6 ms·

Practical Radio Circuits (2003) [pdf]

157 points by _Microft 2y ago

tessierashpool9 2y ago
i'd love to see some grassroots-powered clandestine para-web running at least partially on radio. obviously such a project would either immediately or at some point face the usual issues like: spam, cp etc. that's why i believe such a network would have to be slow. it would have to be so slow (and just fast enough) for text-based communication and simple protocols. and i mean text as in < 1kB ... not sufficient for transmitting sth like base64(videoclip). that would be so cool.
- jsilence 2y ago
  Internet via Ham Radio aka Packet Radio is a thing: https://themodernham.com/ip-over-ham-radio-via-new-packet-radio/ 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) https://en.wikipedia.org/wiki/Gemini_(protocol)
  - michaelt 2y ago
    Isn't ham radio no-encryption-allowed, no-commercial-use-allowed?
    - myth2018 2y ago
      It is. That doesn't disallow mesh networks, but Gemini would be off-limits due to TLS. Gopher would be OK.
    - deknos 2y ago
      Signatures are okay though. And you can do encryption, when you have to control remote devices which belong to you. and internet still can be non commercial.
    - bityard 2y ago
      Sort of, yes, but it's quite a bit more nuanced than that. The actual rules say you're not allowed to obscure the meaning of a message. Use of encryption itself is not specifically prohibited, but you're not allowed to hide the information being sent. So, "encryption" is technically allowed for things like authentication and signatures, under most interpretations of the rule. It is correct that you're not allowed to use your ham license for any commercial purpose. But again, there are narrow exceptions: a teacher getting paid to teach a class on amateur radio or science in general can transmit to demonstrate the technology, or an astronaut or military member making contacts with amateurs for goodwill purposes or as part of an exercise.
    - tessierashpool9 2y ago
      at the risk of this not flying well with some ham people here but i'd say the heck with those regulations i'm encrypting and that's the end of the story it's called clandestine for a reason after all
      - bityard 2y ago
        "Not flying well" has nothing to do with it. If you are transmitting on the amateur bands without a license, that's illegal. If you do it with any regularity, you are causing interference and some hams are better than you'd think at locating sources of unwanted interference. There are plenty of other anything-goes bands for you to use, there's literally no reason to do your pirate radio on the ham bands. Except to get those warm fuzzy counter-culture feels I guess.
        tessierashpool9 2y ago
        then let's go off-ham
        tonyarkles 2y ago
        That's the tricky part... if you're going for legal and license-free you're pretty much left with the ISM bands and very limited transmit power. There's nothing stopping you from getting a real spectrum license and narrowband licenses in the 2m and 70cm bands aren't actually that expensive but there's also equipment certification requirements, generally.
      - cruffle_duffle 2y ago
        The ‘no encryption’ rule in ham radio is intended to encourage experimentation and openness. Ham radio has always been about exploring, learning, and sharing knowledge, much like open-source software. If transmissions are encrypted, it becomes nearly impossible for others to decode, learn from, or experiment with them. The idea is that anyone with the right knowledge of the protocol should be able to communicate with anyone else on the airwaves, supporting the spirit of why this spectrum is reserved. That said, balancing this with modern needs for security and privacy is a real challenge. Good communication protocols today are designed with these protections in mind, and the inability to use encryption arguably limits