[Elecraft] [K3] FM and AM Bandwidth

[Jack Smith]

No, Carson's rule is occupied bandwidth = 2*(deviation + maximum 
modulating frequency)

For 5 KHz deviation and 3 KHz highest modulating frequency, bandwidth is 
16 KHz.

For 4.5 KHz and 3 KHz, it's 15 KHz, not 13.

Jack K8ZOA


Lyle Johnson wrote:
>> Typical FM bandwidth is 5Khz, so the DSP really needs to be changed as 
>> in its current state the K3 is chopping off 1Khz of received signal in 
>> FM, or 20% of the bandwidth.
>>     
>
> There is more than one FM standard in use in Amateur radio around the 
> globe.  In some parts of the U.S., 2 meter channels are on 20 kHz 
> spacing, some are on 15 kHz spacing.  In some parts of the world, 
> channels are 12.5 kHz apart, or moving towards 12.5 kHz spacing.
>
> The rule of thumb for FM signals is that the bandwidth is (2 * 
> deviation) + Fmod where Fmod is the highest audio frequency.  This is an 
> oversimplification, but serves to illustrate the idea.
>
> In the K3 we have a 13 kHz wide IF filter.  By limiting deviation to 4.5 
> kHz and Fmod to 3 kHz, we occupy about 12 kHz.
>
> If we allowed 5 kHz audio and 5 kHz deviation, we'd occupy 15 kHz.  Such 
> operation leaves no room for frequency error or adjacent channel 
> rejection in a 15 kHz channel region.
>
> By limiting the audio response to about 3 kHz, we ensure that we are 
> compatible with existing channels and will be compatible with future 
> narrower channels.
>
> In the case of AM, we will be increasing the upper audio frequency response.
>
> 73,
>
> Lyle KK7P
>
>
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