[Elecraft] K3 Roofing Filter Gain Setup
gol...@charter.net
I am searching without much luck for recommendations for the gain
setting recommendations for roofing filters.
Specfically I have a 700 hz 8 pole and a 200 hz filter 5 pole. There
is a gain setting in the k3 setup menue and I remember there were
recomendations on how to choose this setting. However, I have not been
able to find reference on the net.
Please can anyone provide some guidance as the performance when these
filters are engaged with digital modes is rather disapointing. What I
mean by this is that a signal can be very clean with the 2.7 or 2.1
filter engaged but if I use on of these filters the signal becomes very
poor. I want to use these to isolate close in signals but there appears
to be a lot of distortation so they are basically of little use.
I am betting that there is more to this gain setting than meets the eye
and that is where my problem is. I have put the gain for these two
filters at 1 and the 2.1 & 2.7 at zero.
I will be playing around with the settings, but there is a method to set
this parameter so I need to learn what and why so I can make them work
the way they are supposed to work.
Thanks and have a great holiday.
Don
KD8NNU
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Matt Zilmer
Use VFO A to set the gain in dB. In general,
you’ll want to add 1-2 dB for 400-500 Hz
filters, and 3-4 dB for 200-250 Hz filters.
I left the 1.8, 2.8, 6 and 13K filters alone. The 250 Hz I have set
for 3 dB gain.
matt W6NIA
--
Gary Hvizdak
"I am searching without much luck for recommendations for the gain
setting recommendations for roofing filters."
=== = = = ===
Don,
See Wayne's "K3 crystal filter offset/bandwidth/gain setting guidelines"
post, dated 13 FEB 2009. You will find it in the Reflector archives at
http://mailman.qth.net/pipermail/elecraft/2009-February/105445.html
73,
Gary KI4GGX
gol...@charter.net
I am looking at PSK31 signals not SSB and my definition of distortion is
my visual observation on the PC waterfall in DM780 and the fact that
decode of the signal by the PC starts to fail when I engage the narrow
filters. This is observed when I have clean signals using the 2.1 or
2.7 filters and only DSP. I do understand the how strong signals can
create havoc in the band which is why I have the narrow filters. The
issue is until I get them setup to work well without interference I will
not expect them to help much when I have close signals or weak signals
that I want to pull out.
I do have all the offsets per the documentation with the filters so this
should not be the issue.
Folks have pointed to some articles regarding the setting of the filter
gain and have privided insight on how to use information on the K3
display to help quantify signals.
My biggest problem is I have zero results when I do searches on these
types of topics. One of the responses was a link directly to a writeup
that I had been searching for, go figure. :-)
All I know for sure is that again the user community has helped me get
to the info I needed and now I have a basis of logic on what I will be
looking at when I make some adjustments.
Now I need to get in front of the radio and follow the advice of the
wise ones.
Thanks Everyone!!!
Don
KD8NNU
On Sat, May 28, 2011 at 3:17 PM, gol...@charter.net wrote:
> Gents,
>
> I am searching without much luck for recommendations for the gain
> setting recommendations for roofing filters.
>
> Specfically I have a 700 hz 8 pole and a 200 hz filter 5 pole. There
> is a gain setting in the k3 setup menue and I remember there were
> recomendations on how to choose this setting. However, I have not
> been able to find reference on the net.
>
> Please can anyone provide some guidance as the performance when these
> filters are engaged with digital modes is rather disapointing. What
> I mean by this is that a signal can be very clean with the 2.7 or 2.1
> filter engaged but if I use on of these filters the signal becomes
> very poor. I want to use these to isolate close in signals but there
> appears to be a lot of distortation so they are basically of little
> use.
>
> I am betting that there is more to this gain setting than meets the
> eye and that is where my problem is. I have put the gain for these
> two filters at 1 and the 2.1 & 2.7 at zero.
>
> I will be playing around with the settings, but there is a method to
> set this parameter so I need to learn what and why so I can make them
> work the way they are supposed to work.
