Author Topic: I need a bit of advice please  (Read 1863 times)

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Telequipment

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I need a bit of advice please
« on: July 10, 2013, 05:55:51 am »
Hello,  Firstly I need to build a wide range VFO, I have a feeling these are a bit of a black art, to get them right. Secondly I need to build a Noise source that quite rich in noise content, and do you shield these ?
 

Online PA0PBZ

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Re: I need a bit of advice please
« Reply #1 on: July 10, 2013, 06:02:20 am »
What is a wide range, and what is the range?
Let's say you want 0-100Mhz, the normal way to do that is to mix 2 higher frequency sources to get what you want, so for instance a 500Mhz fixed source and a 500-600 Mhz VFO. You can't just make a VFO that goes from 0 -100Mhz...
Keyboard error: Press F1 to continue.
 

Telequipment

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Re: I need a bit of advice please
« Reply #2 on: July 10, 2013, 06:05:41 am »
What is a wide range, and what is the range?
Let's say you want 0-100Mhz, the normal way to do that is to mix 2 higher frequency sources to get what you want, so for instance a 500Mhz fixed source and a 500-600 Mhz VFO. You can't just make a VFO that goes from 0 -100Mhz...

That would do nicely, I thought it was more complicated :phew: There are parts of our hobby I just don't understand.
 

Offline vk6zgo

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Re: I need a bit of advice please
« Reply #3 on: July 11, 2013, 01:12:41 pm »
A 500-600 MHz VFO is no pushover,either!

You're not going to make a  stable free running one,you are looking at a PLL or similar for that sort of frequency.
Oh,& its output should be within a dB or so over that range! ;D

Maybe you can crystal lock the 500MHz fixed oscillator,but you will probably have to either multiply it up from a lower frequency,or use another PLL.

You are then stuck with designing a mixer & output stage which is flat from 0--100MHz!

Complicated?----No,but incredibly difficult to actually do!

This is why test equipment manufacturers charge big bucks!
 


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