[RTTY] K3

[J. Edward (Ed) Muns]

> 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.

> For RTTY I never use front-panel WIDTH settings below 300Hz, so the
> passband width is normally determined by the 260Hz xtal filter while the
> DSP handles the skirt selectivity.

That's fine.  I've just never had a problem with a slightly wider crystal
filter and using the DSP for final bandwidth.

> 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'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.

Ed - P49X (W0YK)