Choose date/time to transmit

[michelinok]

It would be really really great if you can add the ability to specify the date/time to tx. Great work!

PS: Do you know if an ALREADY synched weather station will try to re-synch in future?

[schmiernippel]

Hopefully this app het some upgrades.....

But you can manually set yout PC to a specific time and connect your flipper...then you have the modified time on your flipper!

[arha]

I haven't had enough time to add new features, sadly, and with one in two API changes pushed every new kernel release, motivation has been low to add features only to be forced to rewrite them later :) But patches are welcome.

Don't mess with your PC's clock, that's not very convenient. Instead you can run this from flipper's CLI to update its date: date 2024-03-04 05:06:07 3

I'm curious what is your usecase for setting a clock wrong. Bar checking bad firmware and/or old clocks without MCUs for weird states (like showing minute 69), building a transmitter is not really feasible, so you won't be able to, ahem, prank your neighbours.

[schmiernippel]

Xtreme and Unleashead Firmware(maybe other) have the option to "ignore api mismatch" so your app still works for me :-)

Thanks, good idea!

Here is an DCF77 transmitter with an Atmega and antenna, so its makeable :-)

https://www.0x7.ch/text/dcf77.pdf

Greets!

[arha]

Oh, I had no idea ignoring api mismtch was an option. I've been messing with other radioclock formats lately. Good to know.

It's makeable all right, but it's not gonna be very efficient (thus not radiate very far). The wavelength of 77.5khz is about 4km, so a dipole antenna would have two arms of 1km each.

The shorter your antenna is compared to lambda/4, the worse it will radiate. So it's kind of the same deal as with FZ, not a great transmitter for anything but a few centimeters. Maybe give it a meter with a high-Q circuit.

But if you do make a 4000m band radiator that works indoors, do let me know :)

LE: Read the article, the 15.5 khz hack on audio is quite nice. It might actually work from FZ too, on the 5th harmonic. I've seen it working from headphones playing a 15.5khz carrier near watches.

[schmiernippel]

For any other purpose there are so many antenna options, but for DCF77 only the ferrid rod one...Is there no option for a compact directional antenna, or array antenna, or antenna with parasitic elements, or...... ??? :-)

[arha]

There are a lot of options for RX antennas, like the ones you mentioned, because receiver sensitivity can be increased by filtering, adding more IF stages and DSP/software. Some people make "end fed long wire" antennas which are just that, a random length of wire, sometimes tuned to a common harmonic of all interesting bands.

TX antennas have one single constraint: they have to be close to half a wavelength long to be efficient, regardless of shape. This is the bane of commercial and amateur radio stations everywhere, and sadly, it's inescapable.

If you push significant RF power in an antenna that's not resonant, your energy will not radiate, but it will become heat and is reflected back into your amplifier, destroying it in the process. Unless you have an antenna tuner, which will let your amplifier survive such reflections without increasing efficiency.

You can try TX magloops, but they're pretty quirky, dangerous if you never worked with HV and require quite some exotic components to get any significant power through (vacuum variable caps, which are mostly soviet surplus). Also, RF burns are nasty - and when in use, magloops throw enough HV that they make fluorescent lights shine.

Its also why 125khz long distance rfid readers are implausible.

However, you can even drive a lightbulb with 77.5khz (there's even a challenge to use bulbs as antennas in ham radio), but you're going to need large amounts of power to get even 1W of radiated power :)

LE: weird typos, didn't intend to close the issue, am mobile, misclicks ahoy. Check the Mainflingen transmitter to see what kind of antennas they're using, and IIRC, even they are just 33% efficient (since antennas also need to be about half a wavelength away from the ground)

[schmiernippel]

Thanks for your answer... So much learned from one post 😳 I will check the Mainflingen and IIRC thing you said. With your Info, maybe i find a good/compact antenna solution for this usecase. I know from 10 years RC FPV experience its a problem with low frequency and small antennas...

[arha]

Oh, ha, IIRC means "if i recall correctly". But do check the antennas at Mainflingen.

There are people playing in the VLF/LF bands, but everything there is quite esoteric. Some transmitters are modified audio amps that are feeding antennas.

472khz.org and abelian.org have some amazing experiments with (mostly) DIYed VLF transmitters.

Sadly, the problem of low frequencies and small antenas isn't easy, that's why every modern piece of electronics uses UHF/GHz, where antennas are in the centimeters range.

Given your interest in this, and in HF antennas for FPVs, perhaps give the ham radio hobby a new look? It's gotten quite automated and you can see the reception area of whatever you make in a few minutes, with data modes like WSPR, QRSS, or even FT-8.

It's not DCF-77 VLF, but it can scratch that itch.

[schmiernippel]

I am very interested in RF, i have HackRF, Flipper, SDR, Proxmark3. Since i know "signals are really everywhere" it is so interesting.But in my country, Austria, most RF data is transmitted with GSM,3/4/5G, TETRA and some other RF standards i am to stupid to understand, so i play with things like RTL_433 and so on....but i lost my interest for more learning because of this digital, for me to complicated, protocols.

A good reception with DIY polarised or linear antennas, DIY antenna trackers, DIY SWR meters up to 6ghz, filtering the electronic systems in the copter/plane...and so on...