FW: Attenuation at narrow bandwidths NOT!

[Dan Barker]

Do overs!

What I really proved is that the AGC circuit works really well<g>.

Nobody spotted the error in my Setup, I.E., AGC OFF not specified.

I just reran the test with AGC off. Results are still excellent, but not as
perfect as I reported yesterday.

Bandwidth
Setting  Peak
0.00      -41
0.10      -35
0.20      -34
0.30      -31
0.40      -30
0.50      -29
0.60      -29
0.70      -29
0.80      -30
0.90      -31
1.00      -30
1.25      -32
1.50      -32
1.75      -33
2.00      -34
2.25      -32
2.49      -33
OP1       -36

My perception of "No Attenuation" comes from my standard practice of cycling
between 0.90, 0.50 and 0.20 (-31, -29 and -34 respectively) plus the AGC
working made me think it was flatter than it is. However, 5db isn't too bad
if the S9+ interfering signal disappears.

Dan / WG4S / K2 #2456

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]]On Behalf Of Dan Barker
Sent: Thursday, December 09, 2004 8:25 AM
To: Elecraft
Subject: [Elecraft] Attenuation at narrow bandwidths NOT!


Don, you got me thinking. Why would you say something like that? My K2
filters are EXCELLENT! But, I decided to test it out to prove my belief.

Test Setup:

Freq 7.040.

Mode CW Normal.

Set FL4 width to 0.00 (FL4 has the BFO for a "reasonable" left skirt. I
didn't want to change frequency, just bandwidth.

Broadband noise source on ANT2, Antenna selector to ANT2.

Spectrogram on Fixed Audio Out (top of AF pot).

Peak Hold on, wait for the graph to "fill in".

Measure the peak, and the amplitude of the -6db points for bandwidth
calculation.

Note: BWs above 1,200 hz have significant ripple (not unexpected). However
these bandwidths are not particularly useful to me. I measured the peak as
above, and measured the -6db points on the far right hump. The ripple is at
most 10db, but I'd measure the -6db point of the next hump. Not that it
matters anyhow at 2.49! I imagine anyone wanting really wide CW reception is
going to use OP1 anyway.

Repeat measurements with FL4 bandwidth 0.10 (or more) higher. After 2.49,
use OP1. Finally, return FL4 bw to operating BW, in my case, 0.20. Verify
trace is still centered on my sidetone (it was).

Raw data available at ftp://ftp.visioncomm.com/k2filter.xls, anonymous, your
email address, bin, get.

As these numbers appear to powerfully demonstrate the extremely excellent
job done by the designers, I'll be happy to compare notes with any K2 owner
with less stellar performance. EVERY K2s filter plots should look this good.
I'm not sure what to compare tho, to find a discrepancy<g>. Wayne? Eric?
Ideas?.

As I normally S&P with the 0.90, and work heavy QRM at 0.20, the ZERO db
attenuation is what I notice. If I lose AF volume with FL4, then I AM OFF
FREQ. It's not my filter<g>.

Dan Barker / WG4S / K2 #2456

Summary:

Bandwidth   -6db Bandwidth
Setting  Peak  Measured
0.00      -43    109
0.10      -43    133
0.20      -43    158
0.30      -42    178
0.40      -42    200
0.50      -42    231
0.60      -42    263
0.70      -42    292
0.80      -42    352
0.90      -43    421
1.00      -42    450
1.25      -43    663
1.50      -43    897
1.75      -42   1231
2.00      -43   1574
2.25      -44   1894
2.49      -45   2103
OP1       -47   1784

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