[Elecraft] 6 Meters

[Ian White GM3SEK]

Ron D'Eau Claire wrote:
>
>As Wayne's often mentioned here, the advanced up-conversion design of 
>the K3 is superior for HF but makes incorporating VHF a real challenge.

No challenge at all... had it been thought about at the design stage.

Since the K3 is top-of-the-line in so many other respects, it rankles 
that the 6m sensitivity is poorer than that of many 'inferior' 
transceivers. Even my old IC746 has a built-in alternative preamp for 6m 
which makes it easily capable of hearing antenna noise, which my K3 
cannot (and yes, it does meet the published sensitivity specification). 
Phil just discovered something very similar with his old FT100.

I'm not shouting or getting angry, but do remain quietly insistent that 
the inferior 6m sensitivity is a blemish on the K3's otherwise excellent 
performance. With great respect, it doesn't matter whether 6m is a 
minority interest or not; this is about excellence and what's needed to 
achieve it.

All the K3 does need for 6m is an alternative preamp with slightly more 
gain and a lower noise figure than the existing preamp (which was 
optimized mainly for strong signal handling). That's all it takes to 
shift the K3's window of dynamic range downward by several dB, which 
will make it capable of hearing antenna noise on 50MHz at a quiet site; 
which presently it isn't [1].

Although a preamp can improve the sensitivity by a few dB, the penalty 
is that a greater number of decibels must always be lost at the 
strong-signal end of the dynamic range. However, the K3 is better placed 
than any other transceiver to trade off a little of its dynamic range 
for a marked improvement in weak-signal performance.

The PR6 and many alternative preamps have proved those points. But the 
point that many people are making is that an adequate 6m preamp did not 
*have* to be an external accessory. Much of the size and complexity of 
the PR6 is due to its being an external unit. With forethought, 
something similar but *much* smaller and simpler could have been 
designed as an integral part of the KXV3 assembly - there's plenty of 
space in there. A selectable internal preamp is still possible as a 
modification involving a few track cuts (watch this space).

All the above can be expressed in more technical detail, in terms of 
antenna  noise temperatures and signal/noise ratio on weak signals, but 
that's the Sunday evening version... oops, Monday morning.



[1]  if anyone can distinctly hear 6m antenna noise on a bare K3, yours 
is not a "quiet" site. If you can't hear antenna noise but still claim 
to be able to hear "all the weak signals"... are you sure you've heard 
them *all*?


-- 

73 from Ian GM3SEK
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek