Ian White GM3SEK wrote:
On the subject of 50MHz, Wayne, please could you say more about the
receiver sensitivity specification?
At present the sensitivity spec is the same on all bands, namely:
"-136 dBm (typical), preamp on, 500Hz b/w"....
Hi Ian,
The K3 is optimized for high dynamic range, which requires a
high-intercept preamp and mixer as well as the narrowest possible
band-pass filters (consistent with good return loss). We also used PIN
diode T-R switching to eliminate relays during QSK. There are small
front-end losses associated with each of these design choices.
However, there is a way that one could have the best of both worlds.
Those who would like an extremely low NF on 6 meters (or other bands)
could patch in an external low-noise preamp between the RX ANT IN and
OUT jacks. I've asked one our staff engineers to look into such a
design, although there may be third-party products already available.
You'd need the KXV3 option. The KXV3's RX ANT IN/OUT jacks are fully
isolated from the transmit path, so high-sensitivity devices could be
used in the preamp. The RX ANT IN/OUT jacks are also pre-BPF and can be
turned on/off per-band. A 6-meter-only implementation with its own
optimized BPFs could provide a world-class NF.
Further, you could power the external preamp from the K3's 12-V DC
accessory output (up to 0.5 A, switched).
I personally prefer this means of achieving a very low 6-meter NF,
because it doesn't result in compromises to the rest of the design.
There are other rigs on the market that incorporate a second,
switchable preamp specifically for this purpose, but none of these can
match the K3's close-in dynamic range on HF.
73,
Wayne
N6KR
---
http://www.elecraft.com
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