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K3 Filter advice...

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drewko

K3 Filter advice...

I'm wondering what minimum complement of filters would work for me in
a K3. I am only interested in general coverage reception of SWBC
stations, plus operating CW. I am a little unlclear about what filter
would be required for AM (reception only), with the KBPF3 option.

For CW I generally prefer a wide filter (my K2 is set at 2.0 kHz most
of the time). I suppose I would want a narrower filter as well but
can't decide whether 500/400 or 250/200.

Does a 2.1 kHz + 200 Hz filter pair seem like a useful combo for CW?

Finally, I don't have a clue what noticeable difference there would be
between a 200/5-pole and a 250/8-pole. If the difference is really
subtle or limited to very occasional use I suppose I'd go for the
cheaper one.

73,
Drew
AF2Z

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John W2XS

Re: K3 Filter advice...

There were many great posts about the filter options. Thanks to all who provided good advice. I read all of them. This is my take on all of the postings about filters.

1. The shape factor of a roofing filter is not as important as the shape factor of a conventional main IF filter. Therefore, a 5-pole will be fine for a roofing filter. Based on this, I went with the default 5-pole 2.7kHz filter. Since I am a CW operator, I also went with the 500 Hz and 200 Hz CW filters. The 200 Hz may be overkill since the rig has the "shift" control, but it was not that much more money.

2. The widest roofing filter determines the widest receiver selectivity. In other words, you must have a roofing filter installed - you cannot "jumper" over a slot for wide hi-fi selectivity. Based on that, since I also like to listen to SW and AM BCB, I added the 6 kHz AM filter.

So my widest bandwidth will be 6 kHz and the narrowest bandwidth will be whatever the DSP can do (50 Hz or so) in series with a 200 Hz roofing filter.

That sounded like a good combination to me. The biggest problem will come when trying to listen to a weak station who is near another station with a "noisy" transmitted signal.

Time will tell if my assumptions are valid, but I was happy with the choices when I ordered.

73,

John W2XS

KX1 (S/N 015 and S/N 925) w/KXPD1, KXAT1, KXB30
K2 (S/N 1116) w/KAT2, KSB2, K160RX, KIO2, KBT2, KNB2, KAF2, FDIMP
K3/100 (S/N TBD) w/KAT3, KBPF3, KUSB, KFL3A-200, 500, 2.7K, 6K
HexKey (S/N 113 )
DL1, BL1, BL2, N-gen, XG1, BNC-MM

Don Wilhelm-4

Re: K3 Filter advice...

In reply to this post by drewko

Drew,

For AM you will need either the 6 kHz or the 15 kHz filter - an AM
signal will not fit through the 2.7 kHz filter without seriously
degrading the fidelity.

The 2.7 kHz filter along with the DSP filtering does an acceptable job
for casual CW, but if a strong (S-9+30) station comes on the air within
that 2.7 kHz bandpass, the DSP input can be overloaded, so you may want
to consider a filter more narrow than the 2.7 - I think 500 Hz is a good
choice. For data modes, 200 Hz is a good choice, and IMHO is a bit
narrow for normal CW.

If you are into operating during periods of heavy band use (like contest
times), then the 8 pole filters with their steeper skirts may be
helpful, but for more casual use, the 5 pole filters do a great job.

Remember that the filters are 'roofing filters', and not the final
filtering (which is done in DSP). Their purpose is to reduce the
strength of undesired signals ahead of the DSP ADC - as long as the DAC
is not overloaded, the DSP can provide all the filtering needed. Right
now, I have only the 2.7 kHz filter in my K3 and it does quite well on
CW with only the DSP filtering - but then I have not operated on a
contest weekend yet either.

73,
Don W3FPR

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w7aqk

Re: K3 Filter advice...

In reply to this post by drewko

Drew and All,

I'll take a stab at giving you an answer. For AM reception (and shortwave)
you would want the 6 khz filter. For CW, you need to make a choice, but I
suspect that in order to limit the number of filters you would be best
advised to select either the 400 hz or 500 hz filter. You can look at the
graphs to see which has the characteristics you prefer. I have the 400 hz
and the 200 hz filters. Most of the time I use the 400 hz, and only invoke
the 200 hz filter when things get really tough. But I'm glad I have the
narrower filter. However, if I only had one CW filter I would probably opt
for the 400 hz. I am very pleased with how the 400 hz filter works and
sounds. I think I saw someone suggest the 500 hz would be a better choice,
but I'm not sure I remember why. Personally, I want the narrower filter for
those occasions when you need just a little tighter bandpass. Besides, I
don't find using the 400 hz filter to be unpleasant at all, so I don't think
I would necessarily be better served with a 500 hz in the alternative. I
suppose you might find the 500 hz filter to be sufficient, when combined
with the K3's DSP capabilities, but I think you would actually have to do
some "hands on" to be sure you like the result.

O.K. That's my answer. I bet you get several others.

