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| Agilent 8753ES A24 Microwave transfer switch substitute |
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| Joel_Dunsmore:
The most common way the switch is damaged is one of the gate-fingers get shorted to the drain and so the FET is turned on. Based on the symptoms, I would guess it is the shunt FET on the load side. The GaAs switch has a series FET going of each way from the common terminal to each output and also a shunt FET at each output, so one shunt is on the main line, and the other is actually shunting across the 50 ohm resistor (well, its more like 47 ohms as the series FET has 3 ohms resistance). I suppose, if you were super careful, and and a high power microscope with a fine diamond scribe, you could cut shunt FET out. Maybe 5-10% chance. If the series FET were bad the loss would have been affected when switch on. |
| inaxeon:
Picture of the switch die attached. If you could point the FET in question, maybe just maybe it could be attempted.. Couldn't help but notice that this switch is completely different to the newer one? Was there a compelling reason to re-design it? |
| inaxeon:
I've attached some DC resistance measurements too. Multimeter polarity of measurements is noted. |
| inaxeon:
My latest PCB order finally turned up, including the transfer switch substitute I showed previously (image of PCB with connectors attached). It'll be at least a few weeks until I can actually build it because the chip shortage shunted me into shady sourcing avenues particularly with the voltage regulators. |
| inaxeon:
I finally got around to building this thing. I swept it on the 8753ES with test port power at +10dBm. Isolation figures: 80 dB to 1 GHz 70 dB to 2 GHz 65 dB to 3 GHz Sadly only 45 dB at 6 GHz (Had to use my spectrum analyser for this test) No match for JPD, but, for 50 bucks and only a few hours of design and build time. I'm pretty satisfied with the result! |
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