[Elecraft] K3 Design

[Dick Dievendorff]

I'll guess.

The way my other rigs get general coverage is to up convert to an IF that's higher
than all the frequencies the radio supports. In the ICOM HF rigs I've owned (761, 775,
7800), that's around 70 mHz.  At that high IF, it's difficult (expensive or
unobtainium) to purchase a tight mode-specific filter (like 500 Hz wide with steep
skirts for CW).  So a relatively broad "roofing filter" is applied at the first IF and
further selectivity is applied at the 2nd and/or 3rd intermediate frequencies (or
DSP).

Although the K3 sports general coverage, I bet it gets a little touchy around the
first IF frequency, somewhere in the 8-9 mHz range, where the roofing filters can be
quite sharp and are available at reasonable cost.  By "a little touchy" I mean that
the rig's performance there might be different, or at the very least there is some
clever engineering to deal with that range.

Dick, K6KR


-----Original Message-----
From: elecraft-bounces at mailman.qth.net [mailto:elecraft-bounces at mailman.qth.net] On
Behalf Of Don Rasmussen
Sent: Sunday, July 15, 2007 3:41 PM
To: Elecraft
Subject: [Elecraft] K3 Design

After seeing the QST ads for the OMNI VI+ for so many
years, where they showed the noise floor rise to cover
up small signals inside your passband by larger
signals outside of the passband - and knowing that the
OMNI VI+ is a ham bands only rig, it seemed to
indicate that any of the radios that offered General
Coverage in the main receiver suffered that fault. 

The numbers seemed to prove that K2, OMNI VI+, Drake
R4C, Corsair II, all ham band only have the best
numbers as compared to the very best broadband designs
- most often from Japan.

The Orion only seemed to prove that one more time, the
main transceiver is ham bands only with the weaker
broadband second receiver for general coverage.

That's a long way to go to provide ham plus general
coverage unless those ham band only strips are
fundamentally important.

According to the early K3 info, the transmitter is
broadband, the only limitation is where they place the
bandpass filters and in theory they could arrange that
any way they want. 

It would be interesting to know what the real design
issues are and (no offense to Elecraft), how they were
the first to find the best of both worlds.  
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