Digital Attenuators - your experiences , suggestions and comments - Page 1
Forum section: electronics / testgear

author: noreply
author_rank: Frequent Contributor
timestamp: July 07, 2020, 06:42:50 pm
content: For the forum members who are involved with testing medium to moderate signal levels - its mandatory to have some form of attenuation between the signal and your 'expensive' test equipmentI would like to share some experiences, suggestions and comments hereTo kick-offI am awaiting delivery of this device ...Digital Attenuator Module, OLED Display 6G Digital Programmable Attenuator 30DB Step 0.25DB RF ModuleIt costs £36 on Amazon.co.ukWhen I receive the actual device I will put it through its paces and publish my findings herePlease share any digital attenuator experiences you may have had

author: Bassman59
author_rank: Super Contributor
timestamp: July 07, 2020, 10:48:16 pm
content: Quote from: noreply on July 07, 2020, 06:42:50 pmWow, I remember when I worked with L-band microwave stuff, you couldn't buy a simple directional couple for £36.I wonder how this will measure for flatness, accuracy of attention, all of it.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 08, 2020, 01:02:57 am
content: I wasn't able to sort out if you can program it from the USB or using the TX/RX pins. Looking forward to seeing your review. There appears to be some data here:https://www.aliexpress.com/item/32818703642.html

author: noreply
author_rank: Frequent Contributor
timestamp: July 08, 2020, 01:20:36 am
content: Quote from: joeqsmith on July 08, 2020, 01:02:57 amNot sure myself at this moment in time - but I suspect with all the test gear I have already accumulated - I will be able to debug any comms with this deviceI suspect the 'attenuator' IC is anAnalog DevicesPeregrine Semiconductor Corporation component - so should be able to get detailed data on itHere is something you could try ...The communication baud rate is 115200bps.The command is limited to lowercase letters a ~ z, numbers 0 ~ 9, and the end symbol of each command is a newline character (hex represents "0x0a "Or '/ n')Communication commands include three types of commands: w commandwv0 Command: Set output attenuation.The format is: wv0xxxx + 0x0a, a total of 8 bytes;where "xxxx" is the attenuation value represented by 4 numbers, for example: wv01150 n: indicates that the write attenuation is: 11.5DB (the maximum attenuation is: 0-6350 , With a step of 25). Converted to hexadecimal: 0X77 0X76 0X30 0X31 0X31 0X35 0X30 0X0aVersions after 2019 with a return value: "ok r n" text format value returned after receiving the correct data.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 08, 2020, 01:38:37 am
content: Sounds great.Do you have access to a VNA that you can use to measure it?

author: noreply
author_rank: Frequent Contributor
timestamp: July 08, 2020, 02:01:19 am
content: Quote from: joeqsmith on July 08, 2020, 01:38:37 amSomething better a Siglent SVA1032X - which started life as a SSA3021x Plus originallySo will be able to do some accurate attenuation tests - but unfortunately only to 3.2GHzBut for doing comms debug will use the Rigol MSO5000 - can directly decode the data.Lets hope that thePeregrine Semiconductor Corporationdatasheet will give you more details on how to communicate with the device

author: noreply
author_rank: Frequent Contributor
timestamp: July 08, 2020, 02:01:51 am
content: I just did some digging - its NOT an AD semiconductor ...Its most likely a device made byPeregrine Semiconductor Corporation- like this one ;-https://www.psemi.com/pdf/datasheets/pe43711ds.pdfIn Summary ..The PE43711 is a 50Ω, HaRP™ technology-enhanced, 7-bit RF digital step attenuator (DSA) that supports abroad frequency range from 9 kHz to 6 GHz. It features glitch-less attenuation state transitions and supports1.8V control voltage and an extended operating temperature range to +105 °C, making this device ideal formany broadband wireless applications.The PE43711 is a pin-compatible upgraded version of the PE43502, PE43503, PE43602 and PE43702. Anintegrated digital control interface supports both Serial and Parallel programming of the attenuation, includingthe capability to program an initial attenuation state at power-up.The PE43711 covers a 31.75 dB attenuation range in 0.25 dB, 0.5 dB and 1 dB steps. It is capable ofmaintaining 0.25 dB monotonicity through 4 GHz, 0.5 dB monotonicity through 5 GHz and 1 dB monotonicitythrough 6 GHz. In addition, no external blocking capacitors are required if 0 VDC is present on the RF ports.The PE43711 is manufactured on pSemi’s UltraCMOS® process, a patented variation of silicon-on-insulator(SOI) technology on a sapphire substrate

author: joeqsmith
author_rank: Super Contributor
timestamp: July 08, 2020, 02:45:27 am
content: From the datasheet, seems like the TX/RX tie to the micro, then that controls the attenuator. If it does and they release details on the protocol, that would make it more useful. Even better if you can run control it right from the USB port.I saw that Psemi and thought Pericom Semiconductor. I've never heard of Peregrine.Depending how many people are making it, once you have it you may want to post a link for the one you purchased. I would imagine the board will make a fair bit of difference. Once you know what part it is, it may be interesting order the manufactures eval board to compare its performance.

