tony sayer wrote:

--------------------
Brian Gaff


I've often wondered why they don't add low power transmitters to telephone
cell masts.



It would cost a lot of money to do and not work that well on FM,


** Breaks the broadcasting principle that with AM and FM you cannot allow multiple transmitters to operate in the same service area on the same frequency.

While it may supply some listeners good signal for the first time, others who previously had a good signal would lose it due to severe mutual interference.



..... Phil


..... Phil

In article , Phil
Allison scribeth thus
tony sayer wrote:

--------------------
Brian Gaff


I've often wondered why they don't add low power transmitters to telephone
cell masts.



It would cost a lot of money to do and not work that well on FM,


** Breaks the broadcasting principle that with AM and FM you cannot allow
multiple transmitters to operate in the same service area on the same
frequency.

While it may supply some listeners good signal for the first time, others who
previously had a good signal would lose it due to severe mutual interference.



Yes but it has been done and can be done but its only usually done for
filler stations on the edge of the service area.

To do that normally you use what's called a "translator" thats where
there is a different local TX frequency to the incoming one you want to
use to feed the relay transmitter.

To make it work you have to take the studio feed and set delays on each
TX which have the be line fed to each site and matched within a very
tight tolerance in the order of microseconds.

The FM transmitter carrier drives are usually referenced to a Rubidium
frequency standard or to GPS so their set exactly the to same frequency

It does work and quite well its been done in America a bit and a French
company used to make the gear for the European market. There is a
traffic service in Franc that uses 107.7 IIRC they also IIRC used this
gear. It wasn't cheap though


However you can do this much easier with a DAB repeater, use the best
aerial isolation you can, we look after one here in Cambridge at the
Catholic church in Hill road around -64 dBm in from the parent
transmitter and some 30 odd watts out the other side albeit a 22 foot
square belfry and Cardioid aerial in use, some 20 dB back to front
ratio.

We did have it up to around 50 odd watts before it went unstable but
good aerial isolation and crafty signal processing make it work .

Its often used inside large metal shed warehouses to boost the DAB
signals to make DAB portable sets work.

Heres the one we use.


http://www.txdigicast.com/dabrpt.htm




.... Phil


.... Phil

--
Tony Sayer