The SpyVerter is a new upconverter that has recently gone on sale. It is created by Youssef (he programmed SDR# and worked on the development of the Airspy SDR) and Bob W9RAN (of rantechnology.com and youtube.com/user/ranickel). In this post we'll review the SpyVerter and compare it against some other up converters that we have used in the past.
Radio transmissions between 0 - 30 MHz can travel all the way around the world. At these frequencies many interesting signals such as international shortwave radio, ham radio communications and several military transmissions exist.
The RTL-SDR's lowest tunable frequency is 24 MHz, and so it can only receive a small portion of the interesting transmissions that occur between 0 - 30 MHz. In order to listen to frequencies below 24 MHz an upconverter is required (either that or perform the direct sampling mod). An upconverter works simply by shifting these lower frequencies up to a higher frequency that the RTL-SDR can receive. For example, a 5 MHz signal might be upconverted to 105 MHz.
To date, most decent upconverters (such as the popular ham-it-up upconverter) have been based on the double balanced mixer architecture implemented by the ADE-1 mixer chip from Minicircuits. The SpyVerter on the other hand is based on a different type of architecture which is inspired by the H-mode mixer design that was used in the unreleased HF7070 communications receiver. The expected major advantage that this design has over a ADE-1 based design is better IIP3 performance. This essentially means that strong signals will not cause overloading issues in the SpyVerter, meaning less noise and spurious images.
Another advantage of the SpyVerter is its use of a 120 MHz low phase noise/low jitter clock, meaning less reciprocal mixing and thus greater SNR and a lower noise floor. A low phase noise clock is essential for getting good performance when receiving the very narrowband signals that are typically found between 0 - 30 MHz. The other upconverters do not specify their phase noise performance as far as we can tell.
The SpyVerter comes in a metal box, with three SMA adapters. A metal box is great because it helps keep strong interfering signals from entering the signal path, as well as stabilizing the internal temperature, keeping frequency drift to a minimum. Most upconverters only come with a metal box as a paid add on, but the SpyVerter comes in one by default.
Although the SpyVerter is designed to be used with the Airspy, it is fully compatible with the RTL-SDR as well. The SpyVerter can be powered via a USB cable, or via 5V bias tee (and this is compatible with the bias tee used on the RTL-SDR Blog units sold by us).
|Upconverter||Clock||Bias Tee?||LNA?||Architecture||Enclosure?||Extras?||Price (USD)|
|Spyverter||120 MHz, low phase noise||Yes||No||H-mode mixer inspired||Yes, in metal box by default.||Three SMA adapters.|
|Ham-It-Up||125 MHz||No||No||ADE-1 (v1.0) / ADE-1 Reversed (v1.3+)||Available as extra add on for $21.95.||Optional noise source circuit (but not populated by default)||$44.95 + enclosure $21.95|
|Nobu||100 MHz||No||No||ADE-1 Reversed||Available as extra add on.||None.||$56 + enclosure $25|
|SV1AFN||200 MHz||No||Yes||ADE-1 Reversed||None available.||None.||$57|
The creators of the SpyVerter, Youssef and Bob (W9RAN), sent us a unit for review a few weeks ago and below we present some real world test results. We compare the SpyVerter against two ADE-1 based designs. A Ham-It-Up V1.0 and an upconverter designed by Nobu of Japan. The ham-it-up V1.0 uses the ADE-1 in a standard configuration, whereas Nobu's upconverter uses the ADE-1 in reverse. Using the ADE-1 in reverse allows better operation near DC, but can create impedance mismatch problems. If you want more info about this, see this post where Mile Kokotov reviews the SV1AFN upconverter (also uses the ADE-1 in reverse) and the ham-it-up and discusses a bit about the ways the ADE-1 can be connected. We note that newer versions of the ham-it-up (v1.3) use the ADE-1 in reverse as well, so the performance of a modern ham-it-up may be closer to that of Nobu and SV1AFN's design.
