"NOSE SOURCE BG7TBL   2016-03-06" - Page 1
Forum section: electronics / testgear

author: rhb
author_rank: Super Contributor
timestamp: October 09, 2017, 11:54:07 pm
content: Submitted for your amusement. Just off the boat from China.A scope trace of the output from the SMA into a DS1102E through a 6 dB attenuator with 9 V input.I'll post the input to the zener after supper.

author: rhb
author_rank: Super Contributor
timestamp: October 10, 2017, 12:53:20 am
content: Here's the voltage applied to the zener diode.For the benefit of those who are new to electronics, at every setting of the horizontal sweep, the output trace attached to the previous post should look the same. That would be the case if DC were applied to the zener. But if you apply a modulated voltage to the zener you get modulated noise which does not have a flat spectrum.Sadly, almost any attempt at designing a diode noise source would be better. I'm amazed that these things are still being sold.The 3 MMIC amplifiers are Qorzo SSB5089Z parts which expect Vcc of 5 V. There is no 5 V regulator that I can see. The Qorzo parts are specified for 50 MHz to 4 GHz. So woe unto anyone wanting to check HF filters with one of these.If anyone knows of a schematic please let me know. I *think* it could probably be hacked into something sensible. Meanwhile I'm going to take up the matter with Paypal.

author: DaJMasta
author_rank: Super Contributor
timestamp: October 10, 2017, 06:51:56 am
content: I assume this a broadband RF noise source? So the important part is how it looks on an SA, right? I also wouldn't expect a DS1102E to have anywhere near the bandwidth to get any good information on its performance if it extends up to 4GHz...

author: technogeeky
author_rank: Frequent Contributor
timestamp: October 10, 2017, 11:23:06 am
content: Quote from: DaJMasta on October 10, 2017, 06:51:56 amYes. Unless the noise source has been redesigned:1) It requires a 12V, not 9V.2) An oscilloscope (especially not a 100 MHz one) is not the intended target.3) The intended target is a spectrum analyzer which can normalize/calibrate out the noise source, then passing the same signal through a DUT (or through coupler or bridge).In other words, the quality of the noise source at any particular frequency or bandwidth isn't the goal. It's supposed to be use in cases where you don't have a tracking generator (or you can't use the tracking generator you have).

author: Cerebus
author_rank: Super Contributor
timestamp: October 10, 2017, 12:31:40 pm
content: I think what several posters are missing is that a noise source is very definitely not supposed to have obvious periodicity and any noise source is pretty lousy if it doesn't either have something close to a Gaussian spectrum or some other well known spectrum such as 'pink' noise.However, if you turn the oscillograph through 90 degrees, it does look like quite a good repeated nose source.

author: technogeeky
author_rank: Frequent Contributor
timestamp: October 10, 2017, 12:39:15 pm
content: Quote from: Cerebus on October 10, 2017, 12:31:40 pmCouldn't this be explained by providing insufficient voltage to the device? I haven't taken mine apart or reversed it, but I do remember powering it with different voltages and the spectrum changed pretty wildly at 3 volts underneath.

author: rhb
author_rank: Super Contributor
timestamp: October 10, 2017, 02:05:15 pm
content: I didn't have a connector to feed it 12 V so I used a 9 V wall wart on my bench. I shall repeat with an adjustable PS once I locate a barrel plug.However, the pulse input to the zener diode is pretty damning.As for the DSO vs SA. I don't have an SA. But the fact remains that a true white noise signal is fractal in the time domain. At every sweep setting the scope trace should look the same, a constant amplitude noise.I suspect that switching from linear X scale to log X scale will show that the low frequency end of the spectrum is really bad at any voltage. But please, if you have one of these and an SA, post some traces.

author: wraper
author_rank: Unknown
timestamp: October 10, 2017, 02:19:16 pm
content: Quote from: rhb on October 10, 2017, 02:05:15 pmhttp://www.amateurtele.com/index.php?artikel=218

author: wraper
author_rank: Unknown
timestamp: October 10, 2017, 02:22:05 pm
content: Quote from: rhb on October 10, 2017, 02:05:15 pmHave you heard about aliasing on DSO?

