Re: [Repeater-Builder] Audio Reproduction

9 Apr 2004 04:34:05 -0000

Hi Brad,
 
As audio is discussed over and over often I see there
is less and less content in the answers.
 
Uh-oh. Our stock arguments must be getting boring...  :-)
 

I have a question . I run several repeaters all
employing pre-de-emph as per standard to a star
network.

What is the major decision between going "flat " or
shaped audio? I would take it that running up of the
repeater and links is a breeze as it is what goes in
must come out .
 
This was recently posted:
 
*****
RF Links: The Land Mobile radio equipment was never designed to be used for RF point to point links, but as there are people that want to get by with as little expense as possible most anything will be put to use.
*****
 
The frequency response of all narrowband FM equipment has to be limited so that users stay within the bandwidth allowed. Land Mobile radio equipment uses simple filters and thus must start rolling off the audio response at ~3 kHz.
 
When you build repeaters and links with unmodified Land Mobile equipment, these rolloffs cause additional loss of high-end audio to the already limited response of the user's radio.
 
Some repeater owners run audio from the discriminator to the modulator (with a new limiter), bypassing deemphasis and preemphasis. I like the idea of leaving most everything alone except to widen the transmitter's response by replacing its limiter and filter. If the filter response stayed flat to a higher frequency, say 4.5 kHz, then stopped abruptly, the bandwidth is maintained but the system is more transparent. Some folks on the list are working on that.
 
73,
Bob


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