J5D2 amplifier - Page 1
Forum section: electronics / rf-microwave

author: bob91343
author_rank: Super Contributor
timestamp: June 16, 2020, 12:07:10 am
content: Has anyone used this item? It's inexpensive but I cannot find information on whether it's a linear amplifier and if so, how much distortion it has.https://www.ebay.com/itm/0-1-2000MHz-30dB-Low-Noise-RF-Amplifier-LNA-Broadband-Module-Receiver-J5D2/263149992172I want it to provide a stronger output signal from my signal generator but I want to use it in AM mode so it needs to be low distortion.

author: mio83
author_rank: Regular Contributor
timestamp: June 19, 2020, 07:43:51 am
content: Hi,I don't know about the specific amplifier you linked, but I have got a similarly priced 2W amplifier (rated 2Mhz->700Mhz) from Aliexpress:https://fr.aliexpress.com/item/32908210979.html?spm=a2g0o.productlist.0.0.15c07d2e6aEsCp&algo_pvid=3e001541-c71c-415a-8935-2797c18875d0&algo_expid=3e001541-c71c-415a-8935-2797c18875d0-7&btsid=0ab6f8ad15925525792663124e2f81&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_and I have done some measurements. In case it might be useful/interesting for you, here is a video:https://youtu.be/B5Hzju63ik0

author: bob91343
author_rank: Super Contributor
timestamp: June 19, 2020, 07:16:35 pm
content: Thank you for that. Actually I can't really understand what's going on. My ears don't work as well as they used to so I couldn't understand most of the description. And I don't see what the source signal is like nor the rest of the setup.Basically I would like to see the output spectrum and waveform when the input is an amplitude modulated wave. There should be no change in the harmonics nor the sideband amplitude ratio.I want to use this as a booster for my old signal generator so I can get larger output signals. I want at least +13 dBm fully modulated up to 2 GHz. With 20 dB gain that should require only -7 dBm from the generator. A side benefit would be to know exactly how much output I am getting.

author: mio83
author_rank: Regular Contributor
timestamp: June 19, 2020, 09:35:25 pm
content: Quote from: bob91343 on June 19, 2020, 07:16:35 pmSorry for my italenglishQuote from: bob91343 on June 19, 2020, 07:16:35 pmOk thank you for this. It's instructive (I am really not very knowledgable)!I will try to make this measurement and let you know.However, as I said, this specific amplifier only works up to 700mhz. So it does not fit your needs for 2Ghz.But still... I'll do the experiment you suggested and will be back to you, out of curiosity.

author: bob91343
author_rank: Super Contributor
timestamp: June 19, 2020, 11:21:51 pm
content: Thank you. I would really like to see that test made on the original amplifier type.These are very inexpensive, and really are nothing more than a good transistor with bias resistors and some capacitors mounted on a PC board. As I am not competent building one, buying one for around $10 US is an attractive temptation.As a matter of fact, 700 MHz is fine for me, as I don't usually get up that high. I do have a VHF bridge that works to 1 GHz that I could excite with this amplifier.If I had the amplifier I could test it but then I would have to buy it first. If it didn't do the job,it would be a waste.As for your speech, it would be intelligible if my computer could be louder, but I can barely hear it.