author: tggzzz
author_rank: Super Contributor
timestamp: October 10, 2017, 02:22:32 pm
content: Quote from: rhb on October 10, 2017, 02:05:15 pmSo, let me get this right, you are criticising the component despite knowing that you are providing an incorrect and invalid PSU?

author: TurboTom
author_rank: Super Contributor
timestamp: October 10, 2017, 03:07:50 pm
content: The flyback converter that´s included on the PCB to generate the ~36V to bias the 24V "nose" zener (IIRC) is crap. I tried everything (different inductors, capacitors, feedback networks...) to keep the output voltage from oscillating without success. To me it seems the STM flyback controller (MC34063A) just isn´t able to provide a sufficiently clean output voltage at the low current load (loop oscilation). Otherwise, the noise performance of the little gadget doesn´t seem too bad.Cheers,Tom

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 10, 2017, 03:51:28 pm
content: Quote from: rhb on October 09, 2017, 11:54:07 pmQuote from: Cerebus on October 10, 2017, 12:31:40 pmyeah the noise is inconsistent thats why you see the "I" keep missing...

author: cdev
author_rank: Super Contributor
timestamp: October 10, 2017, 04:40:44 pm
content: What we should also be concerned about is the almost certain ripping off by somebody of BG7TBL's callsign as a sort of trademark in order to market this thing.If anybody here has interacted with the real BG7TBL, could they maybe shoot him an email notifying him of this situation so he can take it up with whomever might be able to help him if such an entity exists (it very well may not in China but I suspect web sites like ebay and taobao would likely see the point, that this was abuse of what amounts to a sort of trademark or name and stop this.)Were it not for the misspelling this trick would likely have been more successful.Next time they will likely consult a dictionary before posting their ad.

author: technogeeky
author_rank: Frequent Contributor
timestamp: October 10, 2017, 04:50:21 pm
content: Quote from: cdev on October 10, 2017, 04:40:44 pmbg7tbl is a Chinese seller. His or her primary storefront is on taobao, I think.

author: rhb
author_rank: Super Contributor
timestamp: October 10, 2017, 04:56:21 pm
content: I did a lot of searching for BG7TBL and found nothing. I think it is probably a fake call sign. I looked in vain for a schematic to avoid having to create one from the board.A call sign query at:https://www.qrz.com/dbproduced a "no data" response. BG is a Chinese prefix.

author: DaJMasta
author_rank: Super Contributor
timestamp: October 10, 2017, 05:10:41 pm
content: While there's certainly a chance, I suspect it's too elaborate of a fake to be true. This is the primary taobao storehttps://bg7tbl.world.taobao.com/There is an email listed, I have read documentation (though only the block diagram and specs in English) for other BG7TBL devices, and the scope of the products offered is pretty much limited to RF and timing related electronics designs - exactly what you'd expect from a ham who's making designs to make some inexpensive tools available.I don't have the noise source and am unable to test for myself as a result, but it really seems to me like you're jumping down the throat of whatever designer made it without even trying it under normal conditions or in the intended manner. Undervoltage measurements on equipment that has a bandwidth of a tiny fraction of that it should be outputting means aliasing city if not unintended low voltage consequences (like periodicity from the RC time constants as the power parts charge).Would be interesting if anyone had actually contacted the person, as the equipment has shown up here a few times, but I get the impression that their English may be limited from the documentation/storefront/etc.

author: technogeeky
author_rank: Frequent Contributor
timestamp: October 10, 2017, 05:28:43 pm
content: Quote from: DaJMasta on October 10, 2017, 05:10:41 pmI already own the noise source. I will capture some example time and frequency domain measurements and report back later today.

author: cdev
author_rank: Super Contributor
timestamp: October 10, 2017, 09:04:16 pm
content: We should ask Blueskull what he thinks - he would also be in a position to send him a heads up in Chinese or via qq or whatever..EDIT: looks like his email is : bg7tbl@126.com(Alternatively, one doesnt need to know English or Chinese to send him photos of the device, the oscilloscope output, the PCB with his name on it. Just like any of us looking at a schematic likely can understand some basics of what its doing without speaking another language. Ive often witnessed scientists who speak virtually no common language communicating via the blackboard, expressing whatever concepts they want to communicate often doesnt require grammar.. Usually they use math.. its the same thing. )Suppose it is his, completely getting away from the functionality or lack of it, we've all made our share of spelling and grammatical errors, even if it is genuine, he would deserve to know how ridiculous "nose source" sounds to us.But I suspect that BG7TBL is likely a real ham, and more likely than not he's an RF engineer, or close to one in terms of his skill, who is being ripped offHe likely is well enough informed and speaks good enough English that he likely wouldn't make such a bad spelling mistake, (but not so good that he feels comfortable attempting to communicate in it)and that instead, somebody is stealing his call sign to distinguish a inferior product from others.If thats the case we should make an effort to let him know this is being done.My mother used to say "let there be peace on earth and let it begin with me"

