[Elecraft] 2.7 vs 2.8

[Don Wilhelm]

Garry,

The amount of the actual offset is small for the 8 pole filters.  It is 
not important on wide filters, but with the more narrow ones, it becomes 
increasingly important - so yes, for maximum performance in diversity 
mode (and only in diversity mode) setting the offset midway between the 
measured offset of each filter is a prudent thing to do - although I 
would not bother with anything wider than a 1 kHz filter - the offset 
expressed as a percentage of the filter width is the 'telling' parameter 
- 10 Hz at 2.8 kHz is only 0.34% which is insignificant, but 10 Hz at 
250 Hz is 4% which is significant.

It is easy to determine the actual filter center (the K3 has the AFV and 
dBV displays built-in) - just scan through the response to a constant 
signal input level to the K3 to see where the -3 (or -6) dB points are 
(the filter center is midway between those two points).  Ifyou do not 
have an XG2 or other signal generator, run another transmitter into a 
dummy load and pick up an S-6 level signal with a short 'antenna wire' 
on the K3.  Nothing exotic is needed with a little bit of thought put 
into what needs to be accomplished.

73,
Don W3FPR

Garry Shapiro wrote:
> Apparently, from what has been previously discussed here, not all the 
> 8-pole filters are "no offset" in practice and some models in particular 
> might benefit from offset adjustments. And one should not forget that 
> these filters are roofers. Unless money is no object, I would say to 
> leave the stock filter in place and add another, narrower SSB filter. As 
> to what its BW should be, there have been scads of opinions expressed on 
> that subject, as well.
>
> Garry, NI6T
>
> On 4/12/2010 5:05 AM, David Ferrington, M0XDF wrote:
>   
>> Since you seem to favour 8 pole, I'd say do it. You should be able to get a rebate on the 2.8kHz against the 2.7kHz.
>> Also, if you are going to get the KRX3, it's simple to align the 8 pole filters - otherwise you need to tell Elecraft what the offset of your 2.7kHz is
>>    
>>     
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