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Electronics => Beginners => Topic started by: Telequipment on July 09, 2013, 07:55:51 pm

Title: I need a bit of advice please
Post by: Telequipment on July 09, 2013, 07:55:51 pm
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 ?
Title: Re: I need a bit of advice please
Post by: PA0PBZ on July 09, 2013, 08:02:20 pm
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...
Title: Re: I need a bit of advice please
Post by: Telequipment on July 09, 2013, 08:05:41 pm
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.
Title: Re: I need a bit of advice please
Post by: vk6zgo on July 11, 2013, 03:12:41 am
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!