author: noreply
author_rank: Frequent Contributor
timestamp: July 08, 2020, 03:11:41 am
content: ... its a trademarks of pSemi CorporationI just cut / pasted the name from the datasheet.. yes micro has its 'own' command language & controls the simple interface to the attenuator IC's internal register.. you should be able to issue commands (see datasheet) to the command register on the chip - so be able to control the attenuation settings - the truth tables for attenuation levels are shown in the data sheet

author: noreply
author_rank: Frequent Contributor
timestamp: July 08, 2020, 03:16:05 am
content: .. just got notification - my device arrives today

author: jjoonathan
author_rank: Frequent Contributor
timestamp: July 08, 2020, 04:16:11 am
content: 2 years ago these were pretty rough.https://photos.app.goo.gl/fdysAuMYQ8JX3yY86Here's hoping they've improved!

author: edigi
author_rank: Regular Contributor
timestamp: July 08, 2020, 08:02:44 am
content: Quote from: noreply on July 08, 2020, 02:01:51 amAnother (more likely) option is this:https://www.psemi.com/pdf/datasheets/pe43703ds.pdfI have a probably older/less capable variant (PE43702 based, without OLED but with micro switches) and I wouldn't say it's bad. I've tested it with the 1.5GHz NanoVNA (the older design, I've still not received the new 3GHz variant so I cannot retest and I'm too lazy to check it with the SSA).Attenuation is roughly between 2-3dB when no attenuation is set, reflected power is roughly -20dB.With max attenuation set it's roughly 32dB more (within spec) and reflected power is roughly -30dB.(All of the above with NanoVNA, calibration including the wires.)Naturally a decent VNA would allow more precise measurements, but I didn't need that.If I remember correctly from Dave's review of the Siglent SSA (too lazy to search it now), Siglent is also using some PE variant in their SSA...I still would be afraid to use it before some expensive equipment. Although the datasheet states that it powers up with max attenuation my variant without power is 10dB less than max (OK it's not the same as with power but still).I've thought that only the more expensive OLED variants can take commands from the USB side (as I didn't see this advertised for the cheaper variants) but if this is not the case it's pretty good. But then it's another issue still how commands can be given without USB unless a separate chip is used for the conversion and the micro has serial input for that which makes it very easy.

author: noreply
author_rank: Frequent Contributor
timestamp: July 09, 2020, 01:53:40 pm
content: Today, my Digital Attenuator finally arrivedI was eager to start to put it through its paces – BUT this was unfortunately not possibleMy device was a DOAFirst, a visual inspection, after opening the package – see attached photos – showed some ‘crushing’ due to poor packaging.Fortunately this was ‘fixable’ – I managed to straighten the microUSB connector and the interconnecting header top pins, in essence enough to at least check-out the device and power it up.After connecting the microUSB cable – and flicking the ON/OFF switch to ‘ON’ the power LED illuminated – BUT the OLED display was dead.Despite the above – I was still keen to see if there was ‘functionality’ without the display – so connected to signal generator and set at 1GHz at 0dBm – the output connected to the SVA and we get the attenuation ‘stuck’ at -12dB – despite button presses – nothing working.Next step was to check the ‘insides’ just in case there was something obvious that could be fixed.Again – nothing to see here – I checked the voltages – got the 3.3V all okWell – I guess I could start to debug with the MSO – but , nah.. what’s the point of paying top $ (bought via Amazon for speedy delivery and peace of mind if return necessary) and then spending half a day trying to fix something which should be working in the first placeI guess you have to expect hit and miss for items shipped from China – especially these cheap devices which are made without any QANot sure if I’m going to get a replacement unit – not keen to wait another 6 weeksSo my contribution on a full review of this digital attenuator has just ended – before it even startedHope your experiences had more mileage than my short lived one just now

author: noreply
author_rank: Frequent Contributor
timestamp: July 09, 2020, 02:53:39 pm
content: Quote from: jjoonathan on July 08, 2020, 04:16:11 amWOW ... that's not very good at allFrom the photos - it looks like the identical deviceANDLooking at the IC data (if indeed it used the psemi device) - it should definitely have better performanceNot sure if the 'soldering' or PCB tracks (dirt or any other debris) might have anything to do with your poor responseIts a pity , I could not do some testing myself - I guess DOA means DEADBUTHaving said this, part of me thinks if I would get similar or worse results - perhaps getting a DOA and returning it immediately might have spared me having an ineffective device, when wanting to use it for precision attenuation(s)

