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Practical Radio Circuits (2003) [pdf]

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Re: Practical Radio Circuits (2003) [pdf]

#41

Post by zh3 »

aidenn0 wrote: post #38
zh3 wrote: post #22

Earlier quoted context omitted.

If you're into receiving low frequency time signals, you can receive them directly with nothing more than a piece of wire connected to the mic input of a modern sound card (via a capacitor). Sample at 192kHz and downsample in software (simplest: mix with a similiar frequency sine and listen to the result, say 59kHz for WWVB or MSF).

Really just a piece of wire? I would have thought that there would be too much noise to pick up WWVB without a somewhat more selective antenna (loopstick maybe?)

Yes, depends of course on distance, aerial layout and on the decoding technique. Anything over a few hundred miles needs amplification/attention to aerial resonance etc, simply mixing (multiplying) the received signal wth a sine wave close to the same frequency results in a quite audible signal (strength varies throughout the day though).

Used to be easy to pick up Loran signals in the same way (esp. with untuned aerials) but they're all turned off now.

Re: Practical Radio Circuits (2003) [pdf]

#42

Post by [deleted] »

wbl wrote: post #35
seiferteric wrote: post #18

Earlier quoted context omitted.

I always wanted to do something like this with "earth mode" radio. That is, signals sent through the ground. You can put a couple conductors in the ground spaced far apart and send signals into them and it can be picked up miles away apparently. Would be really slow, so probably text only, but also probably no one would notice. I also vaguely wonder if this would still be regulated by the FCC since it's not through t…

You end up exciting the ionosphere this way so it's regulated. But there is a band way down there to play with if you have your ticket.

[deleted]

Re: Practical Radio Circuits (2003) [pdf]

#43

Post by carltg_ »

wbl wrote: post #35
seiferteric wrote: post #18

Earlier quoted context omitted.

I always wanted to do something like this with "earth mode" radio. That is, signals sent through the ground. You can put a couple conductors in the ground spaced far apart and send signals into them and it can be picked up miles away apparently. Would be really slow, so probably text only, but also probably no one would notice. I also vaguely wonder if this would still be regulated by the FCC since it's not through t…

You end up exciting the ionosphere this way so it's regulated. But there is a band way down there to play with if you have your ticket.

While 9kHz[3e-7/cm] (for an earth mode radio example) is lower than the plasma frequency of the ionosphere, 9MHz[3e-4/cm] (critical so that the ionosphere acts as a waveguide), would this be significantly lower, and hence have a high attenuation--a large imaginary component to the refractive index? If so, would this excite the ionosphere? Genuinely curious

Re: Practical Radio Circuits (2003) [pdf]

#44

Post by cushychicken »

tessierashpool9 wrote: post #21
cushychicken wrote: post #8

Earlier quoted context omitted.

Reticulum qualifies as that. It’s designed to run over LoRA. (The radio protocol, not the LLM thing.)

i can't help it but hear LoRA spoken by a parrot in my head. LoRA, LoRA, ...

Great, now I can’t help it either.

Re: Practical Radio Circuits (2003) [pdf]

#45

Post by wbl »

carltg_ wrote: post #43
wbl wrote: post #35

Earlier quoted context omitted.

You end up exciting the ionosphere this way so it's regulated. But there is a band way down there to play with if you have your ticket.

While 9kHz[3e-7/cm] (for an earth mode radio example) is lower than the plasma frequency of the ionosphere, 9MHz[3e-4/cm] (critical so that the ionosphere acts as a waveguide), would this be significantly lower, and hence have a high attenuation--a large imaginary component to the refractive index? If so, would this excite the ionosphere? Genuinely curious

The earth ionosphere capacitance. See longwave for details

Re: Practical Radio Circuits (2003) [pdf]

#46

Post by namibj »

wildzzz wrote: post #23
jsilence wrote: post #3

Earlier quoted context omitted.