In each of these tests we used an RTL-SDR Blog dongle, SDR# and the special decimation driver for the R820T released by Vasilli. Vasilli's decimation drivers make viewing HF signals in SDR# much more pleasant as it allows for a high resolution decimated zoom and thus improved visual SNR. This makes spotting narrowband weak signals much easier. His plugin also has a "Use SpyVerter for HF" option which simply automatically sets the correct frequency offset value of -120 MHz for the SpyVerter. Each upconverter was powered by an external battery pack.
The testing was performed sequentially, but all three units were tested within 5 minutes to ensure that HF conditions did not change too much. All tests used a roof mounted Miniwhip antenna (except for one test which used a Magnetic Loop).
AM Broadcast Band
Here we tested all three units on the AM broadcast band between DC and 2 MHz. Gain settings were kept the same for all tests. Click on the thumbnails to see screenshots from the other upconverters.
From these comparison images it is clear that the SpyVerter has the lowest noise floor and highest SNR on the signals.
With significantly less noise and weaker signals received by the Magnetic Loop the SpyVerter and Nobu's upconverter were similar. However, here the ham-it-up shows some significant overloading issues near DC, has an image of the DC signal near 2 MHz and also some FM band interference.
9 MHz Shortwave
In this test we used a Miniwhip and an RTL-SDR dongle to tune to the 9 MHz shortwave band. We used a sample rate of 2.56 MSPS and zoomed in using a decimation value of 4.
The screenshots show that the SpyVerter clearly has the lowest noise floor, best SNR and the least amount of noise artefacts. We think the artefacts and higher noise floors in ham-it-up and Nobu's upconverter may be caused by overloading in the mixer, and from reciprocal mixing from the use of clocks with higher phase noise. The artefacts in question are the yellow smudge like areas in the images.
11 MHz Shortwave
Again, this test at the 11 MHz international shortwave band shows similar results with the SpyVerter overloading much less and thus having a lower noise floor and less noise artefacts.
Non-Directional Beacons (NDBs)
Here we tested the upconverter on non-directional beacon (NDB) reception at VLF frequencies of around 250 - 300 kHz. We used a decimation value of 16 to get a nice zoom.
Non directional beacons are used to aid with aircraft navigation. All three performed similarly, but the SpyVerter had a slightly lower noise floor and less noise. These signals may not have been strong enough to notice any significant difference.
20 kHz VLF
In this test we tried to receive some military signals at a very low frequency of 20 kHz. We're not sure what these signals are, but they appear to be some sort of military direction finding signal. Here, the SpyVerter and Nobu's upconverter performed similarly, but the ham-it-up V1.0 could not receive the signal well due to it's standard use of the ADE-1.
Signal Generator Test
The final test we did was artificial in nature. We used a HackRF to inject a tone at 10 MHz and took screenshots. The more the noise floor rises up around the signal, the poorer the upconverter is performing.
Again the results show that the Spyverter had the least overload, followed by Nobu's upconverter and then finally the ham-it-up.
From the specs and results I think that it is quite clear that at the moment the SpyVerter is probably the best upconverter you can buy for the RTL-SDR. It is priced similarly when compared to the other upconverters, but comes with a low phase noise clock and metal enclosure by default. From our tests we think that its architecture appears to be superior compared to ADE-1 based designs when it comes to issues caused by strong signals. If we were able to receive even stronger signals in our tests then the difference would probably be even more significant.
So, if you already have an upconverter should you run out and upgrade it to the SpyVerter? That depends. You'll probably only see a significant advantage with the SpyVerter if you are able to receive strong signals. People with properly set up DX or ham antennas will probably see a significant improvement, but if you have just strung up a short wire antenna and your signal levels are low then you may not see much of a difference.
In a later review we will compare the performance of the SpyVerter on its designated SDR the Airspy.
The SpyVerter costs
$59 $49 USD, ships from China and can be bought from iTead Studio.
Update July 2016: The price of the SpyVerter has been reduced by $10, and now only costs $49 USD.