Dangerous Congressional Bill being

[ph...@ux1.cso.uiuc.edu]

From: ka...@ka9q.bellcore.com
> Paul,
>
> As counterintuitive as it may seem, narrower modulation methods do not
> necessarily result in more efficient use of spectrum -- at least when
> frequency reuse is considered.
>
> I recently compared medium bandwidth FM (as used in cellular radio) against
> SSB, using a per-transmitter metric of (bandwidth x geographical area) as
> the quantity to be minimized. I discovered that for equal performance (i.e.,
> standard telephone quality) you're actually better off with FM because its
> superior capture ratio allows you to place transmitters much closer. This
> more than compensates for the wider bandwidth occupied by each transmitter.
>
> Phil

From: pa...@Jessica.stanford.edu
>
> Hmm, well that result contradicts some of the empirical work that Bruce
> Lusignan did in ACSB, especially the recent stuff, with digital filters.
> In particular, they were able to operate ACSB channels interstitially with
> existing NBFM systems!

My understanding of compandoring, or at least one flavor of it, is that the
dynamic range of the audio is tightly compressed so that a logarithmic range
of say 50 db becomes a range of 10 over the air. The receiver changes each
db of incoming dynamic range into 5 db (for this example). A base reference
is needed, hence the pilot tone giving a fixed reference of signal strength
so that the compressed range can be restored to its original position.

The co-channel interfering signal might perhaps be 10 db lower. It will add
10% to the pilot level, dropping the uncompressed output in the receiver by...
(10% is pilot increase of 0.414db, signal ratio decrease of same, uncompressed
as 5*0.414db or...) 2.07db. The interfering signal, however will already be
10% lower, hence is 10 db weaker, and when uncompressed, is 50db weaker, and
this appears to be 47.93db lower.

By dealing with things in a logarithmic way, there can be an APPARENT capture
effect. Narrow band FM does not even have that good of an effect under many
of the conditions I frequently hear on 2 meters.

73 de ka9wgn

--Phil howard-- <ph...@ux1.cso.uiuc.edu>