Jonny 290 posted:

sdr sticks require a little bit of Focus because they can do so much.

one weak point of them is they were basically designed as least-cost receivers for asian digital TV. Digital codecs don't care about distortion or overload because they have so much error correction, so the automatic and manual gain controls are very lacking.

Ideally if you want to use one of the rtl sdr "v3" sticks (which have built in shortwave functionality) on lower frequencies, you'd put a box that is a combo antenna matcher and attenuator in front of it, because it has no gain controls down on AM/shortwave. everything is full throttle. and as a result, since AM broadcast signals are like 10000x stronger than weak shortwave ones, the former just overloads and you hear local nazi sports talk radio every 10khz. They do very well when you have a preselector or attenuator ahead of them, between the SDR and the antenna.

Stack Machine posted:

So speaking of super-cheap gear along the lines of RTL-SDR dongles, I just picked up a nanovna:



Here we see a capacitor putting on its inductor hat above 22MHz. I don't really have any one use planned for this but antenna tuning/SWR and a reasonable LCR meter are worth the price of admission, and I'm sure I'll be characterizing filters and amps with it before long.

Achmed Jones posted:

i was trying to check out the ISS flyover and the lovely app i was using completely poo poo the bed. i'm really salty about it, cause it maxed out at 54 degrees. there'll be another one on monday but it'll only be 19 degrees so might not be visible behind buildings

i mean, we didn't see it anyway, but it would've been nice to have had a better chance

horse_ebookmarklet posted:

When I use a VNA, am I essentially radiating a CW signal at my sample points and measuring various parameters of the reflection, right?
And I am probably sweeping outside of my specific band(/license) I want, because I want to see where it is tuned.

So essentially the VNA is unintentionally radiating and this is bad. ?

My nanoVNA2 is prolly pretty low power, but sometimes I use the work $$$$$ VNA at like -10dB....

Achmed Jones posted:

c radio s: got my rebroadcaster code ported to golang rather than ruby. it runs quite well on the raspberry pi zero. it's not quite feature-complete yet (it doesn't actually write its state to the state file) but that's trivial to implement. i've spent the last few days tracking down a bug that was leading to duplicate processes being spawned

i had a goroutine that runs the play-the-stream command and then blocks until it exists. i was using cmd.Run() inside the goroutine. what happened was that in the time between the implicit cmd.Start and cmd.Wait(), the process's pid was still unset, so the reconciler and other code would think that we weren't broadcasting when we were. just needed to call cmd.Start() outside the goroutine (which blocks and sets pid when it returns) and then call cmd.Wait() in the goroutine. that blocks until complete, and after that i write to the "the command is terminated" channel and everything works

it sucked bc it worked perfectly on my server - it was only on the much slower raspberry pi zero that the delta between Start and Wait was observable

anyway that's done now. i also bit the bullet and moved the ui out of standard forms and into a js thing that just writes a blob of json state. it's basically a dumb little spa with no framework or anything like that beyond jquery and bootstrap lol. it works much better now.

Achmed Jones posted:

haha yeah i have mutexes for the state changing operations, that's why it was so fuckin confusing! the turnOn funcs were finishing and releasing their locks before the process had spawned and put the pid in the cmd struct

it's not public on github yet, i probably won't release it until i have a full "build a raspberry pi image" pipeline set up

LifeSunDeath posted:

Big Mackson posted:

any way for me to get a transverter for vhf and have this 1 in all setup so i can stop changing cables etc?

Jonny 290 posted:

Let me look in the junk shed this week