[Elecraft] K3 in AM mode

[Joe Subich, W4TV]

 > A while ago, I bought a 6 KHz AM filter.  I was a little confused
 > when I could only open the filter width up to 5.0 KHz in AM mode.

A little study of the Owner's Manual will reveal that the displayed
bandwidth is the "audio" bandwidth (High - Low).  In AM, RF bandwidth
is *twice* the audio bandwidth because AM is a DOUBLE SIDEBAND mode.
While one can, in fact "open up" the DSP to 5 KHz even with the 6 KHz
IF filter installed, the received bandwidth will be limited to about
3 KHz (carrier +/- 3 KHz) by the IF filter unless one selects Sync
AM mode which used only one sideband (again, study the Owners Manual).

> So, I just bought the FM filter and installed it. To my dismay, I
> still can only widen the bandwidth to 5.0 KHz in AM mode. I have AM
> mode checked in the mode list for the FM filter.

That is correct, the DSP is limited to 5 KHz (and the audio chain
contains a 4.2 KHz "brickwall" lowpass filter in any case).  The FM
filter still provides 13 KHz (carrier +/- 6.5 KHZ) selectivity in
the IF stages which allows the full 5 KHz maximum detection bandwidth
in the DSP (demodulator). However, again AM is a *double sideband*
mode - the detected audio bandwidth will always be no more than
*one half* of the IF/RF bandwidth.

 > The 6.0 KHz filter is still configured for TX on AM.

Correct, transmit *audio* bandwidth is limited to 3 KHz and that
requires an IF filter *at least* 6 KHz wide.

 > Also, when increase the audio in the AM mode to more than half,

What do you mean by "increase audio ... to more than half"?  Half
of what?  What audio - transmit or receive?

73,

    ... Joe, W4TV


On 9/1/2013 11:48 PM, Michael Marx wrote:
> Hi to the group!
>
> I have been slowly loading my K3 up.  I concentrated on CW at first,
> but now I am adding other stuff.
>
> A while ago, I bought a 6 KHz AM filter.  I was a little confused
> when I could only open the filter width up to 5.0 KHz in AM mode.  I
> called the factory and they told me that, yes, you could only open it
> up to 5 KHz with the 6 KHz AM filter.  They told me that if I bought
> the 13 KHz FM filter, then I could open the bandwidth all the way to
> 13 KHz.  So, I just bought the FM filter and installed it.  To my
> dismay, I still can only widen the bandwidth to 5.0 KHz in AM mode.
> I have AM mode checked in the mode list for the FM filter.  The 6.0
> KHz filter is still configured for TX on AM.
>
> Also, when increase the audio in the AM mode to more than half, the
> audio becomes distorted and just a little more advanced from that,
> the audio shuts off altogether.
>
> Any ideas are appreciated.
>
> 73 Mike WB0SND
>
>
> Michael Marx sndtubes at vacuumtubes.com
>
>
>
>
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