[Elecraft] Re: K3 as a SW receiver

[Joe Subich, W4TV]

> Also note that our 6-kHz 8-pole filter is targeted specifically 
> at AM operation, and will provide better adjacent-channel QRM 
> rejection than the FM filter, if needed. 

"Targeted specifically at AM operation" is correct only in 
the context of amateur "communications."  The 6 KHz filter 
bandwidth limits the audio bandwidth to 3 KHz before the 
skirt selectivity starts to create significant rolloff.  If 
one is looking for SW or MW broadcast reception the 13 KHz 
FM filter would provide significantly better fidelity - 
particularly if the 4 KHz DSP audio frequency limit was 
increased to 5.5 or 6.0 KHz (at least for AM).  

> A 6-kHz filter is also required for AM transmit (enforced in 
> firmware). This ensures excellent 2nd-I.F. image rejection. 

This could certainly be relaxed to allow use of the 13 KHz 
filter for AM transmit.  Even if the 13 KHz filter had only 
a 2:1 shape factor, with the carrier centered in the filter 
response at the image frequency (30 KHz away) should be very 
close to the filter's ultimate rejection ... shifting the 
filter 2 or 2.5 KHz away from the image in transmit would 
provide even more insurance against unwanted image response.  

73, 

   ... Joe, W4TV 
 


> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of wayne burdick
> Sent: Wednesday, December 31, 2008 4:17 AM
> To: KM5Q
> Cc: elecraft at mailman.qth.net
> Subject: [Elecraft] Re: K3 as a SW receiver
> 
> 
> KM5Q wrote:
> 
> > For AM SW listening be sure to get the "FM" filter (13 
> kHz). It gives
> > you the width you need for the audio bandwidth you expect. 
> The normal 
> > SSB filter (I have the 2.8) is too restricting for AM.
> >
> > However, I find that switching mode from AM to SSB reduces severe
> > fading and distortion, much like AM synchronous detection 
> does (fills 
> > in the missing carrier). It's a good technique, at least 
> until synch 
> > detection is implemented in the firmware.
> 
> Windy,
> 
> Also note that our 6-kHz 8-pole filter is targeted specifically at AM 
> operation, and will provide better adjacent-channel QRM 
> rejection than 
> the FM filter, if needed. A 6-kHz filter is also required for AM 
> transmit (enforced in firmware). This ensures excellent 
> 2nd-I.F. image 
> rejection.
> 
> 73,
> Wayne
> N6KR
> 
> ---
> 
> http://www.elecraft.com
> 
> _______________________________________________
> Elecraft mailing list
> Post to: Elecraft at mailman.qth.net
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft    
> 
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com