A cooler for a Narda LNA to help maintain a steady temperature to maintain a steady S21 power level (around 36dB).

Without a heatsink, the Narda LNA (Model Number: LNA-30-04001200-15-10P) heats to around 60c and has a S21 power loss of around ~1.5dB with large variation which makes makes the noise floor larger and adds noise to the amplified signal. This case encloses a fan and heatsink to cool the amplifier and also to keep the temperature more stable so there is less S21 variation to improve measurements.

Final results keep the temperature of the heatsink at 28.10 +/- 0.13°C over a 2 hr test in an A/C controlled room at 22°C. The temperature range over a 2 hrs was 0.53°C. The average S21 power was 35.26 +/- 0.01 dB at 8GHz over the 2 hr test. The S21 power varied by 0.04dB at 8GHz over 2 hours.

The potentiometer is used to tune the turn on temperature of the fan. I used a digital hot plate to calibrate the turn-on temperature to 23c and then adjusted the potentiometer in our setup until the temperature curve was flat. Youre looking for a equilibrium between the amp temperature (which will allow greater gain) and the temperature variation (A lower value will result in less gain variation).

• The heatsink is available here.

• Thermal Paste

• I designed the PCB inside the case to control the fan given the heat sinks temperature. The gerber files are available for download in the downloads. The circuit for the PCB was shamelessly taken from here due to it being completely analogue and not containing any onboard clocks. If you don't want to manufacture the circuit board, then this board from amazon should work. The board from amazon will introduce kHz noise into your amplifier due to the onboard clock.

For the PCB you'll need:

• 50k Potentiometer
• 10k Thermistor
• 40mm 12v Fan
• IRF540NPBF MOSFET
• 12V Regulator
• 2.2uF 16V Capaictor
• Fan Headers
• Molex Mounts
• ... and some electronics knowledge.

The Mounting bracket can be printed from plastic but better cooling results can be seen if you fabricate an aluminium bracket.

Uses 8 m3x20mm bolts, 6 m3x12mm bolts, 8 m3 nuts, and 4 m2 screws.

At a 0.2mm printing layer height, pause the print at layers 41, 216, and 269 to insert the m3 captive nuts into the main case.

16.4.24 V1.1: Moved BNC hole from case to cover. Adjusted lid to be the same width as the case for a more flush full assembly. Moved the heatsink pegs down by 4mm to fit both the fan and the heatsink under the lid. Added another hole to the fan mounts to reduce the thickness from 3mm to 1mm so the m3 screws fit.

19.4.24 V1.2: Made the BNC hole bigger and longer by 4mm to account for any wires coming out of the BNC. Moved the fan slot on the cover from the bottom to the top as this placement made more sense to reduce the amount of wires hanging around. Add through holes for the main case for a bolt and nut

20.5.24 V1.3: Added a 8mm hole to the cover near the potentiometer for easier access without having to take the cover off each time.