Internet via Ham Radio aka Packet Radio is a thing: https://themodernham.com/ip-over-ham-radio-via-new-packet-ra... Pair it with the Gemini protocol and you're there: https://en.wikipedia.org/wiki/Gemini_(protocol)

Too many narcs on the ham bands would track you down for operating encrypted ham packet radio. You're better off using something like LoRa over the ISM bands. Build out a network of hidden mesh nodes over the area you'd like to operate and that's probably the closest you'll get to a true clandestine network. Of course the major issue with transmitting any RF energy is that someone can watch the spectrum and look for…

Actually LoRa uses chirps designed for iiuc partially analog demodulation to be very energy-efficient.

For hiding you'd be able to use actual DSSS with e.g. AES encrypting a suitably fine grained clock piggybacking on GPS as a time reference, keyed by a shared secret. Then just hone in with e.g. a Costas loop like a GPS receiver does to it's satellites (where the sequence is sourced from a simple clocked logic circuit that's cheap and offers better than random spreading gain at the cost of being cryptographically useless) and demodulate the payload the same way.

You could start off at GPS synchronous sequence generator timing, and slowly shift it at increasing delay until lock in is archived or an implausibly long implied travel distance (signal loss!) is reached (then you can give up and start over, go to sleep and try later, etc.).

Re: Practical Radio Circuits (2003) [pdf]

#47

Post by kazinator »

drivers99 wrote: post #39
rjsw wrote: post #37

Earlier quoted context omitted.

I worked through this [1] book (PDF) as a child, everything worked fine but have no idea if component availability has changed. [1] https://www.worldradiohistory.com/BOOKSHELF-ARH/Technology/M...

Nice, I ran across that a month or two ago and it was great. I got to the OC71 germanium transistor and found out they're obsolete.

Silicon PNP transistors should work in those circuits.

It's also trivial to reverse all the polarities in the circuits and switch to NPN. Use a positive supply voltage rather than negative, flip the rectifier diode around as well as all the electrolytic caps.

Re: Practical Radio Circuits (2003) [pdf]

#48

Post by [deleted] »

zh3 wrote: post #22
cushychicken wrote: post #9

You can pick up a pretty reasonable amount of radio signal with the right length of wire and a properly tuned LC circuit tank. I didn’t believe it until I tried it, but it’s a surprisingly good first pass at an FM frontend.

If you're into receiving low frequency time signals, you can receive them directly with nothing more than a piece of wire connected to the mic input of a modern sound card (via a capacitor). Sample at 192kHz and downsample in software (simplest: mix with a similiar frequency sine and listen to the result, say 59kHz for WWVB or MSF).

[deleted]

Re: Practical Radio Circuits (2003) [pdf]

#49

Post by accra4rx »

zh3 wrote: post #40
accra4rx wrote: post #36

Earlier quoted context omitted.

are there any good circuits for radio transmitter (circuit for low freq esp 60KHz)

It's super-easy for very short range, super-difficult for long range. Reason is the wavelength is so long (speed of length/60KHz = 5Kms) that you need a massive aerial for lange range, however for short range you can feed the MW or LW coil of an AM radio to spoof a time signal (ideally make it resonant by adding the right amount of capacitance, look up "tank circuit"). Watch out if you add amplification though, due t…

Thank you sir, I am going to get a sound card with 192Khz and try that out

Re: Practical Radio Circuits (2003) [pdf]

#50

Post by kazinator »

kazinator wrote: post #47
drivers99 wrote: post #39

Earlier quoted context omitted.

Nice, I ran across that a month or two ago and it was great. I got to the OC71 germanium transistor and found out they're obsolete.

Silicon PNP transistors should work in those circuits. It's also trivial to reverse all the polarities in the circuits and switch to NPN. Use a positive supply voltage rather than negative, flip the rectifier diode around as well as all the electrolytic caps.

In that most advanced circuit where are two diode drops against the BE junction of the transistor, you almost certainly want silicon diodes to go with the silicon transistor. The diode type is not otherwise critical. Other than that, I don't see any transistor biasing that depends on a detailed model of the germanium transistor.
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