[RTTY] K3

[Ian White GM3SEK]

Ed Muns wrote:

>> Sorry, I had forgotten to mention that. My K3 has a 400Hz filter, and is
>> configured to use the 260Hz filter at all bandwidth settings below
>> 350Hz. This gives a reasonably smooth reduction in passband width.
>
>How is this a "smooth transition"?  Your IF bandwidth goes from 350 Hz to
>260 Hz in one step (that would normally be a 50 Hz step). Then it stays at
>260 until you get below 200 Hz, or so, on the DSP.  From your next
>statement, I guess you don't really care about smooth transitions and
>consistent steps.
>
Well, I did say "reasonably smooth", and the K3's system of switching in 
filters at the same time as reducing the DSP bandwidth will always make 
some steps larger than others.

But you're right, Ed: the irregular steps don't worry me anyhow.


>> For 40m contesting in Europe, many weak and distant multipliers can only
>> be worked by beaming directly into a wall of extremely strong QRM. If
>> you want those mults, the receiver bandwidth must be reduced to the
>> minimum possible *AND* the receiver must maintain a very high dynamic
>> range at this narrow bandwidth. The second part of this requirement is
>> where the problems arise.
>
>Yes, but I'm surprised that a 260 Hz vs. a 370 Hz crystal filter will
>improve things noticeably.

I was surprised too, but on those rare occasions when the wider roofing 
filter allows a very strong off-frequency signal to activate the 
hardware AGC, the effect on copy is very "noticeable" indeed.

>I'll reserve final judgment, though, until I try
>it.  I never built up any 260 or 280 Hz crystal filters because I didn't
>believe it would help.  At these minute differences other attributes of
>those strong signals will both you the same with either crystal filter.
>
>> In this intensely competitive situation it is often necessary to use a
>> 250Hz bandwidth for hours at a stretch, because very strong stations are
>> operating close by. Stations that are using 250Hz filters can coexist
>> quite comfortably. But with wider bandwidths such as 500Hz, strong
>> nearby tones are highly likely to capture the AGC and de-sense the
>> receiver.
>
>I haven't seen this in Aruba with the 370 Hz crystal filter, but like I say
>above, I'll give the narrower crystal filter a try and see for myself.
>

You may never see it from Aruba, as 40m is not so crowded in NA and the 
multipliers tend to come to you. The QRM in Europe may also improve in 
the next few years as stations begin to adopt the new band plan and 
spread out more.



-- 

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