author: technogeeky
author_rank: Frequent Contributor
timestamp: October 10, 2017, 11:45:06 pm
content: I took some measurements with my oscilloscope (Rigol 1054z).edit: I didn't check until I was done with all measurements, but my unit indeed saysNOSE SOURCE. Heh.The test setup is as such:power supplybg7tbl noise sourceSMA dc block (18 ghz)SMA 10dB pad (18 ghz)sma cablesma to bncbnc 50 ohm through terminatorRigol 1054zTIME DOMAINFirst, your measurement:20us/div, measure rms, vpp, avg.9V inputNote: Your settings were 10V/div, trigger at 10V, unknown termination.Note: My settings are 200mV/div, trigger at 540mV, 50 ohm termination.Second, same measurement but12V input:And finally, this one I'm happy about:Same measurement but input voltagesweptfrom 12.0V to 8.88V (CH2).FREQUENCY DOMAINFor the next two, low frequency (first few MHz) FFT:Measurement Settings:100 ms/divFFT (Memory*)500kHz/div10.0dBV/div2.50MHz center-60dbVNoise SourceOFFNoise SourceONFor the next two, same thing but over the full bandwidth of the Rigol 1054z (approx. 130 MHz)Measurement Settings:100 ms/divFFT (Memory*)25.0MHz/div10.0dBV/div65.0MHz center-60dbVNoise SourceOFFNote the spurs and the noise floor level assuming no spurs:Noise SourceON(note: This is accidentally 200 us/div, but it doesn't matter)Note the relative flatness across the range (horizontal marker 2 is about 130 MHz, the 3db point).I think the jumping is either due to triggering or FFT window edge effects, or both, or neither. I really don't have a clue. Hence AC triggering to randomize.Here is the 200us/div version, but with the 20M bandwidth limiter on (as a sanity check):I will follow up later tonight with actual spectrum analyzer measurements.I'm not a noise, RF, or any other relevant kind of expert so I'll let others draw conclusions from these pictures, if any can be reached. I think the difference between 12V and 9V is quite significant, though.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 11, 2017, 12:10:07 am
content: there are plenty of sub harmonics there, or aliasing? not sure, but why the op hasnt thought of utilizing all of them into good use? he'll be sorry arse to know his dreamed monotonic is of no use on other than the nose freq, for the purpose he intended to do (filter respond) .. and, i suspect it will not be long that the op will joint ebay treasure hunt club. Or worst, too long than expected because he join applied mathematics club beforehand...

author: cdev
author_rank: Super Contributor
timestamp: October 11, 2017, 01:21:01 am
content: Is this device the same one both of you two gentlemen have?The jpeg compression artifacts on my screen make it impossible to tell from this whether it says "noise" or "nose".it says he has sold 6 of them. So you have two?

author: Dwaine
author_rank: Frequent Contributor
timestamp: October 11, 2017, 01:28:43 am
content: I love the screenshots. How did you get the animation?

