[R-390] 16kHz filter and SWL/BC listening

[Sheldon Daitch]

I can only discuss IBB transmitters, not other SW broadcasters,
but our transmitters will all pass 5 kHz audio, unless there is
something wrong with them.

Our proof of performance requirement for MW and SW
transmitters is:

"Audio Frequency Response - The audio frequency response
of the transmitter shall be measured over the range of 100 Hz
and 5000Hz.  Within the range, the level of the demodulated
test tone shall not deviate more than +/- 1.0 dB with respect
to its level at 1 kHz and 85% negative modulation of the carrier."

In fact, the Orban audio processors will allow up to 20-dB boost
at 5 kHz, although we don't run that amount of high frequency
boost.

In the "old" days, when we had limited bandwidth audio circuits,
i.e. phone lines or microwave circuits, those circuits, too, had a
minimum of 5 kHz bandwidth.  Today, IBB uses satellite
systems for program distribution and almost all the circuits
have at least 15 kHz bandwidth.  It is overkill for HF and MW
broadcasting, or course.  In many cases we are also using FM
transmitters, and we need the extra audio bandwidth for
technically quality programming.

Your observation of simply more hiss is essentially correct.
In theory, there should be a slightly better audio response
in the 16 kHz position, as the 8 kHz filter should roll off
transmitted audio in the 4 to 5 kHz range, which the 16
kHz filter should pass.

I think if you look at the historical use of the R-390 family,
the 16 kHz filters were designed when the receiver was
used for 4 channel point to point communications networks,
which required the full 16 kHz.

73
Sheldon
WA4MZZ


Steve Byan wrote:

> On Aug 28, 2005, at 4:49 PM, Tim Shoppa wrote:
>
> > To my ear when listening to SW and BC broadcasts (voice, music,
> > whatever)
> > the 16kHz filter setting always sounds pretty much just like 8kHz just
> > with more hiss.
>
> > Is this a fundamental limitation of the AF chain, or is my hearing just
> > wacky, or is there some simple technical fix?
>
> On SW and BC broadcasts, the transmitted signal is bandwidth-limited,
> so there isn't much more bandwidth to let through with the 16 KC
> filter, especially if  the 8 KC filter is tuned off to the side a bit.
> On SW broadcast, you're lucky to get 5 KC of transmitted bandwidth.
>
> Regards,
> -Steve
> --------
> Steve Byan <stevebyan at mac.com>
> Littleton, MA
>
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