[hpsdr] 20MHz ref. for Horton LO

[Phil Harman]

Hi Grant,

Thanks for you input - I will most certainly consider your suggestions.

73's Phil....VK6APH



----- Original Message ----- 
From: "Grant Hodgson" <grant at ghengineering.co.uk>
To: <hpsdr at hpsdr.org>
Sent: Tuesday, July 11, 2006 3:58 PM
Subject: [hpsdr] 20MHz ref. for Horton LO


> ***** High Performance Software Defined Radio Discussion List *****
>
> Some comments about generating the 800kHz comparison frequency for the 
> Horton
> uW LO :-
>
> I would have thought that if Horton needs a 20MHz reference signal, then 
> it
> should be Horton that generates it - not Gibraltar - it would seem to be a
> much neater engineering solution to keep the 20MHz signal on the Horton 
> PCB only.
>
> There are a couple of easy ways to double the 10MHz signal :-
> 1) use a transformer and a dual-schottky diode pair to make a full-wave
> rectifier.  You could buy one from the likes of Mini-circuits, but this
> would be a very expensive solution, a couple of discrete components is a 
> very
> cheap, but effective solution.  A buffer may be required for the 20MHz 
> signal,
> but most PLL ICs have one on-chip already.  The output doesn't really need
> much filtering - the odd harmonics should be fairly well down if the
> transformer is balanced and the diodes are matched, and the even harmonics
> don't matter - the PLL IC would be just as happy with a 20MHz square-wave 
> input.
>
> 2) Use the internal reference doubler in one of the frac-N PLL ICs such as 
> the
> LMX2486.  The doubler adds negligable phase noise.  You wouldn't need to 
> use
> the fractional part of the dividers within this IC; you could use it just 
> like
> a normal integer-N PLL with no additional fractional spurs.
>
> The LMX2486 has a few other features as well that I'm investigating for 
> use on
> Horton.
>
> I wouldn't try to synthesise a 20MHz signal from 10MHz - far too 
> complicated
> with worse performance and more cost.
>
> regards
>
> Grant   G8UBN
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