How to amplitude modulate a [GHz] sinwave with a [MHz] sinewave? - Page 1
Forum section: electronics / projects

author: Plasmateur
author_rank: Regular Contributor
timestamp: April 17, 2022, 05:23:19 am
content: Hello,I have an application where I have some  frequency and I want to modulate it with a  signal.The purpose is to have two  frequencies at a distance of some  frequency. For example,I haveF1 = 1.001 F2 = 1.000 In frequency space.From the above we can see the difference frequency isdF = 1.000 Then we can seesin(2*pi*t*F1)+sin(2*pi*t*F2) = sin(2*pi*t(F1-dF/2) * sin(2*pi*t*dF/2)So, if am able to multiply a 1.001 frequency by 0.5 , then in frequency space I will haveF1 and F2.But I cannot find such a device, or I don't know the name for it. At least mini-circuits doesn't sell this. Is there a specific name for such a device?Thank you.

author: bob91343
author_rank: Super Contributor
timestamp: April 17, 2022, 06:40:33 am
content: They are variously called mixers or modulators. Or just diodes.

author: ledtester
author_rank: Super Contributor
timestamp: April 17, 2022, 07:02:28 am
content: Have a look at minicircuit's RF Frequency Mixers:https://www.minicircuits.com/WebStore/Mixers.htmlAnd here's a video on how diode ring mixers work:#167: How a Diode Ring Mixer works | Mixer operation theory and measurement -- w2aewhttps://youtu.be/junuEwmQVQ8

author: Plasmateur
author_rank: Regular Contributor
timestamp: April 17, 2022, 08:27:38 am
content: Quote from: bob91343 on April 17, 2022, 06:40:33 amQuote from: ledtester on April 17, 2022, 07:02:28 amQuote from: evb149 on April 17, 2022, 07:03:41 amThank you for the replies.I was under the impression the standard mixers at Mini-circuits would still have the carrier frequency. So there would be 3 frequencies like shownfor the upconversion case. Unless I'm mistaken, sorry if I am, but that won't work for my application.I need to suppress the carrier frequency. Perhaps a DSB-SC (Double Side Band Suppresed Carrier) spectrum is possible using those mixers?

author: geggi1
author_rank: Frequent Contributor
timestamp: April 17, 2022, 09:50:52 am
content: You might be able to modulate the supplyvoltage on an MMIC.You will not be able to get 100% modulation but probably close to 50% modulation.Another option is to build a FET AM modulatorhttps://cz.pinterest.com/pin/349029039847739500/Something similar can also be made with transistors.You just have to find a transistor or FET that is capable of the frequencies you are using.

author: PA0PBZ
author_rank: Super Contributor
timestamp: April 17, 2022, 10:53:02 am
content: Quickly bodged together for your entertainment:F1 in: 100MHz, F2 in 500KHz, output:Due to the nature of the construction F1 leaks through more than it should with proper construction, it should be more like 35-40dB suppressed.Mixer: SBL-1https://www.minicircuits.com/pdfs/SBL-1+.pdf

author: Terry Bites
author_rank: Super Contributor
timestamp: April 17, 2022, 12:16:37 pm
content: use a low cost ic mixer eg LT5560

author: Plasmateur
author_rank: Regular Contributor
timestamp: April 17, 2022, 04:48:16 pm
content: Quote from: PA0PBZ on April 17, 2022, 10:53:02 amWow....I mean wow.Hahahah! This is so awesome! If I can get 40dB supressed, I'm in there. Just have to trace out some rogers board and use an old housing.

author: moffy
author_rank: Super Contributor
timestamp: April 17, 2022, 11:52:24 pm
content: Quote from: PA0PBZ on April 17, 2022, 10:53:02 amImpressive carrier suppression, you make it look easy.

author: nctnico
author_rank: Super Contributor
timestamp: April 18, 2022, 12:39:43 am
content: Another way is to use a PIN diode as a voltage variable attenuator:https://www.rfwireless-world.com/ApplicationNotes/PIN-diode-AM-modulator.html

author: David Hess
author_rank: Super Contributor
timestamp: April 18, 2022, 02:05:20 am
content: Quote from: Plasmateur on April 17, 2022, 08:27:38 amA balanced mixer suppresses the local oscillator and a double balanced mixer suppresses the local oscillator and intermediate frequency. Most mixers are double balanced and inherently produce a double sideband suppressed carrier output.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: April 21, 2022, 11:34:25 am
content: >you make it look easy.ha ha, the 100MHz center freq is what made it simple,now, lets see the same circuit at 1GHz as the OP asked for ?:-)

author: PA0PBZ
author_rank: Super Contributor
timestamp: April 21, 2022, 11:49:50 am
content: Quote from: oz2cpu on April 21, 2022, 11:34:25 amI would but the SBL1 only goes up to 500MHz, I'll check if I have other DBMs in stock.