Tagged: R820T2

GUI for Controlling the R820T2 Filters and Registers

Recently a program called R820T2Tweak_Patched was released which is a GUI for GQRX that allows you to manually control not only the three RF gain settings on R820T2 RTL-SDRs, but also the four filter settings as well as the registers directly. The R820T2 is the most commonly found tuner chip on RTL-SDR dongles, and is generally considered the best for most applications. 

The GUI could be useful for advanced users wanting to experiment with the various lower level R820T2 register settings, or for anyone that wants ultimate control over the filters in the RTL-SDR. 

The software is based on the original R820Tweak which has the same features except the ability to control the registers directly.

R820Tweak_Patched GUI. Control Gain, Filters and Registers.
R820Tweak_Patched GUI. Control Gain, Filters and Registers.

Investigating the Adjustable IF Bandwidth on the R820T Chip

Over on his blog, Thierry Leconte has been writing about some IF bandwidth experiments that he's performed on the R820T2 chip. This is the tuner chip that is used in most RTL-SDR dongles, and well as on the Airspy R2 and Mini SDRs. It has a programmable IF bandwidth and high pass filter which can be used to filter neighboring interfering signals out to reduce imaging and overload problems. In the RTL-SDR and Airspy drivers the bandwidth is adjusted to a fixed setting depending on the bandwidth selected.

To perform the tests he uses a noise source connected to his Airspy, varies the IF filter bandwidth and then plots the results. He finds that there are two adjustments for the IF filter, one coarse and one fine, as well as an additional high pass filter. By manually reducing these settings it's possible to get better filtering at the expense of reduced bandwidth. 

He notes that reducing the bandwidth is useful for his two apps, acarsdec and vdlm2dec which receive ACARS and VDL aircraft signals. These signals are not high in bandwidth so they can easily benefit from tighter filtering.

Adjusting the High Pass Filter on the R820T2
Adjusting the High Pass Filter on the R820T2

R820T2 Chip Discontinued: Low Cost R820T2 RTL-SDRs will Continue, Airspy Will Redesign

The R820T2 is the main tuner chip used in most RTL-SDR dongles. Several months ago Rafael Micro ceased regular production of their R820T2 chip, and the older R820T has also been discontinued for some time too.

However, Rafael are still producing new quality R820T2 chips for factories if they make very large bulk orders. Since it is one Chinese manufacturer producing all of RTL-SDR.com V3, NooElec, FlightAware and most generically branded dongles, the volume restriction is not a problem for them as long as the RTL-SDR is still in demand. So most dongles using R820T2 RTL-SDRs should be able to continue business as usual for the forseeable future. But we have also recently seen that a lot of generically branded RTL-SDR dongles presumably produced at other factories have started to ship with the less desirable FC0012/13 tuner chips instead.

The R820T chip is already 8 years old, and the R820T2 has been around for the last two years. The R820T2 was a slight improvement on the R820T, due to a higher quality manufacturing process used to produce it. The change in manufacturing process resulted in mostly higher yields, less chip-to-chip variance, better sensitivity, reduced L-band heat VCO lock issues, and wider filters. 

Recently the Youssef from the Airspy team announced the likely early retirement of their Airspy Mini and R2 line of products (see update below, Airspy Mini/R2 production will continue) These are SDRs that used the R820T2 tuner chip combined with a 12-bit ADC, allowing for significantly better performance compared to an RTL-SDR. It seems that they were able to acquire R820T2 chips from a distributor, but the stock proved to be very low yield. Possibly once discontinued a lot of low quality chips were dumped onto the distributors for final sale. They write:

I have some bad news. Rafael Micro officially discontinued the R820T2 since a few months. This is the tuner we use in the Airspy R2 and Airspy Mini.

We tried to secure an extra batch from Rafael (even at a higher price) but the quality of the silicon of the samples we received wasn't very good and most units didn't pass our automated QA tests. Sacrificing the performance is out of question. The alternatives proposed by Rafael are not pin compatible and require both a significant hardware redesign and new tuner control code - and this is a large investment with very little guarantees on the final result.

