[Elecraft] [K3] Variable filters? And what filter is best for AM broadcast reception?

[Don Wilhelm]

  Thomas,

As I recall, the variable filter concept has been dropped.  Even if it 
were to be available, it would be only a narrow filter, not a wide one.

The 13 kHz filter can be used for FM transmit and receive, but only for 
AM receive - you must have the 6 kHz filter for AM transmit.  The folks 
at Elecraft are reluctant to allow the 13 kHz filter to be used for AM 
transmit because of the potential for spurs.  A couple of users have 
reported here on the reflector that they have "lied" to the K3 about the 
filter width and tried it, but I am not certain how rigorously that 
setup was tested.

So the bottom line is that you need the real 6 kHz filter to transmit AM 
or ESSB.  The 13 kHz filter will work nicely for AM receive, although 
synchronous AM reception can be used with just as wide an audio 
passband, so you might want to investigate that approach and get the 6 
kHz filter if you do not anticipate using FM.

73,
Don W3FPR

On 5/13/2011 6:06 AM, Thomas Horsten wrote:
> Hi,
>
> I read somewhere, some time ago, that there was a plan to introduce variable
> filters to the K3.
>
> Do any such filters exist, either as 3rd party mods or official by
> Elecraft/Inrad? And is there any firmware support for this?
>
> I already have 2*2.7kHz and 2*500Hz in my K3, plus a 2.1kHz in the main
> receiver only, but I would like a wider filter for AM-broadcast SWL and AM
> TX/RX.
>
> Also, I would like to listen to shortwave broadcast stations so I was
> planning to get the KBPF3 and additional filters. As far as I can tell the
> best filter for this would be KFL3B-FM, to capture the wide signals of the
> broadcast stations in the highest possible quality, is that correct or is
> the KFL3A-6K more useful? And can I transmit 6kHz AM with the 13kHz FM
> filter or must I have the 6kHz one as well?
>
> 73, Thomas M0TRN
>