[Elecraft] Re: K3 receiver sensitivity on 50MHz

[wayne burdick]

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


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