author: edigi
author_rank: Regular Contributor
timestamp: July 09, 2020, 07:48:06 pm
content: I remembered wrong in my earlier post, it's not the Siglent SSA but the lowest frequency SVA that uses these PE attenuators.https://youtu.be/HxBcQDooAYs?t=1491These OLEDs are bad combination with the heavy stuff from shipping perspective. It's too bad that you can't make the review now.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 09, 2020, 11:30:05 pm
content: That's too bad. If they send you another and allow you to keep the bad one, maybe you could control the attenuator directly. At least it would let you try it out.

author: noreply
author_rank: Frequent Contributor
timestamp: July 10, 2020, 01:07:44 am
content: Quote from: joeqsmith on July 09, 2020, 11:30:05 pmYeah that would be nice - but bought it through Amazon - so they want you to return the item - you don't deal with the supplier in China directly.The good thing was that Amazon had stock in their local warehouse - so my delivery was only a few days - hence my purchase.Now there is no more stock - so must ship from china and the 6 weeks shipping.Good thing about Amazon - there is no arguing - if not happy / DOA - you get free return and full refund

author: Bud
author_rank: Super Contributor
timestamp: July 10, 2020, 03:10:28 am
content: I will sooner believe I am the Pope than that gizmo has a genuine Peregrine chip in it.

author: noreply
author_rank: Frequent Contributor
timestamp: July 10, 2020, 02:58:03 pm
content: Quote from: Bud on July 10, 2020, 03:10:28 amWell, we could do some 'critical analysis'These devices 'retail' for as little as $25, so it the genuine 'chip' retails for >$25 alone - then these guys are busted and you are DEFINATELY not the pope.At least wen looking at the 'pinouts' on the genuine datasheet - thy are the SAME as used on the physical board / chip (see previous photos) - but since they also scratched off the markings on the chip - most likely a clone chip if they do have clones of this device?the post fromjjoonathan- with his poor results for this device - which are worse than the genuine spec sheet - also confirms your theory of not genuine peregrine chip

author: tv84
author_rank: Super Contributor
timestamp: July 10, 2020, 03:26:48 pm
content: Quote from: noreply on July 09, 2020, 01:53:40 pmMany of your photos are f... up by the forum!They have nothing to do with the thumbnails!I don't understand what is happening recently in the forum regarding the attachments...

author: noreply
author_rank: Frequent Contributor
timestamp: July 10, 2020, 06:46:48 pm
content: Quote from: tv84 on July 10, 2020, 03:26:48 pmYeah .. seen your comments on this before - BUT It obviously happened above - so thanks for the heads - up.Hope Dave is doing something about it!

author: Nanoman
author_rank: Newbie
timestamp: July 12, 2020, 08:57:51 pm
content: I used the PE4312 from PSemi in a project some years back. Nice and cheap and works down to DC if you keep the signal small* ( less than +/-700mV at the switch) but not the best RF match.*Psemi don't condone using it in this mode but if the input power is limited they work well

author: Kean
author_rank: Unknown
timestamp: July 14, 2020, 01:24:31 am
content: I've got an older/cheaper version of this attenuator module that I bought on ebay a few years back from seller elecdesign2015.It is adjustable in 0.5dB steps 0-31.5dB at 3GHz, but otherwise looks exactly the same.This onehttps://www.ebay.com.au/itm/172382353163Another one to look at is from SV1AFN, which uses the pSemi PE4306 for 0-31dB in 1dB steps. He sells an SPI attenuator module and OLED/rotary encoder controller separately.https://www.sv1afn.com/en/products/rf-step-attenuator-spi-module.htmlI just received my new nanoVNA V2, but have already broken the screen on it... so I can't play till I get a replacement display module.If you'd like me to measure anything on either of the above modules, I do also have an xavna unit somewhere, and several SA's with TG (Rigol DSA815 and Signalhound SA44B).While I've got some gear, I am an really just an RF noob because I've just never had the time to focus and learn more than doing simple measurements.

