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  • Date : September / 22 / 2013
  • Author :
Digital Radios Fail at Navy Yard Shooting Response


P-25 Digital radios again face the heat of repeated malfunction during crisis; long history of diversion away from the problem; long history of the same problem and same associated problems with digital P-25 communications failing under critical situations as well as normal everyday use. The underlying critical issue is that the problem has been known since P-25 was developed in deference to existing very good digital modulation protocols, making P-25 a unique protocol which went through many alterations then changes to facilitate its use in narrowband (12.5 KHz) channels.

a. There were approximately 13 or more vocoder types available and in use at the time of P-25 creation. Of this group, several were international standard types for use in telephonic and radio circuits, some were USA Federal standards, DoD specification types, and some were NSA standard types.

b. Despite the vast availability of vocoders back then, the P-25 unit was developed as a unique device.

c. Despite the prominence of the problems in the news and technical journals, the history remains difficult to locate and obtain, as if it is well hidden from being exposed.

1. The difficulty with and “failure” of the P-25 Vocoder remains to be multi-fold, however the main issues are:

i. its inability to handle ambient noise being picked up by the transmitter microphone,

ii. The bit error rate required for proper operation requires significant higher radio signal strength as compared to analog (a software “gain” was added to attempt to compensate for this and demonstrate operation at an equivalent signal strength to that of analog FM)

iii. The generation of voice and sound artefacts when the error rate increases, these artefacts are not understandable and cause distortion of the words to the point of being unrecognizable, commonly called twiddly-whurps, wheezes, squeals, buzzes, toy-voice, etc.

2. The P-25 was pushed as being absent of the disruptive noise of analog FM radio signals.

i. However the real situation is that the analog noise which is not present in P-25 recreated voice, is replaced by the disruptive artefacts: twiddly-whurps, etc.

ii. The net result truly is no improvement over analog FM radio, but the addition of a detriment to radio communications.

iii. The detriment being the loss of an indication to the radio operator of the “channel” signal strength and hence the reliability / dependability of maintaining connection

iv. When the analog signal degrades, it gets noisy and the radio operators then detect impending disconnection,

v. the digital signal gets twiddly-whurps and suddenly becomes silent, without notice, without indication of impending loss. Too serious of a fault to be usd in Mission Critical Communications.

vi. Analog works better.

3. The repeated cry covered over by propaganda, promises, faux “laws” and “regulations”

a. “Digital radio did not work”

i. Had to send runners from command inside building to outside to make radio contact.

ii. Repeated problem for years. ,

4. Problem so serious that fireman’s union is acting boldly; drafting letter “calling for resignation of all who had anything to do with the purchase and deployment of the radios”

5. Issue is not unique to Wash DC Navy & Fire, it is nationwide.

6. Issue is not with spectrum, as the Interoperability channels were designated by FCC & DHS.

a. It is of important note here that the designated interoperability channels in the various frequency bands are all analog FM Radio channels, and NOT P­25. Seems that someone knows what the bottom line for interoperability and connection really is, and it is not digital P-25 modulation, it is analog FM.

7. It is an important step is to eliminate the P-25 modulation from use in mission critical situations. Next it is important to review the international radio-scape to see what works for them (it is universally accepted Tetra Radio) and next to include changes and additions based on FCC Rules & Regulations by the creation of a “safety of life” radio operator and radio system design license having commensurate duties, responsibilities and authorities. And next creating a mission critical radio system classification and standards specification in the FCC R&R.



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