Welcome to my Circuit Testing Help Page!
Like everything else in life there is very little certainty that can be found and Telephony is no exception so realistically you should only trust about 80% of circuit testing information found on this website. I have had very little formal training so this is just information that I have learned throughout my 21+ years of being a Maintenance, Provisioning and DSSC/911 Tester and it is intended only to be a help and is not endorsed by any telephone company as official training material.
Analog Special Circuits
Analog Circuits and associated Channel Banks are the icing on the cake, you can do without them by why would you? Most of them have been around for a long time and cost of them has been paid for a long time now and they are not leaving the inventory anytime soon because of their minimal cost to maintain!
Analog Circuits - What is their purpose?
The purpose of a Analog Circuit in telephony is to move analog signals for communicating. It comes in 2 varieties.
1- Analog Voice
2- Analog Data
How in the world does a Analog Signal such as words coming out of my mouth get onto a telephone circuit?
Codecs and Sampling. This discussion will be an overview and not getting into specific’s. The incoming analog words i speak into a telephone are sampled a telephone standard of 8000 times per second or 8kHz. Humans can hear in the range of 20Hz to 20kHz.
We are talking about analog signals why are you talking about sampling rates?
My house is probably a quarter of a mile to the next door neighbor and If I see him at his front door while standing on my front door and decide to “holler” at him, well my analog voice will only go so far and then die somewhere in the horse field. That is the nature of analog signals. The telephone companies learned this lesson early in their start up. They learned it is better to convert the analog to digital because digital is better to transmit at longer distances. Analog signals start as Analog and end as Analog but most are digital in the middle.
I have a circuit that is showing a Analog card in the D4 Channel bank. Is the D4 Analog or Digital?
The D4 is a digital device. It transports a DS1 (digital signal 1) across it. The CODEC (code/decode) works to change the Digital DS1 channel to Analog and it resides in the channel unit (FXO, FXS, ETO, etc).