author: noreply
author_rank: Frequent Contributor
timestamp: July 14, 2020, 01:32:33 am
content: Quote from: Kean on July 14, 2020, 01:24:31 amJoin the clubIts nice to finally be able to do the things you wanted but were unable due to various factors in earlier life timeline.Hopefully, if lucky, what starts as a hobby can be a source of some $$, if you apply some creative skills and knowhow

author: noreply
author_rank: Frequent Contributor
timestamp: July 18, 2020, 04:07:54 pm
content: I thought I should make an update postGuess what?I was monitoring the 'buy it again' on my Amazon account - and noticed that the ...Digital Attenuator Module, OLED Display 6G Digital Programmable Attenuator 30DB Step 0.25DB RF Modulewas once again available -for next day delivery- from Amazon.So, since I don't have to wait another 6 week for snail mail from China - I took the plunge to get another module - to complete my testing.(The original DOA module - is being sent back to Amazon - for refund)So, I receive the 'new' module - and this time its working - but the 'on off' switch is broken (I still managed to turn it on despite this)Initial test results will be posted soon.Unhappy with the broken switch - I decided to yet buy another(next day delivery) module - hoping it will be fine & I can return the broken switch module.Today the module arrives (3rd) - I inspect - the swith is OK, I power-up , display is working, settings work - all okSo I leave the module 'on' and start writing this post update - then GUESS WHAT??The display goes blank - module LED still onI check and power-on again - just in case - still no display (same as original DOA module) - so I guess its another dead module - but I think the OLED display is what died in the original module and just now in the 3rd replacement module.So - these modules have bad batch of OLED displays - they keep dyingI will perform some tests on the working module with broken switch today - and post results.Unless the performance results are exceptional for this class of device - this module is also going back for a full refund.I guess its really hit and miss with this devices.The good thing is that I did not have to wait 6 weeks x 3 - timewise - to come to the same conclusion.+1 for Amazon return policy and 'prime' shipping

author: noreply
author_rank: Frequent Contributor
timestamp: July 19, 2020, 02:36:46 am
content: Ok, I finally managed to do some frequency response testing on the digital attenuator module.To do a very thorough test – is not an easy task and would take a very long time to acquire and more importantly present the data in a meaningful way.So, I decided to do some ‘hands-on’ testing to see how effective the device is for real day to day use and how well it behaves in relation to its ‘claimed’ specifications.Since the actual attenuation ‘chip’ has been defaced (etched) so that it cannot be identified – possibly because it’s an inferior specification ‘clone’ , I am assuming that the device which ‘should’ be inside is this;-https://www.psemi.com/pdf/datasheets/pe43713ds.pdfSpoiler alertThe results obtained – don’t reflect the specifications in the above data sheet.However – there is a relatively linear response up to about 700MHzANDThere is also ‘expected’ (close to linear) behavior at the 3.1GHz point for most of the attenuation settings.This, together with a closer look at the Evaluation Kit Layout for PE43713 (see attached pictures) – will reveal that the PCB used in the evaluation design is nothing like the POOR quality of the actual module under test.You will note that the RF line microstrip for the input and output on the Evaluation Kit Layout for PE43713 is precise with a series of through vias to the ground plane – which will ensure a better response at higher frequencies.I suspect that even if the semiconductor used is NOT a clone – its PCB layout is responsible for the poor frequency response.Further experimentation could ultimately verify this.As a possible confirmation to the above theory – I made a frequency response plot with NO POWER to the device.To some expend this should give a ‘loose’ indication of the ‘transmission path’ response within the device under test.You can see that the frequency response plot follows the same ‘peaks’ and ‘thoughts’ as does the device when operations – a small indication that there is a definite problem with the signal path before the device is even ‘powered-on’.Anyway, I made a few assumptions for the testing.The tracking generator was set to 0dBm outputThe sweep frequency was from 0Mhz to 3.2GhzI set the marker to catch the highest peak – so we can see the ‘lowest’ attenuation figure when set to a predetermined value – as this will be more critical than having a higher attenuation figure if this attenuation module is used in some design under test.The interesting thing is that the ‘lowest’ – most true to the setting – attenuation occurs at 3.02GHz - sorry I was unable to see what happens beyond the 3.2 GHz as my SVA does not cover above 3.2GHz – perhaps someone else with same device could perform higher frequency testing?At -20dB attenuation – the module had a ‘peak’ response at 776.53MHz – where it reported an attenuation value of -21.21 dB – this figure is within the PSEMI PE43713 device specifications – again a possible clue that the PCB layout used in this module is killing the performance and not the ‘chip’ itself?You can see the attenuation vs. frequency is relatively linear up to 700MHz – yet another ‘clue’ to poor PCB design as frequencies above this and beyond 1GHZ definitely need to take into account the PCB dielectric and the PRECISE microstrip design calculations in relation to the copper tracks used in the layout.I also did not make any deviations on the TG power level – all measurements at 0dBmI suspect that using variable input power would have ‘shifted’ some of the frequency and attenuation values – as the behavior of the ‘transmission’ of the RF signal would change with the higher power.Perhaps I will be able to do this test later – if some of you think is would help?My guess, we have enough data at the 0dBm level to get a good feel as to how this device behaves.I also noted that the displayed frequency on the OLED display is ‘fixed’ at the 6.0GHz Level – irrespective of what the input frequency into the attenuator is set to!I feel this is misleading advertising – I had the impression that the device would show the Frequency of the attenuated signal – a useful feature to have – but obviously not supported by the PSEMI chip – so no way to implement.Then why have it??Could display some other meaningful data or leave the 2nd line on the OLED blank.ConclusionWould I buy this device?For myself – probably not – because for me an attenuator’s value is CRITICAL in all of my circuit designs and devices under test.I need to ‘trust’ that the attenuator will provide a ‘flat’ response within its specifications and at a constant attenuation level.My alternative – although not as convenient as a digital module – would be to use a SMA Attenuator Kit - Bundle of 6pc 2W 50 Ohm SMA In-Line Attenuators which Provides Highly Linear Attenuation from 1dB to 42dB in 1dB Increments. With the following individual adaptors 1dB, 2dB, 3dB, 6dB, 10dB & 20dBThis set of attenuators will cost about GBP41 compared to GBP32 for the module under review.Is this device useful?Yes – potentially to someone who will use this at lower frequencies – say between 10MHz and 100MHz – where it will provide linear response – close to published specifications – but NOT precise to the level of fixed attenuators.Can this module be ‘fixed’?Yes, I suspect this would be a nice project to ‘fix’The microcontroller module is on a separate PCB attached with a through header set of pins – linking the two PCB’s together.You would need to remove the main PCB with the PSEMI PE43713 device (I am assuming it’s not a clone chip) and redesign the PCB – or use the layout (section of) the Evaluation Kit Layout – with appropriate PCB substrate.If my theory is correct – you will then be able to have a much better performing digital attenuator – working within the published datasheet specifications – which are quite impressive.Hope that above ‘quick and dirty’ review is useful in your decision in purchasing this moduleBe warned – out of 3 units purchased – 2 had OLED display failures – one was DOA and the other failed within 3 minutes of being powered-on.The packaging used for these modules is VERY BAD – it is highly likely that some damage will occur if the anti static package containing the attenuator module and cable is not wrapped in lots of bubble wrap and not simply put inside an Amazon type large cardboard envelope.If you decide to purchase, hope you have better luck than me –– and when your device arrives it is not DOA or damaged during transit.If you are still reading this last line - thanks for your patience.

