Cooling your RTL-SDR (AMAZING tests..)

Why cooling is important

Electronic chips generate noise and heat during use: your digital camera or smart phone gets progressively hotter the more you use it. Sensitive applications, such as astrophotography MUST eliminate this heat, as heat is noise, black sky will be grainy black sky.
This heat is also present with the RTL stick, appears as frequency drift and internal noise – radio will not stay on a frequency.
Gain applied in Configuration panel increases heat, hunt weak signals and need to increase gain = increases internal noise generated by the stick.
Improve cooling – reduce noise.
Recently introduced temperature-controlled oscillator promises to solve this issue, around 50 dollars. Regular RTL stick sells for 8 USD. Hmm.

Do you need to worry about it?

No: Leave the stick warm up for 15 minutes – half an hour, let it reach thermal equilibrium, after stick is warmed up set ppm correction. My particular stick drifts 4 ppm from cold to warmed up, then stays on frequency.
Yes: You are a perfectionist, or you want less internal noise with high gain settings.
Performance increase with modifications below will be really, really small, less noise on shortwave, maybe one or two less noisy lines on WXSat images.

Air cooling

The brain of the stick lives under the plastic cover, open up the stick and drill holes, especially above the black squares, or leave the board bare without its plastic cover.
Stick will run cooler, frequency drift will be reduced somewhat.
Heat-sinks are a possible solution, reliable connection is hard to achieve due to small surface area, edge of the chip can break off.
Additional airlow with PC fans, run on 5V, telephone chargers can be used. Two PC fans installed outside a PC power supply case, with stick in the middle provides a cheap air-cooled solution.

Using fans have the following drawbacks: 1) Needs external power source, 2) magnets in close proximity to the stick, 3) the awful sssssssh noise fans generate.

Water cooling

Electricity plus water equals disaster, insulator (hot glue or epoxy) must be used to seal electrical components from water. Tried several methods back in the Pentium 4 days, messy, expensive, hot glue won’t dry evenly, epoxy eats components: water cooling is unsuitable.

Oil cooling

Place stick into metal can, with antenna and USB cable connected and led through lid of can, position stick middle of can, slightly above bottom.
Pour sunflower or vegetable oil into can with the RTL stick inside, completely fill up can.
Repeat: fill up can as much as you can, any interior surface will pick up condensation.
Cover with lid, plug in USB and connect antenna, fire up SDRSharp.
Oil will provide cooling, it is not conductive, see stick blue light on image below.

RTL-SDR, Software Defined Radio

Place can in the fridge or freezer: sunflower oil theoretically has a very low freezing point, practically after one night at -20 degrees Celsius can will be very cold to touch.
Active heating is unnecessary, oil volume and metal can surface will be enough to dissipate heat.

Cherry on the cake: FM Noise Reduction

Metal can also acts as a Faraday cage, FM broadcast pickup will be greatly reduced.

Traditionalists love to place stick in metal enclosure for the same reason, not realizing that heat buildup will effect performance – a chip running at a very low temperature will have lower internal noise and greater performance.

Cleaning stick after oil cleaning

Stick should not be connected to computer or any other electricity.
Lukewarm water in sink, spoonful washing powder or cup of liquid detergent, the more the better, dissolve until glassy reflection and feel of glove on hand. Pour liquid detergent on stick/  place stick and USB cable in washing powder, wash off oil and detergent with lots of water.
Repeat steps above 2-3 times, wash hands, clean with towel / toilet paper.
Leave stick to dry for a day. small heat, not close to radiator, never on top of a heater.
Will be good as new.


Reducing electrical noise in our RTL-SDR (best results EVER! thanks sdrformariners!)

RTL-SDR, EMI, RFI, Noise reduction, noise suppression, SDRSharp,

– You can use alu foil, but make sure it touches the metal part of the USB plug.
– Remove the metal support from the USB extension cable on the end where you connect the RTL stick. This will eliminate noise picked up by the USB extension cable.
– If you have a spare car battery, connect the metal part of USB plug to the negative terminal.
– Mobile operation or no car battery? Wrap the center conductor of coax around the metal part of the USB plug, then place the stick in the middle of coiled coax.

Testing setup

Your antenna receives noise and signal. Without an antenna any signal received is by the RTL stick and the cables, and you do not want that.
For this test: Nooelec RTL-SDR 820T stick, max gain, no antenna. Weak local FM radio station signal 5/5, clear and enjoyable. That is unwanted signal entering the reception chain.
On the images the middle signal is the radio station – that should not be there, smaller peak is better.
Also note the waterfall display for received signal strength.