I can say this has been one of the longest running designs that resisted the new silicon tuner SDR's popping in and out while setting a standard for performance and price.

For now, our distributors are running out of R2/Mini's very quickly and, until a final solution is found or a new replacement is designed, there won't be any new batches out.

Youssef from Airspy also notes that he's beginning work on designing a new unit:

I was checking my notes for alternatives to the current Airspy R2/Mini design and wondered if consulting the community would give some constructive input. As the market is already crowded with low cost receivers and transceivers, but yet Icom manages to sell a 4 figures SDR, I was thinking of making something that is as open as possible for extensions and work good enough for the most demanding operators and pro's, all while being affordable.

The idea is to replace the R820T2 tuner with one of its latest high performance siblings, then replace the old LPC4370 with the brand new i.MX RT1020. This MCU can be interfaced with a good ADC and has enough processing power for oversampling and decimation through the Cortex M7 core, which will bring the final resolution higher.
The general goals:

  • Better RX performance than the general purpose low cost silicon transceivers
  • 12 bit RX at 10MHz bw and up to 16bit at narrow band
  • Coverage from 30 MHz to 1.8 GHz or more
  • Switched pre-selectors
  • Open source
  • Same form factor as the Airspy HF+ (same box actually)
  • Leverage the RF manufacturing and testing capability developed at Itead Studio
  • Affordable

UPDATE (May/2018): The Airspy team have managed to acquire a new batch of good R820T2 chips, so production of the R820T2 based Airspies can continue as per usual.

So in conclusion there is no need to panic buy R820T2 RTL-SDRs as production will continue as per normal for the forseeable future as the RTL-SDR demand is high enough for factories to make large bulk orders of new R820T2 chips. Even if the R820T2 is fully discontinued, there are alternative tuners with the same performance that we can switch to after a minor redesign.

Note that we're currently out of stock of RTL-SDR V3's on Amazon and low in stock on our store but this is not related to R820T2, but rather simply shipping delays. We should be fully back in stock within a few weeks.

The R820T2 on an RTL-SDR
The R820T2 on a RTL-SDR V3

An R820T2 Breakout Board

The R820T2 is the tuner chip used on most RTL-SDR dongles. It is also used on the Airspy, a more advanced higher end SDR. All in all, it is a very good tuner chip, but it is mostly limited by the low-bit ADC on the RTL2832U chip in the RTL-SDR.

We’ve just been informed that there is now a custom DIY breakout board available for the R820T chip which is made by Eric Brombaugh who is an SDR experimenter. This is great for those wishing to do home brew SDR experiments with the R820T2 chip, for example you could perhaps implement your own SDR with a higher end ADC chip on a development boards.

The breakout board is essentially the exact implementation which is shown in the R820T datasheet. It is available as a 4-layer PCB on Osh Park and it “provides a simple 4-pin interface with power, ground and I2C bus for controlling the tuner. A broad-band RF input and 10MHz IF output are provided on SMA connectors.” Eric has also provided us with a simplified driver based on the Airspy and Linux media driver code which allows you to control the R820T2 from an STM32F0xx processor.

The assembled R820T2 breakout board.
The assembled R820T2 breakout board.

Showing how the R820T stops receiving at 1.4 GHz+ with increasing temperature

Over on YouTube RTL-SDR experimenter Adam 9A4QV has uploaded a video showing how the R820T dongle can fail to receive properly at frequencies above about 1.4 GHz as the temperature in the dongle rises. This is a known problem that may cause issues when trying to receive satellite signals like Inmarsat at 1.541450 GHz. In our own tests, the R820T2 chip appears to be much less prone to this behaviour when compared with the R820T, but still fails if the ambient temperature gets too hot, for example if left in direct sunlight. We’ve had several R820T2 RTL-SDR’s running at 1.5 GHz+ for over 48 hours when left in the shade, but not one R820T ran for more than a few minutes at those frequencies. Of course the E4000 tuner is the best RTL-SDR tuner for these GHz level frequencies, but that tuner is now rare and expensive.

