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Using Cheap Asian Electronic Imports – by Jim Rowe New w.i.d.e.b.a.n.d UPCONVERTER RTL-SDRs – Part 2 Last month, we described two of the latest compact wideband RTL-SDRs, which used direct conversion for reception below 25MHz. This time we’re reviewing some of the larger units, which have inbuilt upconverters for improved reception below 25MHz. L Another option is the BA5SBA. This appears to be alike the direct-conversion SDRs, many of the upconverter RTL-SDRs also come in a metal case for most identical both inside and out, apart from the BA5SBA unit having a wrap-around dress panel. It is available from shielding. But with the first unit we’re examining, its metal case is various suppliers on eBay, for about A$75. I decided to get one of the N300U units first, but during about twice the size of those simpler SDRs, at around 83 x 50 x 20.5mm. It has two SMA input sockets at one end initial testing, I discovered that while it worked quite well on the VHF-UHF range, it did not work at all on and a mini USB socket at the other end. the LF-HF upconverter range. So I ordered A mini toggle switch is provided for LF-HF/VHFa BA5SBA from a supplier on eBay, and UHF range switching, along with a 3mm began testing it as soon as it arrived. LED which changes colour to inStrangely enough, it didn’t work on dicate which range has been acthe LF-HF range either! tivated (green for VHF-UHF, red I went through all of the inforfor LF-HF). mation I could find on the web reCurrently, the most popugarding these upconverter SDRs, lar of these upconverter RTLin case I was not using them corSDRs is the N300U “Convert rectly. Wide Range SDR”, available from But after a lot of testing and reBanggood for A$68 including GST testing, I had to conclude that they and postage. It comes with a short The BA5SBA: USB cable and a coil-loaded whip like the N300U SDR were both faulty. That was when I opened up both ‘test antenna’. (above), faulty out of the box! 42 Silicon Chip Australia’s electronics magazine siliconchip.com.au Looking at each end of the Azeuner RTK-H800 – our “best choice” if you’re interested in frequencies above 3.6MHz. units to check for faults. As you can see from the photo overleaf, both have two PCBs, with the upper PCB being a DVB-T dongle board just like the one in the two compact RTL-SDRs we looked at last month. The larger PCB underneath has the extra circuitry for the upconverter plus the two SMA input connectors, the range switch, indicator LED and mini-USB socket. I probed around with a DSO and found that in both cases, the 100MHz local oscillator wasn’t producing any output when the range switch was set to for the LF-HF range. I did find that they both worked fairly well on the VHF- UHF range, by the way. Frustrating! I tried contacting both suppliers to see if they were able to provide replacement units, but in both cases, all they were prepared to do (eventually) was offer me a partial refund. That simply isn’t good enough, given that these products didn’t do what they claimed to at all. But it’s all too common these days when buying from overseas. So I ordered yet another upconverter RTL-SDR; one which, according to the pictures on the eBay supplier’s website, looked as if it was on a completely redesigned single PCB. –60dBm (224 V) –70dBm (71 V) RF SENSITIVITY FOR >12dB SINAD –80dBm (22.4 V) Auzeuner RTK-H800 on LF-HF (upconverter) range Blog V3 RTL-SDR on LF-HF (dir sampling) range Auzeuner RTK-H800 on VHF-UHF Range Blog V3 RTL-SDR on VHF-UHF range BA5SBA RTL-SDR on VHF-UHF range –90dBm (7.1 V) –100dBm (2.24 V) –110dBm (710nV) –120dBm (224nV) –130dBm (71nV) –140dBm (22.4nV) 100kHz 200kHz 500kHz 1MHz 2MHz 5MHz 10MHz 20MHz 50MHz 100MHz 200MHz 500MHz 1GHz 2GHz SIGNAL FREQUENCY Fig.1: a comparison of the sensitivity (minimum signal level needed for a reasonable reception signal-to-noise ratio of at around 12dB) for three SDRs over a wide range of frequencies. Lower figures (ie, higher negative dBm values) indicate better performance. siliconchip.com.au Australia’s electronics magazine June 2020  43 Fig.2: a spectral analysis of the signal from the Auzeuner RTK-H800 over the range of 0-1.1MHz with no input signal (its input was terminated with 50Ω). This should be a flat line but instead shows a field of spikes which interfere with the reception of AM broadcast band signals and longwave transmissions. For this reason, the Blog V3 RTL-SDR described last month is better for low-frequency AM reception. This was the Auzeuner RTK-H800 or N300_V2, which came from eBay seller cybereveryday (2835) and was priced at A$78.31 with free postage (it’s also available on AliExpress for a similar price). Waiting with bated breath I had to wait a few weeks for that one to arrive, as it was delayed due to the Coronavirus. When it turned up, I found that it was significantly smaller than the other two upconverter SDRs, measuring 62.5 x 41.5 x 23.5mm. It also came with a 3m long USB cable; longer than the one supplied with the Convert and BA5SBA units, and fitted with a micro-USB plug to match the socket on the unit itself. As I had expected, all its components are indeed mounted on just one double-sided PCB measuring 60 x 39mm. The only real disappointment was finding that despite the claim made in the sales description, there was no ‘thermal tape’ under the PCB to improve heat transmission out to the case. Another nice feature of the Auzeuner is that it is supplied with a 3m USB lead – most SDRs have a 2m – or even 1.8m – which often simply isn’t long enough! 