RTL-SDR, EMI, RFI, Noise reduction, noise suppression, SDRSharp, Results

Direct vs USB cable connection: USB cable (76cm) increased noise by 13 dB.
USB plug metal connected to 1m coax: coax cable center conductor connected to the metal support of the USB plug. Decreased noise by 7db.
USB plug metal connected to 10m wire: further noise reduction by 5dB.
USB plug metal connected to 12V car battery negative (-) terminal: noise almost completely eliminated.
USB plug support connected to 10m coax, RTL stick nesting in the middle: noise completely eliminated.
Aluminum foil, metal cans, metal enclosures: aluminum foil NOT touching either the antenna jack or USB connector, half roll of aluminum foil: no effect. Metal from Seven 0.5 l cans wrapped on top of the alu foil: no effect. Metal enclosure: no effect. Note that if the alu foil/metal/enclosure is connected to the metal part of the USB plug, immediate noise reduction of 15-20 dB, station still heard, speech distinguishable.

USB connector mod

RTL-SDR, EMI, RFI, Noise reduction, noise suppression, SDRSharp,

A reduction of 10 dB, stick still safely connected.
Remove the USB metal part that keeps the RTL stick in place,  from the end of the USB extension lead where you connect the RTL stick. 
Only USB signal and power connectors remain. Mow  shielding in the cable is not connected to the signal chain.
Do not remove the other end of the USB extension lead, the one going into the computer USB port, no further reduction realized, but the extension cable will easily come out of the port.


Organize cables at home

If it has a plug or battery, it will radiate electrical noise, either the cable / power lead or the actual device itself.
A simple solution is to place cables and extension leads into a computer case or a similar metal enclosure.
In the following example, unmodified original RTL stick, no antenna so it only picks up noise, connected with 1.24m (5 foot) USB extension cable. Stick resting on the edge of the PC case where I keep cables/extension leads.
PC case panel off: Local station washed away in electrical noise, audibly louder noise.
PC case panel on: Relief from the loud noise, local station understandable.
If I’m after a distant signal: laptop unplugged, electricity turned off in the house, candles on. Optionally: LNA and shortwave upconverter running off batteries.
Best is no electricity: listen to a far-flung Caribbean station in candlelight with your significant other.


Ferrites are rings, beads or clip-on pieces of iron used to reduce noise.
Coil the USB cable around a ferrite ring, or use clamp-on ferrites.
Use ferrites at the terminations of your
– USB cable between computer and stick,
–  on the cable between stick and antenna.

6-7 dB reduction of noise visible, audible decrease of the FM station with 4 turns on a ferrite ring and ferrite beads on the USB cable (USB plug metal removed both ends).
Also did experiments with turns around ferrite rings – 8 turns made no difference.
Conclusion: invest in clamp-on ferrites, the bigger and more, the better.

Maximum noise reduction

Stick wrapped in alu foil, foil touching the metal part of the USB plug, connected by an USB extension cable with the metal removed. Stick inside a metal enclosure, in the middle of 10m coax coil.
Result: no signal whatsoever, FM band is clear, waterfall is uniform blue.
Optional: ferrites if you have them.

Closing thoughts

If you chase very weak signals, such as shortwave with an upconverter, or a weather satellite just on your horizon you need the best noise reduction solution.
In all of the above tests I had gain to the maximum, so any reduction is clearly visible.
Noise as called here (same thing, complicated words):  electromagnetic interference (EMI) or radio frequency interference (RFI).
You know a better option? Curious to hear from you, use the comment section here.

Note on Nooelec: As their customer support might recommend the hardware guide on this blog, Nooelec sent a free RTL-SDR stick to my former high school physics lab.
I like this attitude.


Round-Up of RTLSDR Upconverter Choices

I’m trying to catalog all the different HF upconverters on the market for the RTLSDR. The RTLSDR stack, a combination of radio software such as GNUradio or SDR# with a Realtek RTL2383 + Elonics E4000-based DVB-T tuner using a modified driver, is getting to be very popular among amateur radio enthusiasts because it’s cheap and highly versatile to allow you to receive on a very wide frequency range. Unfortunately, the chip has some limitations – that wide range only goes from about 50-2200MHz with most in the 64-1700MHz range. That’s well above the HF bands where many ham radio operators and shortwave or AM stations are found.

Fortunately, the marketplace has taken care of that limitation, and quite a few choices for an HF converter / up-converter are now available which use a mixer and crystal oscillator to add around 100MHz to the incoming signals, shifting them into the tuner’s frequency range. There are several choices out there, including pre-built boards, partially built kits, and plans depending on your skill level and interest. An assembled board or a partially assembled kit will probably set you back about $50-100; if you’re savvy you can probably make it for $10-20 in parts – if you don’t mind winding your own coils. Your mileage may vary.

So, getting to it, these are your choices arranged with built boards near the top, partially built boards and kits near the middle, and plans and project logs near the end.

