[RTTY] What are the best K3 filters for digital use?

[iw1ayd - Salvatore Irato]

Hi Dave et all.
In my short experience with the K3 I still use the 250 Hz and the 400 Hz 
8 poles filters.

BTW Dave I assume you mean RTTY for speaking of digital usage, for other 
DIGITAL modes, including CW as JT65, there are different criteria and 
choices.

The 200 Hz "roofing" even kicked in at some  wider frequency is 
definitively too tied, not useful for RTTY IMHO.

The 400 Hz and the 250Hz 8 oles will suffice. If I have to buy only one 
I would buy the 400 Hz, but not for contesting.

They are respectively tailored at 500 Hz and at 350 Hz. I mean that the 
kick in of the "roofing" filters is at those frequencies of the DSP 
filters intervention.

When RUNning in RTTY contests I use at first a 800 Hz DSP filters on 
arrive, just to be sure that I have nobody near more than that, +/- 400 
Hz. Then, when somebody get too near my RUN QRG I kick in the 500 Hz, 
via a CAT command. The  last 350Hz cut, more tightened by hands if in 
needs but not that much, is used when the nearby signals are getting too 
near. This  may happened too often since the latest production firmware 
for the K3. The TX FSK signal is definitively right tied now, but too 
tight for all those that have theirs FSK/AFSK signals still too wide and 
good RX filters ;-( ...
S&P is done on crowded bands at 500 Hz with the help of the right SPAN 
onto P3. In not congestionated bands even the 800 Hz is enough, if you 
don't get too much near to a much large signal out of the one you are 
searching for - listened or viewed.

DXing is the same beast, still having single receiver inside my K3, I 
use almost the same tight filters but I have also a more larger CAT 
defined filters, to search the DX when it spotted with a casual QRG. 
When searching by myself a use the 1800 Hz filter.
It maybe that having a second receiver and attempting to catch the by 
now responder, when in a pile up, a something more wide filter than 
300/500 Hz is needed. But I have not experience at all for it. Just 
doing VFO reverse with the help of the P3 is already somewhat helpful 
for me. But this practice is becoming  not useful with multiple streams 
decoder in use by the DX.
Last but not least. Even if the 8 poles filters are advertised as 
centered in the MF I moved a little bit all the 4 filters in the two K3 
I own. Just empirically the waterfall of MMTTY wasn't centered around 
tones that much, just an hair was enough.

With the 800 Hz tailoring, or the 1000 Hz tailoring at home, DSP slices 
as the kick in filter here is a 1800 Hz, the AGC is pumping a lot with 
strong nearby signals, judging on the waterfall saturation and ears.

There are much more experienced operators than me here that could add 
more or correct me.

   73 de iw1ayd Salvo

PS the only way to use DUAL FB, that work for any couple of tones and be 
arranged itself by the bandwidth control, is with the tied filter you 
have, the 350 Hz cut of the 250 Hz is critical but quite good to listen 
those elusive DX signals. Unfortunately multiple demodulator loose half 
of their brightest capacities to decode when used with a tied filter and 
DUAL FB. But this is a know factor,  no way to eliminate this  side 
effect under some circumstances.

On 27/11/2013 18:00, rtty-request at contesting.com wrote:
> Message: 2
> Date: Wed, 27 Nov 2013 11:01:45 -0500
> From: Dave Barr<recordupe at verizon.net>
> To:rtty at contesting.com
> Subject: [RTTY] What are the best K3 filters for digital use?
> Message-ID:<52961769.2000702 at verizon.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Which two of the 200/250/400 and 500 filters are best for digital use,
> primarily RTTY contests and dx.  I understand that for JT-65 and PSK the
> standard ssb filter, or even an AM filter is useable.  I am concerned
> that the 200 hz might be too narrow for RTTY.  I look forward to any
> advice given.
>
> 73, Dave, K2YG
>