unable to adequately decode the digital audio. My receive point is roughly equidistant from two (2) of the simulcast radio transmitters, both located at municipal water towers, approximately 120-150 AGL. So far, I have resisted the use of any type of directional antenna, as, in actual service, the field handheld units will also not be using type of directional antennas. I have no doubt that my radios are incapable of receiving and decoding the digital voice signals due to the high level of multi-path distortion at the radio receive location, multi-path created by the simulcast of two identical modulation envelopes from two separate transmitters, each located about 3 miles from my receiver. Hearing the garbled audio, I wondered how-in-the-hell police officers, using a handheld transceiver, might establish reliable voice communications with dispatch and each other? Apparently, Carrollton officials are now wondering the same thing.
In my opinion, the technology of digital voice CODECs does not work well and sometimes does not work at all in a distributed or simulcast radio system. The problems recently published by the NTECC and WFAA-TV are a good indication that my poor receive and decode experience is not unique.
The police officers and City Manager of the City of Carrollton are dissatisfied and disgusted with the Harris radio problems.
As is evidenced by the recent audio coming from my scanner receiver tonight and observing the scanner's display, Carrollton, Addison and Farmers Branch have now transitioned back to their legacy Motorola trunked radio system, using the old, reliable, 9600 baud digital control channel and the old, reliable ANALOG voice. Analog voice, complete with picket-fencing, noise, squelch-tails and other distortions we are familiar with is 100% intelligible and not subject to failures related to computer software and GPS failures. Thumbs down to Harris! Go Motorola!
TexasTalker
