roofing filter loss and method of compensation

[DOUGLAS ZWIEBEL]

Can you discuss the loss of the "narrow" roofing filters and elaborate
on "how" you compensate for that?  How does that compensation impact
rx peformance specs (ie, do some "get worse)?

Thanks,
de Doug KR2Q
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[wayne burdick]

Like other roofing filters, the narrower the passband, the more loss.
In general the loss is similar to those shown for the FT-1000 8.215 MHz
filters shown on the INRAD web site. Our 5 pole filters in some cases
have a little less loss.

The loss at this point in the radio (the first I.F.) has very little
impact on MDS or other characteristics, because the noise figure is
established in earlier stages.

When you install any roofing filter, you use the menu to tell the
firmware what the filter's bandwidth is, any small offset from 8.215
MHz, and what the relative loss of the filter is. The DSP adjusts the
15-kHz I.F. gain based on the entered loss amount, so all filters have
the same overall gain.

Once a filter is installed, you can specify which modes it is available
in (or all modes).

73,
Wayne
N6KR


On Apr 29, 2007, at 3:57 AM, DOUGLAS ZWIEBEL wrote:

> Can you discuss the loss of the "narrow" roofing filters and elaborate
> on "how" you compensate for that?  How does that compensation impact
> rx peformance specs (ie, do some "get worse)?
>
> Thanks,
> de Doug KR2Q
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>

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[dj7mgq]

The big questions are:

1) Why would I want a 8 pole file and not a 5 pole with almost the
same bandwidth? Rejection, ringing, etc. etc.?

2) What is the difference between the 2.7kHz and 2.8kHz -
advantage/disadvantage?

3) How do the fixed bandwidth filters compare with the variable
bandwidth roofing filters?

I have ordered the K3 with various goodies via fax, but am holding
back on the filters (apart from the 6kHz and the FM filters) until
more is known.

vy 73 de toby

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[wayne burdick]

On Apr 29, 2007, at 11:50 AM, Toby Deinhardt wrote:

> The big questions are:
>
> 1) Why would I want a 8 pole file and not a 5 pole with almost the
> same bandwidth? Rejection, ringing, etc. etc.?

The 8-pole filters will have somewhat sharper skirts. This could be
useful in certain QRM situations. Of course the DSP will provide
incredible ultimate attenuation -- the opposite sideband simply won't
exist, at any signal level.


>
> 2) What is the difference between the 2.7kHz and 2.8kHz -
> advantage/disadvantage?

We wanted our 5-pole filter to be slightly narrower. As I mentioned
above, the 8-pole filter will have steeper skirts, at a higher price.

You can install additional filters at any time, by the way. We hope to
have variable-passband CW and SSB crystal roofing filters within a few
months, so you could save a slot or two.


>
> 3) How do the fixed bandwidth filters compare with the variable
> bandwidth roofing filters?

We haven't nailed down the variable bandwidth selections, but chances
are we'll have a CW-range variable filter (maybe 300-800 Hz) and an
SSB-range variable filter (say, 1.8 to 2.5 kHz).

73,
Wayne
N6KR


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[dj7mgq]

Hi Wayne,

I know that this is a really loaded question, and I am sure that if
you put three hams in a room you would get 7 opinions...

What combination of filters (fixed and/or variable) would you feel are
appropriate for:

1) Primarily CW contesting/DXing?
2) Primarily SSB contesting/Dxing?
3) Mixture of CW and SSB contesting/Dxing?
4) CW ragchewing?
5) SSB ragchewing?
6) Digital modes?
7) "General usage" (compromise for all of the above)?

This might be a topic for one or more white papers.



Slightly less loaded: When will data for the filters be avaidable?


vy 73 de toby


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[wayne burdick]

Wow, Toby, that *is* a complicated question, partly because we haven't
nailed down the specs for our variable-passband roofing filters yet.
I'd leave room for at least one of those (CW or SSB bandwidths).

Here's a set that covers all modes including AM and FM:

   FL1 = FM bandwidth (something like 13 kHz)
   FL2 = 6 kHz (AM; wide SSB)
   FL3 = 2.8 kHz (workhorse SSB filter)
   FL4 = 500 Hz (nominal CW)
   FL5 = 200 Hz (narrow CW)

If you were doing primarily SSB, you might want to go with 1.8 or 2.1
kHz at FL4. At present these filters are only offered by INRAD. We plan
to offer a variable-passband 5-pole filter that covers something like
1.8 to 2.5 kHz that would fill this bill in the future.

Having used something different at FL4, you'd then need to reevaluate
FL5. It could be 400 Hz (INRAD fixed), 500 Hz (Elecraft fixed), or even
an Elecraft variable CW/DATA bandwidth filter -- TBD, but probably
something like 300-600 or 300-800 Hz.

Of course this assumes that you want AM and FM-bandwidth filters. If
you don't operate in these modes, you'll have more SSB/CW/DATA filter
flexibility. You could also put narrower filters on the sub-receiver.

