[SOLVED] Negative Power Supply in Radio links

[hamidreza_h]

Hi every one
Can some body tell me , why Negative voltage (nominaly -48 V DC) is used as power supply in Radio links?
Thanks

 

[D.A.(Tony)Stewart]

Telco's use -48V battery banks.. maybe that's why you see them

 

[chuckey]

Its a hangover from old phone exchange practice. The reason that the + is earthed is to reduce the electrolytic corrosion on buried lines.
Frank

 

[hamidreza_h]

Hi chuckey
Isn't it related to Power Amplifier Protection at all ? do you mean that the only reason for negative powering is reducing the electrolytic corrosion on buried lines ?

 

[andre_luis]

it is because of the negative voltage (positive grounded) give fewer problems on the battery terminals. (the chemical reaction that appears on the battery terminals of vehicles). As this bus is distributed over long distances, this would increase the cost of maintenance.

 

[chuckey]

" Isn't it related to Power Amplifier Protection at all ? , pre dates electronics by at 50 years !
Frank

 

[Audioguru]

Vacuum tubes used a positive supply. The first transistors were germanium PNP ones that used a negative supply.