[Elecraft] 2.7 vs 2.8

[Fred Jensen]

David Ferrington, M0XDF wrote:
> I didn't say in all this not to get a narrower filter too - I think
> Bob said he was buying other filters too.

I thought I understood this filter subject but now, after the thread, 
not so much.

I thought the xtal roofing filter[s] are at the 1st IF [~8 MHz], and 
their purpose is to restrict the passband coming out of the 1st mixer so 
that strong adjacent signals don't make it to the 2nd mixer and DSP. 
Thus, it seems to me that tweaking the roofing filters will only have 
noticeable effects if you are plagued with very strong neighbors close 
in on your frequency ... often.

If that is your plague, then I would expect an 8-pole filter to have 
steeper skirts and would be a little more effective.  If that isn't your 
plague, I sort of doubt you could notice any difference at all.  The AGC 
loops in the K3 are a little complex, but I think the roofers keep 
close-in adjacent signals out of them as well.

If you have the second Rx, I think it would make sense to have the same 
filters in it as in the base K3.  I don't have the 2nd Rx, I have the 
"stock" SSB and CW filters, and I have no problem getting within a KHz 
of Jack, KF6T [1.5 KW 2.7 km away] on CW.  Ditto with WX6V and K6IDX.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2010 Cal QSO Party 2-3 Oct 2010
- www.cqp.org