[RTTY] K3

[Joe Subich, W4TV]

> 200Hz is a wee bit too tight, IMO. I think the ideal setup 
> would be 400Hz for general RTTY operation, and a 250Hz for 
> those times when you have strong stations moving in on both 
> sides.

I can confirm that the 200 Hz filter is a bit too tight.  My 
200 Hz filters measure 170 and 180 Hz which puts both RTTY 
tones at the -6dB points with most of the switching sidebands 
well down the filter skirt.   

Having both the Elecraft (Inrad) 250 Hz and 400 Hz filters 
is a bit redundant.  Per data on the Elecraft web site 
(http://www.elecraft.com/K3/K3_8_pole_plots.htm), the 400 Hz 
filter is 435 Hz wide (-6 dB) and the 250 Hz filter is 370 Hz
wide (-6 dB).  There is hardly enough difference to justify 
the cost of the 250 Hz filter.  

For reference, I have measured four of the 500 Hz/5 pole filters 
(two in each of my K3s) ... three were 480 Hz, one was 470 Hz at 
-6 dB.  Elecraft have posted e-mail giving component changes for 
the 200 Hz filter (two capacitors) that will reduce the insertion 
loss by about .7dB and increase the nominal bandwidth from 225 Hz 
to 260 or 290 Hz.  GM3SEK has modified his 200 Hz filter and 
confirms that the 260 Hz modification works as predicted.  

Given the price difference between the 5-pole and 8-pole 
filters, I recommend sticking with the 500 Hz 5-pole filter 
for most operation and considering a modified 200 Hs 5-pole 
filter for RTTY if necessary.  Note that the narrow (Inrad 
250 or modified 5-pole filter) will only effect interfering 
signals (IMDDR) in a very narrow range (+200 to 350 Hz and 
- 200 to 350 Hz) on either side of the basic filter as the 
ultimate selectivity in the K3 is produced by the DSP which 
can be adjusted independently of the "roofing" filter. 

73, 

   ... Joe, W4TV 
 





> -----Original Message-----
> From: rtty-bounces at contesting.com 
> [mailto:rtty-bounces at contesting.com] On Behalf Of Iain 
> MacDonnell - N6ML
> Sent: Tuesday, January 06, 2009 2:41 PM
> To: Terry
> Cc: RTTY
> Subject: Re: [RTTY] K3
> 
> 
> 
> 
> Terry wrote:
> > I'm considering purchasing a K3.  Which filter do I want for RTTY 
> > (both
> > DX & contesting)?  200 Hz 5-pole or 250 Hz 8-pole?  Or is 
> there some 
> > other configuration I should consider?
> 
> 200Hz is a wee bit too tight, IMO. I think the ideal setup 
> would be 400Hz for general RTTY operation, and a 250Hz for 
> those times when you have strong stations moving in on both sides.
> 
> I ran the whole RU on a 400Hz, and mostly got away with 
> shifting it slightly to one side or the other, but there were 
> times when a 250Hz would have been nice to have.
> 
>      ~Iain / N6ML
>