High Frequency Variable Oscillator

nos_slived · Mar 25, 2005

Hey, I'm attempting to build a high frequency variable oscillator on a range of 18 MHz to 48 MHz(preferably 48, but 42 would work if 48 is too high) using the 4011 quad NAND. I want it to work on the circuit that I'm posting, and I just need the values for C1, R1(pot), and R2(pot). Id like it if only one of the resistors was a Potentiometer, but if it cant cover the entire range, I would use 2. Can anybody help me out?

Sebi · Mar 25, 2005

I mean, this cct can work up to 10..15MHz only. For higher frequencies build one with BJT or FET.

audioguru · Mar 25, 2005

Sebi,
How did you make a 4011 oscillator go so high? With only 27pF and both resistors 1K with a 12V supply mine barely reached 2MHz.
I have heard that a 4049 high current buffer can reach 6MHz without the input resistor.

Do I dare try using a 74HC00 high-speed Cmos IC for 15MHz or do you think it might melt?

nos_slived · Mar 25, 2005

Anybody have a circuit that could reach that range?

Or even if I could hit 1MHz-5MHz, and multiply by 12. Anybody have any ideas?

All I have to do is stay under $10(preferably $5).

audioguru · Mar 25, 2005

The VCO of a 74HC4046 can go up to 17MHz.
https://www.electro-tech-online.com/custompdfs/2005/03/74HC_HCT4046A_CNV_2.pdf

nos_slived · Mar 25, 2005

I need much MUCH higher.

Nigel Goodwin · Mar 26, 2005

nos_slived said:
I need much MUCH higher.

You should probably be looking at LC or crystal oscillators then!, RC are really only suitable for fairly low frequency use.

Sebi · Mar 26, 2005

This cct can work safely on 10MHz, but need 15V supply. Some good pieces work up to 15MHz. I strongly recommend the MC1648 for wideband tuning.

nos_slived · Mar 26, 2005

Once again, I need much higher. I need to hit a controlled range of variable 18-48MHz.

Russlk · Mar 26, 2005

With C3=250Pf, the frequency is 20 mHz. With C3=10pF, the frequency is 45 mHz. A tuning capacitor from an AM radio would probably have that range.

nos_slived · Mar 26, 2005

Thank you, thank you, THANK YOU SO MUCH!

What are V1 and L1?

nos_slived · Mar 26, 2005

Thank you, thank you, THANK YOU SO MUCH!

OOPS: Double post. Could a MOD please delete this post.

Russlk · Mar 27, 2005

V1 is the 5 volt power supply but supply voltage is not critical. L1 is 7 turns #20 enameled wire on a 1/4 inch form (a standard pencil will do). The turns should be close and don't forget that the leads are part of the inductor, so keep them short.

nos_slived · Mar 27, 2005

OK.

Thanks. I have changed the pic a bit. Would this still work? Also, what is the difference between the 2 outputs? Could Q1 be substituted for any other transistor? Why does L1 say 275nH (what does it mean)? Did I mention, "Thank You"?

Russlk · Mar 28, 2005

I had used this circuit as a crystal checker (substitute the crystal for L1, C3 & C4). Out_2 was a 50 ohm drive to my frequency counter. 275 nano-henries is 275*10^-9 henries. Any transistor with Ft greater than 100 mHz should work, eg: 2N3904.

nos_slived · Mar 28, 2005

OK.

Thanks again.

Does anybody know a cheap circuit that I can add on to one of the outputs to compare that clock to an existing one and light an LED when they are the same?

nos_slived · Mar 29, 2005

Please don't let this fade to the land of unread threads.

I need this circuit before Friday so I can test it and finish my NES overclocking guide.

Sebi · Mar 30, 2005

I've just found this cct, probably work.

nos_slived · Mar 30, 2005

It says what IC2 is, but I don't see what IC1 is. Anybody know?

FRIED · Mar 30, 2005

74xx74

High Frequency Variable Oscillator

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