Dave W7AQK

----- Original Message -----
From: <[hidden email]>
To: <[hidden email]>
Sent: Wednesday, December 26, 2007 8:36 AM
Subject: [Elecraft] K3 Filter advice...

> I'm wondering what minimum complement of filters would work for me in
> a K3. I am only interested in general coverage reception of SWBC
> stations, plus operating CW. I am a little unlclear about what filter
> would be required for AM (reception only), with the KBPF3 option.
>
> For CW I generally prefer a wide filter (my K2 is set at 2.0 kHz most
> of the time). I suppose I would want a narrower filter as well but
> can't decide whether 500/400 or 250/200.
>
> Does a 2.1 kHz + 200 Hz filter pair seem like a useful combo for CW?
>
> Finally, I don't have a clue what noticeable difference there would be
> between a 200/5-pole and a 250/8-pole. If the difference is really
> subtle or limited to very occasional use I suppose I'd go for the
> cheaper one.
>
> 73,
> Drew
> AF2Z
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

Vic K2VCO

Re: K3 Filter advice...

In reply to this post by John W2XS

John W2XS wrote:

> The biggest problem will come
> when trying to listen to a weak station who is near another station with a
> "noisy" transmitted signal.

Since I've had my K3 I've become even more aware than before that a
couple of ham neighbors (within a mile) are radiating really awful crap
around their signals. One of them runs 1500 watts, too.

If a spurious signal is 50 dB down from 1500 watts, it's a 15 mW signal,
which is pretty loud. And I don't think some of these spurs are 50 dB down.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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Bill VanAlstyne W5WVO

Re: K3 Filter advice...

In reply to this post by Don Wilhelm-4

Don Wilhelm wrote:

> For AM you will need either the 6 kHz or the 15 kHz filter - an AM
> signal will not fit through the 2.7 kHz filter without seriously
> degrading the fidelity.

True enough -- but if you are a SW DXer trying to verify the ID of a weak,
rare SWBC station, and therefore not particularly interested in fidelity, you
can listen to AM in USB/LSB mode quite satisfactorily by zero-beating the
carrier. This is especially cool because by switching between LSB and USB, you
can pick the sideband that is the least interfered with by adjacent-channel
signals. Having chosen the sideband to listen to, you can then tailor the DSP
passband to maximize intelligibility. I use this mode often when DXing on
broadbanded GC receivers in preference to using the wide AM mode provided.

Bill / W5WVO
K3 in February 2008

>
> The 2.7 kHz filter along with the DSP filtering does an acceptable job
> for casual CW, but if a strong (S-9+30) station comes on the air
> within that 2.7 kHz bandpass, the DSP input can be overloaded, so you
> may want to consider a filter more narrow than the 2.7 - I think 500
> Hz is a good choice. For data modes, 200 Hz is a good choice, and
> IMHO is a bit narrow for normal CW.
>
> If you are into operating during periods of heavy band use (like
> contest times), then the 8 pole filters with their steeper skirts may
> be helpful, but for more casual use, the 5 pole filters do a great
> job.
> Remember that the filters are 'roofing filters', and not the final
> filtering (which is done in DSP). Their purpose is to reduce the
> strength of undesired signals ahead of the DSP ADC - as long as the
> DAC is not overloaded, the DSP can provide all the filtering needed. Right
> now, I have only the 2.7 kHz filter in my K3 and it does quite
> well on CW with only the DSP filtering - but then I have not operated
> on a contest weekend yet either.
>
> 73,
> Don W3FPR
>
> [hidden email] wrote:
>> I'm wondering what minimum complement of filters would work for me in
>> a K3. I am only interested in general coverage reception of SWBC
>> stations, plus operating CW. I am a little unlclear about what filter
>> would be required for AM (reception only), with the KBPF3 option.
>>
>> For CW I generally prefer a wide filter (my K2 is set at 2.0 kHz most
>> of the time). I suppose I would want a narrower filter as well but
>> can't decide whether 500/400 or 250/200.
>>
>> Does a 2.1 kHz + 200 Hz filter pair seem like a useful combo for CW?
>>
>> Finally, I don't have a clue what noticeable difference there would
>> be between a 200/5-pole and a 250/8-pole. If the difference is really
>> subtle or limited to very occasional use I suppose I'd go for the
>> cheaper one.
>>
>> 73,
>> Drew
>> AF2Z
>>
>>
> _______________________________________________
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> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
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> Elecraft web page: http://www.elecraft.com

drewko

Re: K3 Filter advice...

In reply to this post by John W2XS

Thanks to everyone for their comments on filters for a CW+AM K3. They
are very helpful.

I was aware of the distinction between roofing filter and DSP
filtering but didn't know (or forgot) about the 2.7 kHz standard
filter.

As for the "hoped for" multi-bandwidth filter, I guess it is probably
too soon to talk about. My first questions would be how wide it would
go and how much it would cost.

73,
Drew
AF2Z

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