author: technogeeky
author_rank: Frequent Contributor
timestamp: October 11, 2017, 04:49:43 am
content: Here are some measurements with a spectrum analyzer. For instrument limitation reasons, I split the overall measurement into two bands:500.0 kHz to 375.0 MHz375 MHz to 2.7 GHz(addendum: 500.0 kHz to 1.00 MHz)In all measurements that follow, the equipment setup is connect as follows:noise source10dB pad (DC to 18 GHz)SMA to Type N adapterAgilent E7495aAnd I show bothPeakdetector (which is "normal" for a spectrum analyzer) andSampledetector (which is perhaps more appropriate when measuring no signal at all - e.g. noise)To start, the insertion loss characteristics of the noise source (thisincludesthe insertion loss of a good quality 18 GHz type N to SMA adapter):DC to 375 MHz375 MHz to 2.7 GHz2.0 GHz to 2.2 GHz (spectrogram)500 kHz to 1.0 MHzFinally, we can take a detailed look at the behavior of this noise source where it has far too much harmonic structure to be considered noise of any kind. As far as I can tell, this really only takes place in the first 1 MHz or so (this effect was visible a little in the Rigol, including in screenshots I didn't take). In this frequency range, the noise source isvery(I meanvery very) sensitive to the input voltage. Changes of 0.1 to 0.2 volts can have a dramatic effect. It looks pretty much fine here at 12.0 to 12.1 volts input (not shown - it looks the same as the 11.2 volts picture). But take a look at these:: I picked this band because I was getting very clear spikes from wifi in the band I wanted to target (2.3 to 2.5 GHz).

author: technogeeky
author_rank: Frequent Contributor
timestamp: October 11, 2017, 04:57:17 am
content: My conclusion, if I may be so bold, is that this is actually a pretty damn good broadband noise source.Especiallyfor $20. Granted, I don't have any professional counterparts to compare (they cost in the many hundreds to many thousands). But if you exclude the periodicity in the DC to 1 MHz range (which can be avoided by careful choice of input voltage), then overall this is certainly a sufficient source of noise to use as an input for things like amplifier bandwidth testing, antenna sweeping, noise combining, etc. All of the things you might want to do if you do not own a tracking generator. Heck, this can be useful even if you don't have a spectrum analyzer: a cheap $20 SDR can be used along with spectrum sweeping software and a directional coupler or RF bridge would be a pretty powerful way to sweep antenna.If anyone has any follow up questions or measurements you want me to make, please feel free to ask.

author: technogeeky
author_rank: Frequent Contributor
timestamp: October 11, 2017, 05:04:18 am
content: Quote from: cdev on October 11, 2017, 01:21:01 amI'm not sure what you mean by moves (please quote a specific image), but I don't think I made any mistakes with regard to termination nor did I use any bad cables or connectors. The only cables I used were SMA cables known to be flat to 6 GHz, and interconnects known to be flat to 18 GHz. Of course, the Rigol 1054z is only known to be flat to about 130 MHz.I don't have any other noise sources. I have a few other choices when it comes to sweeping frequencies, including a 25 MHz function generator, a pair of devices also made by bg7tbl (25 mhz - 6 ghz SMA spectrum analyzer, 135 mhz - 4.4 ghz SMA spectrum analyzer) which can be used to generate RF singals, and highest quality of all, the bidirectional source of the Agilent E7495a which can output -90 to -23 dBm of power from 375 MHz to 2.5 GHz in 0.1 dBm steps.This leaves some overlap between the Agilent and the Rigol, but when I compare devices where possible (e.g. the 25 MHz function generator into the E7495 spectrum analyzer, or the 25 mhz - 6 ghz into either/both the Rigol and the E7495) everything behaves as expected.

author: technogeeky
author_rank: Frequent Contributor
timestamp: October 11, 2017, 05:08:52 am
content: Quote from: Dwaine on October 11, 2017, 01:28:43 amThank you! I have spent some time getting good at making them, because I think they are a great way to share stuff here.It's pretty simple, really:I useRigol Bildschirmkopieto capture screenshots at "as fast as possible" or every 1 secondI import the screenshots as layers into a GIMP file, then Optimize for GIF, and save as GIF with "replace" turned onIt's important to get the smooth fast images to use USB and not LAN. LAN can only capture about 1 picture every 3 seconds, whereas USB can capture 3 to 4 pictures a second.If you use the fastest capture rate, some display elements (like the measurements at the bottom) will be slow to update and thus will be incorrect in the screenshots. Even worse, some display elements (like the FFT itself!) will never actually get computed because the screenshot requests interrupt them. In these cases, I have to slow down the acquisition to once per second.If you have any more questions, feel free to ask here or in PM.

author: rhb
author_rank: Super Contributor
timestamp: October 11, 2017, 01:55:05 pm
content: @technogeekyVERY nice work! Many thanks. Based on your work, putting it in a proper metal enclosure with a high pass filter on the output and an LM317 trimmed to produce the best spectrum will turn it into a useful tool.

