Amplifier which can take a DDS signal to 5watts? - Page 1
Forum section: electronics / rf-microwave

author: Plasmateur
author_rank: Regular Contributor
timestamp: May 21, 2017, 02:19:15 am
content: Hello,I'm trying to amplify a signal (2-30MHz) from mySDG2042Xfunction generator. I need 5watts(37dBm) so I can drive theTC-300amplifier.The signal generator I'm using can only achieve 5Vpp into 50Ohms at the frequencies of interest - so about 60mW (18dBm)I've tried searching the internet to see if such an amplifier exists. I believe I've only found onehere, but it appears to generate some high 2nd and 3rd harmonics in the signal according to the pictures which are posted.Ultimately I will want to do the following.1. Signal generator2. Amplifier to 5W3. Amplifier to 150W4. Matching network5. Digital SWR meter6. AntennaDoes such an amplifier exist commercially or will this need to be built by myself?

author: Plasmateur
author_rank: Regular Contributor
timestamp: May 21, 2017, 04:40:38 am
content: Quote from: evb149 on May 21, 2017, 02:40:23 amYes. This is for plasma production and scientific purposes. I would like to be able to produce a plasma with something other than a clean 13.56MHz or 27.12MHz sinusoidal wave. I would like to do some kind of amplitude modulation.The Faraday shielding will be taken care of. The copper can be found pretty cheap off McMaster-Carr.With that said, I have ALOT to take in with your first post and all of your suggestions. Thank you for the information!As for the LZY-22+....we have one of those in the lab! Unfortunately it is way outside of my personal price range. Hahaha. Otherwise I would love to use it.After doing a little more digging online I've found that people are driving the TC-300 under 3watts.So I think thisdevicemight be able to do the trick for me.

author: G0MJW
author_rank: Regular Contributor
timestamp: May 21, 2017, 08:25:40 am
content: Firstly - there is a good reason why certain frequencies are used for industrial/scientific/medical purposes. It is very difficult to not inadvertently radiate RF and cause interference to other users. Screening it will help but don't underestimate just how difficult this can be. Its important to keep away from especially sensitive frequencies.A potential solution for you is to use some of the more modern 50V LDMOS RF power transistors in a broadband transformer coupled circuit. These devices are quite costly but designed to be very robust to output miss-match - which I expect will be the case. Their inputs are very sensitive to overdrive, but also very sensitive so you only need 1W of drive and probably less. Its easy to generate 1W at 2-30MHz and there are loads of circuits and kits about. The high power stuff is basically the same as an amateur HF broadband amplifier like W6PQL produces.You might want to look at this sitehttps://www.qrp-labs.com/While their ultimate 3S kit seems nothing like what you want, it actually is pretty close and would just need you to write different code for its microcontoller, use the arduino shield, or ditch that board and adapt whatever it is you are already planning to use. There are filters and power amplifiers up to a few watts.Mike

author: G0HZU
author_rank: Super Contributor
timestamp: May 21, 2017, 07:12:21 pm
content: If you don't mind buying old/used gear then the (very old) Marconi TF2167 50kHz-80MHz 10W amplifier would be OK for this. However, it can be tricky to find a fully working example these days.The good news is that they are usually quite cheap, I bought one last year for £40 and once I'd fixed the PSU inside it works fine. A fully working one might be £150. However, your TC300 150W CB amplifier looks like it will be quite dirty. I'd expect the odd order harmonics to be -15dBc or worse at full power from the TC300 if there is no LPF after it? So the low distortion in the TF2167 will be wasted if you feed it to that CB amplifier. At 5W output I'd expect the harmonics from a typical TF2167 to be much lower than this.

author: tautech
author_rank: Super Contributor
timestamp: May 21, 2017, 08:08:03 pm
content: Quote from: Plasmateur on May 21, 2017, 02:19:15 amYes.It's an accessory for Siglent AWG's.SPA1010http://siglentamerica.com/prodcut-fjxx.aspx?fjid=1289&id=1364&tid=16&T=2Recently mentioned in the SDG2042X thread also:https://www.eevblog.com/forum/testgear/the-siglent-sdg2042x-thread/msg1205372/#msg1205372

author: G0HZU
author_rank: Super Contributor
timestamp: May 21, 2017, 08:41:09 pm
content: That SPA1010 looks like it is limited to a 3dB BW of about 1MHz. Probably less if you want to run high power. So I don't think it is going to be a good choice in this case.

author: G0HZU
author_rank: Super Contributor
timestamp: May 21, 2017, 08:52:36 pm
content: I dug out my old Marconi TF2167 amp and tested it at 5W output across 2-30MHz and the worst case harmonic was the third harmonic and it was -42dBc or better at 5W output at all test frequencies. This is unfiltered at the amplifier output but the sig gen feeding it was filtered to produce a clean driving signal to the TF2167. So the TF2167 was the weak link here and it still managed -42dBc harmonics or better at 5W output.

author: David Hess
author_rank: Super Contributor
timestamp: May 21, 2017, 11:55:20 pm
content: What distortion performance is achievable with a modern shunt feedback amplifier over that frequency range and with that power requirement? I checked some shunt feedback complementary amplifiers used in function generators and they are about 10dB low in power and 20dB low in distortion performance.I believe some modern wideband no-tune HF push-pull amplifiers could handle it; they manage to meet FCC requirements for output harmonics without changing output filters. Even better, they use input and output transformers which can be constructed relatively easily using ferrite elements, coaxial cable, and maybe some brass sections.

author: Plasmateur
author_rank: Regular Contributor
timestamp: May 22, 2017, 02:41:51 am
content: Quote from: tautech on May 21, 2017, 08:08:03 pm3dB @ 1MHz. Not sure that is going to work. Can I get 5watts @ 30MHz?If I could send a software trigger to trigger both channels of the SDG2042x AND use this function generator amplifier. Well that would be the bees knees.

author: CJay
author_rank: Super Contributor
timestamp: May 22, 2017, 07:03:39 am
content: Dump the CB amplifier if you want to use a range of frequencies though, it's be passable if it was on one or two spot frequencies because you'd be able to clean it up but by the time you'd designed and built suitable filtering for your intended range you might as well have saved your time and money to buy/build a better amplifier.