1
\$\begingroup\$

I'd like to make a circuit that essentially produces very brief bursts of an RF signal, for example RF at 10MHz to 200-300MHz bursts of tens to hundreds of nanoseconds. For example this could be just one half of a sine wave at 10MHz, or for a few cycles of a 100MHz signal.

I'm familiar with some techniques for doing amplitude modulation (eg: varying the supply voltage of a linear amplifier), but I don't know of any way to do amplitude modulation this fast, or with 100% modulation depth.

The output should also be synchronized with the phase of the RF carrier in a predictable way, so it could always get a complete half-sine, rather than a random portion of a sine each time.

At the moment I'm imagining some kind of fast switch that diverts an RF oscillator to the output or to a dummy load. This is unfortunately not synchronized. Is there a better way of doing this? Perhaps something from ultra-wideband (UWB) type circuits?

\$\endgroup\$
  • 1
    \$\begingroup\$ I think you might be able to do this with an analog devices DDS. I did something similar a long time ago. \$\endgroup\$ – mkeith Dec 2 '17 at 5:53
  • 2
    \$\begingroup\$ 300MHz, even 500, is well within the range of FPGAs and fast CMOS. However, mr keith's suggestion puts it all in one IC, many DDS ICs have fast pulse modulation ability built in. \$\endgroup\$ – Neil_UK Dec 2 '17 at 6:22
  • 1
    \$\begingroup\$ It's not 100% clear what you exactly need, but to me it sounds like if you need this for testing, research or prototyping, you'd save a ton of development time (and thus, money for your own time and failed prototypes etc) by just buying a software defined radio peripheral. \$\endgroup\$ – Marcus Müller Dec 2 '17 at 9:56
  • \$\begingroup\$ @Marcus Muller Yes, I thought about that, I was looking at HackRF. I can't figure out what types of modulation they support, maybe I'm not looking in the right part of the docs. Can they do 100% amplitude modulation, ie digital 1=carrier on, digital 0=carrier off? If yes, that mostly solves the problem \$\endgroup\$ – Alex I Dec 2 '17 at 11:15
  • 1
    \$\begingroup\$ SDR isn't about devices "supporting" modulations. You define the signal (as samples) in software, and send it to the SDR, which is only a "stupid" digital-to-analog converter, with an adjustable mixer, essentially. So, if you want to send e.g. a short burst of 100 MHz, you could e.g. generate samples of a 1 MHz complex sine in software, followed by some zeros, and tell the SDR device to mix that up by 99 MHz. But, you could, with the very same device, also send e.g. digital audio broadcast (DAB radio), because the device doesn't do any specific modulation – it just translates your digital… \$\endgroup\$ – Marcus Müller Dec 2 '17 at 11:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.