>
> Thanks and have a great holiday.
>
> Don
> KD8NNU
Dick Dievendorff
Setup", indexed, on page 46) :
Use VFO A to set the gain in dB. In general, you'll want to add 1-2 dB for
400-500 Hz filters, and 3-4 dB for 200-250 Hz filters.
and there is a table (with essentially the same guidance) in K3 Utility Help
for the Filter Configuration page. I've lost the table formatting in
cut/paste from Help, but here's the information:
Narrow crystal filters tend to have more passband loss than wide filters.
You can compensate for this effect by specifying an amount of added gain to
use for each filter in receive mode. Enter the desired gain "boost", in
decibels, for each filter. You may specify a value between 0 and 8 dB.
Elecraft recommends using the initial loss compensation values below. You
may wish to further adjust the values for your particular filters.
Part Number Bandwidth Gain
KFL3A-200 0.20 kHz 3-4 dB
KFL3A-250 0.25 kHz 3-4 dB
KFL3A-400 0.40 kHz 1-2 dB
KFL3A-500 0.50 kHz 1-2 dB
KFL3A-1.0K 1.00 kHz 0 dB
KFL3A-1.8K 1.80 kHz 0 dB
KFL3A-2.1K 2.10 kHz 0 dB
KFL3A-2.7K 2.70 kHz 0 dB
KFL3A-2.8K 2.80 kHz 0 dB
KFL3A-6K 6.00 kHz 0 dB
KFL3B-FM 13.00 kHz 0 dB
73 de Dick, K6KR
drewko
readings on my K3's AFV meter I arrive at the following compensations:
2.70 KHz = 0db
500 Hz = 4 db
250 Hz = 8 db
This is way more aggressive than the suggested amounts but these
figures do sound equalized to my ears for real signal conditions. The
factory settings are noticeably weak. Maybe my particular filters are
just not up to par.
73,
Drew
AF2Z
______________________________________________________________
Brian Alsop
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Brian Alsop
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______________________________________________________________
Brian Alsop
multiple messages.
Drew,
Interesting.
Did the same with a signal generator, S3 signal, AGC off and Spectrogram
to match the peak. I'm primarily interested in weak signal CW work and
don't want to fool with the AF gain when filter settings changed.
My results:
2.7 0 db
1.8 2
400 5
250 8
200 8
Have others say they didn't think 8db gain was enough for the narrowest
filters. The only way I can see to get 4db for the narrowest filters is
to somehow set a negative value for the 2.7 filter. That might not be
all that bad to have such a capability.
I wish somebody would explain excatly what the RF gain calibration does
and how it works. This is typically done after the crystal filter gains
are set. The procedure asks one to set the filter width to 100 Hz.
That of course would kick in the 200 Hz filter here. But some have said
this procedure sets the gain of the stage before the filters. So why
specify a filter width setting? What is monitored during the RF gain
adjustment process?
73 de Brian/K3KO
Lyle Johnson
the K3's receive gain, in dB.
It uses a narrow filter setting to improve the S/N of the signal
measured by the DSP as the gain decreases and the signal being measured
is reduced in amplitude due to that decrease.
The hardware AGC voltage is applied after the 8.215 MHz roofing filters,
so the accuracy of the filter gain compensation is of no practical
consequence as long as the roofing filter selection is not changed
during the calibration process.
Becasue the hardware AGC calibration may affect the reported S Meter
values, S Meter calbration should be checked and adjusted if required,
after RF Gain Calibration is completed.
73,
Lyle KK7P
> I wish somebody would explain excatly what the RF gain calibration does
> and how it works. This is typically done after the crystal filter gains
> are set. The procedure asks one to set the filter width to 100 Hz.
> That of course would kick in the 200 Hz filter here. But some have said
> this procedure sets the gain of the stage before the filters. So why
> specify a filter width setting? What is monitored during the RF gain
> adjustment process?
______________________________________________________________