Over on Reddit, some people have been discussing this issue, and have proposed that the likely cause is related to the PLL failing to lock properly at higher temperatures. A fix may be to apply a blob of solder to the vias underneath the R820T chip, and then attach a heatsink. The problem also does not occur on the Airspy, a higher performance SDR that also uses the R820T2 chip in its design. This may be due to better drivers for the Airspy, or better heat dissipation in the Airspy’s hardware design.

R820T stop receiving @ higher frequencies

New Products: $20 RTL-SDR with 1PPM TCXO, SMA F Connector and R820T2 now available in our store

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We have just released a new and improved RTL-SDR unit in our store, which we are currently pricing at $19.95 USD, or $24.95 USD including 2x telescopic antennas. The unit comes with the following improvements:

  • 1 PPM temperature compensated oscillator (TCXO) – Accurate tuning and almost zero temperature drift (2 PPM initial offset, 1 PPM temperature drift)
  • SMA female antenna port – Most dongles use the less common MCX or PAL antenna ports. Ours use SMA which is much more common so more adapters and antennas are available for it. It is also more durable and has lower insertion losses.
  • R820T2 tuner – More sensitive/lower noise floor than the older R820T tuner. 100% compatible with software for the older R820T.
  • Improved component tolerances – Allows the RTL-SDR to work more optimally over all frequencies.
  • Experimental: 4.5V USB powered bias tee – Can be enabled by soldering two pads on the PCB together. This allows the RTL-SDR to power LNA’s (like the LNA4ALL and HABAMP) and active antennas through the coax cable.
  • Experimental: Break out pads for direct sampling – Allows easier soldering to pins 4 & 5 on the RTL2832U for enabling the direct sampling mod.

See our products page to purchase these items!

Shipping Information

For US customers we highly recommend that you buy from our Amazon store as if you spend over $35 you will receive free shipping from a local Amazon warehouse. This usually takes less than 1 week for delivery. Prime subscribers can also get free 2 day shipping if bought on Amazon. If you like you can also use our international cart to buy from our Chinese warehouse with free shipping.

International customers can get free shipping from our warehouse in China. We will always try to use the fastest tracked air mail shipping method available to us, which will be ePacket, EMS air mail or similar if possible. This should get the parcel at your door within 2 weeks, but please note that this time is heavily dependant on the customs and postal agencies within the destination country which we have no control over. Countries such as Italy, Canada, Brazil, Russia and middle eastern countries are known to have extremely slow customs agencies.  If you prefer you can also pay more for express shipping and we will use DHL, UPS, FEDEX or EMS Courier. Just use our cart to select the shipping method you prefer. We also kindly remind customers that with international shipping you are responsible for any customs duties or taxes incurred by the shipment.

Shipping status meanings: ‘In process’ means that your order information has been sent to the warehouse and the parcel is being packed. A tracking number will follow usually by the next business day.

Please note that tracking updates may take a few days to show up.

Warranty Information

We will provide 6 months warranty on manufacturing defects. Please note that if you try the direct sampling or bias tee mods then any warranty will be voided, so please ensure your dongle is working before trying these.

If you suspect a manufacturing fault please email us at [email protected] and include your order number and name. Please include details of the fault and a picture of the fault if it is physical damage. If the unit is faulty we will issue either a refund or send a new unit out depending on your preference.

Specification Discussion

Temperature Compensated Oscillator (TCXO)

The 28.8 MHz oscillator used in most RTL-SDRs is passive and not frequency accurate. This means that when you tune to a known frequency, it will likely be offset by a few kHz. Usually the PPM offset on a normal RTL-SDR is in the range of 30 – 150 PPM. Furthermore, as the dongle warms up, the frequency will drift up to ~20+ PPM until the temperature stabilizes.

The 1 PPM Temperature Compensated Oscillator (TCXO) in our units provides accurate tuning with an initial offset of 2 PPM and a 1 PPM temperature drift over time. This means that a known signal will appear where it should on the frequency spectrum and will not significantly drift in frequency as the dongle warms up. 