author: rhb
author_rank: Super Contributor
timestamp: October 30, 2017, 12:44:04 am
content: I've been playing around. I built a -40dB attenuator so I could feed it to my SDRplay RSP2. With 12.1V (as close as my old PS could be adjusted. To be fixed) it looks pretty good overall. There is an issue with spurs in the RSP2 which is quite predictable from the scope trace. I thought I'd show those.First image is just the spur using 4096 point averaging. The noise generator is off. Second is with the noise generator on and shows the low frequency noise convolved with the spur in the mixer.It looks far worse than it is. This is a zoom. In practice one would shift the center frequency of the RSP2 to move the spur and associated artifacts away from the region of interest.

author: rhb
author_rank: Super Contributor
timestamp: October 30, 2017, 01:47:12 pm
content: I neglected to mention that the spur is LO bleed thru. I posted it because it was exactly what looking at the output on a scope predicts., lots of crud for 2 MHz around any significant mixer products.The really interesting part is comparing spectra from different SDR programs. They have been very different in some instances. Not sure if software or user error yet.The -40dB attenuator I put together in a 2" x 3/4" x 1" Pomona box appears to have some flatness issues above 1 GHz. Unfortunately, tough to analyze with 10 MHz chunks of RF. I suspect it's due to standing waves in the box. Anyone know of a readily available RF absorbing material?With a hi pass filter to kill the crud below 1 MHz and a microstrip switched attenuator it should prove very useful for examining SDR performance.

author: technogeeky
author_rank: Frequent Contributor
timestamp: October 31, 2017, 09:32:52 am
content: Quote from: rhb on October 30, 2017, 01:47:12 pmI just want to point out that you originally mentioned that you were going to put the noise source in a metal box. Just make sure that isn't the source of whatever problems you are having.

author: rhb
author_rank: Super Contributor
timestamp: October 31, 2017, 11:18:29 pm
content: I'll get to putting it all in a box. But it doesn't change the point. Without a high pass filter the low frequency crud gets replicated either side of the LO signal once it hits a mixer.The really interesting part is how different the spectrum looks with the same radio and setup and 3 different SDR packages.

author: medical-nerd
author_rank: Regular Contributor
timestamp: November 01, 2017, 12:04:36 am
content: HiyaI've only used these to look at a few filters in the 300Mhz-1500Mhz range and bought one after reading:https://www.rtl-sdr.com/rtl-sdr-tutorial-measuring-filter-characteristics-and-antenna-vswr-with-an-rtl-sdr-and-noise-source/I've found this and a cheap rtl dongle sufficient for my needs thus far.They have also been used as a noise source in the input pathway of amateur radio telescope setups when cooled.I agree that for $20 and a cheap dongle it gives hobbyists an instrument that would be beyond their normal reach.Cheers

author: rhb
author_rank: Super Contributor
timestamp: November 01, 2017, 01:11:15 am
content: Take a look at this:https://www.rf-microwave.com/datasheets/6107_generic_NSG-10B_01.pdfin particular, note the comments about the size of the enclosure and the need for RF absorbing material for larger enclosures.

author: medical-nerd
author_rank: Regular Contributor
timestamp: November 01, 2017, 01:38:11 am
content: Hiyaa suggestion for microwave absorber material:https://www.rf-microwave.com/en/shop/0/377-microwave-absorbing-materials.htmlCheers

author: tggzzz
author_rank: Super Contributor
timestamp: November 01, 2017, 08:48:11 am
content: Has anyone hacked things likehttp://www.lakeland.co.uk/13008/Microwave-Plate-Warmers?

author: rhb
author_rank: Super Contributor
timestamp: November 01, 2017, 09:13:21 pm
content: I built a 1 MHz 3 element capacitor input LC filter in another Pomona box using thruhole parts. It's OK for VHF but will obviously need to be redone for UHF work using SMD and microstrip construction.First image is a scope shot. Top trace is filtered, bottom trace is the noise source output. Somewhat cleaned up, but still needs improvement.2nd image is from the RSP2 using SDRuno. It shows the images of the low frequency components visible on the lower scope trace.3rd image is with the filter inserted which suppresses the images by about 6 dB.I'll try a 2nd iteration using a 5 or 7 element filter, but I doubt that I can achieve good isolation between the input and output using the parts I have on hand. But worth a try.Hopefully this explains my initial criticism. It really needs an output high pass filter. That should not cost more than a few cents using SMD parts.