author: TheMG
author_rank: Frequent Contributor
timestamp: June 20, 2020, 01:32:19 am
content: Quote from: bob91343 on June 19, 2020, 07:16:35 pmNot really, unless you characterize the amplifier over the full range of frequencies and create a lookup table or graph so you know what its gain will be at a specific frequency. I managed to find the specs for that $10 eBay device... the amplifier gain varies by 12dB over the full operating frequency range, pretty typical for such an amplifier since it has nothing in the way of feedback or gain compensation.Gain will also change slightly based on temperature variations and any supply voltage variations.Also it's only rated to a max of +10dBm output power, but you would likely never use it at such a high level. I can guarantee you the harmonics and IMD will be atrocious when pushing it anywhere near that maximum output.If it sounds too good to be true, I'm afraid it probably is. Making a wideband amplifier with very good gain flatness, low IMD, low harmonics, is no easy feat. That is why such amplifiers usually fetch a pretty high price tag.There do exist some amplifier hybrid modules made primarily for CATV applications that have some pretty good characteristics as far as gain flatness and linearity. Sometimes when I need a little more "oomph" from my signal generator I have an amplifier I put together from an MHW591 (for 1-250MHz) and another from a MHW6185 (for 40-600MHz). Both are able to output +20dBm (100mW) with ease over their whole frequency range with minimal distortion/harmonics (about -40dBc second harmonic) and the gain flatness is to within less than +/-1.5dB. Not perfect but good enough for my needs.I pulled mine from junked CATV and analog TV broadcast equipment (free) but you can find these and similar other modules on the internet used and NOS (new old stock) for pretty reasonable prices. They are are simple to use as providing a regulated power source with a bit of bypassing (simple choke and cap suffices) and hooking up your input and output coax.I've attached a pic of one of the boxes I made up using this. Don't mind the input attenuation resistors, I only put those in there to protect the hybrid in case I accidentally set my signal generator to its maximum of +13dBm, which would be above the +3dBm absolute maximum rating for input power without the attenuation. Ain't pretty but it works.

author: bob91343
author_rank: Super Contributor
timestamp: June 20, 2020, 05:47:23 am
content: Actually my preferred action would be to repair my signal generator. It will put out about 0 dBm nicely but any more than that and I get lots of distortion. In all other respects it's great. It's an HP 8657B and should put out +13 dBm, which it nearly does, but the waveform is horrible.I only have occasional desire for more output, especially when driving my Wayne Kerr VHF conductance bridge. But I don't even need that any more, now that I have a nanoVNA.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 20, 2020, 07:02:28 am
content: I'll see about getting my hands on one and trying to measure it with a VNA. Since it's low-noise, I won't do any power calibration of the VNA output though. If you can wait till the end of the year, I can even use our newer VNA at work that can do full power-sweeps and non-linearity measurements too.

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 20, 2020, 10:20:57 am
content: Quote from: bob91343 on June 16, 2020, 12:07:10 amThe MMIC used is an INA-02184 or 02186, datasheet here:https://www.qsl.net/n9zia/metricom/ina02184.pdfLook at Figure 5 for the info you want: linear up to about 11 dBm output @ 750 MHz, down to 3 dBm @ 2 GHz (depending on the current)

author: mio83
author_rank: Regular Contributor
timestamp: June 20, 2020, 10:32:04 am
content: Hi bob,so I did the measurement you suggested and reposted my video (also correcting some editing issues I discovered) here:https://www.youtube.com/watch?v=B5Hzju63ik0.At the end I have added the measurements you requested.But one picture can be clearer than any video, look at this:https://www.dropbox.com/s/9nnr7n5061s8zqw/screenshot.pngIn this picture you see the result of amplifying a 3Khz tone AM modulated at 14Mhz.As you can see the amplifier creates a lot of new harmonics (6khz, 9khz, 12khz) etc.So a lot of distorsions! I think it's a class-D amplifier. It would work great for CW, I think, but not for SSB/voice, because it's not linear.So this is no good for your applications.Thanks a lot for telling me how to do this distorsion verification. I have learnt something.PS: if you have hearing problems (my father has too!) it can be useful to activate the subtitles which are automatically generated by youtube (after a few hours from the time they are uploaded) by artificial intelligence algorithms, and they are generally pretty good!

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 20, 2020, 10:59:18 am
content: Quote from: mio83 on June 20, 2020, 10:32:04 amWhat was the input and output level? It should be reasonable linear up to about 1W / 30dBm, I believe it uses a RD01MUS1 mosfet:https://www.mitsubishielectric-mesh.com/products/pdf/rd01mus1.pdf

author: mio83
author_rank: Regular Contributor
timestamp: June 20, 2020, 11:15:54 am
content: Quote from: PA0PBZ on June 20, 2020, 10:59:18 amPlease note that I am talking about the ~10usd amplifier i bought from Aliexpress (see my first answer in this thread) and not what was originally linked by bob.Anyway, I was feeding the amplifier with a -10dBm AM-modulated signal at 14mhz.The amplifier was running at 12V and it produces an amplified signal with carriera at 30dbm (it becomes -30dmb in the SA because I haveincluded -60db of attenuation).

