[Elecraft] Re: Better receiver: KX1 or Sierra?

[Wayne Burdick]

dmaliniak at penton.com wrote:
 
> On the Wilderness Radio website, QRPBob quotes a Sierra receive
> sensitivity spec of "better than 0.5uV for 10dB S+N/N selectivity."
> 
> On Elecraft's website, I can't find any comparable specification for the
> KX1.
> 
> I guess what I'm asking is: Which rig has the better receiver? Any
> opinions from QRPers who own both? While we're at it, how about the K1?
> Where does that fall in the mix receive-wise?

Hi David,

We spec both the K1 and KX1 at a slightly better figure (0.2 uV for 10 dB S+N/N;
see the owner's manuals, which can be downloaded). However, I used a very
similar receiver front-end design for all three rigs, and in typical operating
conditions they should all be about the same. The primary differences are in the
AF amplifier and AGC circuitry. Of the three, the K1 has the tightest band-pass
filters, especially the four-band version.

The Sierra uses an MC1350 I.F. amp to get most of its overall gain, and also for
AGC. This is why there's a second crystal filter (1 crystal) following the I.F.;
the '1350 generates some significant noise of its own. In both the K1 and KX1
there's no I.F. amp, which improves the noise figure a bit, eliminates the need
for that extra crystal, and reduces current drain. But since there's no I.F.
amp, we applied AGC directly to the mixers in the K1 and KX1. This technique
works well if used carefully.

In the K1, we wanted to have plenty of speaker drive, so we followed the first
AF amp with an AF output stage. But the KX1 is intended for use only with
headphones, so we kept things simple. In fact the basic KX1 receive strip is
almost identical to the NorCal 40A's, which has an excellent NF. But the KX1 has
much better AGC. The '40A uses JFETs as variable resistors for AGC, and this has
a much lower upper limit on signal handling than does the KX1/K1 style AGC,
which varies DC bias on the mixers.

So while there are minor differences between the receivers, the choice of which
rig to use comes down more to ergonomics and available options:

- The Sierra has band modules for 160-10, so it has the widest band coverage. 

- The 4-band K1 covers the most popular bands and doesn't require module
switching, and is smaller than the Sierra. 

- The KX1 is a different animal entirely, being extremely small but covering
only the three most popular QRP bands. 

Finally, the K1 and KX1 both have internal battery and ATU options, which the
Sierra lacks. Still, the Sierra and the monoband 40A (and SST) are very easy to
build and so are good choices for first-time builders. 

Having designed all of these rigs I find it a little hard to be completely
objective, so get other opinions  ;)

73,
Wayne
N6KR

-- 

http://www.elecraft.com