The Smell of Molten Projects in the Morning
Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Electrical & Electronic gadgets
Just like all those EULAs we click through without reading, nobody pays any attention to the Customs declarations on packages:
The pick-and-place strip across the top contains ten U.FL connectors, a few of which might make their way onto the Ham It Up board. They cost a grand total of $2.09 (not the $12.00 shown on the label) delivered halfway around the planet in a bit over two weeks.
I confess: I just couldn’t pass up some new fashion accessories…
The SMA-to-N cables arrived unexpectedly early, so I fired up the spectrum analyzer to see how the Ham It Up Upconverter behaved at 60 kHz (think WWVB), a smidge below its 100 kHz minimum input frequency spec. It’s worth noting that you can’t do a frequency sweep of the 100 kHz to 50 MHz upconverter response using the tracking generator, because the output sits 125 MHz above the input; yes, it took me a while to dope that out…
Anyhow, the 60 kHz sine wave from the (sub-audio-frequency up to 2 MHz, 600 Ω -ish output) signal generator, passed through a 5X attenuator, and terminated in 50 Ω:
It emerges from the H-I-U in Passthrough mode 3.6 dB lower:
In Upconvert mode, the output sits 14 dB below the Passthrough output and 17.6 below the input:
At that span setting, I don’t trust the frequency resolution of that 125.0605 MHz marker readout.
Cranking the signal generator to produce -10 dBm at the H-I-U output in Passthrough mode brings up a bunch of harmonics:
In Upconvert, they’re down 13.9 dB from the Passthrough output:
The H-I-U should have about 10 dB conversion loss at 100 kHz, so losing another 4 dB beyond the thing’s rated low end isn’t entirely surprising.
All in all, it works fine…
The adapter stack to attach the spectrum analyzer to the Ham It Up noise source turned out to be:
Which puts a serious lever arm on the spectrum analyzer end of the chain:
Ya gotta have stuff, but a pair of cables going directly from the Ham It Up’s SMA female to the analyzer’s N female are on their way around the curve of the planet even as I type.
That peak at 300 MHz is about +10 dBm, but averaging 25 peak values at each frequency trims off 5 dB and makes it easier to see:
The reference level at the top of the graticule is +30 dBm, not the usual +10 dBm, so the left end of the trace doesn’t obliterate the marker readout.
So the noise seems good for VHF to UHF projects, which seems reasonable. The noise at the low end falls dramatically with narrower bandwidths, as you’d expect; it’s reasonably flat around -30 dBm below 100 MHz.
You’d want a bandpass filter in front of whatever you were doing, so as to keep that 300 MHz hash out of everything else.
Some rummaging produced a tiny DPDT switch that actually fit the holes intended for a pin header on the recently arrived Ham It Up board, at least after I amputated 2/3 of the poor thing’s legs:
The new SMA noise output jack sits in the front left, with the white “noise on” LED just left of the switch:
There’s no way to measure these things accurately, at least as far as I can tell, but the holes came out pretty close to where they should be. The new SMA connector lined up horizontally with the existing IF output jack and vertically with the measured / rounded-to-the-nearest-millimeter on-center distance:
The Enable switch doesn’t quite line up with the LED, so the holes will always look like I screwed up:
That’s OK, nobody will ever notice.
Now, to stack up enough adapters to get from the SMA on the Ham It Up board to the N connector on the spectrum analyzer …
For reasons not relevant here, I tore down a battery pack containing three 18650 lithium cells. After a major struggle that involved drilling access holes into the side of the case and hammering the cells free of their silicone potting restraint, I was confronted with this:
Battery may explode or fire if mistreated. Yeah, that could happen.
Having pretty well ignored all the warnings, the damaged cells spent two days in the cold on the patio:
They seem unchanged, so I’ll dispose of them at the next electronics recycling event.
As it turns out, the gadget containing the pack subsequently died of a whoopise while trying to figure out how the pack’s boost regulator worked, so it joined the cells on the outgoing pile.
So it goes …
The dual switch controlling the bathroom lights began requiring some fiddling, which was not to be tolerated. After replacing the switch, I cracked the old one open to see what’s inside…
The failed side of the switch controlled the lights over the sink:
The side for the ceiling vent fan + light got much less use, still worked, and look a bit less blasted.
Not much to choose between the two. It’s been running for nigh onto two decades, so …
An RTL-SDR receiver & Ham It Up RF upconverter arrived, with the intent of poking at LF signals. The upconverter circuit board also contains a mostly populated RF noise source:
Being a sucker for noise sources, I spent some time pondering the circuitry.
The as-built board has a 0 Ω jumper instead of the 6 dB pad along the upper right edge:
The previous version had a pi bandpass filter in place of the pad and you could certainly repopulate it with two caps and a teeny inductor if you so desired.
I added the SMA connector, which isn’t quite identical to the IF output connector above it:
That will require a new hole in the end plate that I’ll get around to shortly. It also needs an external switch connected to the Enable jumper, but that’s in the nature of fine tuning.
I’m awaiting a handful of adapters & cables from halfway around the planet…
The Smell of Molten Projects in the Morning 