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 20, 2020, 11:39:43 am
content: Quote from: mio83 on June 20, 2020, 11:15:54 amYes, I know what amplifier you are talking about. Can you try the same test with a lower input level, say -20 dBm? You can also vary the input level and see what it does with the sidebands/distortion. If it's intermodulation products you should see it rise much faster than the carrier when you increase the input.

author: mio83
author_rank: Regular Contributor
timestamp: June 20, 2020, 01:25:22 pm
content: QuoteOk, I just didn't want to create confusion.QuoteOK! I have done measurements with input signals at -20dBm, -25dBm, -30dBm, -35dBm, see pictures below:-35:https://www.dropbox.com/s/kj3h6kxk60fsm4x/35db.png-30:https://www.dropbox.com/s/bncaef7wddt0epd/30db.png-25:https://www.dropbox.com/s/vb71gujr25al2t3/25db.png-20:https://www.dropbox.com/s/thspc6g43lpho6l/20db.pngas you can see, the harmonics are almost nonexistent with input signal at -35, but they start to grow quickly and by the time the input is -20dbm, they are strong.in the -35dbm picture, the carrier is shown at -45dBm, but since there is a 60db of attenuation, that really is 15dBm.In the -30dbM picture, simlarly, the carrier is shown at -40dbm, so really it is more or less 20dBm (and the harmonics are still 30 db down at least.)So it looks like this amplifier can be used linearly (at least at the measure 14Mhz band) with -30dbm inputs and 20dbM (50db gain) output.Please let me know if you want me to do further tests. I am happy to do them!

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 20, 2020, 03:45:55 pm
content: What you could do is do the -25dBm again but insert an extra 10dB attenuation between the amp and the spectrum analyzer. That way you can easily see if it is the amp or the sa that produces these products.

author: mio83
author_rank: Regular Contributor
timestamp: June 20, 2020, 04:37:56 pm
content: Quote from: PA0PBZ on June 20, 2020, 03:45:55 pmOk. My SA (HP 8591E) has various "internal attenuator settings", from 0db to 40db.In the following pictures, I vary this internal attenuator from 10db to 20db and then 30db, using:SIGNAL GENRATOR (3Khz sine wave modulated at 14Mhz with -25dbm) --> Amplifier (12V) --> 60 db attenuator --> SA (with its internal attenuator settings):10db attenuationLhttps://www.dropbox.com/s/wpwdccreqiemgxg/atten10db.png20db attenuation:https://www.dropbox.com/s/0qysprjh66zowv5/atten20db.png30db attenuation:https://www.dropbox.com/s/13dnmf4tr4ad0z9/atten30db.pngSo, it looks like the harmonics are generated by the amplifier and not by the HP.Please let me know if you want to see further experiments!

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 20, 2020, 05:02:32 pm
content: Quote from: mio83 on June 20, 2020, 04:37:56 pmYes, this proves that it's not the SA. There's one last thing you could test to see if it's not the signal generator: hook it up to the SA without the amplifier in between at -25 dBm. It will probably be fine and then you can be sure it's the amplifier.QuoteI think we should stop here, we hijacked the thread enough by now

author: bob91343
author_rank: Super Contributor
timestamp: June 20, 2020, 05:59:40 pm
content: I want to thank all of you for the sensible, cogent and pertinent replies to my original post. I have learned a lot and will do more study before making any decisions. What is very obvious here is that there are some dedicated hobbyists who only want to play with this stuff and help one another. And that is a good thing.

author: mio83
author_rank: Regular Contributor
timestamp: June 20, 2020, 06:54:38 pm
content: QuoteYes, of course I did that at the very beginning. The signal generator works fine. It's the amplifier.Thanks a lot you guys for the interesting dicussion!