[Elecraft] KX3 as a base station? Yes, because it's all relative

[Wayne Burdick]

Joe Subich, W4TV wrote:

> If Elecraft are marketing the KX3 as anything other than a trail  
> radio the design missed the mark by 5 km.  ... lack of headphone  
> amplifier, and lack of separate line in and line out
> audio connections, the rig is severely lacking is the "home station"  
> department - particularly for digital (RTTY/PSK/JT65/etc.) operation.

Joe,

Does "home station" actually imply a fixed set of requirements? Prior  
to starting Elecraft with Eric, my entire home station was a  
Wilderness Radio Sierra transceiver (one of my earlier designs). I was  
quite happy to change bands with modules, log with a pencil, match  
antennas with a manual tuner, and key the rig with a homebrew keyer  
based on a Curtis keyer chip.

Surely the KX3, with all-mode/all-band coverage, full I.F. DSP, dual  
watch, a generous user interface, attached keyer paddle, battery pack,  
ATU, roofing filters, and full remote-control command set, could be  
considered a home station -- at least for some operators.

I also differ on some of your comments on the KX3's audio. There is no  
"lack" of a headphone amplifier. The KX3 has a headphone amp that is  
quite capable of driving any type of headphones to more volume than  
you need, at low distortion. This same jack can drive virtually any  
type of powered external speakers. Since the KX3 excels at stereo  
audio effects, including dual watch, I would think most operators  
would want to use dual external speakers anyway. Yes, the internal  
speaker is small, but it was never intended as the primary transducer.

True, there's no separate line in/out. We will, however, be adding  
separate gain controls for data modes.

Once we add the 100-W companion amp, the distinction between the KX3  
and a much larger "home" transceiver will be further blurred.


> ....with a SIS-570 based local oscillator and direct conversion
> the jury is still out as to whether the phase noise/reciprocal mixing
> performance is sufficient for use in strong signal (receive) and high
> power (> 10W) transmit environments.  Unless SiS have improved their
> products greatly or Wayne has some magic in his implementation, I am
> very concerned (witness the phase noise in the XG3).

Actually, the jury is in :)

The XG3--a very small device--uses a CS-2100 to keep cost and current  
drain low. It has a noise floor of about -105 dBc/Hz at all offsets.  
This is appropriate for a simple RF generator.

The KX3's phase noise was recently tested a well-known third-party  
test organization. They measured -142 dBc/Hz at a 2.5 kHz spacing, and  
-145 dBc/Hz at a 20 kHz spacing. The noise was still going down  
monotonically all the way to 500 kHz (their last data point). This is  
better than almost all "home station" transceivers.

So phase noise is not an issue.

Of course a transceiver like the K3, with a superhet architecture and  
very narrow crystal filters, will outperform a zero-I.F. receiver in  
close-in dynamic range (0-2 kHz). But the KX3 is no slouch.

73,
Wayne
N6KR