Elecraft

K3 2.7 k Filter vs. 2.8 k

Classic

List

Threaded

5 messages Options

Bill W4ZV

K3 2.7 k Filter vs. 2.8 k

This topic has drifted from "2.7k versus 2.8k" to "2.7k
versus 400 Hz". *Of course* a 4-500 Hz filter is needed for CW
and will have vastly better IMD/BDR than a 2.7k/2.8k. But I
repeat that there will be very little if any difference between a
400 (actually 435 Hz) 8-pole and 500 ( 565 Hz) 5-pole. In my
opinion, you are really wasting money to buy 8-pole filters for
improved RX performance, unless the 130 Hz BW difference
is important. In practice, this implies the difference in a signal
spaced 435/2 = 218 Hz versus 565/2 = 283 Hz...65 Hz is not
much difference, and I actually prefer the wider BW to catch
more off-frequency callers. From Eric's posted data:

Filter 20kHz 10kHz 5kHz 2kHz

400 Hz, 8 pole 100+ 100+ 100+ 95
500 Hz, 5 pole 100+ 100+ 100+ 94

Again in my opinion the 250/200 Hz filters are
redundant and unnecessary if you have a 400/500.
They do not improve 2 kHz IMD significantly as
seen below (1 dB difference is meaningless as
that is well within measurement error):

Filter 20kHz 10kHz 5kHz 2kHz

200 Hz, 5 pole 100+ 100+ 100+ 95
250 Hz, 8 pole 100+ 100+ 100+ 95

You could argue that the 250/200 would be better
for IMD fom extremely close-spaced signals (e.g.
<200 Hz spacing from your TX frequency), but at
that spacing other factors such as the transmitted
signal's phase noise, key clicks, etc. will override
any theoretical IMD advantage (i.e. the IMD becomes
"noise limited" in ARRL terminology).

Remember also that Passband Tuning can be used
to shift a 400/500 Hz filter if you actually do need
to eliminate a signal spaced at 200-250 Hz from your
TX frequency...not that it would actually do any
good to eliminate phase noise or key clicks.

73, Bill W4ZV

_______________________________________________
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

dj7mgq

From the shipping status page...

> We are still short several key components and are waiting
> for replies from our vendors. We will update the shipping
> status by end of day Tuesday, 9/18 PDT. (Before 0700Z 9/19).

Sounds like more delays...

Time to go to bed here - G'night

_______________________________________________
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

Bob Cunnings NW8L

Re: K3 2.7 k Filter vs. 2.8 k

In reply to this post by Bill W4ZV

I took the reasoning a step further since the data for the 1 kHz 8
pole filter is:

Filter 20kHz 10kHz 5kHz 2kHz
---
1 kHz, 8 pole 100+ 100+ 100 94
---

So I ordered the 1 kHz filter since I'm just a ragchew type cw
operator. It's nice to be able to run as wide as 800 Hz or so when
tuning around, something I couldn't do with the narrower filters - but
with numbers like this I don't think I have much to worry about!

Bob NW8L

On 9/18/07, Bill Tippett <[hidden email]> wrote:

>
>
> This topic has drifted from "2.7k versus 2.8k" to "2.7k
> versus 400 Hz". *Of course* a 4-500 Hz filter is needed for CW
> and will have vastly better IMD/BDR than a 2.7k/2.8k. But I
> repeat that there will be very little if any difference between a
> 400 (actually 435 Hz) 8-pole and 500 ( 565 Hz) 5-pole. In my
> opinion, you are really wasting money to buy 8-pole filters for
> improved RX performance, unless the 130 Hz BW difference
> is important. In practice, this implies the difference in a signal
> spaced 435/2 = 218 Hz versus 565/2 = 283 Hz...65 Hz is not
> much difference, and I actually prefer the wider BW to catch
> more off-frequency callers. From Eric's posted data:
>
> Filter 20kHz 10kHz 5kHz 2kHz
>
> 400 Hz, 8 pole 100+ 100+ 100+ 95
> 500 Hz, 5 pole 100+ 100+ 100+ 94
>
> Again in my opinion the 250/200 Hz filters are
> redundant and unnecessary if you have a 400/500.
> They do not improve 2 kHz IMD significantly as
> seen below (1 dB difference is meaningless as
> that is well within measurement error):
>
> Filter 20kHz 10kHz 5kHz 2kHz
>
> 200 Hz, 5 pole 100+ 100+ 100+ 95
> 250 Hz, 8 pole 100+ 100+ 100+ 95
>
> You could argue that the 250/200 would be better
> for IMD fom extremely close-spaced signals (e.g.
> <200 Hz spacing from your TX frequency), but at
> that spacing other factors such as the transmitted
> signal's phase noise, key clicks, etc. will override
> any theoretical IMD advantage (i.e. the IMD becomes
> "noise limited" in ARRL terminology).
>
> Remember also that Passband Tuning can be used
> to shift a 400/500 Hz filter if you actually do need
> to eliminate a signal spaced at 200-250 Hz from your
> TX frequency...not that it would actually do any
> good to eliminate phase noise or key clicks.
>
> 73, Bill W4ZV
>
>
>
> _______________________________________________
> 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
>

