Probably the easiest way to add amplitude modulation would be to use a couple of low capacitance (small signal) diodes -- one in series with the output, and a second one following the first one, shunted to ground. A DC return to ground at the output of the signal generator is needed. The signal generator may already have such a DC return. If not, add a DC return via a choke (or even a resistor, about 500 ohms).
The two diodes are wired in series (cathode to anode connection). Connect the cathode of one diode to the RF output of the signal generator. The anode of the other diode goes to ground. Feed the audio signal into the junction of the two diodes via a resistor, 500 ohms or larger. A choke could be added if desired to reduce RF loss a bit. Also from this same point, pull off the modulated RF output through a capacitor (to decouple the audio). Feed enough audio (bipolar voltage) to get 10 to 20 mA of current through the diodes on the peaks. The resulting modulation will not be pretty. It will be more like square wave modulation. The modulation depth will be very close to 100%. Harmonics of the RF may rise somewhat. But since we want to do radiated immunity testing, a "dirty" signal is not necessarily a bad thing. Side note: If you are fortunate enough to have some PIN diodes laying around, use them. You will get more linear modulation and lower RF harmonic generation. Donald Borowski Senior EMC Compliance Engineer Schweitzer Engineering Labs Pullman, WA, USA From: Ken Wyatt <[email protected]> To: [email protected] Date: 11/04/2013 07:48 AM Subject: Re: [PSES] Inexpensive RF generator Hi Scott, Yup, you're right. I don't see any easy way of modulating the RF on this generator. I'll ask the designer if he can think of a way and get back to the group. Ken _______________________ Kenneth Wyatt Wyatt Technical Services LLC 56 Aspen Dr. Woodland Park, CO Phone: (719) 310-5418 / Toll Free: (877) 443-9275 Email Me! | Web Site | Blog The EMC Blog (T&M World) Subscribe to Newsletter Connect with me on LinkedIn On Nov 4, 2013, at 8:34 AM, S Drysdale <[email protected]> wrote: Hi Ken, In my experience, a device may sometimes pass CW, but fail when modulated. Can you advise an economic way to modulate the RF? Best Regards, Scott Drysdale OOO - Own Opinions only On Sat, Nov 2, 2013 at 8:10 PM, Ken Wyatt <[email protected]> wrote: Hi All, I just uploaded a new posting - "Review: inexpensive RF generator" http://www.edn.com/electronics-blogs/the-emc-blog/4423710/Review--inexpensive-RF-generator Thought this might be helpful for some applications. Cheers, Ken _______________________ Ken Wyatt Wyatt Technical Services LLC [email protected] www.emc-seminars.com Phone: (719) 310-5418 - David Heald <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
