Cheapest way to generate 100Mhz sine wave - Page 1
Forum section: electronics / testgear

author: freebil
author_rank: Regular Contributor
timestamp: August 11, 2016, 03:56:20 pm
content: Hello. Is there any cheap way to generate 100Mhz sine wave? I have 2 ad9850 dds. Is it possible to add the frequencies of each 9850 sine wave and see the result to the oscilloscope?

author: Fungus
author_rank: Super Contributor
timestamp: August 11, 2016, 07:03:27 pm
content: Quote from: evb149 on August 11, 2016, 06:38:34 pmThe cheapo eBay modules go up to about 25MHz before they start falling apart.

author: joeqsmith
author_rank: Super Contributor
timestamp: August 12, 2016, 01:05:08 am
content: Quote from: evb149 on August 11, 2016, 06:38:34 pmAgree with evb149. Really depends what you need. Here's a simple 80 - 100MHz single 2n4401 transistor oscillator I stuck on some protoboard. Cheap.

author: joeqsmith
author_rank: Super Contributor
timestamp: August 12, 2016, 11:45:32 am
content: Quote from: evb149 on August 11, 2016, 06:38:34 pmAgain I agree with evb149's comment. I had to search for it but I had posted a fair amount of data using 7400 logic.https://www.eevblog.com/forum/projects/waveforms-in-a-74ls04-ring-oscillator/

author: bobaruni
author_rank: Regular Contributor
timestamp: August 12, 2016, 12:05:52 pm
content: You could put the ad9850's output through a frequency multiplier with a tuned output for ~100Mhz.A single transistor amplifier with a tank in the collector tuned to 100Mhz should do the trick.Just feed a sub-harmonic of the desired exact frequency (near to or on 100Mhz) on the input and the tank will resonate at an integer multiple of the input.If you want to combine the outputs of both ad9850's, you will need preferably a double balanced mixer with a similarly tuned output.

author: KE5FX
author_rank: Super Contributor
timestamp: August 13, 2016, 05:52:34 am
content: All you need is a filter of some sort. Your AD9850 will put out a healthy signal at 100 MHz in its second or third Nyquist zone.

author: freebil
author_rank: Regular Contributor
timestamp: August 13, 2016, 07:48:28 am
content: Thanks for the answers. Is it possible to use the built in ds1054z filters?

author: Kalvin
author_rank: Super Contributor
timestamp: August 13, 2016, 01:25:58 pm
content: If you need a better frequency accuracy, you can add a simple and cheap PLL which will keep your $0.10 oscillator stable.You can use the AD9850 as the reference oscillator for the PLL so you can fine-tune or adjust the output frequency easily.

author: ADT123
author_rank: Regular Contributor
timestamp: August 13, 2016, 03:25:39 pm
content: If you are more worried about the frequency accuracy than purity of the sine wave then a quick way would be to buy a 100MHz CMOS crystal oscillator (couple of dollars/pounds/euros). They are available in 4 pin DIP packages (power, ground and output).It will output a square wave in theory but in practice the output driver will not be fast enough to produce the 3rd, 5th and above harmonics so it will be pretty sine wave like anyway. To improve check the output impedance from the datasheet and then choose a capacitor value to make a low pass filter (cap between the output and ground) with a corner frequency of about 80MHz. That will attenuate the 100MHz signal a bit but will get rid of most of the 200MHz and above frequency components. On a scope it will look like a sinewave, you might see small harmonics if you FFT it but for many applications its not an issue.