On Tuesday, Dick K5AND wrote:
Ciao, from CY0X, Sable Island.....
[...]
Since it is so easy to switch out the outboard preamp, we have frequently
done this on some of the weak sigs just to see if we could still hear them.
In many cases we could hear them Q5 with just the internal preamp. Ian,
GM3SEK, et al, have pointed out that the stock radio NF is somewhere in the
8-10db range, which is not stellar as six meter radio specs go. Nonetheless,
you'd be surprised at how many weak sigs we can still hear with only the
internal preamp engaged.
That's not surprising at all, as the K3 is only slightly lacking in
sensitivity on 6m. But contrary to other reports from users in very
quiet sites, my stock K3 can NOT hear background noise at 50MHz.
Before making that statement, I took a couple of days to confirm that
nothing else is wrong with the system. Receiver sensitivity meets
Elecraft's 'typical' specification with a few dB to spare. Feeder loss
was re-measured. And above all, I re-confirmed that my old IC-746 CAN
hear background noise from the same antenna/feedline with a comfortable
3-5dB margin.
A good operator like Dick can often make up for a few dB lacking in
signal/noise ratio... but only at the expense of greater operator
fatigue, and with the knowledge that some marginal QSOs *will* be lost,
when a more sensitive receiver could have pulled them through. That is
precisely why the receiver at CY0X has a prototype Elecraft preamp.
One small correction: Elecraft's specification for a typical MDS (noise
floor) of -136dBm in a noise bandwidth of 500Hz corresponds to a noise
figure of about 13dB (significantly more than 8-10dB). Cutting through
the technicalities, at a genuinely quiet 6m site that deficit *is*
noticeable - a gap in the K3's otherwise all-round excellence.
--
73 from Ian GM3SEK
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