author: edigi
author_rank: Regular Contributor
timestamp: July 19, 2020, 08:27:07 am
content: Quote from: noreply on July 19, 2020, 02:36:46 amI assume that at some point of time they had such ambitious plan that the attenuation is compensated with measurement results possibly stored in the micro (maybe not in this, but a more expensive device)For that the micro has to know which frequency to compensate.This could be given via USB command or as a very unlikely case measured by the device itself.Probably I'm assuming way too much here as it shows only the upper frequency limit currently which is blatantly misleading (and will create burn in the OLED module pretty soon - from my personal experience this kind of modules are very prone to it).Quote from: noreply on July 19, 2020, 02:36:46 amI have more or less that kind of SMA attenuator series (although shifted right so having also 40 and 50dB), in some situations they are better than the electronic one, sometimes the electronic one could be simpler to use.Quote from: noreply on July 19, 2020, 02:36:46 amThe reason why I've bought just a PCB without any extra stuff (basically just a breakout board of the chip) was pretty much along these lines (if you check my earlier photo it even seems to have proper via stitching).Just using the datasheet I was able to control dozens of various devices since they have typically some kind of SPI interface and reasonable control.I've burned myself once with these OLED stuff, never again. (That was a frequency counter 1 out of 2 working but with horrendous resolution and accuracy - if we can talk about any of these, since it was 5 magnitudes of order below of hobbyist grade stuff and I'm not kidding here).So far I have not done this (still not entirely abandoned the idea though) but if those micro switches on my PCB will break maybe it will create a new surge to this project.

author: edigi
author_rank: Regular Contributor
timestamp: July 19, 2020, 10:21:37 am
content: I've decided to make a quick test of my PE43702 breakout board (this is a 4GHz device, not 6GHz) at max attenuation.For fun, I've done the testing with both Siglent SSA and NanoVNAv2. Both set to 5dB/div calibrated with everything the same (as far as it was possible).Due to that this is just unshielded PCB, I can influence the result especially in the higher frequency range with a mere touch of the ground of the SMA connector...The big deviation at low frequencies is due to the capacitors at the input/output (I also suspect that they don't improve the flatness of the curve...).In the NanoVNAv2 thread I've posted some test results with SMA attenuators, should you want to compare with them.https://www.eevblog.com/forum/testgear/nanovna-v2-aka-s-a-a-2/msg3137696/#msg3137696

