I had a request from VK6EH recently for a 10 ohm "thin film" resistor to allow him to make this modification to his radio. After discussing the pro's and cons of thin film resistors and standard surface mount resistors we concluded a "thin film" part was not going to be any different from DC to 430 MHz when used in series with the gate. I don't know where this recipe originated but it reminds me why everything you read has to be treated with scepticism. Peer review is not the same as something is just repeated ad nauseam.
I can't recollect seeing a datasheet for a surface moiunt resostir that wasn't a film construction.So how bad is a standard off the shelf 10 ohm 1206 resistor with regard to parasitics? Since 1nH has 1ohm of reactance at 160-MHz (that's how I deal with stuff in my head), at 430MHz 1ohm of reactance requires around 400nH. (F increased say 2.5 times, so inductance divided by 2.5).
I measured an ordinary 10 ohm 1206 resistor:
I can't see how the small parasitics present in a 1206 resistor would make any difference at 430MHz. At HF they parasitics are truly small.. I don't have any 0805 or 0603 size10 ohm parts to compare this with but I suspect they are even better with regard to parasitics.
I'm calling the need for a special thin film resistor busted. And looking at some of the information on the web about these failures is like reading tea leaves and hearing mumbo jumbo.
The PD55015 is a very rugged part. I dragged the S parameters into RFSim and immedialtely saw that at 50MHz it is potentially unstable. However, the 10 ohm resistor is only a marginal improvement. It might be enough given the radio's remaining circuitry was excluded from the analysis.If I was doing this I'd tend towards 22 ohms and any SMD part that fitted.
73's
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