SMA F Antenna Port

On standard RTL-SDR’s the antenna port is either a MCX or PAL connector. MCX connectors are relatively uncommon and are susceptible to connector strain when using an adapter. PAL connectors are common with some TV connections, but no decent radio or antenna will use PAL due to its high insertion losses above ~100 MHz.

We’ve made these RTL-SDR dongles with SMA female antenna connectors. SMA is a very common connector in the radio field and provides a sturdy and secure connection. In addition SMA antenna adapters are much easier to find and insertion losses are lower.

We know some people prefer the F-type connector used in the previously sold ThumbNet dongles, but from our previous polling we believe the majority (~80%) of users prefer SMA. We may bring out F-type RTL-SDR’s again in the future if there is demand.

Note: Remember to not get confused between RP-SMA and SMA! RP-SMA or “reverse polarity SMA” is used for WiFi equipment only. In the normal radio world, most devices use standard SMA. RP-SMA is reversed, it has the male pin on the female connector, and the female hole on the male end. To be clear: This device is a radio device so it uses normal SMA connectors.

R820T2 Tuner

As discussed when we brought out our previous generation, the R820T2 tuner has slightly better sensitivity than the R820T and also works better at frequencies around 1.5 GHz. It also works better with the experimental HF drivers.

Improved Component Tolerances

We have these units manufactured with tighter tolerances on all passive components.

Telescopic Antennas

In our $24.95 USD package we provide two telescopic antennas. The smaller one goes from 6 cm to 20 cm, and the larger one goes from 20 cm to 1.5 m. The antenna base is also larger with a 4.5 cm diameter, when compared to the smaller bases shipped with most models. This provides more stable operation when using the larger antenna.

With antennas, usually the larger the antenna is the lower the frequency it can receive. These two antennas allow you to tune to almost the entire range of the RTL-SDR. Of course the antenna should be placed outdoors and up as high as possible to get the best performance. Placing the magnetic mount on a metal surface can also help complete the antenna as a quarter wave ground plane.

When fully collapsed the small antenna works decently at 1090 MHz for ADS-B frequencies.

Experimental 4.5V Bias Tee

A bias tee allows you to power external RF devices such as Low Noise Amplifiers (LNA’s) and active antennas through the coax cable. Since LNA’s should be placed right after the antenna, it can be sometimes hard to get power to them if a bias tee isn’t used.

We have included a simple (experimental) bias tee option in our latest units, inspired by mods made by other experimenters. The bias tee is disconnected by default, but it can be activated by soldering two pads together on the PCB. Connecting the pads connects the antenna output to the USB 5V rail. The resistance in the fuse and inductor can reduce the output voltage to about 4.5V.

Bias Tee Instructions
Bias Tee Instructions

The USB power rail is protected from over current and shorts through a PTC resettable fuse with a hold current of 80 mA and trip current of 200 mA. This means that the fuse will become a short circuit if greater than 200 mA tries to flow through it, which may happen during a short or with faulty equipment. Between 80 mA and 200 mA is an unknown state, where the fuse may or may not trip, depending on the temperature. In practice we’ve tested it with a hold current of 120 mA in a ~16 degree ambient environment (and much hotter inside the dongle casing) and had no issues with premature tripping.

We used a 4.7 uH 250 MHz SRF inductor as the bias tee choke. At the highest frequency tunable by the RTL-SDR (~1700 MHz) this should only give a (simulated) ~1-2 dB loss through the inductor. For better performance at frequencies above 1 GHz you could experiment with a smaller value inductor and possibly with removing the static protection diode, though in our tests we saw very little difference with the diode removed.

We have tested the bias tee with an LNA4ALL and HABAMP both in bias tee mode. Both worked fine running for a number of hours. The HABAMP really improved ADS-B reception a lot and we highly recommend it. We also tested the unit with two LNA’s connected together, both powered by the bias tee and this also worked fine. An LNA like the LNA4ALL draws about 60 mA of current, so running two at once is pushing the hold current of 80mA on the fuse, but we had no trouble with about 120 mA of current, though we need to note that people in hot climates may have different results as the trip current reduces with higher temperatures. We also tested an active GPS antenna (active antennas contain built in LNA’s) which also worked. 