author: noreply
author_rank: Frequent Contributor
timestamp: July 19, 2020, 03:57:12 pm
content: Interesting ...I guess for a low cost device - the NanoVNA is OK to give you the 'trend' - but hard to get actual measurements from this device compared to a proper SSA.Your NanoVNA - definitely shows similar response as SSA.Your SSA response if VERY similar to the device I tested - maybe the 'semiconductor' - since they etched the markings - is same for ALL digital attenuator modules coming out of China via eBay and Amazon because its a cheaper clone version rather than original PSEMI device?In your SSA frequency response - you get a 'peak' at about 3 GHz - same as I did, its also relatively 'flat' up to 700MHz.I'm not sure if your PCB layout is same as the module I tested (there is a photo of the PCB in an earlier post) - if it is - then this could be the reason, it it is NOT same - then my PCB layout theory might not be so 'strong' in trying to improve the quality of the resultant attenuated signal.If your board has some additional vias - or looks similar to the Evaluation Kit Layout for PE43713 (photo of layout posted in thread above) - then this will be a big clue thatthe 'response' is most likely 'chip' related and not PCB layout or microstrip - lack off - related.With your results - on a different design to what I tested - my guess is that its 'chip' related - probably why they scrubbed the marking off the semiconductorThere is still some millage left in this investigation - if you are willing to 'enhance' your PCB layout to see if it can temper the resultant frequency response to that closer to thereal device'spublished specifications?I would have done some experimentation with my device - but I decided to return this instead (after all it had a broken switch) - because its simply not possible to use it for my needs - as I need ACCURATE attenuation values always - throughout the specified frequency range!Thanks for your valued feedback

author: edigi
author_rank: Regular Contributor
timestamp: July 20, 2020, 06:20:03 pm
content: Quote from: noreply on July 19, 2020, 03:57:12 pmAs long as you stay within the limits of NanoVNA (and the PE43702 module that I've tested is comfortably within) it's actually fairly easy to use it for actual measurements. Although I could challenge it with my SMA attenuators, it's still a great value in my view.Quote from: noreply on July 19, 2020, 03:57:12 pmDue to that the forum engine messed up the thumbnail to photo matching I cannot really check any of your photos, but based on even the thumbnail PCBs look different.Out of curiosity (and possibly to have a better attenuator although even what I have is OK for me till around 1.2-1.4GHz) I've ordered a PE43703 board. Based on the advertisement photos it's more similar to what I have currently, but still different. Let's see if it's any better (probably it takes quite some time till it arrives to me).Sorry I'm not willing to waste any time on trying to mod the PCB (it's harder than it looks and it has already a usable range).I include a high res photo of the chip if anyone is able to identify anything based on that (to me it looks like it follows datasheet marking but that's it).

author: noreply
author_rank: Frequent Contributor
timestamp: July 20, 2020, 08:36:59 pm
content: Quote from: edigi on July 20, 2020, 06:20:03 pmAt least your PSEMI device looks genuine - it certainly did not have its markings removed - that's a good thing.Here is a link to an application note for your specific device - to help you 'tune' and play with ithttps://www.psemi.com/pdf/app_notes/an26.pdfI guess that we are getting 'similar' SVA peeks - would indicate to me that my device in the 6HZz version is probably a genuine PSEMI but most likely same as yours - a 4GHz and not 6GHz device - hence why the scrubbed the markings.Not every 'dude' who buys this module on eBay will have a $5000 SVA to check if they are getting ripped of with an inferior specification moduleI am attaching my close-up and wide shot of the CHIP and PCB again*** I just noticed - see p8.jpg ***I think they tried to do 'on the fly' microstrip design - possibly applying solder to the copper strip as maybe while looking at the SA frequency response??It certainly look unusual with all the solder 'sculpture'?What do you think?I guess its an easy way to experimentLooking forward to you 'new' feedback - when you receive your new module.

