Roofing Filters

[Walter V. Gilles]

Greetings,
 
One more question on roofing filters, specifically about using identical BW filters in adjacent slots.  Lots of roofing filter blurbs on the reflector, but I could not find anything specific to this question.
 
In reading the owners manual, it states that roofing filters are to be placed in decreasing BW order, starting from slot #1, with the option of bypassing slots along the way, with the filter configuration setup taking care of letting the firmware know who is where and for what purpose.  The manual also indicates that the firmware relates the DSP BW to the filter setup, and routes the IF to (only) one of the five roofing filter slots, depending on the aforementioned filter configuration/setup.
 
So here's my question.  Is it possible, albeit perhaps not terribly beneficial at first glance, to put another 0.40 roofer in the next downstream slot from my current 0.40 roofer?  Would the F/W even accept that setup?  If it would allow that configuration, would the F/W just select the first 0.40 slot, or would the F/W route the IF through both 0.40 roofers?  So the real question is whether there is a way to configure two identical 8 pole roofers (i.e. 0.40 kHz) such that the F/W treats that as 16 poles? 
 
I'm guessing the answer is most likely a definite no, per hardware and firmware design, but the remote possibility seemed intriguing nonetheless. I guess this is what happens sometimes when there aren't enough sunspots to keep one productively engaged in this hobby.  But hey, if you don't ask, you don't learn. ;-)   Thanks.  73
 
Walter   WB2IDK
 


     
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[Bill W4ZV]

Walter V. Gilles wrote

Is it possible, albeit perhaps not terribly beneficial at first glance, to put another 0.40 roofer in the next downstream slot from my current 0.40 roofer?  Would the F/W even accept that setup?  If it would allow that configuration, would the F/W just select the first 0.40 slot, or would the F/W route the IF through both 0.40 roofers?  So the real question is whether there is a way to configure two identical 8 pole roofers (i.e. 0.40 kHz) such that the F/W treats that as 16 poles? 
 
I'm guessing the answer is most likely a definite no

The answer is a definite NO.  Only one filter at a time can be selected.

73,  Bill

[Dick Dievendorff]

I'm not the "definitive source" for the answer to this question, but I'll
hazard an educated guess.

The firmware probably wouldn't mind if you put two identical width filters
in adjacent slots.

The firmware would pick one or the other as you dialed the bandwidth to the
appropriate values. I don't know which one it would choose.

You could "lie" to the configuration tool and say one of the filters was 450
Hz and the other 400 Hz and be able to use one and then the other at those
bandwidth settings.

I don't think you'll find a way to run the output of one filter into the
other. For any given bandwidth the firmware chooses one of up to five
filters; there's no provision for routing the output of one filter into the
input of another, and making them the same width wouldn't change that.

I'll guess that 5 poles is often enough, 8 poles is almost always plenty and
the benefit gained by going from 8 to 16 poles wouldn't often be very
important.

Dick, K6KR


-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Walter V. Gilles
Sent: Tuesday, June 16, 2009 12:58 PM
To: [hidden email]
Subject: [Elecraft] [K3] Roofing Filters

Greetings,
 
One more question on roofing filters, specifically about using identical BW
filters in adjacent slots.  Lots of roofing filter blurbs on the reflector,
but I could not find anything specific to this question.
 
In reading the owners manual, it states that roofing filters are to be
placed in decreasing BW order, starting from slot #1, with the option of
bypassing slots along the way, with the filter configuration setup taking
care of letting the firmware know who is where and for what purpose.  The
manual also indicates that the firmware relates the DSP BW to the filter
setup, and routes the IF to (only) one of the five roofing filter slots,
depending on the aforementioned filter configuration/setup.
 
So here's my question.  Is it possible, albeit perhaps not terribly
beneficial at first glance, to put another 0.40 roofer in the next
downstream slot from my current 0.40 roofer?  Would the F/W even accept that
setup?  If it would allow that configuration, would the F/W just select the
first 0.40 slot, or would the F/W route the IF through both 0.40 roofers? 
So the real question is whether there is a way to configure two identical 8
pole roofers (i.e. 0.40 kHz) such that the F/W treats that as 16 poles? 
 
I'm guessing the answer is most likely a definite no, per hardware and
firmware design, but the remote possibility seemed intriguing nonetheless. I
guess this is what happens sometimes when there aren't enough sunspots to
keep one productively engaged in this hobby.  But hey, if you don't ask, you
don't learn. ;-)   Thanks.  73
 
Walter   WB2IDK
 


     
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[Bill W4ZV]

Dick Dievendorff wrote

I'll guess that 5 poles is often enough, 8 poles is almost always plenty and
the benefit gained by going from 8 to 16 poles wouldn't often be very
important.

Don't forget that the roofing filter is cascaded with the DSP filter, which is typically equivalent to an 8-pole crystal filter at a setting of 400 Hz, so the effective selectivity is already ~16 poles.

73,  Bill