[Elecraft] K3 IF Design

[Shane White]

Thanks Dave. I'll read your review.
Having been out of HAM radio for over a decade, I'm just trying to
understand where each company involved in selling radios is heading and what
their priorities are.


Dave G4AON wrote:
> 
> Shane
> 
> In the case of 14 MHz and the K3, the first IF is 8.215 MHz. An 
> oscillator at 22.215 MHz mixes with 14 MHz to give the difference 
> frequency of 8.215 MHz, however there is another difference of 14 MHz 
> minus 8.215 MHz which is 5.785 MHz which is the image frequency. The 
> ratio in dB between the wanted frequency and the image gives the image 
> rejection. There are other images involving the 2nd IF of 15 KHz too.
> 
> With the K3, the main images are greater than 70 dB below the wanted 
> signal. My own measurements give figures of 70 dB on 28.1 MHz (worst 
> case) to better than 110 dB on 1.8 MHz and 50 MHz.
> 
> The big advantage of a low 1st IF is the ability to use narrow "roofing" 
> filters to reject nearby interference. The disadvantage is potential for 
> poorer image rejection.
> 
> Image rejection is only one aspect of a transceiver design, of model A 
> was better in all respects than model B (and was cheaper) everyone would 
> buy model A, but life isn't so simple!
> 
> 73 Dave, G4AON
> http://www.astromag.co.uk/k3/
> ----------------------------------------
> Does the K3 manage to obtain image rejection comparable to Icom's and
> Yaesu's flagships? If so then it seems to me that Icom and Yaesu seem to
> be
> relying on a proven RF design and instead are concentrating their current
> efforts on ergonomics and presentation. There's nothing wrong with that
> though.
> 
> Thanks,
> Shane
> VK5ABQ
> 
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