With the bias tee and LNA’s we were able to improve weak signal reception and also receive several signals not usually receivable by the RTL-SDR alone such as L-band satellites like Inmarsat, GPS and Iridium with an appropriate antenna.

Experimental break out pads for direct sampling

The direct sampling mod is a hardware modification that allows you to tune to HF frequencies with an RTL-SDR. The best way to apply this mod is to directly solder your antenna or matching transformer to pins 4 & 5 of the RTL2832U chip. However, these pins are very small and so the mod requires extreme soldering ability.

These units have break out pads for these pins which make soldering to them much easier.

Direct Sampling Instructions
Direct Sampling Instructions

Let us know if you have any questions about these units, or feature requests for future units. We’ve tried to make the most popular changes that don’t increase the cost too much, but we are always open to ideas for future improvements.

RTL-SDR Tests: R820T vs R820T2 Stability Tests for Radio Astronomy

Amateur Radio astronomer Peter Kalberla recently wrote in to let us know about a paper he has written exploring stability issues and comparing the R820T and R820T2 RTL-SDR tuner chips (pdf warning). The R820T2 tuner is an upgrade to the R820T tuner which is used in the most commonly found RTL-SDR dongles.

Peters first results show that the R820T2 has better reception and less spurious features at frequencies above about 1.45 GHz and improved frequency stability (with the newer R820T2 dongles that use the SMD oscillator). His second set of results explore issues that are more closely relevant to radio astronomy including observed spectra, Allan variance (frequency stability) tests and determining the shape of the R820T/2 internal bandpass filter.

In the conclusion of the paper Peter writes:

Two Newsky RTL2838U dongles were tested, the R820T2 device against the R820T. The evaluation results in a clear preference for the new RTL2838U/R820T2 dongle. In the L-band the new dongle is at least 2.7 dB more sensitive. According to the radiometer equation the effective system temperature is reduced by almost 50%. Most important for reliable radio astronomical observations are stability issues. Allan variance tests have shown that the R820T2 dongle is far better then the older version. The stability is comparable to that of professional radio astronomical devices. The tests have shown that using the full bandwidth of the RTL-SDR devices results in spurious baseline ripples. For a good performance it is recommended to use the dongles at reduced bandwidth. rtl power with the crop option -c 0.5 appears to be a good choice.

Broad band performance of the R820T dongle (top) and R820T2 (bottom)
Broad band performance of the R820T dongle (top) and R820T2 (bottom)

Mods and Performance of an R820T2 RTL-SDR

Over on his blog, RTL-SDR experimenter Laidukas had added a post showing how he modded his R820T2 RTL-SDR for improved noise performance. The mods he applies are:

  • Addition of 100nF, 1nF and 100pF bypass capacitors on the power supply rail.
  • Added a common mode choke to the 5V line.
  • Added a MuRata NFM21 EMI suppression filter to the 5V line.
  • Replaced the oscillator with a 0.3 ppm temperature controlled oscillator (TCXO).
  • Disabled the internal RTL2832U 1.2V switching supply and provided external 3.3V and 1.2V supplies.
  • Replaced the MCX connector with an SMA female connector.
  • Enclosed circuit in a metal box.
Modded R820T2 RTL-SDR Dongle
Modded R820T2 RTL-SDR Dongle

In addition to the mods, Laidukas also made some measurements on the performance of the R820T2 on some metrics. In the first test he measured the input insertion loss or SWR. He found that the SWR was below 2 between frequencies of 25 MHz to 1076 MHz. At higher frequencies the SWR reached levels up to about 8.

Another test showed that with the LNA disabled the R820T2 had a lower noise floor by about 7dB, when compared to the R820T.

SWR Plot of the RTL-SDR Antenna Input
SWR Plot of the RTL-SDR Antenna Input with LNA disabled