[Elecraft] 2.8 Khz vs 2.7 Khz roof

[Bill Tippett]

K5WK:
 > I am looking for something somewhere that will help
me decide between the two.

         Since you're a previous Orion II owner I assume
you know all of its filters are 4-pole.  As W2VJN ofInrad and Rob 
Sherwood have previously written, shape
factor has *very little* impact on performance as roofing
filters beyond about -30 dB on the skirts.

The following dats is from Elecraft:

http://www.zerobeat.net/mediawiki/index.php/K3_Roofing_Filters

1.  6 dB bandwidth and 6/60 dB shape factor:

Filter  BW(-6dB)     Shape Factor

2700    2910*            2.9
2800    2888             1.6

*The 2.7k may have wider BW than the 2.8k.  This is
Elecraft's measurement and my 2.7k closely agrees with it.



2.  IMD performance:

Filter            20kHz  10kHz  5kHz  2kHz

2.7 kHz, 5 pole   100+   98      92    n/a
2.8 kHz, 8 pole   100+   100     93    n/a

(You'll never notice 1-2 dB of IMD performance)



Price:  2.7k included, 2.8k $125.  If you order
a 2.8k in place of the standard 2.7k in your
initial order, the incremental cost is $95.



         If you are seriously interested in better
filtering for SSB, I would spend my $125 for a
1.8k (or possibly even the rumored 1.5k) in
addition to the basic 2.7k, rather than using
it for a 2.8k.

                                         73,  Bill  W4ZV