[Elecraft] Let's Try This Again -- was "[K3] ... A 750 Hz, 8-Pole ... Filter?"

[Ian White GM3SEK]

Bill W4ZV wrote:
>
>
>Gary Hvizdak wrote:
>>
>> If instead you think that there might be a greater demand for some other
>> bandwidth 8-pole INRAD roofing filter, please email me (off-Reflector) to
>> let me know that width and include your reasoning for desiring that other
>> width.
>>
>
>I'd be interested in a **true** 6 dB BW 8-pole for 200-250 Hz (Inrad's "250"
>is actually 370 Hz BW and I don't want that).

Yes, the real gap in the available range of roofing filters is an 8-pole 
with a *true* 6dB BW of 250Hz.

As for the choice between 250Hz and 200Hz, I have tried both bandwidths 
by modifying a stock 200Hz 5-pole filter (with design help from Wayne).

In real-life contest QRM there is no noticeable difference between the 
two bandwidths on CW, but there is a huge difference for RTTY.  With 
170Hz shift, a 250Hz filter is very close to the lower limit of usable 
bandwidth, but definitely on the right side of the line - in heavy RTTY 
QRM, a 250Hz filter can be a game changer. But 200Hz is below that 
limit, not usable at all.

For those reasons I would support 250Hz because it would meet the needs 
of more users, but would vote against 200Hz (and in this, I do literally 
mean "vote with my pocketbook").


-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek