What is the smallest AM/shortwave radio on a chip? Also, cheap. - Page 1
Forum section: electronics / projects

author: cdev
author_rank: Super Contributor
timestamp: March 18, 2015, 01:10:06 am
content: Also, Important! a radio made with it would have to not leak local oscillator signals!I'm not building anything, just wondering.

author: radix
author_rank: Contributor
timestamp: March 18, 2015, 01:12:40 am
content: A crystal radio? If a diode counts as a chip... It can also be made with a razor:https://en.wikipedia.org/wiki/Foxhole_radio

author: Zad
author_rank: Super Contributor
timestamp: March 18, 2015, 01:16:37 am
content: http://en.wikipedia.org/wiki/ZN414No local oscillator, so no radiating noise... It is, however, a TRF so highly dependant on the Q of the C and L to provide selectivity. The original is no longer available, but there are direct copies still being made.

author: barry14
author_rank: Regular Contributor
timestamp: March 18, 2015, 02:36:15 am
content: I don't know if it's the smallest but the most powerful chip is the Silicon Labs SI4734. It is a complete AM/FM/SW radio using digital processing. It is available in radios sold on Ebay from China for a very nominal price although the chip itself is made in the US.

author: German_EE
author_rank: Super Contributor
timestamp: March 18, 2015, 07:54:01 am
content: This is the first time I've seen a good reason for someone not using their country flag. Add my vote for the 414 chip which can easily make a receiver that fits inside a matchbox (including the battery).Good luck with your project.

author: Warhawk
author_rank: Frequent Contributor
timestamp: March 18, 2015, 09:49:41 am
content: What about TEA5767 ?

author: dannyf
author_rank: Super Contributor
timestamp: March 18, 2015, 11:25:31 am
content: 414 is probably the smallest one. No local oscillator too.SI47xx family has a bunch of chips and you should check them out too.

author: LaserSteve
author_rank: Super Contributor
timestamp: March 18, 2015, 01:45:08 pm
content: It needs a good front end filter on it, with good matching. This allows for a shorter antenna.Also the bad Ex-Communist guys have a Communist Era toy. It produces a few tens of watts of RF at some UHF frequency, typically 300 or 900 Mhz. It then looks for second harmonic coming back from semiconductor junctions. It works in the near field, say 10-20 feet...Thus good shielding and a an LC filter on the front end is required, as well as a few ferrite beads.Steve

author: Seekonk
author_rank: Super Contributor
timestamp: March 18, 2015, 01:56:25 pm
content: Three pin TA7642.

author: LaserSteve
author_rank: Super Contributor
timestamp: March 18, 2015, 02:17:43 pm
content: Here's how to use TA7642 with a gain control:http://theradioboard.com/rb/viewtopic.php?t=2791Wish I had seen that when I played with the ZN series.Steve