what amateur radio enthusiasts can do with newer radio technologies. Privacy, however, has traditionally not been part of ham radio—this is why you’re required to identify yourself with a call sign, and contact info is publicly available. The identity of the sender is expected to be open. Maybe there’s room to allow for some privacy around the content of the message itself, but the sender’s identity should still be clear. I’m not sure what the right balance is, but simply allowing complete encryption that hides the message, the transmitter’s identity, and the transmission protocol itself doesn’t seem to align with the purpose of amateur radio. The ‘trash bands’ (ISM bands) are probably a much better place for experimenting with full-bore encryption and privacy. From these experiments, we might learn a balanced approach that could be backported to the amateur spectrum, preserving the spirit of why these bands exist while adapting to modern privacy needs.
  - bityard 2y ago
    Ham radio is actively unfit for the requirement of "clandestine" for the parent commentor's purpose.
  - wildzzz 2y ago
    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 those transmissions and eventually track down your nodes. LoRa uses DSSS which if operating at minimum power, could help hide transmissions. If you want to add some illegality to the system, you could piggyback on amsats or open relay satellites like FLTSATCOM to expand your network and hide better.
    - namibj 2y ago
      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.).
- hbrav 2y ago
  This should interest you: https://meshtastic.org/ https://meshtastic.org/
  - tessierashpool9 2y ago
    looks interesting. a network of maybe solar-powered scrapped commodity hardware or cheap raspis. maximum of 1kB/sec bandwidth. fully encrypted. no logging. all peer to peer networked. messaging / chat, text-based websites. maybe some simple images (black / white, svg) but optional. i don't think this would be in and off itself a game changer but it could be a seed for further development of anarchistic technology culture.
- cushychicken 2y ago
  Reticulum qualifies as that. It’s designed to run over LoRA. (The radio protocol, not the LLM thing.)
  - tessierashpool9 2y ago
    i can't help it but hear LoRA spoken by a parrot in my head. LoRA, LoRA, ...
    - cushychicken 2y ago
      Great, now I can’t help it either.
- seiferteric 2y ago
  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 the air...
  - tessierashpool9 2y ago
    that sounds interesting. never heard of that. are those conductors passive? just a mesh of copper wire or sth like that?
  - wbl 2y ago
    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 2y ago
      [deleted]
    - carltg_ 2y ago
      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
      - wbl 2y ago
        The earth ionosphere capacitance. See longwave for details
- itomato 2y ago
  Check out the DigiPi and all it can do.
cushychicken 2y ago
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.
- zh3 2y ago
  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).
  - elzbardico 2y ago
    The 2024 version of the crystal radio. :-D
  - accra4rx 2y ago
    are there any good circuits for radio transmitter (circuit for low freq esp 60KHz)
    - zh3 2y ago
      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 to the lnog wavelength and the high inductances involved (if you get that far) it is possible to end up with dangerous voltages at the aerial feed. A sound card with a true 192Khz sample rate should be enough to fool a radio clock next to the transmitter coil - though be aware a lot of sound cards may not actually output the 60kHz carrier frequency required.
      - 2y ago
JKCalhoun 2y ago
The regenerative receiver, followed by the superheterodyne receiver? Edwin Howard Armstrong might be the man who fell to earth.
- mannykannot 2y ago
