On Sat, 14 Feb 2015, bilou wrote:


"Michael Black" wrote in message
news:alpine.LNX.2.02.1502132039210.10100@darkstar. example.org...
On Fri, 13 Feb 2015, gareth wrote:

Do I remember correctly that there is a way of generating NBFM by
taking an SSB signal and merging it linearly with the original carrier
shifted in phase by 90 degrees (PI/2 radians)?

Actually, it takes a DSBsc signal, and reinserts the carrier with the
proper phase shift.

I forget the specifics, but yes, it can be done along those lines. That's
why some of the early phasing rigs like the Central Electronics rigs
included an FM position. It was too cheap to not include.

But I don't think you get much deviation. Fine for the HF bands, but not
for converting up to the VHF and UHF bands.

This method was actually Armstrong's.


Michael

Hi
If you add a constant amplitude signal (carrier)
with a variable one (DSB)
There is no way that the result will be constant amplitude.
As NBFM should be.
Some clipping is required
it can be done on the receive side
But the transmitter must be linear to avoid broadening of the spectrum

Since it was Armstrong's method, and he was interested in wide deviation,
the amplitude would have been removed by the multipliers to get it up to
the desired signal frequency.

Michael