New RTL-SDR Blog Units Now Available in Store: HF via Direct Sampling, Software Switchable Bias Tee, Less Noise/Spurs

A few months ago we brought out a poll asking readers of this blog what they might like to see in a revised RTL-SDR dongle. We’ve now taken some of those suggestions and implemented them into a brand new dongle. For now the price of the new dongle will remain the same as before at $24.95 USD for the dongle + antenna kit and $19.95 USD for the dongle only, but we may need to increase the price by $1 – $2 within the next few weeks due to our slightly increased manufacturing costs. Worldwide shipping remains free from the Chinese international warehouse, and US customers can order either from the Chinese international warehouse or from Amazon who will give you free shipping if you are a Prime member, or spend over $49. The Chinese warehouse is currently stocked and ready to ship, and Amazon is now stocked and should be ready to ship by the end of this week.

Please go to our store page at for information on purchasing.



Here is the short version of the biggest changes:

1) HF support via direct sampling. Connect an HF antenna directly to the SMA connector and tune from 500 kHz – 24 MHz with the direct sampling mod. (No hardware modding or soldering required)
2) Lower internal noise. Less spurs, lower noise floor etc.
3) Software switchable bias tee. No need to do any soldering to enable the bias tee. Can be turned on and off in software.

We call this version three of our RTL-SDR Blog dongles. The first was version zero and was simply the standard MCX dongles with better antennas. Next came version 1 with the bias tee and SMA connector, and version two introduced the metal case.

Here is the long list of improvements and changes, and why they were made:

1) Improved ESD protection on the radio front end. The BAV99 diode which is used on most dongles is not a true ESD rated diode. We have added a real ESD rated diode for better protection. The BAV99 remains in the circuit as a strong signal clipper, to prevent damage to the R820T2 from overly strong signals. Please remember that not even this will save your radio from a lightning strike, and any permanently outdoor mounted antenna system must have its own lightning protection.

2) Longer SMA connector. One or two customers had problems with the shorter SMA plugs which could not fit some of their antenna connectors. The longer shaft fixes this and also allows us to add a nut to fasten it to the aluminum body which provides a better low impedance connection (although this is not strictly needed as the PCB side ground tracks already provide a good connection).

3) Improved front end circuit. The standard matching circuit on the RTL-SDR was designed for DVB-T use, and tends to attenuate signals above ~1 GHz. The new matching circuit has less attenuation above 1 GHz and similar performance below. We used very high quality, high SRF, high Q inductors in this circuit.

4) Added a software switchable 4.5v bias tee. In previous versions of our units the 4.5v bias tee needed to be activated manually, by soldering a bridge between two pads on the PCB. However we found that many customers who want to use the bias tee do not have the skills or tools to be able to perform this mod. The new unit makes use of a low noise LDO and one of the GPIO pins on the RTL2832U to activate the bias tee in software. This of course requires a modification to the drivers, but we will shortly upload a program called rtl_biast and batch files (available now) to turn the bias tee on and off in Windows and Linux.

This bias tee is great for powering a remote LNA (like Adams PSA5043+ based LNA4ALL) or something like the SpyVerter upconverter. We’ve tested it with both and found them to be running just fine. 

Warning: The bias tee LDO can be damaged if you short circuit it. Before turning on the bias tee, ensure the circuit to be powered is not shorted, or that the RTL-SDR is not connected to a DC shorted antenna!

5) Added several access pads on the PCB. Access pads for the unused GPIO pins, CLK in/out, 3.3V, GND and I2C pins have been added. The CLK input/output is disconnected by default (see change 6). Access pads for the I branch have also been added as some users and industrial customers are using these in special projects. These pads are only for advanced users who need them for special projects. Take care as these pins are not ESD protected.

6) Added a clock selector jumper. By soldering in a 4 pin 1.27mm pitch jumper header and removing the default 0 Ohm resistor, one can now easily select between the onboard clock, an external clock, or having the on board clock be the output for another dongle. This is for advanced users only who want to experiment with things like passive radar, and coherent receivers.

