[Elecraft] Re: Roofing Filter question (+ some K3 receiver philosophy)

[Lance Collister, W7GJ]

wayne burdick wrote:
> Mike, W9QS wrote:
>
>> I have a K3/10 on order.  I have used my K2 for over a year and find 
>> the filters to be very good.  I operate 90% on the time on QRP CW.  
>> I'm looking for opinions on which roofing filters I might include.
>
> Mike,
>
> If you operate CW at all, you'll almost surely want at least one 
> narrow filter. Either our 400 Hz or 500 Hz filter would be a great 
> all-around choice.
>
> I'm *not* just trying to sell filters  :)  The reason you need a 
> narrow filter is that the K3's entire receiver architecture is based 
> on the premise that the 1st I.F. filter should be close to the 
> communications bandwidth in use. This is what sets the K3 apart from 
> other transceivers that use an up-conversion architecture, and thus 
> very wide front-end filtering (at least in relation to CW or data 
> modes -- 3 to 15 kHz).
>
> The K2 has a similar architecture to the K3. In that case, a single 
> crystal filter covers bandwidths from about 200 to 2000 Hz. The K3 
> builds on this concept, using multiple fixed-bandwidth filters with 
> much lower ripple, stronger signal handling in all stages, and a 
> synthesizer with extremely low phase noise. But both receivers use 
> low-noise 2nd IFs that really should be protected from out-of-band 
> signals. (In this case, out of band means "outside the crystal filter.")
>
> If you're a K2 owner, you're already use to the protection you get 
> from narrow filtering. You'll probably want that same kind of signal 
> handling performance in your K3 if you use it on Field Day, or during 
> a contest, or just when the band is open and signals are strong.
>
> If you look at Sherwood's receiver performance chart 
> (http://www.sherweng.com/table.html), you'll see that the K2 has 
> respectable  IMD dynamic range at 2 kHz: close to that of the Icom 
> IC-7800 (at 1/10th the price :)  But the K3 is at the top of the chart 
> -- 15 to 20 dB better, depending on the filter bandwidth. To obtain 
> this benefit from having a K3, IMHO you really need narrow filtering.
>
> 73,
> Wayne
> N6KR
>
> ---
>
> http://www.elecraft.com
>
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>
I got the 6, 2.7 (standard), and 1.8 KHz filters in my K3.  I realize 
that a narrower filter will be good for crowded CW with strong stations, 
but was waiting for the release of the "variable" filter mentioned on 
the website.  Is there any more recent information on the status of that 
option?

MNI TNX and VY 73, Lance

-- 
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: (406) 626-5728
URL: http://www.bigskyspaces.com/w7gj
2m DXCC #11/6m DXCC #815