Substitution of stock 2.7 for the 2.8

[Bob-165]

I am looking for a consensus as to the value of switching the stock
2.7Khz for the 2.8Khz filter at time of order and paying the
difference based on a $30 credit? I would like some input as to what
the difference really is and what it would mean in terms of
functionality. Additionally,  if the 2.8 is that much better, why
would it not be part of the basic radio offering visa vis the 2.7?

Thanks

Bob

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[Matt Zilmer]

One man's simple answer is ... well .. simple.

Keep the 2.7KHz 5-p filter.  You will find that the DSP provides
mighty fine ultimate rejection.  In this configuration, the 2.7 filter
provides quite adequate protection from strong in-band signals.

If you're a contester, buy one or both of the 1.8 KHz or 2.1 KHz 8-p
filters for extra protection.  I know I will.  Just not sure when.
Operating and learning the radio is keeping me too busy for this to be
a priority.

Right now I only have the basic 2.7KHz 5-p and 250Hz 8-p filters. This
might be termed "a basic SSB and a somewhat picky CW" op's choice.  It
has worked quite well as a combo, so far.

Now - if you find yourself freqently or often in the presence of S9+60
filled-with-splatter signals, nothing will help and you'd be better
off switching bands.  Nothing can help with that.  I just came across
that with an OT last night, only 1/2 mile from here.  Runs a KW to
talk across the state.  Go figure.

matt - WA6EGJ
K3 # 24

==


On Wed, 05 Dec 2007 23:15:14 -0500, you wrote:

>I am looking for a consensus as to the value of switching the stock
>2.7Khz for the 2.8Khz filter at time of order and paying the
>difference based on a $30 credit? I would like some input as to what
>the difference really is and what it would mean in terms of
>functionality. Additionally,  if the 2.8 is that much better, why
>would it not be part of the basic radio offering visa vis the 2.7?
>
>Thanks
>
>Bob

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[Alan Bloom]

On Wed, 2007-12-05 at 20:15, Bob wrote:

> I am looking for a consensus as to the value of switching the stock
> 2.7Khz for the 2.8Khz filter at time of order and paying the
> difference based on a $30 credit? I would like some input as to what
> the difference really is and what it would mean in terms of
> functionality. Additionally,  if the 2.8 is that much better, why
> would it not be part of the basic radio offering visa vis the 2.7?
>
> Thanks
>
> Bob

I suspect you would be hard-pressed to see any difference at all between
the 5-pole 2.7 kHz filter and 8-pole 2.8 kHz filter in on-the-air
operation.

According to the K3 FAQ, only the first 30 dB or so of stop-band
rejection is important in the roofing filter - the DSP takes care of the
rest.  Of course, the 5-pole filter is actually slightly narrower at the
-6 dB attenuation point.  Let's say the 8-pole filter is narrower at
attenuations beyond 10 dB.  So the only practical advantage it would
have is a few dB better attenuation between the -10 and -30 dB points.

If there were a VERY strong signal in that range (say from +/- 1.5 to
2.0 kHz from center frequency) the 8-pole filter might prevent it
overloading the ADC/DSP system where the 5-pole might not.  To make the
more-expensive filter worthwhile, the signal strength would have to be
right in that few-dB range where the 8-pole filter would work and the
5-pole would not.  I think that's a rare enough occurance not to be
worth worrying about.

Al N1AL


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[w7aqk]

Al and All,

I think you are right.  I had wrestled with this possibility, and tried to
make a change to the 8 pole at the last minute.  But my K3 went out the door
before they could make the switch.  Probably a good thing.  So far, I can't
detect any detriment.  Of course, I can't switch between the two, so it's
hard to tell.  If I had made the switch, I'd probably be thinking it was a
good decision as I would feel things were working great.  Well, things are
working great anyway!  Some folks may be more discerning that I am, but at
this point, in my ignorance perhaps, I'm satisfied!

Dave W7AQK

----- Original Message -----
From: "Alan Bloom" <[hidden email]>
To: "Bob" <[hidden email]>
Cc: <[hidden email]>
Sent: Wednesday, December 05, 2007 10:36 PM
Subject: Re: [Elecraft] Substitution of stock 2.7 for the 2.8 in the K3

> I suspect you would be hard-pressed to see any difference at all between
> the 5-pole 2.7 kHz filter and 8-pole 2.8 kHz filter in on-the-air
> operation.
>
> According to the K3 FAQ, only the first 30 dB or so of stop-band
> rejection is important in the roofing filter - the DSP takes care of the
> rest.  Of course, the 5-pole filter is actually slightly narrower at the
> -6 dB attenuation point.  Let's say the 8-pole filter is narrower at
> attenuations beyond 10 dB.  So the only practical advantage it would
> have is a few dB better attenuation between the -10 and -30 dB points.
>
> If there were a VERY strong signal in that range (say from +/- 1.5 to
> 2.0 kHz from center frequency) the 8-pole filter might prevent it
> overloading the ADC/DSP system where the 5-pole might not.  To make the
> more-expensive filter worthwhile, the signal strength would have to be
> right in that few-dB range where the 8-pole filter would work and the
> 5-pole would not.  I think that's a rare enough occurance not to be
> worth worrying about.
>
> Al N1AL
>
>
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>

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