[Elecraft] K3 Filter Configurations and Explanations

Tue Apr 1 08:15:52 EST 2008

I think Dick has put together an excellent summary regarding the available 
filters.  I sure don't see much to contradict based on my experience.

I would mention one thing, however, and i'm curious if others are 
"experiencing" the same anomoly.  I opted for both the 400 hz and the 200 hz 
filters (in addition to the 2.7 khz and 6 khz filters).  I am quite happy 
with the 400 hz filter.  Perhaps the 500 hz would have been sufficient, but 
I do like the 400 hz just fine.  My question is about the narrower 
filters--the 200 hz and the 250 hz.  I was almost certain I would use the 
narrow filter fairly often.  With other rigs I frequently found myself 
trying to 'tighten" things down to eliminate QRM.  However, I find myself 
rarely needing to go down that far on the K3.  I probably haven't really 
given it the "acid test", like Field Day, but it does surprise me that I 
tend to not even need something narrower.  I can only attribute that to the 
fact that the roofing filter system on the K3 is superior--that it does such 
a good job compared to other receivers I don't have to fight QRM as much.

I'm not into the digital modes yet on any kind of serious basis, so maybe 
that will turn out to be where the narrower filter proves to be most useful.

I would also be inclined to endorse Dick's suggestion of a 1 khz filter for 
casual CW use.  I don't have one though, so I can't say for sure.  But I 
strongly suspect it would be more pleasant to use.  I like not having to go 
too narrow, but QRM usually forced me to do so.  But since these are roofing 
filters, and not just crystal filters we usually rely on, I think QRM will 
still be minimized.  I am thinking seriously of ordering a 1 khz filter when 
I get my 2nd receiver.  If it works like I think it might, I may do some 
reassessment of my filter complement in the 1st receiver.  I'd be interested 
in hearing how others with the 1 khz filter like using it.

Dave W7AQK

----- Original Message ----- 
From: "Dick Dievendorff" <dieven at comcast.net>
To: "'Jim Miller'" <JimMiller at STL-OnLine.Net>; "'Elecraft Reflector'" 
<elecraft at mailman.qth.net>
Sent: Tuesday, April 01, 2008 12:17 AM
Subject: RE: [Elecraft] K3 Filter Configurations and Explanations

> The most comprehensive writeup I've seen is here:
> http://www.elecraft.com/K3/Roofing_Filters.htm
>
> I'd agree that you probably don't want to order 200, 250, 400 and 500.
> However two of these four makes sense for some buyers, including me.
>
> If you configure the radio correctly, roofing filters are selected
> automatically as you turn the "width" knob.  You may also directly select 
> a
> roofing filter.  I just twist the width knob to adjust the DSP bandwidth 
> and
> the appropriate roofing filter is selected for me.
>
> One "reasonable" starting configuration is just the stock 2.7 KHz filter.
> If you want to transmit AM, you'll need the 6.0 KHz AM filter.  If FM is
> important to you, you'll need the FM filter.  I'm not currently interested
> in transmitting in either of these modes, so I skipped those two filters 
> and
> I can receive AM with adequate (for me) fidelity by using my 2.8 KHz 
> filter
> and listening to one sideband.  Discerning AM buffs might well have a
> different definition of "adequate fidelity".
>
> If you're interested in CW or "data" modes (RTTY, PSK, etc), then you'll
> perhaps want to invest in one or more narrower filters, perhaps one or two
> of 200, 250, 400, 500 Hz.  If it's only one narrower filter, I'd suggest
> either the 400 or 500 Hz filter. I think of the 200 and 250 as 
> alternatives
> and 400 and 500 as alternatives.  I wouldn't think you'd want both 200 and
> 250 nor would you probably want both 400 and 500.
>
> I personally don't think the difference between the 2.7 and 2.8 Hz filters
> matters much, but I did choose all 8-pole filters. As a result I have
> slightly wider SSB transmit bandwidth and sharper skirts on receive with 
> the
> 2.8 KHz 8-pole filter.
>
> I like the 1.0 KHz filter as a "normal" CW bandwidth in contest 
> situations.
> It's not so tight that I can't hear off-frequency callers.
>
> The 1.8 KHz filter is a wonderful filter for phone contests and other
> shoulder-to-shoulder situations on phone. Others prefer 2.1 KHz for their
> narrowest SSB roofing filter.  With the 1.8 I find that the off-frequency
> crud often disappears, and the signal I'm isolating is comprehensible, but
> "communications" fidelity rather than natural sounding.
>
> I have to defer to the RTTY and PSK experts, but I think a 400 or 500 Hz
> filter would be my 2nd filter (after the 2.7 or 2.8 decision).
>
> My experience before the Elecraft K3 was with a series of up-converting 
> ICOM
> rigs including the 7800, whose narrowest roofing filter (after the roofing
> filter upgrade) is 3 KHz.
>
> I chose 8-pole filters at 2.8, 1.8, 1.0, 400, and 250. I probably have 
> more
> than I need for almost all situations.  Most of my QSOs don't tax the
> capability of any current-generation radio, but when the situation is very
> competitive I don't want to be in mid-contest or mid-pileup and at that 
> time
> wish I'd spent the relatively small amount (compared to all the other
> expenses in building a station) that these filters cost.
>
> You don't have to decide all this at the time you receive the radio.  You
> can add roofing filters easily at a later date.
>
> You just have to remove a handful of screws (top cover and half the bottom
> cover), and the filter plugs in and is held in place by one lock washer 
> and
> nut.  You might need to rearrange your existing filters when you add a new
> one so that they're in a natural sequence.
>
> Filter configuration takes a few minutes after you get the hang of it, and
> it'll be even quicker with the next revision of the K3 Utility.
>
> If you decide to add the 2nd receiver option, you'll need filter(s) for 
> that
> receiver as well.  You might make the same decisions again or maybe not.
> I'm going to make different choices for my 2nd receiver.
>
> Sorry it's not a crisp answer.  It's like a lot of topics, the answer is
> always "it depends"...
>
> 73 de Dick, K6KR
>
>
>
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jim Miller
> Sent: Monday, March 31, 2008 8:59 PM
> To: Elecraft Reflector
> Subject: [Elecraft] K3 Filter Configurations and Explanations
>
> Thanks for bringing up the filter topic -
>
> This is one of my main questions now.  I finally ordered mine with no
> optional filters and plan on adding them to the order before ship BUT I do
> not know which will be the best for me.  I suppose the answer to that is
> that it will be different for everybody.  I do expect to add the second
> reciever board at some point, maybe not before initial ship.
>
> Some sub-topics:
>
> 1) Is there any point in ordering the 200, 250, 400 and 500? Probably not.
> Somebody explain how the filters are selected by the radio and recommend a
> couple of reasonable configurations please.  I want to be able to run 
> PSK,
> RTTY, CW and SSB and mainly I want to not have to deal with nearby 
> signals,
> I want them GONE.
>
> 2) a. Why would you order a 2.8 when you get a 2.7 with the radio?
>  b. Can you order the 2.8 instead of the standard 2.7 and receive "some"
> credit for the 2.7 you didn't want?
>
> 3)  Will the 1.8 make the SSB hard to understand vs possibly the 2.1?  I
> almost ordered the 1.8 but wasn't sure so didn't order anything yet.
>
> 4) What would be the best filter for RTTY?
>
> 5) Which filter will be best for PSK?  A 6K filter or a 2.8 or narrower
> looking at just part of the band at a time?
>
> Pick one (or all) and give me your thoughts,
>
> THANKS,
> de Jim KG0KP (NewBee)
>
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