  And FM. Tragically, he was driven to suicide by his battles with Sarnoff, principally over the IP rights to his own inventions.
hezag 2y ago
Loved this practical guide publication format. Anyone know other magazines like this Everyday Practical Electronics?
- zh3 2y ago
  There used to loads of magazines like this. 'Everyday Practical Electronics' was from the merger of Everday Electronics and Practical Electronics IIRC, separately just in the UK there was Practical Wireless, Wireless World, Electronics International and many others (I may be getting the names a bit wrong here, but I have Practical Wireless dating back to 1963 or so - mostly valves then of course!). Elektor [0] is still around (online), also see things like the ARRL Handbook and associated publications (plus RSGB [2] in the UK, plentyof others out there). [0] https://www.elektor.com/collections/magazines https://www.elektor.com/collections/magazines [1] https://www.arrl.org/ https://www.arrl.org/ [2] https://rsgb.org/ https://rsgb.org/
buescher 2y ago
Some thoughts - this is a good overview of how stagnant the hobbyist state of the art was 20 years ago. You could probably have built all of these circuits with the those exact parts in 1973. Pretty much everything in this collection but the superhet and direct-conversion receivers is obsolete and was at best obsolescent at the time. You can think of a typical SDR as a dual-conversion receiver with a conversion stage in the digital domain. Superregens were used in remote controls right up through the turn of the century, but by the time this was written no one was designing new ones. I saw a TRF front end on a commercial ultrasound device in that era but it was not typical. Many RF transistors are no longer available in through-hole though you can probably find small quantities for hobby projects. The msph10 is long gone. And good luck sourcing dual-gate mosfets even in smt. Infineon might still make a couple. As a digression, it does make me think TRF receivers are probably a better learning tool than the my-second-radio regenerative receiver. Crystal radios, of course, are pure magic and it’s sad that so few people get to build them as kids.
drivers99 2y ago
A friend and I have been trying to build an AM radio. We got a few working, like the basic "crystal" (germanium diode) one with an earpiece, generally picking up 1 or 2 stations very faintly. Then some attempts with an AM radio IC (TA7642), some that use a couple diodes and LM386 op-amp but they're generally terrible, if they work at all. It seems that following random schematics off the web or a youtube screenshot doesn't work very well. I do have an RF design book I haven't started (by Chris Bowick) as well as this PDF now, which should be even more practical, so I'm hopeful I can figure it out. I also have some test equipment such as nanoVNA, tinySA, and an oscilloscope which makes it possible to get visibility into how stuff behave beyond "I don't hear anything; no idea what's wrong." I was able to see how the tank circuit was behaving as you tune it.
- wbl 2y ago
  Application notes can be pretty informative. Also ARRL handbook
  - drivers99 2y ago
    Application notes as in the examples on datasheets? Cool, I do have the ARRL handbook (100th edition). I also got the 50th (1973) and 66th (1989) editions partly out of curiosity (for the 1973 one) and because someone told me a late 80's edition might be good for info about building stuff.
- buescher 2y ago
  Ronald Quan’s Build Your Own Transistor Radios is pretty good but I have only read it, not built any of the radios in it. The Bowick book is solid for fundamentals like impedance matching and basic filter design. The old brown edition is more concise than the new one.
- rjsw 2y ago
  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/Making-a-Transistor-Radio-Ladybird%20Books-1972.pdf https://www.worldradiohistory.com/BOOKSHELF-ARH/Technology/M...
styczen 2y ago
where can I buy new these f&*(( headphones