44 Silicon Chip Like all of the other SDRs we have looked at lately, the Auzeuner uses the combination of a Rafael Micro R820T2 programmable tuner IC and a Realtek RTL2832U COFDM demodulator chip. So it is correctly described as an RTLSDR. The printed legends on the input end of the Auzeuner unit are a bit puzzling. As you can see from the photo, the VHF-UHF input socket is labelled ‘RF OUT’ while the upconverter LF-HF input socket is labelled ‘UP RF OUT’. So it seems that something has been “lost in translation”! Anyway, a quick check showed that this unit definitely did work on both the VHF-UHF range and on the upconverter LF-HF range (whew!). So I fired up my RF signal generator, hooked up the Auzeuner RTK-H800 to my PC fitted with the SDR# application, and ran a series of sensitivity tests from 100kHz to 25MHz on the LF-HF range, and from 30MHz to 1.7GHz on the VHF-UHF range. Fig.1 shows the results, which also shows the response of the Blog V3 RTL-SDR reviewed last month, and the VHFUHF response of the BA5SBA SDR. The Auzeuner unit’s performance on the VHF-UHF range is broadly comparable to that of the Blog V3, and both of them are 10-20dB better than the BA5SBA. On the LF-HF range, the Auzeuner unit is 3-7dB better than the Blog V3 between 4MHz and 25MHz, but about 12dB less sensitive than the Blog V3 at 2.2MHz and about 2dB poorer at 230kHz. The Auzeuner’s response is not shown below 230kHz because I found that measurements were getting quite difficult (or meaningless) at these lower frequencies due to a large number of spurious ‘spikes’ present in the Auzeuner’s output, even when the upconverter input was connected to a shielded 50Ω termination. Australia’s electronics magazine siliconchip.com.au The Auzeuner is made on a single PCB (as distinct from many others which have two sandwiched boards). In this pic of the BA5SBA, you can just make out the “piggy backed” PCB sitting above the middle of the lower board. This is shown in Fig.2, which covers an effective frequency range 0Hz to 1.1MHz. range of about 30MHz to 180MHz. It’s on the LF-HF range that the comparison becomes a bit more confusing. The Auzeuner is equal to or better than the Blog V3 from 3.6MHz to 25MHz, with the gap between the two being about 8dBm at 5MHz and just on 7dBm at 10MHz. But below 3.6MHz, the sensitivity of the Auzeuner unit is worse than that of the Blog V3, with the gap between the two widening to about 12dBm at 2.2MHz. Still, even then its sensitivity is quite reasonable, at -99.5dBm or 2.4uV. Presumably, it’s the Auzeuner’s upconverter that is responsible for the excellent sensitivity of 120dBm (224nV) between 5MHz and 25MHz. But it also seems that it is to blame for the worse sensitivity below 3.6MHz, and the forest of spikes below 300kHz. This makes it hard to decide which is better for LF-HF reception – the Blog V3 with its direct conversion approach, or the Auzeuner RTK-H800 with its upconverter. I guess it boils down to the part of the spectrum you’re most interested in. If you’re mainly interested in reception below 3.6MHz, go for the Blog V3 (see last month). However, if you’re more interested in reception at frequencies above 3.6MHz, the Auzeuner RTK-H800 is the better choice. SC Summary As Fig.1 shows, the sensitivity of the Auzeuner RTKH800 upconverter RTL-SDR is quite impressive from 30MHz to 1.15GHz. It needs a signal of just -125dBm (126nV) or less for an SNR (signal-to-noise ratio) of better than 12dB. It only becomes a little less sensitive at frequencies above 1.15GHz, but still only needs a signal of -118dBm (282nV) to achieve an SNR of 12.7dB at 1.65GHz. This is quite comparable with the performance of the Blog V3; it is actually about 3dB more sensitive over the   Useful Links A size comparison, not far off life size, between three of the units: the BA5SBA at the top, the Auzeuner RTK-H800 in the centre and the Blog V3 (which we looked at last month) at the bottom. siliconchip.com.au Australia’s electronics magazine • www.airspy.com – the best source of the SDR# application • www.hdsdr.de – source of the HDSDR application • www.rtl-sdr.com – an excellent source of information on RTL-SDR • www.rtl-sdr.com/big-list-rtl-sdr-supported-software • www.sdr-radio.com/download • www.secomms.com.au – Australian supplier of the RTL-SDR Blog V3 • https://zadig.akeo.ie – the source of Zadig, the Windows generic USB driver installer (needed by most SDR software) June 2020  45