7) Reduced noise with a modified PCB design. This significantly reduces spurs and noise pickup due much lower impedance grounding and blocking of interference. Also added a USB common mode choke to reduce USB noise, several ferrite chokes on the PCB, and a lower noise LDO. A larger ground plane also improves on heat dissipation. 

8) Added an experimental HF direct sampling circuit, which is diplexed out from the SMA connector. This has little to no effect on VHF/UHF operation, but allows us to make use of the Q branch on the RTL2832U chip for direct sampling, which allows us to receive from about 500 kHz to about 24 MHz. (Below 500 kHz is unavailable due to attenuation from the bias tee circuit). We used a ~10dB 50 Ohm preamp as a buffer and to overcome losses in the transformer and filter. We also added a strong 24 MHz low pass filter, and added an impedance matching transformer coil to ensure good direct sampling performance.

Of course direct sampling can never be as good as using an upconverter. It can overload easily if you have strong signals since there is no gain control. And you will see aliasing of signals above 14.4 MHz due to Nyquist. But this should at least give the majority of users a decent taste of what’s on HF. If you then find HF interesting, then you can consider upgrading to an upconverter like the SpyVerter (and the SpyVerter is of course compatible with our bias tee for easy operation).

We’re still classing this mode as experimental (and will be interested to hear any feedback on results), but we have had good results in our testing of this mode when receiving signals that are not too strong, getting sensitivity as good as an upconverter. We found that very good reception was obtainable with a long wire antenna and 9:1 unun combination.

9) Antenna bases now come with a stronger magnet and a conductive copper sticker on the bottom. The stronger magnet adds very good stability when using our large 1.5m antenna and the copper sticker ensures that good electrical contact can be made between the base and whatever piece of metal you use underneath as the ground plane. This significantly improves the antenna’s performance as a quarter wave ground plane.


10) Added corner mounting holes for those who want to stack PCBs. Some customers have been building devices that require multiple RTL-SDR dongles, and these standoff holes should aid in stacking.

As from the previous innovations the units still come with:

1) SMA connector – The most common connector in the radio world. Easy to adapt to other connectors and low loss over a wide range of frequencies.
2) Thermal pad – A thin thermal pad allows heat to transfer from the PCB to the metal case easily. The metal case then cools off to the surrounding air. This helps to solve L-band insensitivity problems.
3) Metal case – Helps block out interference and provides cooling.

We now have a V3 users guide available which explains how to use the new features such as the bias tee, HF mode and CLK jumpers.

What’s coming next?

We think that our unit is now pretty much at the peak of how good a cheap R820T2 RTL-SDR can be, so apart from minor tweaks this is likely to be our last major revision of this model of the RTL-SDR. In a 1-2 months we hope to bring out a FM bandstop filter with metal enclosure and SMA plugs with a target cost of $14.95 shipped. Further into the future we also hope to bring out supporting products like a wideband bias tee powered LNA and wideband antennas. These supporting products will of course be compatible with other SDR’s like the Airspy or SDRplay, or other RTL-SDR dongles.


Notify of

Inline Feedbacks
View all comments
Bob Roberrts

Where can I buy these products? All your links to Amazon state they are “currently unavailable”.


Is this the same unit in amazon?

Did it clear customs? 28 August?

Siphe Ntlangano

Good day all, I am working on a project where i’ll have antenna and some active circuitry to convert the FM signal to IF signal ( at 10.7 MHz). I was wondering if this board would be able to convert the IF signal to a form suitable for processing in a computer. thank you


you’d have to use the I or Q ADCs on the rtlsdr; this one is a bit better to work with because it has pads to solder leads on for exactly this purpose.
you could use an SDRPlay, but thats not supported by SDRSharp (guess why :^))
you could also use an AirSpy but you’d need an upconverter for that ($$).
you could also use a higher IF (~53 MHz) (RTLSDR has a spike on multiples of 24 MHz i think) so you can use the RF input on all the mentioned sdrs instead of modifying them.

also, google for the I/Q-ADC mod for the rtlsdr


I bought a v3 (2 of them actually), and the one I opened so far seems to work okay in that I can hear HF stations.

However in windows 10, audiodg.exe causes sdrsharp to crash after about 10 mins. I can readily repeat this behavior over and over. No driver updates needed for realtek onboard soundcard in PC…

I’m at a loss.