author: noreply
author_rank: Frequent Contributor
timestamp: July 25, 2020, 12:22:52 am
content: Interesting behavior - UPDATEMy 3rd device purchase via Amazon - was '100%' working - and within 10 minutes the OLED screen went blankI presume the 'device' was still functioning - but it was simply not possible to control it via the pushbuttons - when the screen can't be used for letting you know what's happening.So I put this 'now dead' device aside - scheduled for yet another Amazon return (this was the 3rd device which was faulty - the one I did the tests on had faulty switch 2nd device - which I managed to bypass for the testing)Today (some 5 days since powering it on and its ultimate OLED screen failure) I decided to 'power' up the device - just to see if it was really dead or something like a miracle transpired and it working again.So I flick the switch and 'bingo' the device is fully functional - with the OLED screen working as though nothing happened in the first place.I decided to stress test it - by making it go through at least a dozen power-on off cycles - all worked - no problems.So I decided to leave it on - a long term 'burn in' - to see if it lasts longer than 10 minutes as it did last time.One hour later - its still going strong , but 90 minutes later or thereabouts (i did not have clock) - the screen fails - dead again as before.OK, so what just happened?I decided to do a quick 'freeze' dropped the temp of the device by a good 15 dec C - then decided to power-upStill dead - so not an obvious temperature problemI leave the device in 'off state' for about 3 hours - then a quick check - still deadSo, I'm thinking - this is really unusual?I am going to leave it for several days - like before and then power-up again to see what happens.I thought that - this dead then alive - then dead behaviors was a noteworthy observation.I don't have much experience with OLED displays - just wondering if this is something common to the type of small OLED displays as used in this device?Where they can come to life after a while and then die again?Anyway - thought I should share this experiance with you all

author: bicycleguy
author_rank: Frequent Contributor
timestamp: July 25, 2020, 05:15:22 am
content: I've had to much wine and must comment. Why does everyone posting NanoVNA plots leave all kinds of extraneous traces on when you can turn them off? Who needs a smith chart overlay from something on a LogMag thru plot? At minimum please say which trace you are looking at. Nice pictures and observations though.Sorry for the rant but its been building up over time on almost every NanoVNA plot. Not great for nubs.Quote from: edigi on July 19, 2020, 10:21:37 am

author: edigi
author_rank: Regular Contributor
timestamp: July 25, 2020, 02:49:51 pm
content: The Smith chart also provides very valuable information here.You can see from it how well the input impedance of the attenuator is matched.If you compare it with the SMA attenuator charts, you can see that this attenuator is not very well matched at any frequency. In case of the SMA attenuator it's just a single point (at system impedance = 50 Ohm) thus it's very well matched in the entire range, unlike with this attenuator where it's a curve, mostly capacitive (except at the highest frequency range).So please forgive me providing complete information for those who are interested and anyhow it's also allowed to be lazy in EEVblog, isn't it.Instead of starting a (fake) rant, you could have checked perhaps one of the Smith chart videos from w2aew (he has many excellent tutorials related to Smith charts, but not only that also NanoVNA or IQ modulation and so on).As a starting point:

author: bicycleguy
author_rank: Frequent Contributor
timestamp: July 25, 2020, 06:26:34 pm
content: Thanks, great video link and explanation.

author: noreply
author_rank: Frequent Contributor
timestamp: July 25, 2020, 10:34:22 pm
content: Today I received yet another module the 4th - in my quest to get a FULLY functional unit.The good news it that it appears to work - at least for now.The OLED display is functioning.I connected the module to my SVA and did a sweep from 0MHz to 3.2GHz (my limit)See the attached plot.Sorry - I simply forgot to label each of the traces - its obvious though - I started at 0dB then 10dB, 20dB and finally 30dBSince these failed so dismally - I did not bother to check the actual accuracy of the attenuation steps - which are adjustable in .05dB steps.Weather the semiconductor 'chip' will recognize these 0.05dB steps - is debatable - I don't believe from my previous checking. The built-in microcontroller gives you the ability to select such small steps - another lure - to make you think this is a great module to buy and use - but in fact it is deceiving the buyer once againThe results as almost same as the previous module (with faulty switch).This makes me believe that the 'limiting factors' have nothing to do with the individual PCB as the variation in a 'bad' PCB wouldnotproduce almost identical response over the entire 3.2GHz span.So, given that the response is terrible beyond about 700MHz - I would seriously think that the semiconductor used in this module is definitely not specified to operate at the 6GHz upper limit.The additional information - which supports the 'fake semiconductor' theory - is that ALL modules had the chip markings removed - something they would not do if the correctly specified semiconductor would be used.I guess - they are relying on the most plausible scenario - where the person buying a $30 module either from China directly , eBay or Amazon is simply not going to know thatthe module does not work to specifications beyond 700MHz- because they don't have a $5K SVA at their disposal.The lesson here - buyer beware - don't TRUST these modules to work to specifications - without testing it yourself (if you can).I am returning this 'working module' to Amazon - with a copy of the SVA frequency response vs attenuation - asking Amazon to forward this to the seller and make sure they don't make false claims - just to prove my point that not every sale will simply be accepting of false specification claims by the seller.Hope that my investigations and the above exercise was useful but I guess everyone will have their own experiences