73,
Wayne
N6KR

On Apr 29, 2007, at 1:13 PM, Toby Deinhardt wrote:

> Hi Wayne,
>
> I know that this is a really loaded question, and I am sure that if
> you put three hams in a room you would get 7 opinions...
>
> What combination of filters (fixed and/or variable) would you feel are
> appropriate for...



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[n6wg]

Wayne
Will the variable bandwidth filters have better
ultimate rejection/less blowby than the variable
bandwidth filter in the K2?
73, Bob N6WG

----- Original Message -----
From: "wayne burdick" <[hidden email]>
To: "Toby Deinhardt" <[hidden email]>
Cc: <[hidden email]>
Sent: Sunday, April 29, 2007 4:30 PM
Subject: [Elecraft] Re: roofing filter loss and method of compensation

> Wow, Toby, that *is* a complicated question, partly because we haven't
> nailed down the specs for our variable-passband roofing filters yet.
> I'd leave room for at least one of those (CW or SSB bandwidths).
>
> Here's a set that covers all modes including AM and FM:
>
>    FL1 = FM bandwidth (something like 13 kHz)
>    FL2 = 6 kHz (AM; wide SSB)
>    FL3 = 2.8 kHz (workhorse SSB filter)
>    FL4 = 500 Hz (nominal CW)
>    FL5 = 200 Hz (narrow CW)
>
> If you were doing primarily SSB, you might want to go with 1.8 or 2.1
> kHz at FL4. At present these filters are only offered by INRAD. We plan
> to offer a variable-passband 5-pole filter that covers something like
> 1.8 to 2.5 kHz that would fill this bill in the future.
>
> Having used something different at FL4, you'd then need to reevaluate
> FL5. It could be 400 Hz (INRAD fixed), 500 Hz (Elecraft fixed), or even
> an Elecraft variable CW/DATA bandwidth filter -- TBD, but probably
> something like 300-600 or 300-800 Hz.
>
> Of course this assumes that you want AM and FM-bandwidth filters. If
> you don't operate in these modes, you'll have more SSB/CW/DATA filter
> flexibility. You could also put narrower filters on the sub-receiver.
>
> 73,
> Wayne
> N6KR
>
> On Apr 29, 2007, at 1:13 PM, Toby Deinhardt wrote:
>
> > Hi Wayne,
> >
> > I know that this is a really loaded question, and I am sure that if
> > you put three hams in a room you would get 7 opinions...
> >
> > What combination of filters (fixed and/or variable) would you feel are
> > appropriate for...
>
>
>
> > ---
>
> http://www.elecraft.com
>
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[KK7P]

> Will the variable bandwidth filters have better
> ultimate rejection/less blowby than the variable
> bandwidth filter in the K2?

With the IF DSP in the K3, the issues that are of concern in a fully
analog radio are less important.

As long as the crystal filter, which is being used as a roofing filter,
has reasonably good skirts and ultimate rejection, the DSP will take
care of the rest.  The first 20 dB or so of skirt selectivity, the
passband ripple, and the ultimate rejection at the DSP IF image
frequency are the most critical factors.

73,

Lyle KK7P

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[wayne burdick]

Robert Tellefsen wrote:

> Wayne
> Will the variable bandwidth filters have better
> ultimate rejection/less blowby than the variable
> bandwidth filter in the K2?

Yes. The ultimate attenuation on *all* of the K3's filters -- fixed or
variable -- is essentially infinite because of the I.F./A.F. DSP
filtering.

73,
Wayne
N6KR


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[Bill W4ZV]

KK7P:
 >With the IF DSP in the K3, the issues that are
of concern in a fully analog radio are less important.

 >As long as the crystal filter, which is being
used as a roofing filter, has reasonably good
skirts and ultimate rejection, the DSP will take
care of the rest. The first 20 dB or so of skirt
selectivity, the passband ripple, and the
ultimate rejection at the DSP IF image frequency are the most critical factors.

         Below W2VJN (ex-Inrad) says the first ~30 dB of
skirt selectivity is key for IMD issues.  It will be important
for you to specify actual IMD and BDR performance with
each of the various CW filters installed.  So far I count 4
that are 500 Hz or less, not counting the variable BW
option.  I hope you can post this information soon so
that those planning to order will have information to
properly configure a unit.

                         73,  Bill  W4ZV

http://www.qth.com/inrad/roofing-filters.pdf (page 6)

5. If 6 poles work so well, why not 8 poles?
The most important part of the filter
characteristic is from the pass-band on down
to about –30 dB on either side of center. Eight poles would provide much better
stop-band isolation, but it’s not required in a
roofing filter and would make no
noticeable improvement in IMD performance.


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[KK7P]

> "... The first 20 dB or so of skirt selectivity,"...
>
>         Below W2VJN (ex-Inrad) says the first ~30 dB of
> skirt selectivity is key for IMD issues.

Thank you for spotting this error, Bill.  I'll get it updated in the FAQ.

73,

Lyle KK7P

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