[Elecraft] 8 pole vs 5 pole..I knew this would happen

[Brett gazdzinski]

I  thought some rigs also passed the transmit signal
out past the filter, and to save money just fit say
an FM sized filter there.
FM and AM are 'features' also I guess...

The K3 is going to relay switch filters in for
FM, AM, SSB, and CW.

Since they are working at a lower frequency, they will really
work well, and that is the main trick going on in the K3.

Then you get all those DSP extra goodies...

Brett
N2DTS


> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Larry Phipps
> Sent: Thursday, May 03, 2007 9:12 PM
> To: Jack Smith
> Cc: Elecraft Discussion List
> Subject: Re: [Elecraft] 8 pole vs 5 pole..I knew this would happen
> 
> I think the term "roofing filter" is misleading. A narrow 
> filter at the 
> first IF protects a receiver even better than a "roofing filter", so 
> there is nothing inherently distortion reducing in using a 
> wider filter 
> at the first IF and then a narrower one later. The ideal 
> situation for 
> IMD would be a pair of matched narrow filters at both IFs. The real 
> reason for a "roofing filter" it seems to me, is to allow passband or 
> slope tuning. This compromises IMD and AGC performance for 
> the sake of a 
> feature... which may or may not be valuable to the user.
> 
> Therefore, the "roofing filter" should be termed the "passband tuning 
> enabling filter", or "PBTE" filter ;-)
> 
> Thankfully, I think Elecraft has done a brilliant job of 
> giving us the 
> options we want without compromises. By tying the DSP 
> bandwidths and PBT 
> functions to the "roofing filters", we have the ability to have the 
> combination of 1st and 2nd IF BW we want,,, and with the variable 
> "roofing filters", I think we will be able to almost set the relative 
> BWs between the two... allowing a window for PBT or not as we choose. 
> This is an exciting development, and will be copied by many companies 
> over the next year. Kudos to the design team on this.
> 
> 73,
> Larry N8LP
> 
>