It turned out that the virtual audio cable driver was causing some issues, so I removed it all, reinstalled, and things are okay again. Thanks.

george b

Does anyone make a “live cd” or some form of software (sdr sharp with drivers, etc) where you can install/use the device without needing internet connection? this would be great for off gridders and less saavy computer users


I don’t think so, you would need someone to send you a file with all of that info already configured.


try going to
go to the operations page
theres some nice info on installing SDRsharp


So I have already damaged the end of my antenna, ( the end that plugs into the dongle ) I accidentally pulled it right off. Is it possible to order just the antenna?


So I have had my 88-108 Mhz band stop filter for about two weeks now and my RTL-SDR V3 for a couple of days.

First the band stop filter, first let me say for me it is worth every penny it does exactly what it say it stops the FM band from messin with the signals I am trying to listen to. I use SDRSharp to scan through a specific band 138-144 Mhz. Without the RTL-SDR.Com the 138 to 144 Mhz band when scanning resembles something like the ocean with the wave rolling up and down, also the signal line moves up and down at the same time. This is really annoying, I have to tune down my RF gain way back to stop all of this floating and rising signals at I might add the loss off signal strength. When I attach the band stop filter all of this disappears, the signal line is very stable and no more rolling signals. I also crank up the RF gain and there is no change, great job guys.

The RTL-SDR.COM V3 has given me a new toy to play with, that being the HF band. Being that this is the first time I have ever listened to the HF band I have become like a kid again, i am in there all the time. On the higher bands the V3 works perfect, I just wish I had all of this stuff (SDRSharp, DSDPlus and this dongle )when I was a kid i would have been in hog heaven. Thanks for all of your effort in making the V3 and the FM Filter, great job.


Got my RTL-SDR v3 last week, haven;t had much time to play with it yet but I will make up for it this week. One think I would like to see is a longer antenna wire. I think the original is about 3 ft, should be at least 6 ft.

Adam Christian Smith

Hello! I am a longtime HF (shortwave radio) listener. I have many radios and two fantastic antennas (My own dipole and a pro built Wellbrook ALA 1350.

I was wondering what I will need to do with this hardware other than just plug it in? I want to be able to plug it in and run!




Quick question, how does the V3 dongle perform over 1300 Mhz compared to an R820t2?


Thank you, I just ordered mine without a second thought about how it would handle 1545 or 1090 Mhz frequencies.


So all I have to do when I get my v3 rtl-sdr dongle is plug it into my computer attach an inside or out antenna and I am good to go? And if I want to use it for HF I would just change SDRSharp to Direct sampling ( Q branch ).

I am not really sure what the bias tee is for and I definitely don’t want to short the dongle out. Any info would be appreciated.



> we will shortly upload a program called rtl_biast
Do you know when ?

Is it possible to add a bias parameter in the osmocom driver like for the AirSpy source ?


Hello. Today I received in Madrid – Spain my RTL-SDR V3 dongle but the USB is folded or broken. I took photos after opened the plastic bag. I need a new one ASAP.

Rob T.

With regard to not damaging the LDO by accidentally connecting a shorted antenna, would it be possible to use a PTC or something similar to protect it? (I’m not an EE, just a software person, so this could be a dumb question).


I received my V3 today and did a couple of quick comparisons to the V2:
At 1090MHz the noise floor is 6dB lower than the V2
At ATC frequencies there was no noticeable difference
At FM radio frequencies the reception was slightly better

For me the ADSB reception improvement is huge, so I’m really happy with it!


