[Elecraft] Price Comparison and Comment

[Geoffrey Mackenzie-Kennedy]

Keep up the good work Bill!!  May I second you request for comprehensive IMD 
/ BDR  test results. Crystal filters, particularly ladders, do have a habit 
of coming back to bite unless their linearity, or lack of, is taken into 
account while setting Gain Distribution et al during the design activity.

I sometimes wonder whether the use of wide SSB filters e.g  2.7 kHz in our 
ham community is due to poor narrower filter design,  and the reulting group 
delay characteristic. This in turn can result in a SSB voice signal having a 
"raspy" sound. In my opinion based on observation and use, 2.1 kHz  is 
enough for very good soundimg audio IF things are set up properly (carrier 
position, modulator AF drive, ALC, mic, etc, etc),  leaving more spectrum 
for others to use.

73,
Geoff
GM4ESD


On Friday, May 04, 2007 at 7:59 PM, Bill Tippett wrote:
>
> SSB - 2.7 kHz unless you want ESSB (not sure how high
> that goes these days but IMHO we should be trying to
> minimize communications bandwidths rather than playing
> broadcast disc jockey (my personal opinion!).  Those
> folks should go to 29 MHz FM if they want to do that.
.
<snip>
>         A roofing filter's purpose is simply to minimize
> spurious artifacts from being created *inside* the RX
> by external signals.  It does NOT create the ultimate
> selectivity (which is determined by the DSP filter at
> the 2nd IF).  Please read the last sentence again!
> Here's a simple summary:

<snip>

> ...roofing filter prevents very strong signals from
> creating spurious (i.e. *NOT REAL*) signals which
> will then appear inside the DSP.

<snip>

>         The number of poles (i.e. shape factor of the
> filter) can affect IMD/BDR issues inside the RX.  For
> this reason hopefully Elecraft will provide actual
> IMD/BDR measurements with each option to help answer
> the following questions:
>
> 1.  Is the optional 8-pole 2.8 kHz better than the
> stock 5-pole 2.7 kHz (by "better" I mean resulting
> in better IMD/BDR performance which is the primary
> purpose of a roofing filter).

<snip>

>         The variable BW filters are interesting but
> I would not consider them until we have some actual
> results for IMD/BDR.  They are NOT providing ultimate
> selectivity as they do in the case of the K2, which
> seems to be confusing many folks.
>
>                                 73,  Bill  W4ZV