[Elecraft] FM Modulation

[Sverre Holm]

> I wonder why K2 and XV series have only CW and SSB modulation 
> but not FM? Maybe, the answer of this question is very simple 
> but any point of view would be appreciated.
> 

If the K2 were to have FM it would need a wider filter after the
post-mixer amplifier. This filter which is either a variable CW filter
0.1-1.5 kHz or an SSB filter 1.9-2.5 kHz, also determines the large
signal properties of the rig along with the phase noise of the VCO and
the mixer itself. This filter which is called the roofing filter, should
shut out as much as possible of the undesired signals. 

In most other rigs, the roofing filter is much wider to accomodate the
widest modulation of the rig (often FM), and consequently these rigs
need to filter later, with DSP's etc. But by then the damage has already
been done, and the large signal properties suffer. 

The choice is either lots of modes and modulations or good large signal
properties - at least if the price is to be in the ham market. The K2
designers have chosen to focus on the large signal properties.

--
73, 
Sverre

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Sverre Holm, LA3ZA
www.qsl.net/la3za