author: technogeeky
author_rank: Frequent Contributor
timestamp: November 01, 2017, 11:05:29 pm
content: Quote from: rhb on November 01, 2017, 09:13:21 pmAh, ok. That also explains why I wasn't thinking of the same sort of problems. Because the devices I was thinking of using have excellent input filtering (like my spectrum analyzer) which can easily overcome this problem if you just avoid the band in question. If you have a SDR, the LNA's performance will be subject to whatever signal is the most powerful. So you can't get around the spikes. Right?I wonder if there is space on the board to implement this stuff. Also, I wonder -- if there isn't space yet -- if you could remove the last amplifier and replace it with passive filtering.This could be an opportunity to re-make this board/project so that it's compatible with SDRs in terms of performance without prefiltering.

author: rhb
author_rank: Super Contributor
timestamp: November 02, 2017, 02:23:41 am
content: I'm hoping that "BG7TBL" will add an output filter. It really needs an attenuator also. Bota goes into considerable detail on that subject in his description of the noise generators he built for the 18th EME conference in Florence. Mine is just a hack. To be redone later in proper fashion.For my unit, I'll just add another board (or two) with a filter and an LM317 with some large capacitors so that it will run properly using a generic wall wart. I scavenged some zinc coated steel from an HVAC shop and will bend up a box to fit once I know how big it is. I was looking into SMD inductors earlier and it looks as if it will be $3-5 to make a filter. So a bit more expensive than I thought.Lacking a spectrum analyzer I had to rely on my knowledge of the Fourier transform and the scope. Your traces gave me reason to keep going which is greatly appreciated. All the cheap SDRS have rather marginal input bandpass filtering. High order analog filters are hard to build because of part tolerances. Problem is, you need 6dB for each bit of ADC resolution. That's 72 dB for the RSP2. This is why oversampling is so popular. You can use a 2 pole analog filter followed by a digital filter to do the rest of the antialiasing.My next problem is QC on an Instek MSO-2204EA :-)I bought a great load of through hole parts a couple of years back, mostly resistors and capacitors so I had a complete set of values. I was able to build an attenuator and filter without being beat to death which was a real treat. Probably the first time I've been able to build something in a few minutes. Usually I get to play "hunt the wumpus". Not much, 3 parts each, but I was able to calculate the values and then pick them out of the bins. Very sweet.Now I just need to figure out what the various spectrum displays from different SDR software packages are actually showing me.

author: rhb
author_rank: Super Contributor
timestamp: November 03, 2017, 06:24:27 pm
content: To wrap this up. I rebuilt the filter as a 5 element. Except for some large spurs produced by the RSP2, the spectrum now looks clean. Level changes a bit, especially in the HF region. But pretty satisfactory. The filter was designed using Elsie and a couple of slug tuned coils.Shots are:no_filter_5.png - no filter. included to keep all settings the samefilter_5_int.png - just the RSP2 internal MW/FM filterfilter_5.png - external 5 element 1 MHz high pass filter onlyfilter_5_int.png - external 5 element 1 MHz high pass filter with internal MW/FM filter

author: Nauris
author_rank: Regular Contributor
timestamp: November 03, 2017, 08:17:48 pm
content: Quote from: TurboTom on October 10, 2017, 03:07:50 pmMC34063 is on/off hysteretic design it is never going to give clean output. It is just not intended for anything needing clean power as no matter load, it is always running in pulse skipping mode.

author: rhb
author_rank: Super Contributor
timestamp: April 28, 2020, 01:54:32 am
content: For anyone who followed this, here is a comparison to a recent ebay diode noise source of rather better performance. At least in what I expect from a broadband noise source.First the BG7TBL unit:https://www.eevblog.com/forum/rf-microwave/another-ebay-noise-source/msg3038324/#msg3038324and then the new unit:https://www.eevblog.com/forum/rf-microwave/another-ebay-noise-source/msg3036288/#msg3036288except for the reference level, everything should be the same on both sets of sweeps.Reg