NOTICE OF UNLICENSED OPERATION

[Lscott]

Don’t forget WiFi, Bluetooth and satellite radio/TV.

[tcp2525]

3 hours ago, Lscott said:

You can quit using your cellphone. It’s based on wireless two-way radio and digital voice technologies.

Oh trust me, I was pissing and moaning when they transitioned to digital. The sound quality of the analog was far superior to digital. Not a problem now, we're all programmed to accept crappy sounding phone calls. What choice do we really have?

[Lscott]

16 hours ago, tcp2525 said:

What choice do we really have?

Two cans connected by a string still works.

[Lscott]

Unfortunately just about everyone uses some form of a digital voice encoder. The leading favorite is the AMBE, previously IMBE, by DVSI. Their proprietary codec is based on early work done at MIT.

The link below is a short description from DVSI, which doesn't really revel much.

https://www.dvsinc.com/papers/iambe.html

A much more in-depth description can be found here from a report published by MIT for the US Air Force in 1987.

https://apps.dtic.mil/sti/tr/pdf/ADA181146.pdf

My understanding is when the FCC forced the commercial radio services to move to narrow band FM, which was done by reducing the FM deviation, also resulted in a reduction in the signal to noise ratio I believe. At a 12.5KHz bandwidth it's not severe, however at narrower bandwidths it is. The FCC stated at one point they intend to move to a true 6.25 KHz per voice channel width. That's why the major radio manufactures introduced various digital voice technologies. For the moment the FCC seems to be OK with various digital voice technologies that can achieve an "equivalent" voice channel width of 6.25 KHz, example DMR 2 slots in a 12.5 KHz channel. However at some point they may force a move to a true 6.25 KHz channel width, but no official date has been given.

This is stated in chapter 1 of the FCC's narrow banding guide.

https://transition.fcc.gov/pshs/docs/clearinghouse/guidelines/Narrowbanding_Booklet.pdf

In the mean time there are ways to license a true 6.25 KHz channel per the FCC. See attached paper.

 

 

Splitting 6.25KHz Channels.pdf

[tcp2525]

2 hours ago, Lscott said:

Two cans connected by a string still works.

And the audio quality is excellent. 

[tcp2525]

1 hour ago, Lscott said:

Unfortunately just about everyone uses some form of a digital voice encoder. The leading favorite is the AMBE, previously IMBE, by DVSI. Their proprietary codec is based on early work done at MIT.

The link below is a short description from DVSI, which doesn't really revel much.

https://www.dvsinc.com/papers/iambe.html

A much more in-depth description can be found here from a report published by MIT for the US Air Force in 1987.

https://apps.dtic.mil/sti/tr/pdf/ADA181146.pdf

My understanding is when the FCC forced the commercial radio services to move to narrow band FM, which was done by reducing the FM deviation, also resulted in a reduction in the signal to noise ratio I believe. At a 12.5KHz bandwidth it's not severe, however at narrower bandwidths it is. The FCC stated at one point they intend to move to a true 6.25 KHz per voice channel width. That's why the major radio manufactures introduced various digital voice technologies. For the moment the FCC seems to be OK with various digital voice technologies that can achieve an "equivalent" voice channel width of 6.25 KHz, example DMR 2 slots in a 12.5 KHz channel. However at some point they may force a move to a true 6.25 KHz channel width, but no official date has been given.

This is stated in chapter 1 of the FCC's narrow banding guide.

https://transition.fcc.gov/pshs/docs/clearinghouse/guidelines/Narrowbanding_Booklet.pdf

In the mean time there are ways to license a true 6.25 KHz channel per the FCC. See attached paper.

 

 

Splitting 6.25KHz Channels.pdf 103.57 kB · 0 downloads

Of course it makes sense to do it this way. After all it is just voice communications, not audiophile quality needed for land mobile service. I just hate the compression it causes. A lossless CODEC would help sound quality at the expense of bandwidth.