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 700MHz
AND
There 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 output
The sweep frequency was from 0Mhz to 3.2Ghz
I 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 & 20dB
This 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 module
Be 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.