I have been soldering/desoldering parts on one of my v3 dongles. First, I note that the current reviews are using outdoor antennas, I prefer less-sensitive indoor magnetic loops and PA0RDT whips. So performance issues are more obvious to me. I did measure the Noise Figure in direct mode, it was around 12dB. So I disconnected most of the 5dB pad at the output of the LNA (I removed R16 and shorted R6). I did leave one of the 180 ohm resistors to better terminate your filter there. NF improved by a little over 2dB, as did the ability to copy weak signals. I changed L13 from the installed 6.3uH to a 47uH part, and the bottom end resonance was pushed down below 100KHz. Have ordered some 100uH 0805 parts from China and will measure the low end again more accurately when they arrive. All in all, a great design, and it works! I am impressed at how close the RTL-SDR v3 comes to my (modified) Funcube Dongle Pro+ on 80metre SSB. Still not quite as good, though, the FCDP+ is around 3dB better in NF and a smidgin more in gain… Finally I put my LNA (stubbed down to about 8dB gain) on the RTL-SDR v3. Very nice indeed. About 3dB overall NF with the modified RTL-SDR (the chip on the LNA is rated less than 1dB)… Finally, I will admonish others from trying this at home. The SMD components are the tinyest 0402 parts, which easily get lost in the blob of solder on a soldering iron tip. L13, is not so bad, however. Test your mettle on that part first, if you dare…


I put a quality 100nH in series with the 47uH, so the VHF signals will die in the 100nH before they hit the capacitance of the 47uH winding 🙂 There is luckily plenty of space between the L13 contact pads 🙂


Interesting.. Luckily, I kept the 6.3uH inductor you had in L13 originally, I will take a look at them with my Vector Impedance Analyzer, and also look at the two inductor combination I substituted. Will report back next week, pretty busy at the moment…

Interesting that there is so much difference between the ‘birdies’ in your RTL-SDR dongle and the NeSDR. I suspect the balun on your USB wires made quite a difference. Take a look at the 480MHz spectra of the two, your dongle is much cleaner.


Well, I finally tested the original 6.3uH inductor on my NWT300 and NWT4000, and you really don’t want to know the results 🙁 Using the technique of Larry Benko ( ) with a tiny SMD test rig I had handy, the resonance of your orginal 6.3uH inductors came in at 60MHz. By 270 MHz the attenuation in the inductor had fallen below 10dB, and it stayed low up to 2GHz. I really would like greater than 20dB attenuation, implying the Bias-T would not reduce signals perceptibly, but 10dB has to be a lower limit, IMO. At the LF end it significantly attenuates the Noise Figure on 80 metres, and especially on AM broadcast stations. With my 47uH the broadcast band was pretty clear of signal loss, but the VHF died even earlier. Probably why I have been getting benefit from an LNA at the higher frequencies 🙁 Putting a 1uH in series with the 47uH made things a lot better, 20dB through to 300Mhz above 20dB loss. A third inductor of 100nH extended the VHF end up almost to 1.5GHz, but a microwave-quality inductor here would have done better, I think. Anyway, I will be switching to the 3-inductor solution on my own v3 dongles. I had been wondering why people were commenting on lack of sensitivity at 80 metres, whereas it works fine for me on 80M LSB with just a small loop antenna. If I can help more, please let me know, but I would get the parts purchaser to check whether the inductors you are buying are what really you specified them to be 🙂 This v3 dongle is close to perfection, it would be great to see the v4 achieve that goal 🙂


How did you get the 12dB NF? Is it the overall NF to the SNR in the AF channel? I got a different result. Best sensitivity appears to be at 5MHz.
Do you have a (partial) schematic?


To measure NF I used a Noise Generator which generates 22dB of thermal noise at that frequency, then used an attenuator to increase the total received noise by 3dB. Below 5MHz the inductance of the 6.8uH tee-isolation inductor starts to reduce performance, it is absorbing 5dB of signal by 500KHz. The schematic is pretty obvious once you start probing the board. The LNA chip is similar to the SGA1263.


V3: So, you measured the NF=12dB with your modified LNA? Additional gain of 5dB will verify my results.
It is very tedious to design a duplexer for such wide frequency bands. The designers did a marvelous job. They managed to realise a good input match and a reduced NF (-1.5dB) at VHF/UHF with some emphasis on the 2m and the 70cm bands.
A more basic design would be to use a RF switch or a second input connector.
I will further follow a concept of a simple switch isolating the HP part during HF operation. And adding some additional gain to bring the NF down and replace the transformer by a symmetrical output amplifier.


The new RTL-SDR V3’s came out and I’m not going to lie, I’m a little salty I bought three of the older ones now over the past three weeks. These units are much more versatile. If I would have known I would have waited.


