[Elecraft] Hearing the effect of narrower roofing filter

Tue Jul 8 13:41:48 EDT 2008

I'm not completely sure what to do with this capability, other than perhaps
have the switchover occur at a bandwidth that more closely matches the
filter you actually have.  What I've done is tell the K3 that my 250 Hz
filter is really 300 Hz (it's really probably more like 370 Hz). 

I also have a 400 Hz filter. I didn't make a particularly wise choice of
filter bandwidths. To those who have pointed out the error of my ways, my
defense is that I chose the filters on first order day before the curves
were published on the web site.  I don't view this as a severe issue. Maybe
I should have ordered the 200 Hz 5-pole instead, but I got it into my head
that maybe the 8-pole filters were "better" in some way.  I didn't repeat
this mistake when I ordered filters for the subreceiver.

Dick, K6KR

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of David Cutter
Sent: Tuesday, July 08, 2008 10:18 AM
To: elecraft at mailman.qth.net
Subject: Re: Re: [Elecraft] Hearing the effect of narrower roofing filter

But if you leave the setting at its nominal, can you hear the difference as 
that bandwidth is selected?  I'm not sure I understand the advantage you are

gaining by bringing the crystal filter in later; I'll do if there's 
something to be gained, it sounds an interesting approach.

David
G3UNA

>A couple of related points, which may not be new news to anyone:
>
> You can set the K3's filter bandwidth configuration to cause the roofing
> filter to switch at points other than the bandwidth printed on the filter.
> Maybe you would like your (nominally) 500 Hz filter to switch in at 450 or
> 550 Hz.  My 8-pole 250 Hz filter is a bit broader than 250 Hz, and I've 
> set
> it to switch at 300 Hz.
>
> You can also turn off a filter (set its bandwidth to zero temporarily) to
> evaluate whether a change you're hearing is due to the roofing filter or 
> the
> change in bandwidth provided by the DSP.
>
> And you should attempt to adjust the filter gain compensation so that 
> there
> is no change in the volume of the note you're tuned to.  Rene, who guides
> the assembly of K3s built by Elecraft, told me that he uses a voltmeter on
> the speaker terminals when adjusting the gain compensation and can get
> usually get within a half decibel.
>
> I notice a definite qualitative change as the narrower filters switch in. 
> It
> sounds quieter, and it seems like the volume is being turned down. I think
> I'm responding to the reduced low and high frequency components that are
> supposed to be cut off.  The DSP-related changes seem more gradual.
>
> Dick, K6KR
>
> 
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