Re: Oscillator heating element in SDR-1000 Can someone provide the following information concerning the heating element that is soldered to the top of the oscillator case on the TRX board: Resistance: Temperature of the oscillator case after heat up: Why do I ask? The heating element in my SDR-1000 fell off while I was removing the TRX board and sort of disintegrated when I attempted to re-attach. I could not identify the part and it is not provided by Flex, so I decided to try a thick film resistor in a TO-220 case (Vishay LTO-50 series, 47 ohms). This resistor is rated at 50 W with a good heat sink and about 2.5 W in air. The power dissipation (heating) at 13.8 v is 4 W. Since the heat transfer area is small (~ 10 mm square), the resistor gets HOT. It is attached to the top of the oscillator case with a thermal adhesive (Artic Silver Alumina). I had no idea how good the heat sink action would be, so a 22 ohm resistor was added in series to reduce the heating in the Vishay resistor. Without the other boards installed above the TRX board, the measured final temperature at the top of the resistor case was approx. 210 F (using a Radio Shack infrared pyrometer). That seemed excessive, so I increased the series resistance to 30 ohms. The temperature came down to about 170 F and thats where I left it. A photo is posted at http://pages.prodigy.net/w4qcu/heater.jpg Subsequent operation has been quite satisfactory with good stability after a reasonable warm up time. One final note. The heating resistor is slightly thicker (0.125 inch) than the available space with the thin washer in place on the spacer that is right next to the oscillator. I used a slightly wider fiber spacer, perhaps equivalent to two of the thin washers. I dont notice any degradation in the contact between TRX board and the expansion board (which is directly above). Caddock offers a thinner resistor with a 15 W rating (about 1 W in air). Both the Vishay and Caddock resistors are stocked by Mouser.
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