I did a quick frequency response to test the low end of the direct sampling input (as shipped, with bias tee inductor still in place):
0dB at 600KHz; -12@300KHz; -25@220KHz; -10@80KHz; -15@30KHz; -25@10KHz.
There was an interesting dip at 200KHz, rising to a peak at 80KHz, then falling as the frequency dropped below that. I will rip one open and try and figure out what is going on. Perhaps this is the output impedance of the bias-T regulator chip coming into play 🙂


I have some 47uH 0805 inductors I bought (from China) when I was modding my Funcube Pro+ dongles, so I will try those. I typically use the 47uF in series with a VHF-capable inductor. It might also be possible to damp the resonance with a resistor across the capacitor (LDO output), I will take a closer look. It would be nice to allow VLF reception. The gain of the dongle is a little weak in the direct mode, your SGA1263 could do with a little more oomph. I will get around to looking at that in due time 🙂 The gain and noise figure above 50MHz is excellent. Spurs look good, too, but I am sure others will take a closer look at that 🙂


I will try to increase the output stability capacitor of the LDO, too. I have designed before with some of those nice little 5-pin LDO thingys, and recall some of them do not like a larger capacitor…


I’ve ordered a v3 and am waiting for its arrival. In the meantime do you know when the comparisons will be up? I’m keen to see how it looks compared to the v2 (which I currently own)



Question about the direct HF conversion. I’m running SDR# 1457, and just got my v3 yesterday. I didn’t see anything in HF, so I put the same antenna through my Ham-it-up upconverter and into the v3. After applying the -125MHz offset value in SDR# I had lots of signals in the AM broadcast band as well as shortwave. So, am I missing something or is that particular version of SDR# not enabling the direct sampling channel?


That did it. Thank you!!! Actually better performance than through my ham it up!


AMAZON JUST SENT ME A REV 2 instead of a rev 3. I did pre-order the v3 on Wednesday, and a dongle was delivered today. But nowhere does it say “v3” and there is a small box marked on the case for “Bias Tee Enabled”

It looks exactly like the one I bought several months ago… Take a good look if you ordered your new v3 dongle fro Amazon…


Would you mind sharing what ESD protection diode you are using? I keep killing LNA4alls with stray ESD during storms. Was going to put a BAV99 on the input but if there’s something better and readily available I’ll use that.
Fantastic work BTW. I find it interesting comparing your work to kickstarter projects which take years of work and lots of funding.


Hi guys, would it be possible to unsolder the bias t circuitry to help with tuning lower than 500KHz?
If so, where does one start the unsoldering operation?
Thanks in advance.


Thanks for the info, much obliged.


Hi again, any chance on upping the bits a bit? Like to 12 or 16 in some glorious new future model??

Lucas Teske

Then it will not be a RTLSDR anymore 😛


Is the Elonics E4000 really impossible to fabricate anymore? It had a really nice high frequency despite the gap in the L-band.


But I will definitely be getting this for my HF needs. I’m not really willing to get an upconverter, so if I don’t have to, I’ll gladly not.


Outernet has managed to find a couple of thousand to build there L-Band receivers. I bought a DIY kit from them and mine clearly comes up as a E4000.

They are selling them on Amazon with a really nice filter for around $50.


“We found that very good reception was obtainable with a long wire antenna and 9:1 unun combination.”

Could you please show us some diagrams and photos of your successful antenna experiments with the HF direct sampling mode in use.



Hi guys, the 9:1 balun is a good idea but won’t be optimal in some situations where the mismatch between antenna system and radio is very poor. In such case the use of a preselector or transmatch is a great idea, wich also provides for some front end selectivity. These can be built at home or store bought. Here’s a page on preselectors;
Scroll down to the preselectors section(s) at left.


If you want to run Q Branch direct sampling in Linux GQRX here is a reply I got from the GQRX forum written by Alexandru Csete.

“Gqrx supports the direct sampling mode by adding “direct_samp=…” to
the device string:

Enable direct sampling mode on the RTL chip. 0: Disable, 1: use I
channel, 2: use Q channel

So, for using the Q channel the device string would be something like:


You may have to check “No limits” to allow tuning below 24 MHz, I
don’t remember.


