Author: N4GA – Rob
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Biasing Schemes Revisited
So I’ve gone around the block on this one. Tried a bunch of designs, studied a bunch of others and finally designed my own! The goals of the bias circuit include: #4 is the key. As a LDMOS heats up, Ids will rise and the gain changes, causing the LDMOS to drift into a less…
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Transmission Line Transformer Testing
Jerry Sevick, W2FMI (SK) called this the “Soak Test.” He used it to run real power through the TLT network to check efficiency. It’s a pretty simple test whereby you simply run significant power through the TLTs and measure the temperature rise in the cores. If they get hot, they are not as efficient as…
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Nulling the Even Harmonics
There’s a quite famous audio amplifier builder (legendary really) named Nelson Pass that makes very high end audio amplifiers. In some of his amps, he even goes so far as to allow you to manually skew the bias via a knob on the front, so you can slant the harmonic content towards even or odd…
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New 2x LDMOS Bias Supply Front End PCB
Designed this new little front end PCB this weekend. My primary goals were as follows: Provide a regulated bias supply using a precision regulator to provide more accurate regulation and some ripple rejection, unlike a straight zener. Allow for independent adjustment of each LDMOS bias, with absolutely no interaction, i.e., adjustment to one side…
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Redesigning the Dual 188XR Test Pallet
Here I will attempt to chronicle the tear down and rebuild of my primary test pallet, which is a dual BLF188XR pallet. This was one of my early designs and I have since done many more and this one needs updating. Plus I want to try some more new things on this pallet. I usually…