[Elecraft] K3 Roofing Filter Gain Setup

[Brian Alsop]

Sorry guys, having trouble with email program today. Please ignore 
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


On 5/29/2011 14:02, Brian Alsop wrote:
> On 5/29/2011 13:43, drewko wrote:
>> If I use a 50uv signal generator to set the filter gains for equal
>> 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
>>
>>
>> On Sat, 28 May 2011 14:18:45 -0700, you wrote:
>>
>>> 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
>>>
>>>
>>
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