If you have any others I’ve missed, send me an e-mail! 

1. There’s a new Ham It Up v1.2 HF upconverter for software defined radio produced by Opendous which has a large amount of documentation including layouts, and can be purchased mostly-assembled for only about $50. v1.2 makes some small improvements, including a 125MHz crystal instead of a 100MHz crystal to ensure there’s no interference from the U.S. FM Broadcast Band. It also features an input switch and an optional hardware noise source is an interesting, if possibly seldom used, feature. Ham Radio Science has a rather extensive review of the original revision and were pretty happy with it.

2. CT1FFU v5  HF converter is a brand new iteration of the long-standing design which was originally one of the first released. This model features an improved smaller PCB size, improved filtering and am improved ring mixer, and phantom power to eliminate a power cable when attached to certain compatible RTLSDR receivers. The LO is still 65.520MHz or 106.250MHz which might interfere with an FM Broadcast band in some countries, such as the U.S., but there is some filtering incorporated to eliminate that. The price is reduced to 55 Euro shipped worldwide with tracking.

3. Marty KN0CK has developed an incredible upconverter which fits inside the tuner dongle’s enclosure using all 0402 SMD parts. It’s a complete stack, including the RTLSDR tuner and hand-assembled precision converter with a SA612-based mixer and Mini-Circuits MAR-8+ amplifier and 120MHz oscillator. Very powerful, great at picking out weak signals, and requires no external hardware or cabling everywhere – just hook up an antenna and go. Available for $100 US plus shipping (U.S. and International shipping available), this is a addition to your ham shack. Buy it over at Easy-Kits. Bare boards are also available for incorporating into your own project.


4. I’ve been using CT1FFU’s v3.1 dongleGerman retailer Wimo sells completed kits, which have been in stock even when CT1FFU’s own kits have sold out. A no frills HF up-converter, mine came assembled except for the SMA connectors. It’s one of the early generation upconverters but still offers solid performance. V3.1 uses a 106.250MHz IF.

Wimo also sells the FunCube dongle, if you don’t already have an SDR.

5. JA7TDO has produced the Soft66RTL, including an RTL2383u+R820T and an HF converter with a 50MHz local oscillator frequency in what looks to be a nice, 3D-printed case capable of receiving up to 30MHz, or 50MHz and above bypassing the converter.


6. JaniLab has started selling a derivative of the CT1FFU v2.0 on eBay for a bit lower of a price than some of the others. The older revisions work well, although with some more leakage than subsequent designs, and don’t have quite as fancy filtering or switching features.

Janilab actually offers several. There’s both this one with the DBM mixer, above, and another CT1FFU v2.1 derivative with an SPL mixer.

7. Janilab also sells another DBM mixer-based converter, with an antenna switch to bypass the conversion.

8. And if that wasn’t enough, they even rolled their own board and put an RTLSDR and an converter on the same PCB, with an integral antenna switch. This is incredible. Not cheap, though.

9. If you’re looking for a more rugged commercial solution, High Sierra Microwave has an upconverter (FCD-1-55-UC) with a 133MHz IF frequency and BNC terminals with an integral amplifier. I’m a fan of converters whose LO frequency shifts the entire HF range above the FM broadcast band in general and the shielded enclosure will definitely cut down on noise. Looks like it’s suitable for mounting outside at your antenna’s feed point, and it also looks like you’re going to pay for those features. If anyone owns one and wants to share their experience with it, or if High Sierra Microwave wants to send me one to evaluate (*wink wink*) I’d

If you’re more ambitious, you can roll your own up-converter from parts. FAR Circuits appears to have manufactured PCBs for sale for many QST projects, including one upconverter. I’ve only recently discovered this site and there seems to be a lot of good stuff.

10. W9RAN developed a RANverter kit which was featured in the January 2013 issue of QST magazine, using a 125MHz local oscillator. It’s gotten a lot of great buzz on the Internet and offers good performance and even a little bit of conversion gain through the mixer. Unfortunately, he appears to no longer be offering it for sale. I did manage to get a set of boards and will be offering the W9RAN precision converter through before the end of the year!

11. If you’re comfortable speaking  Dutch, or just with Google Translate, you can buy the Kit RF Converter for RTL SDR Sticks DC – 65 MHz. Unlike most other models, this one HF up-converter takes a BNC 50 Ohm antenna input and has an SMA 50 Ohm output with a 100 MHz oscillator frequency and built-in protection. This one also looks like a great starter kit with through-hole components and large coils and looks easy to build. You can also purchase the completed assembled kit in an enclosure, which also includes a power cable and SMA-MCX adapter cable. Looks interesting.