157 points by _Microft 2y ago

i'd love to see some grassroots-powered clandestine para-web running at least partially on radio. obviously such a project would either immediately or at some point face the usual issues like: spam, cp etc. that's why i believe such a network would have to be slow. it would have to be so slow (and just fast enough) for text-based communication and simple protocols. and i mean text as in < 1kB ... not sufficient for transmitting sth like base64(videoclip). that would be so cool.

jsilence 2y ago
Internet via Ham Radio aka Packet Radio is a thing: https://themodernham.com/ip-over-ham-radio-via-new-packet-radio/ 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) https://en.wikipedia.org/wiki/Gemini_(protocol)
- michaelt 2y ago
  Isn't ham radio no-encryption-allowed, no-commercial-use-allowed?
  - myth2018 2y ago
    It is. That doesn't disallow mesh networks, but Gemini would be off-limits due to TLS. Gopher would be OK.
  - deknos 2y ago
    Signatures are okay though. And you can do encryption, when you have to control remote devices which belong to you. and internet still can be non commercial.
  - bityard 2y ago
    Sort of, yes, but it's quite a bit more nuanced than that. The actual rules say you're not allowed to obscure the meaning of a message. Use of encryption itself is not specifically prohibited, but you're not allowed to hide the information being sent. So, "encryption" is technically allowed for things like authentication and signatures, under most interpretations of the rule. It is correct that you're not allowed to use your ham license for any commercial purpose. But again, there are narrow exceptions: a teacher getting paid to teach a class on amateur radio or science in general can transmit to demonstrate the technology, or an astronaut or military member making contacts with amateurs for goodwill purposes or as part of an exercise.
  - tessierashpool9 2y ago
    at the risk of this not flying well with some ham people here but i'd say the heck with those regulations i'm encrypting and that's the end of the story it's called clandestine for a reason after all
    - bityard 2y ago
      "Not flying well" has nothing to do with it. If you are transmitting on the amateur bands without a license, that's illegal. If you do it with any regularity, you are causing interference and some hams are better than you'd think at locating sources of unwanted interference. There are plenty of other anything-goes bands for you to use, there's literally no reason to do your pirate radio on the ham bands. Except to get those warm fuzzy counter-culture feels I guess.
      - tessierashpool9 2y ago
        then let's go off-ham
        tonyarkles 2y ago
        That's the tricky part... if you're going for legal and license-free you're pretty much left with the ISM bands and very limited transmit power. There's nothing stopping you from getting a real spectrum license and narrowband licenses in the 2m and 70cm bands aren't actually that expensive but there's also equipment certification requirements, generally.
    - cruffle_duffle 2y ago
      The ‘no encryption’ rule in ham radio is intended to encourage experimentation and openness. Ham radio has always been about exploring, learning, and sharing knowledge, much like open-source software. If transmissions are encrypted, it becomes nearly impossible for others to decode, learn from, or experiment with them. The idea is that anyone with the right knowledge of the protocol should be able to communicate with anyone else on the airwaves, supporting the spirit of why this spectrum is reserved. That said, balancing this with modern needs for security and privacy is a real challenge. Good communication protocols today are designed with these protections in mind, and the inability to use encryption arguably limits what amateur radio enthusiasts can do with newer radio technologies. Privacy, however, has traditionally not been part of ham radio—this is why you’re required to identify yourself with a call sign, and contact info is publicly available. The identity of the sender is expected to be open. Maybe there’s room to allow for some privacy around the content of the message itself, but the sender’s identity should still be clear. I’m not sure what the right balance is, but simply allowing complete encryption that hides the message, the transmitter’s identity, and the transmission protocol itself doesn’t seem to align with the purpose of amateur radio. The ‘trash bands’ (ISM bands) are probably a much better place for experimenting with full-bore encryption and privacy. From these experiments, we might learn a balanced approach that could be backported to the amateur spectrum, preserving the spirit of why these bands exist while adapting to modern privacy needs.
- bityard 2y ago
  Ham radio is actively unfit for the requirement of "clandestine" for the parent commentor's purpose.
- wildzzz 2y ago
  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 those transmissions and eventually track down your nodes. LoRa uses DSSS which if operating at minimum power, could help hide transmissions. If you want to add some illegality to the system, you could piggyback on amsats or open relay satellites like FLTSATCOM to expand your network and hide better.
  - namibj 2y ago
    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.).
hbrav 2y ago
This should interest you: https://meshtastic.org/ https://meshtastic.org/
- tessierashpool9 2y ago
  looks interesting. a network of maybe solar-powered scrapped commodity hardware or cheap raspis. maximum of 1kB/sec bandwidth. fully encrypted. no logging. all peer to peer networked. messaging / chat, text-based websites. maybe some simple images (black / white, svg) but optional. i don't think this would be in and off itself a game changer but it could be a seed for further development of anarchistic technology culture.
cushychicken 2y ago
Reticulum qualifies as that. It’s designed to run over LoRA. (The radio protocol, not the LLM thing.)
- tessierashpool9 2y ago
  i can't help it but hear LoRA spoken by a parrot in my head. LoRA, LoRA, ...
  - cushychicken 2y ago
    Great, now I can’t help it either.
seiferteric 2y ago
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 the air...
- tessierashpool9 2y ago
  that sounds interesting. never heard of that. are those conductors passive? just a mesh of copper wire or sth like that?
- wbl 2y ago
  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 2y ago
    [deleted]
  - carltg_ 2y ago
    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
    - wbl 2y ago
      The earth ionosphere capacitance. See longwave for details
itomato 2y ago
Check out the DigiPi and all it can do.

cushychicken 2y ago

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.

