Over the next few months, I won’t post until I get a radio telescope for Jupiter built and tested. I’ve got a ton of things to learn and feel excited about making the radio station: [ antennae, power supply, receiver modules ] and then learning how to run the needed digital hardware and software. I’m also studying atomic theory, astrophysics and microwave design.
Here’s what I working on:
Above — Block diagram of the modules I’m working on. Much of the design work is done on paper, however, ++ bench experiments lie ahead to test out my ideas. You’ll notice that most of the work is at audio frequency and I’ve got a good selection of op-amps ready to solder. I love op-amps and bought some low noise, rail-rail devices for use in some of the slots. Great stuff.
This modular system was inspired by my trip to the Dominion Radio Astrophysical Observatory .
At DRAO, I saw countless racks of modules housing their radio telescope hardware. You can swap in new modules to update or tweak the receiver system at any time. Each module lies in a RF tight box with short, low impedance cables connecting well buffered/filtered inputs and outputs. At DRAO, some of their modules lie inside Faraday cages for RF isolation.
The DC receiver and log amp @ audio [ using an AD8307 ] will result in a calibrated measurement receiver — essentially, a calibrated S-Meter. I plan to extend this basic system into UHF and then microwave. I will probably change the DC receiver to a phasing receiver module once I get the whole system up and running.
I’ll show the schematic and just a few measures of the RF Filtration and Amplification module that I’ll complete today.
Above — Jupiter receiver input filters + preamplifier. I chose the MMIC because it presents a wide band 50 Ω output impedance for the input of the mixer [ product detector ] in the receiver module. At 20.1 MHz, the output port return loss = 33.8 dB.
Above — I swept the return loss of the output port and love the great match into 50 Ω across a wide swath of RF. This sweep is just for ~10 – 117 MHz.
Above — A sweep of the input low-pass + band-pass filters. Typical band-pass filters have better high-pass than low-pass skirts. By tapping the coils on the triple-tuned filter + adding a series low-pass filter, the low-pass skirt of my filter looks OK. Essential when you use a preamplifier with gain into microwave.
Above — A sweep out 80.4 MHz of the preamplifier module. Gain at the 20.1 MHz = 9.56 dB.
I wanted <= 10 dB so felt happy with this result.
I threw away some of the gain of the 5 GHz MMIC by not putting an RFC on the MMIC collectors, running a post MMIC 3 dB attenuator pad and by plying 1nF coupling capacitors — these also reduce some of the tremendous low frequency gain possessed by a 5 GHz LNA.
For example, with no input filtration, at ~ 1500 KHz [ the top of the broadcast AM band ], the gain of the MMIC with 1 nF coupling capacitors only = 7.59 dB.
Have a great summer and don’t forget to watch some meteor showers!
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