[Elecraft] Re: K3 on 6 m: the external low-noise preamp project

[wayne burdick]

Ron Spencer wrote:

> Anyone else notice (and I know this will be difficult with hardly any
> openings) that the sensitivity of the K3 on 6 is down? Compared to the 
> 746 I
> have it seems down quite a bit (even with the K3 preamp on).

Ron,

The K3 is optimized for high dynamic range. For example, it has 40 dB 
higher blocking dynamic range and 25 to 30 dB higher IMDDR3 than the 
IC746. It also has narrow ham-band filters, and the one for 6 meters is 
triple-tuned, having about 1 to 2 dB higher loss than a double-tuned 
filter.

The IC746 *does* have a low-noise second preamp that is often used on 6 
meters, improving MDS to around -142 dBm (from the QST review). To 
achieve an MDS this good on 6 meters in the K3 -- with its narrow 
band-pass filters -- requires a preamp at a different point in the 
signal path: inserted between RX ANT IN and OUT. This bypasses other 
loss sources including the KAT3, low-pass filters, and T-R switch.

We've designed a dedicated 6-m preamp for this purpose. It's very 
small, and has its connectors spaced so it can be directly connected to 
RX ANT IN/OUT. Measured MDS on 6-m with the preamp patched in is around 
-142 to -143 dBm. It can be switched in automatically on 6 m only by 
the K3. It also includes a bypass relay so you can still use a receive 
antenna for other bands.

I'm not sure when the new preamp will available. But if you're 
interested in field testing one, please send me an e-mail.

tnx
Wayne
N6KR


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