zh3 2y ago
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).
- elzbardico 2y ago
  The 2024 version of the crystal radio. :-D
- accra4rx 2y ago
  are there any good circuits for radio transmitter (circuit for low freq esp 60KHz)
  - zh3 2y ago
    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 to the lnog wavelength and the high inductances involved (if you get that far) it is possible to end up with dangerous voltages at the aerial feed. A sound card with a true 192Khz sample rate should be enough to fool a radio clock next to the transmitter coil - though be aware a lot of sound cards may not actually output the 60kHz carrier frequency required.
    - 2y ago

JKCalhoun 2y ago

The regenerative receiver, followed by the superheterodyne receiver? Edwin Howard Armstrong might be the man who fell to earth.

mannykannot 2y ago
And FM. Tragically, he was driven to suicide by his battles with Sarnoff, principally over the IP rights to his own inventions.

hezag 2y ago

Loved this practical guide publication format. Anyone know other magazines like this Everyday Practical Electronics?

zh3 2y ago
There used to loads of magazines like this. 'Everyday Practical Electronics' was from the merger of Everday Electronics and Practical Electronics IIRC, separately just in the UK there was Practical Wireless, Wireless World, Electronics International and many others (I may be getting the names a bit wrong here, but I have Practical Wireless dating back to 1963 or so - mostly valves then of course!). Elektor [0] is still around (online), also see things like the ARRL Handbook and associated publications (plus RSGB [2] in the UK, plentyof others out there). [0] https://www.elektor.com/collections/magazines https://www.elektor.com/collections/magazines [1] https://www.arrl.org/ https://www.arrl.org/ [2] https://rsgb.org/ https://rsgb.org/

buescher 2y ago

Some thoughts - this is a good overview of how stagnant the hobbyist state of the art was 20 years ago. You could probably have built all of these circuits with the those exact parts in 1973. Pretty much everything in this collection but the superhet and direct-conversion receivers is obsolete and was at best obsolescent at the time. You can think of a typical SDR as a dual-conversion receiver with a conversion stage in the digital domain. Superregens were used in remote controls right up through the turn of the century, but by the time this was written no one was designing new ones. I saw a TRF front end on a commercial ultrasound device in that era but it was not typical. Many RF transistors are no longer available in through-hole though you can probably find small quantities for hobby projects. The msph10 is long gone. And good luck sourcing dual-gate mosfets even in smt. Infineon might still make a couple. As a digression, it does make me think TRF receivers are probably a better learning tool than the my-second-radio regenerative receiver. Crystal radios, of course, are pure magic and it’s sad that so few people get to build them as kids.

drivers99 2y ago

A friend and I have been trying to build an AM radio. We got a few working, like the basic "crystal" (germanium diode) one with an earpiece, generally picking up 1 or 2 stations very faintly. Then some attempts with an AM radio IC (TA7642), some that use a couple diodes and LM386 op-amp but they're generally terrible, if they work at all. It seems that following random schematics off the web or a youtube screenshot doesn't work very well. I do have an RF design book I haven't started (by Chris Bowick) as well as this PDF now, which should be even more practical, so I'm hopeful I can figure it out. I also have some test equipment such as nanoVNA, tinySA, and an oscilloscope which makes it possible to get visibility into how stuff behave beyond "I don't hear anything; no idea what's wrong." I was able to see how the tank circuit was behaving as you tune it.

wbl 2y ago
Application notes can be pretty informative. Also ARRL handbook
- drivers99 2y ago
  Application notes as in the examples on datasheets? Cool, I do have the ARRL handbook (100th edition). I also got the 50th (1973) and 66th (1989) editions partly out of curiosity (for the 1973 one) and because someone told me a late 80's edition might be good for info about building stuff.
buescher 2y ago
Ronald Quan’s Build Your Own Transistor Radios is pretty good but I have only read it, not built any of the radios in it. The Bowick book is solid for fundamentals like impedance matching and basic filter design. The old brown edition is more concise than the new one.
rjsw 2y ago
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/Making-a-Transistor-Radio-Ladybird%20Books-1972.pdf https://www.worldradiohistory.com/BOOKSHELF-ARH/Technology/M...

styczen 2y ago

where can I buy new these f&*(( headphones