12. Kalle over at DGK Electronics has a great looking compact 100MHz HF converter designed to fit inside of a pre-made RF shielding box. It uses the ADE-1 mixer and an ASEM oscillator. It has some of the most complex filters and great filtering on the incoming power line, it probably performs very well. He describes the filters on his page, and there’s also a full schematic available. There’s a photo of a pile of boards, and he says there’s still some available, one might be left! DGK Electronics

13. David Forsman, WA7JHZ, sent me a photo and plans of his 125MHz HF up-converter with a diode limiter, attenuator, and amplifier all in one from plans featured in Jan ’13 QST magazine. Click through there to the article for a schematic and explanation for more details and a full schematic. Thanks, David!

14. Matt Dawson GW0VNR has a very interesting HF converter using more discrete parts than some of the other ones I’ve seen. It uses hand-wound transformers, an actual discrete diode mixer, and a Saronix oscillator running at 106.25 MHz. It uses a total of 23 parts and looks like it would be pretty easy to build. He doesn’t have any photos of the completed board, but does have a full schematic, overlay, transfer mask and Gerber files for the PCB. I’m pretty sure I have all the parts to build this one in my box as well. It looks interesting and simple. Check it out.

15. Radio amateur Paulino Sato has posted schematics and specifications for using the TA7358AP FM Front-End as an HF up-converter you can build yourself, using small coils wound on your own forms. It’s a bit of a commitment, but only has about 40 parts. The instructions are in PDF format. Download from me directly or the original is available on DropBox. The PDF contains PCB masks and silk screen layouts and a full schematic.

16. Over in the UK at the George Smart Wiki, we see homebrew plans by M1GEO using hand-wound coils with an SBL-1 mixer and 100MHz crystal oscillator. It has around 20 parts to assemble. These coils look like they could be hand wound on a dowel coil form, and the crystal and mixer are very large parts, so you could probably build this on perfboard without any trouble.

17. Bryce Salmi KB1LQC built a very rugged-looking clone of George Smart’s above with some modfiications dead bug style.

18. Romanian amateur Alexandru YO2LDK built a simple HF upconverter circuit using an NE602. This has an amplifier, limiter, regulated supply and 100MHz frequency like several of the ones pictured, but the circuit itself looks quite different. The amplifier stage is ahead of the limiter, which looks like this one is offering a constant gain versus the adjustable gain some of the others have offered. It looks like this one has more tunable components, which means a little more work to dial it in. I didn’t see any photos of the completed product.

19. Nick G0CWA built an interesting switchable upconverter design, complete with instructions and board layout PDFs.

20. Japanese amateur JA2GQP build a rather minimalist upconverter with only a 19 components offering a +50MHz frequency shift. He’s included a schematic and PCB mask for you to build your own very easily!

There are plenty of options to build or buy for getting HF signals into the VHF range for your RTLSDR. With these choices, there are plenty of options for getting HF signals into the VHF ranges for use with the RTLSDR. It’s not difficult to modify these plans for even higher fidelity and accuracy, such as by increasing filtering on the power lines, building a shielded enclosure, improved antenna systems, and more.

I’ve been using my v3.1 Converter from Wimo for a few months, and have been very happy with its performance so far – there’s little noise and leakage, and I use it to pull in shortwave broadcasts from all over the world including the BBC, China, Cuba, Japan, Russia and more from my home in Seattle with only an 80″ long wire and a string of adapters – I highly recommend that model, or any of the models in this family, for great performance. I’m looking forward to trying out some of these other ones.

If you have a design you’d like to see featured here, let me know!

Edit 12/1/2013: Added JA2GQP’s minimalist SDR upconverter.

Edit 10/29/2012: NooElec offers “Ham It Up v1.0″ upconverter which looks to be based on a different design, and seems very high quality. Check it out! 

Edit 2/2/2013: Better info about the Opendous Upconverter, KB1LQC’s DIY Upconverter, and WA7JHZ’s upconverter.

Edit 2/3/2013:Added 9A4QV HF Upconverter SDR UP-100, G0CWA 2012 upconverter, YO2LDK upconverter.

Edit 2/13/2013: Added Vandijken Elektronica upconverter and W9RAN RANVerter 2.0.

Edit 2/19/2013: Added KN0CK SMD HF Upconverter

Edit 2/25/2013: Added Matt GW0VNR’s Upconverter and the DGK Electronics HF Converter.

Edit 4/13/2013: Added JaniLab converters, High Sierra Microwave converter.

Edit 4/25/2013: Informed 9A4QV Out of Stock – Thanks Adam!

Edit 5/14/2013: Ham It Up v1.0 > v1.2, Now Ships with 125MHz Crystal

Edit 8/13/2013: CT1FFU v5 replaces CT1FFU v3.1, and some copy-editing!

Edit 9/2/2013: Updated to reflect availability of some items.

Edit 10/21/2013: Added Soft66RTL

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