[Elecraft] Hearing the effect of narrower roofing filter

[Dick Dievendorff]

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


-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Darwin, Keith
Sent: Tuesday, July 08, 2008 7:43 AM
To: elecraft at mailman.qth.net
Subject: RE: Re: [Elecraft] Hearing the effect of narrower roofing filter

Not sure, David, if your Q was to me or to Hank.  I can only answer for
me.

When I adjust the filter width knob, I'm most definitely hearing the
combined effect of the DSP bandwidth reduction and the change in roofing
filters.  But, since I can change DSP without changing the roofing
filter (by stepping from 1500 Hz down to 550 Hz) I can get a good feel
for how the DSP filter sounds.  Then, stepping to 500 Hz, I can see the
combined effect of one more DSP step plus the insertion of the 500 Hz
roofing filter.  The observed big change from 550 Hz to 500 Hz is
*mostly* due to the roofing filter.

- Keith N1AS -
- K3 711 -

----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of
d.cutter at ntlworld.com

Fine observations when you change the filter setting knob, but what
makes you think you are hearing the effect of the roofing filter and not
the dsp filter?  

David
G3UNA

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