Re: Why is KX3 phase noise so much less than the K3 ?

Posted by wayne burdick on Apr 02, 2014; 3:19pm
URL: http://elecraft.85.s1.nabble.com/Why-is-KX3-phase-noise-so-much-less-than-the-K3-tp7586369p7586376.html

The K3 and KX3 both have very low phase noise. It can vary a bit from band to band and from one unit to the next. Sherwood measured one example of each, but typically both measure right around -140 dBc/Hz at 20 kHz.

When we designed the K3, we were trying to improve on the phase noise numbers usually found in transceivers with synthesized local oscillators. Typical values were -110 to -120 dBc/Hz, and this definitely impacted stations within close proximity of each other. By using a very high C/L ratio in the K3's VCO, we achieved numbers in the -140 range, and our field testers in close proximity could no longer hear each other at all.

This result was corroborated by the Ducie Island DXpedition, the first to use K3s. They told us that they had a 30-m CW station and a 30-m RTTY station both running at the same time within 1 kHz of each other.

The KX3 uses a different type of synthesizer, but the result is the same. In this case an on-chip VCO runs at a very high frequency and is then divided down to get to the HF range.

73,
Wayne
N6KR
 

On Apr 2, 2014, at 5:40 AM, Larry Lopez <[hidden email]> wrote:

> http://www.sherweng.com/table.html
>
> The LO Noise (dBc/Hz):
>
> 144 KX3
> 138 K3
> 130 R390A
> 121 FT-1000D
> 117 ICOM 720A
>
>
> I'm wondering why the KX3 Lo noise is so much better than the K3.
> The R390A value strange since the first local oscillator is a quartz
> crystal.
>
> I've owned a Icom 720A and own a FT-1000D.
> Ive never owned a K3, KX3 or a R390A.
>
> Larry
>
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/Why-is-KX3-phase-noise-so-much-less-than-the-K3-tp7586369.html
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