James Morris
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James Morris
jmorris
Edited 1 year ago
Not sure if this microwave power sensor is repairable. It’s an HP P486A waveguide thermistor mount for 12.4 to 18 GHz. It was bugging out, and I’ve rejuvenated one of these before (using the guidelines in the manual) but it didn’t work this time. I’m puzzled by the mechanics of this, what the adjustment screw actually does, and why is it attached to a small metal block which is maybe held with conductive paste? It’s supposed to finely match the inner and outer thermistors: one is in the waveguide and the other is inside the housing as a reference. The waveguide thermistor is heated by the RF signal, and the power meter detects this, via a bridge circuit which tries to balance the current in each thermistor.
The wonders of 1960s microwave tech. We explored space with this stuff.
#hamradio #amateurradio #microwave #electronics
The wonders of 1960s microwave tech. We explored space with this stuff.
#hamradio #amateurradio #microwave #electronics
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Here's a trace of the power up sequence, with the gate voltage at the top, and drain at the bottom. I'm not sure if the CRO is fast enough to catch the sequence correctly, because I can't tell if there's a gap between gate & drain. IIUC, the negative regulator chip provides a 'voltage ok' signal that is used to switch the gate, so it should be ok. But, I'll keep investigating until I'm sure.
This is the kind of thing that leads to long development times for amateur microwave radio projects, so many (fascinating) rabbit holes and a lot of learning as you go. I wonder if more people knew about this aspect of the hobby, whether we'd see more and younger people joining.
This is the kind of thing that leads to long development times for amateur microwave radio projects, so many (fascinating) rabbit holes and a lot of learning as you go. I wonder if more people knew about this aspect of the hobby, whether we'd see more and younger people joining.
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Load testing the bias power supply. The amp uses an expensive ($650) GaN transistor which must have bias applied before main power, or it will be destroyed - it’s ‘on’ by default and needs bias to switch ‘off’. I’m being extra careful with this, will also verify the power up sequence on a scope, response to short circuit etc.
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James Morris
jmorris
Edited 1 year ago
Just a warning for people thinking about getting into #microwave #amateurradio -- it's an infinite labyrinth of hobbies, knowledge, and equipment. Precision machining, stripline circuits, strange semiconductors (IMPATT diode amplifier, anyone?), exotic electron tubes (which will try and kill you via xrays, lethal voltages, and beryllium oxide), metrology, physics, DIY, vintage equipment resurrection, morse code (modulation? sheer luxury!), scouring ebay, haunting electronics stores, poring over poorly scanned service manuals from defunct companies, and too many hex keys.
Oh, and it's a gateway drug to #radioastronomy.
#hamradio
Oh, and it's a gateway drug to #radioastronomy.
#hamradio
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James Morris
jmorris
Making some hopefully final mods to the azimuth sensor for this az/el drive. Spent ages trying to find screws to match the Hammond enclosure. Turns out to be M3.5, which I have never seen used before. #hamradio #amateurradio #microwave #radioastrnomy
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James Morris
jmorris
Edited 1 year ago
Just tripped across this blast from the past: my first published article, in an .au electronics magazine.
Remember paper magazines? No? Ok.
#hamradio #amateurradio #satellite #electronics
Remember paper magazines? No? Ok.
#hamradio #amateurradio #satellite #electronics
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James Morris
jmorris
Performed some more mm-wave testing at the PNW Microwave build day, looking at the output of the 40-50 GHz quadrupler. Thanks to W7GLF for bringing in his spectrum analyzer & external mixer. Results forthcoming.
#amateurradio #hamradio #microwave #mmwave #electronics
#amateurradio #hamradio #microwave #mmwave #electronics
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James Morris
jmorris
Testing a Ka band LNB, specified for 20.2-21.2 GHz. I could not see any signals beyond 22.8 GHz (well short of the 24 GHz amateur band), but that could be due to issues at the IF level. Worth investigating further. I was able to see a good signals at 22.2, an important radio astronomy frequency. #amateurradio #microwave #radioastronomy
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James Morris
jmorris
Edited 1 year ago
Just received this in gmail. Seems like my ad blocker and/or ublock origin is working well here to stop them tracking my behavior. I have in fact been opening their emails. UbO for the email shows dozens of blocked requests to play.google.com and other related sites.
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James Morris
jmorris
It’s not everyday you get to touch an SR-71. It didn’t quite feel like metal, the paint seems to dampen it?
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James Morris
jmorris
Edited 1 year ago
Got distracted working on slides, used the AI in powerpoint to make some alien cities. Here's one on an accretion-disk world. The "water" is not for swimming.
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