author: edigi
author_rank: Regular Contributor
timestamp: July 26, 2020, 09:11:35 am
content: Quote from: noreply on July 25, 2020, 10:34:22 pmYou keep mentioning the $5K SVA needed thing for checking this attenuator, while in reality the 60$ (or so) NanoVNAv2 is more than sufficient to see that you can't expect very high precision from it.I heavily suspect that even the designer did not have a $5K SVA for checking this thing (not to talk about the seller, the wholesale company and so on; they probably didn't even know what to look for even if there was a decent spec.).You have to have some sense of reality, RF/microwave components are typically expensive and if something is cheap and if it does not have decent documentation/spec (or some forum where it's extensively discussed) you have to live with the suspicion that it's a hobbyist grade stuff at best.Nevertheless this does not mean that what is cheap is necessarily bad or what is expensive is necessarily a good value.This is why I'm usually willing to take risk with not too expensive things (sometimes I look ways to enhance them but not in this category; example is the AWG as many people did that), although I'd have never bought a 3rd and not to talk about a 4th copy of the same thing. Even if the OLED or the power switch or whatever works, the key components like the signal path on the PCB and the attenuator chip is very unlikely to be different...

author: tautech
author_rank: Super Contributor
timestamp: July 26, 2020, 09:16:07 am
content: Quote from: edigi on July 26, 2020, 09:11:35 amSeems that way don't it but it's not as many are converting their $1.6k SSA3021X+ into a 3.2 GHz SVA.

author: edigi
author_rank: Regular Contributor
timestamp: July 26, 2020, 10:35:30 am
content: Quote from: tautech on July 26, 2020, 09:16:07 amI think you've entirely missed my point which was that one does not need a $5K SVA (or a $1.6k SVA converted SSA for that matter) when a 60$ NanoVNAv2 is perfectly capable checking the attenuator of this topic (and a lot more).

author: noreply
author_rank: Frequent Contributor
timestamp: July 26, 2020, 07:35:27 pm
content: Quote from: edigi on July 26, 2020, 09:11:35 am@edigiYou are spot-on with your commentI don't know what came over me - to simply quote that not everyone has a $5K SVA - so they are unable to 'check' the operation of a cheap attenuator module.I was one of the early adopters of the nanoVNA - in fact I have 3 of them - they are extremely useful devices - especially for checking antennas and attenuators - just to name two types of measurements / testing.Just before I performed the Digital attenuator module testing on my 4th device (more on this later) - I was doing some SVA testing of RF signal generators - measuring noise floor levels and harmonic responses - which were beyond the nanoVNA's capability - so I guess I had this 'on my brain' when making the rash remark that you need to have a $5K Test instrumentYou made a good point and I hope those reading this thread - if they get to this post - they should take noteWhy did I preserver with getting a 4th module?I guess I wanted to get a fully functional unit (with no faults , like broken switch and nonworking OLED display) - because I wanted to 'keep' it for use in my lab.What I did not realize, until much later, that the module performance has little to do with the PCB and or its layout (but there could still be a possibility if the layout is total garbage and in essence creates a reflective transmission line after 700Mhz?) and more likely the semiconductor with its scrubbed out markings to conceal that it is not a 6GHz device.I probably will keep the device for the following reasons;-1. It can be used for low frequency applications - up to 500MHz2. The aluminum RF casing with the SMA connectors is alone worth the $$ - as I often need a 'package' to house my microstrip designs.Hope the above makes sense to anyone wanting to purchase & test a similar device to the one tested here.

author: edigi
author_rank: Regular Contributor
timestamp: August 06, 2020, 06:39:39 pm
content: I've received the PE43703 board (see attached picture).Surprisingly the power plug is reversed, so what is GND in the PE43702 board it's 5V here and vice versa. You must pay special attention to this (although probably there is reverse polarity protection).I did the testing with NanoVNA.After seeing the results I've cross checked the NanoVNA with SMA attenuators. With those it's almost perfectly flat.The good thing with these electronic attenuators that the attenuation can be set in fine steps but the price seems to be that there is frequency dependence (at least with these variants).What I particularly dislike is the poor impedance matching and the resulting reflections.

author: noreply
author_rank: Frequent Contributor
timestamp: August 06, 2020, 07:27:03 pm
content: @edigiFirst of all I prefer your board - to the OLED with microcontroller - using dip switches is far more reliable - less things to go wrong (like dead OLED screen).You also seem to have genuine 'chip' - at least they did not deface the markings.The PCB layout looks good - with the micro vias running alongside the input / output traces - but I am not sure if they used the correct substrate.I bet that FR-4 is what they most likely used - not sure if this is good enough to 6Hz?I found a link on Rogers .. interesting reading ...https://www.rogerscorp.com/-/media/project/rogerscorp/documents/articles/english/advanced-connectivity-solutions/circuit-materials-and-high-frequency-losses-of-pcbs.pdfIts a pity - that we cannot reproduce 'flat' response - obviously there are other 'frequency' factors in play on this device