This works great on my Soft66Q HF RTL from Japan in Q mode.

Lucas Teske

I’m adding the support for the Bias T of the V3 Dongle at librtlsdr repository (we made a fork in github because the main one is some patches behind). I did not received (yet) my V3 dongles, but I will test it as soon as it arrives.

Anyways, good work! 😀

Lucas Teske

OK! I added the fix for the GPIO:

About the CP Mod, I will try to simulate the problem and check your branch to see the fixes. This part for the RT8XX we changed some stuff related to the Bandwidth filter (in our branch you can select it manually) so the init function is different. So I will try with more care.

Also I will wait until I receive my new units to test the Bias T stuff, but if you have one there and can test let me know 😀




I have a question about direct sampling . How are you doing that , RF transformer and if so , what is the turns ratio ???????????????


Amazing work you guys are doing. Can’t wait to get my hands of the v3 edition. You guy’s do so much for the community. I love the site and love the dongles.


Went to the shop to buy via the Chinese warehouse but it came up as 17.99 not 19.99.
If I continue, can I guarantee to get sent the v3 our am I trying to buy too early?


What about a comparison between V2 and V3 dongle relative to less spurs, less noise, performance in general ?

European User

I’ would like to see a LNA (Low Noise Amplifier) with RF-Bypass capability. Switch bias ON – LNA works. Switch bias OFF ==> RF Signal pass through the Amplifier and can be INLINE in the Antenna Cable. Maybe only possible with a very small RF-Relay on the LNA-PCBs.


A LNA at or in the receiver is a pretty poor choice.
Read this thread –

A LNA after all noise has entered the system is not going to help you very much. You want the LNA as far away from the receiver to get the maximum benefit from it. So that it can amplify the signal above the level of the additional noise that will enter from the system of cables and connectors on the way to your receiver. You also have to remember that noise and signal are both amplified by exactly the same amount. So having the LNA as the last stage will do very little to improve the signal to noise level of the modulate signal that you are interested in receiving.

European User

for sure, the LNA needs to be close as possible to the antenna. but i want to switch on, only when needed. when the lna is switched off, the rf signal from the antenna should pass to the LNA without amplification. RF Bypass when not switched on.


Sorry, I picked up what you meant the wrong way. I failed to understand that you meant a totally new independent LNA device, which has functionality equivalent to a dual pole relay switch. That when powered on, it moves a short circuit out of the way to be replaced by a LNA. And when power is removed the LNA swapped out and replaced by a short circuit. But a device created using solid state chips instead of a relay which would waste far too much power.


I agree but he is talking about an external LNA using the bias tee and obviously it will be inserted as closed as possible to the antenna,

European User

I’m lucking for some more Filter, not only a FM-Bandstop, maybe a tunable notch filter or a DAB Bandstop (175-230MHz) Filter. We have very strong DAB+ and DVB-T Carriers in Europe.

Carroll Tracy - KF7ELY

I am glad for the upgrades in version 3, I have versions 1 and 2 and love both of them. It will be nice to try HF on the version 3 though I already have an IC-7200 for that, ha ha. Thanks for working so hard on these inexpensive dongles, they have been great to work with! 73, KF7ELY

Bin Kenney

The fact that I just bought your V2 units last month makes me regret not holding off for V3. Of course when you don’t say when you’ll release V3, until now–surprise, should I fork over my money for the V3 dongle, and a better antenna base (although I am still using the one that I got from another RTL-SDR dongle in which it has smaller base, but much much powerful mangetic base)? Is it worth it to get a complete new set of SDR kit from you guys?

Bin Kenney

You are certainly right about me being impatient, especially when I want the unit just before I leave out of ststate so I can take it with me to explore spectrum in Washington.
Just one more question… do you think some time in the future Youssef Touil from Airspy who makes SDR# can add the Bias-Tee checkbox within the RTL-SDR Controller window for those of us who will have the V3 units, or will it be strictly kept to the batch file that we have to run each time just to turn on/off the bias-tee?


I’m in the same boat. Bought a couple of V2s not long ago. While it would be nice to have fewer spurs (I already have a spyverter for HF) I think I’ll stick with these for now.
It is good to see the product being continually improved though. Well done.