[time-nuts] Low phase noise VCO

Don Latham djl at montana.com
Wed Feb 10 04:50:57 UTC 2010


Hi Bob and all:
This is interesting, because I suspect this frequency source is for an
Ettus Research USRP. A little further downtimeline I will be faced with
this problem as well. The SDR is designed already and requires a 64 MHz
clock, especially as this clock is used for the microwave transmit and
receive front ends. I had planned a synthesizer filtered...
The oscillator that is in the USRP that I have is good only to about 1
part in 10^8 or so for accuracy, better in stability. maybe the existing
osc. can be injection locked, or temp controlled in place.
Don

Bob Camp
> Hi
>
> With most SDR's a spur on the clock creates a spur in the radio. No matter
> how you do your multiply, you will wind up with some sub-harmonics running
> around. Much better / easier / quicker to start at 64 or 65 MHz.
>
> Bob
>
>
> On Feb 9, 2010, at 8:32 PM, Bruce Griffiths wrote:
>
>> Thats not very useful when you want the 4th harmonic as its amplitude is
>> zero fro a 25% duty cycle.
>> Using a duty cycle of 1/8, 3/8 or 5/8 will maximise the amplitude of the
>> 4th harmonic.
>>
>> see:
>> http://www.wenzel.com/pdffiles1/pdfs/choose.pdf
>>
>> Bruce
>>
>> Max Robinson wrote:
>>> If you start with a square wave odd order is all you can get but if you
>>> start with a pulse with a 25% duty cycle you can get even order.  It's
>>> best to optimize the pulse width for the harmonic you want.
>>>
>>> Regards.
>>>
>>> Max.  K 4 O D S.
>>>
>>> Email: max at maxsmusicplace.com
>>>
>>> Transistor site http://www.funwithtransistors.net
>>> Vacuum tube site: http://www.funwithtubes.net
>>> Music site: http://www.maxsmusicplace.com
>>>
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>>>
>>> ----- Original Message ----- From: "Nick Foster"
>>> <bistromat at hotmail.com>
>>> To: <time-nuts at febo.com>
>>> Sent: Tuesday, February 09, 2010 6:35 PM
>>> Subject: Re: [time-nuts] Low phase noise VCO
>>>
>>>
>>>>
>>>>> From: bill at iaxs.net
>>>>> To: time-nuts at febo.com
>>>>> Date: Tue, 9 Feb 2010 18:24:39 -0600
>>>>> Subject: Re: [time-nuts] Low phase noise VCO
>>>>>
>>>>> Which leads me to ask a novice question:
>>>>>
>>>>> Why not pull a 16 MHz crystal and multiply to 64 MHz?
>>>>>
>>>>> If you count down from 64 to 10 MHz, isn't the multiplication inside
>>>>> the
>>>>> PLL?
>>>>>
>>>>> Perhaps the noise is multiplied by 4, but would it work for the
>>>>> intended
>>>>> purpose?
>>>>>
>>>>> Bill Hawkins
>>>>
>>>> Can you do x4 multipliers? I thought odd-order harmonics were usually
>>>> used for multipliers. I'd be happy to be wrong!
>>>>
>>>> Nick
>>>>
>>
>>
>>
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>
>
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-- 
Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
www.lightningforensics.com
www.sixmilesystems.com




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