Before NRSC there was no limit on AM BROADCAST frequency response ... I have
proofed many AM stations that were flat response + - 2 DB from 50 hz to at
least 12 KHZ. Before NRSC there were emission limits specified for different
amounts at given frequencies off of carrier frequency. What WAS specified
before NRSC was that AM transmission systems had to have a flat frequency
response between 100 HZ and 7.5 KHZ.
Terry W6RU
----- Original Message -----
From: <w8au@sssnet.com>
To: <tentec@contesting.com>
Sent: Friday, April 18, 2003 5:20 PM
Subject: Re: [TenTec] Enhanced SSB
> At 03:16 PM 04/18/2003 -0400, Paul Christensen, Esq. wrote:
> > > damping to let the microphone hear only the "golden tones" of the ham
> > > transmitting. AM broadcast doesn't even allow going to 15 KHz.
> >
> >Prior to the implementation of NRSC mask in the early '90s, AM Broadcast
> >stations had no upper limit.
>
> Well, they did have an upper freq limit spec as I recall. It was 7.5
> kHz. When we ordered BC quality loaded lines
> from telco years ago it was 7.5 kHz for AM and 15 kHz for FM. I can see
> the correlation now with the later
> NRSC roll-off filters. Before NRSC the 7.5 kHz spec was probably enough
> protection for adjacent stations.
>
> >The NRSC mask now effectively
> >limits the audio passband to approximately 9.5 kHz....and the service
> >still sounds poor despite attempts by broadcast stations and
> >receiver manufacturers to improve the quality.
>
> AM quality today is really a lot better, with tailored processing and PDM
> modulation. (up to +125%)
> If the listener has a good quality RX it's not bad.....
>
> And..... for "talk radio," including sibilant sounds, 7.5 kHz (or 9.5)
> is more than enough.
>
> (I'm sure the majority are tired of this subject now.... I'm quitting
> before the flames arise!) :-)
>
> Perry w8au
>
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