Passively Cooling the RTL-SDR with a Thermal Gap Pad

John Mills recently wrote in to us at RTL-SDR.com to show us how he cools his RTL-SDR by using a thermal gap pad stuck to the entire bottom of the RTL-SDR PCB. A thermal gap pad is a soft pliable material that is often used to interface between electronic chips and heatsinks. The gap pad forms into tight hard to reach spaces and conducts heat towards the heatsink. It is not electrically conductive, so the entire bottom of the RTL-SDR can be stuck to the thermal gap pad, which is then stuck to a metal heat sink.

John uses a thermal gap pad made by Bergquist, with part number GP5000S35-0.100-02. This gap pad is 0.1 inches thick, is easily cut with a craft knife and is tacky so it easily sticks to the heatsink and RTL-SDR PCB. It has a thermal conductivity of 5W/m.k. John uses the pad to help to cool the R820T, RTL2832U and voltage regulator chips. It has been shown in some previous posts that by cooling the R820T chip increased sensitivity can be obtained, especially at frequencies above 1.2 GHz.

He writes that if there is sufficient interest then he may consider selling strips of it on eBay. You can contact him at sdr_AT_milairuk.co.uk.

Below we’ve posted images of Johns thermal pad cooled RTL-SDR’s, along with his comments on them in the captions.

Inside latest SDR / Latest SDR - "This is my latest version using a R820T2 version, and I have also fitted this with a TCXO. In this version I also used a 1Mohm and 47nF to ground the USB shield wire as in a previous post. This version only uses one metal spacer and the end of the PCB is secured by two M2 nylon screws / nuts. Case from China RF on Ebay."
Open SDR – “Just held onto a heatsink with two pieces of string ! Then this sits on another larger heatsink using another piece of Gap Pad to hold it – this has been working in my garden shed now for over 2 years feeding ADSB data”
Diecast Box SDR – "in this one I have made two small threaded metal clamps, lined with gap pad and tightened just enough to keep the PCB in good contact with the gap pad underneath and the diecast box. I use small BNC to MCX pigtails off Ebay to connect to the antenna socket. I also remove the LED and place through the box as can be seen."
Diecast Box SDR – “in this one I have made two small threaded metal clamps, lined with gap pad and tightened just enough to keep the PCB in good contact with the gap pad underneath and the diecast box. I use small BNC to MCX pigtails off Ebay to connect to the antenna socket. I also remove the LED and place through the box as can be seen.”
Inside latest SDR / Latest SDR - "This is my latest version using a R820T2 version, and I have also fitted this with a TCXO. In this version I also used a 1Mohm and 47nF to ground the USB shield wire as in a previous post. This version only uses one metal spacer and the end of the PCB is secured by two M2 nylon screws / nuts. Case from China RF on Ebay."
Inside latest SDR / Latest SDR – “This is my latest version using a R820T2 version, and I have also fitted this with a TCXO. In this version I also used a 1Mohm and 47nF to ground the USB shield wire as in a previous post. This version only uses one metal spacer and the end of the PCB is secured by two M2 nylon screws / nuts. Case from China RF on Ebay.”
Latest SDR - Outside
Latest SDR – Outside

2 comments

  1. Al-91

    I did a similar mod a few weeks ago, I used a thin 0.3mm thermal pad and an aluminium block (slightly smaller than the PCB) to transfer the heat to the die-cast box it is in. To prevent short circuits, I re-worked the through-hole components on the board. The LED and USB connector were removed. The LED was mounted in the box along with a micro USB socket. Two electrolytic capacitors were lifted slightly (1mm) so that the pins didn’t poke through the board. This left the base of the board flat allowing a thin thermal pad to be used. The thinner the thermal pad the better the heat transfer is. Even the best pads (~5W/m/k) are poor conductors compared to aluminum (~200W/m/k). The aluminium block under the board (6mm) raised the board up so that an SMA bulkhead connector could be used directly through the box wall without needing a pigtail to keep losses to a minimum. (I have no idea if the difference is measurable) The components on the board are much cooler than when they were in free air. The outside of the die-cast box is slightly warm after 24h of ADS-B use.

    For those in the UK, CPC sell a die-cast box (EN81984) which is about the right size for the dongle and is £3.40

  2. Justin Davis

    You could significantly reduce the cost by only placing the thermal pad directly under the heat generating components (voltage regulator, and two other large ICs). And then the 5W/m-K stuff is expensive, but you can get 3.5W/m-K stuff in small pieces at $1 a piece.

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