_______________________________________________
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

N8LP

Re: K3 2.7 k Filter vs. 2.8 k

In reply to this post by Bill W4ZV

For my general operating needs, I think either the 2.7 kHz or 2.8 kHz
filter combined with the 500 Hz represent a reasonable approach. I
talked with Eric at W9DXCC this past weekend, and I got the impression
that 2.8 kHz / 500 Hz would be a very good overall combo for all my
needs, but I am waiting to hear some feedback from the first run. Even
though I ordered the first weekend, I specified the second run, partly
because I wanted to see same data and hear some feedback on the filters
before deciding. The variable CW filter might also be a good choice once
it's available, depending on IMD performance. Eric indicated that Wayne
likes the variable filter approach, and it would be a flexible one...
but I want to see performance numbers.

73,
Larry N8LP

Bill Tippett wrote:

>
>
> This topic has drifted from "2.7k versus 2.8k" to "2.7k
> versus 400 Hz". *Of course* a 4-500 Hz filter is needed for CW
> and will have vastly better IMD/BDR than a 2.7k/2.8k. But I
> repeat that there will be very little if any difference between a
> 400 (actually 435 Hz) 8-pole and 500 ( 565 Hz) 5-pole. In my
> opinion, you are really wasting money to buy 8-pole filters for
> improved RX performance, unless the 130 Hz BW difference
> is important. In practice, this implies the difference in a signal
> spaced 435/2 = 218 Hz versus 565/2 = 283 Hz...65 Hz is not
> much difference, and I actually prefer the wider BW to catch
> more off-frequency callers. From Eric's posted data:
>
> Filter 20kHz 10kHz 5kHz 2kHz
>
> 400 Hz, 8 pole 100+ 100+ 100+ 95
> 500 Hz, 5 pole 100+ 100+ 100+ 94
>
> Again in my opinion the 250/200 Hz filters are
> redundant and unnecessary if you have a 400/500.
> They do not improve 2 kHz IMD significantly as
> seen below (1 dB difference is meaningless as
> that is well within measurement error):
>
> Filter 20kHz 10kHz 5kHz 2kHz
>
> 200 Hz, 5 pole 100+ 100+ 100+ 95
> 250 Hz, 8 pole 100+ 100+ 100+ 95
>
> You could argue that the 250/200 would be better
> for IMD fom extremely close-spaced signals (e.g.
> <200 Hz spacing from your TX frequency), but at
> that spacing other factors such as the transmitted
> signal's phase noise, key clicks, etc. will override
> any theoretical IMD advantage (i.e. the IMD becomes
> "noise limited" in ARRL terminology).
>
> Remember also that Passband Tuning can be used
> to shift a 400/500 Hz filter if you actually do need
> to eliminate a signal spaced at 200-250 Hz from your
> TX frequency...not that it would actually do any
> good to eliminate phase noise or key clicks.
>
> 73, Bill W4ZV
>
>
>
> _______________________________________________
> 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
>

Bill W4ZV

Re: K3 2.7 k Filter vs. 2.8 k

On 9/18/07, Larry Phipps <[hidden email]> wrote:

> The variable CW filter might also be a good choice once
> it's available, depending on IMD performance. Eric indicated that Wayne
> likes the variable filter approach, and it would be a flexible one...
> but I want to see performance numbers.

The variable filter sounds great but I would insist on seeing numbers
first. Introducing additional components like varactors may have some
unexpected effects on IMD results. As they say in Missouri..."Show
Me"

73, Bill W4ZV.
_______________________________________________
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