looking for a VCO  - Page 1
Forum section: electronics / beginners

author: electronics man
author_rank: Frequent Contributor
timestamp: March 16, 2014, 04:41:26 pm
content: i am looking for a VCO that can output a wide frequance band from a few kHz to as high as i can get, actual freqance doesnt realy matter, I have looked on mouser, digi key, farnell and rs but they all seem to have a pretty narrow frequancy range. what ineed o do is sweep a an Lo frequancy through an RF mixer so i can pick out specific frequancies from the RF. some help would be greatly apreciated.

author: Andreas
author_rank: Super Contributor
timestamp: March 16, 2014, 05:52:46 pm
content: Hello,How about a 74HC(T)4046 or a CD4046 device (not using the PLL phase comparator)with best regardsAndreas

author: Zero999
author_rank: Super Contributor
timestamp: March 16, 2014, 05:56:05 pm
content: You can build your own using comparators: see page 7 of the LM339 data sheet.http://www2.ensc.sfu.ca/reference/data-sheets/LM339.PDF

author: electronics man
author_rank: Frequent Contributor
timestamp: March 17, 2014, 03:32:55 pm
content: They are a bit low frequancy but I can alwase multiply it with a PLL

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 17, 2014, 03:40:48 pm
content: If you need to sweep from very low use 2 oscillators and a mixer. You can buy vco's that can sweep from 2 to 4 GHz, mixing that with 2 GHz will give you 0-2 Ghz after a low pass filter. Is that high enough?

author: katzohki
author_rank: Frequent Contributor
timestamp: March 17, 2014, 03:43:46 pm
content: Minicircuits has some things that might be what you need. They are not listed on Digikey. Some of their stuff can be pricy, but the through hole parts are the cheapest (they call it plug-in). Good luck!http://www.minicircuits.com/products/Oscillators.shtml

author: electronics man
author_rank: Frequent Contributor
timestamp: March 17, 2014, 03:55:48 pm
content: Quote from: PA0PBZ on March 17, 2014, 03:40:48 pmmaybe a bit too high but it would work with lower ones.so if I use a 200Mhz to 400mhz vco and I put this into a mixer and use a 200Mhz as the lo I can get 0 to 200Mhz after a low pass filter.

author: Zero999
author_rank: Super Contributor
timestamp: March 17, 2014, 07:44:22 pm
content: You're being very vague, so now it's near zero to 200MHz, what about jitter and phase noise?Yes, building a high frequency VCO and a lower frequency oscillator and mixing the two frequencies will give the difference.You can make your own VCO and the fixed oscillator can double as the mixer.

author: electronics man
author_rank: Frequent Contributor
timestamp: March 17, 2014, 08:07:34 pm
content: well the phase noise and jitter dont realy matter alot but should be as low as i can get and the frequancy should be high but not so high that i cant easily design i circuit so anywhere between 100Mhz and 600Mhz

author: electronics man
author_rank: Frequent Contributor
timestamp: March 17, 2014, 08:20:26 pm
content: are these ok:http://uk.farnell.com/crystek/cvco55cl-0200-0400/osc-vco-200-400mhz/dp/1582176this for the fixed oscillator:http://uk.farnell.com/silicon-laboratories/510aba200m000aag/osc-200mhz-50ppm-3-3v-smd/dp/2393952?in_merch=New%20Products&in_merch=Featured%20New%20Produthis for the mixer:http://uk.farnell.com/linear-technology/lt5560edd-pbf/mixer-active-0-01mhz-4ghz-qfn-8/dp/1345583

author: Zero999
author_rank: Super Contributor
timestamp: March 17, 2014, 10:51:57 pm
content: The power supply voltage for the oscillator is different to the VCO.For convenience and to make it easier to interface between components, you should ideally choose devices which can all run off the same voltage.

author: electronics man
author_rank: Frequent Contributor
timestamp: March 18, 2014, 06:24:39 pm
content: Its very hard to find a 5v 200Mhz oscillator I could get a lower frequancy one and multiply it up with a PLL

author: Zero999
author_rank: Super Contributor
timestamp: March 18, 2014, 07:57:54 pm
content: Or you could us a harmonic filter - much easier than PLL.