[Elecraft] K3 Roofing Filter Gain Setup

[Dick Dievendorff]

There are recommendations in the K3 Owner's manual (see "Crystal Filter
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


-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of goldtr8 at charter.net
Sent: Saturday, May 28, 2011 12:17 PM
To: Elecraft
Subject: [Elecraft] K3 Roofing Filter Gain Setup

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
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