author: cdev
author_rank: Super Contributor
timestamp: March 18, 2015, 03:16:06 pm
content: Thank you for this. yes, a non-linear junction detector. I had read about the use of these for bug detection but of course they can pick up any semiconductor device.I was thinking that an RF amp would be a good one way signal path that could isolate a radio butthat would probably not work with one of these. A loop antenna is a narrow band RF filter but might have other resonances. The simplest answer is that people should check all of these things.See the links below for examples of what people there have to deal with.http://www.dailynk.com/english/read.php?num=11891&cataId=nk01500http://www.dailynk.com/english/read.php?cataId=nk01500&num=11885(new criminal code allowing death sentences for listening to radio or calling internationally)Cell phone contact example:Hyesan Man Executed as Example for RestKang Mi Jin | 2014-05-22 18:38The death sentence has been imposed upon at least one person caught making phone contact with South Korea from a location near the Sino-North Korean border, Daily NK has learned via detailed, exclusive testimony from a source in the region.“At the beginning of this year they amended the criminal code,” the source reported to Daily NK on the 22nd. “Then, in Hyesan someone got executed as an example to the rest.”According to the source, the execution came amidst an extensive campaign against cellphone users, smugglers, and people aiding and abetting defections, which began last year and has continued into 2014. The victim, a 49-year old stage lighting engineer called Ri Kyung Ho, was executed in March. His execution, though not public, was used as an example to others, and his family has been incarcerated in a State Security Department (SSD) facility. (concentration camp, seehttp://webtv.un.org/meetings-events/human-rights-council/commissions-of-inquiry-hearings/watch/human-rights-in-north-korea-excerpts-from-the-public-hearings-of-the-commission-of-inquiry-23mins/3339582047001]here[/url http://webtv.un.org/meetings-events/human-rights-council/commissions-of-inquiry-hearings/watch/human-rights-in-north-korea-excerpts-from-the-public-hearings-of-the-commission-of-inquiry-23mins/3339582047001] andhttp://www.ohchr.org/Documents/HRBodies/HRCouncil/CoIDPRK/PublicHearings/for more. Warning, don't watch the videos right before sleeping- not for children. )“Ri Kyung Ho was caught out of town by an SSD agent with a signal detector. He’d been calling his family in South Chosun” the source said, explaining the background to the man’s arrest. “He probably didn’t have time to take the phone apart and hide it before SSD agents got to his house.”In the course of Ri’s subsequent interrogation, it reportedly emerged that not only had he been making regular phone calls, but had also been involved in remittance transfers from South Korea and aiding and abetting defections.“He seems to have started by conveying money from defectors to their families, but then began to help people who asked him to send their families to China,” the source said. “Some people are asking why he was killed just because of the money thing, but there are a few who were close to him and his wife, and they say it was because he had been helping defections.”“In times gone by you could bribe your way out of this, but right now they’re sure to punish you. Nobody knows when or why they might get caught up in it, so everyone is nervous,” she said. “Anyone who uses a cellphone to call ‘that way’ or ‘the other way’ [meaning South Korea or China] is scared.”“The rumor now is that Ri Kyung Ho’s elder brother Ri Song Ho, who is deputy head of a children’s film production team, and his younger brother Ri Chang Keun, who is a senior member of a state merited chorus ensemble, are facing punishment, too,” the source added.Daily NK reported yesterday on the revised criminal code. (http://www.dailynk.com/english/read.php?cataId=nk01500&num=11885)(They have something called "three generations of punishment" also "songbun" which punishes the persons parents, siblings and children, and in some cases grandchildren. Often, close family members are sent to huge outdoor concentration camps - which are the size of a county in other countries- often they occupy a big part of a county- other family members are exiled to remote areas of the country in the northeast.)---------------------------------------------------------------------------------------------------------------------------------------------------------------Quote from: LaserSteve on March 18, 2015, 01:45:08 pm

author: codeboy2k
author_rank: Super Contributor
timestamp: March 18, 2015, 10:46:29 pm
content: There's a guy (ex NK) that has been annoying the north by flying large balloons over the border and dropping "care packages" of information about the regime, and good information about the world outside the north.The latest drop contained DVD's of that stupid movie.I thought.. what?? how can they even PLAY a western made DVD? or any DVD for that matter? maybe they can, I don't know.I think dropping radio and cell phones might be a better idea. Then have Google phone/internet service floating above in balloons too, but they would get shot down too quickly to make it worthwhile.

author: ivan747
author_rank: Super Contributor
timestamp: March 19, 2015, 03:57:22 am
content: Quote from: codeboy2k on March 18, 2015, 10:46:29 pmThey must be electromagnetically silent. I wouldn't be surprised if they manage to get lots of cellphone reception from the south in some areas.Well, a second possibility is that the government jams useful frequencies.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: March 19, 2015, 11:45:17 am
content: The ZN414/MK484/TA7642 is a great chip and a good TRF receiver under 2 MHz.The standard circuits aren't that sensitive.But the mods described athttp://members.iinet.net.au/~cool386/zn414/zn414.htmlmake it much better.It has super low current consumption and gives listenable volume with a 1.5v battery.Demo at:One limitation is the ZN414's upper frequency. It may be 3 MHz or it may be 5 MHz. I haven't tried it there but it may not be high enough to cover the most active shortwave broadcast bands (6 - 18 MHz).

author: dannyf
author_rank: Super Contributor
timestamp: March 19, 2015, 01:34:18 pm
content: If you don't insist on it being a "chip", a single transistor radio is fairly simple to build as well.

author: cdev
author_rank: Super Contributor
timestamp: March 19, 2015, 05:22:35 pm
content: Quote from: ivan747 on March 19, 2015, 03:57:22 amI agree with both of you- What the cell phone issue is about is the fact that all along the Chinese NK border, especially in the far north of NK (Along the "Tumengang" or Tumen River, in North Hamgyong Province) some medium sized cities in NK are within cellphone range of the Chinese border. So, traders who go back and forth between NK and China pick up inexpensive Chinese prepay cell phones and sell them to people in NK try to use them to call family members outside.The problem is, they are getting caught, faster.Some Western electronics companies - perhaps they get them through intermediaries, (they are probably violating some sanction or another- ) but now they are getting expensive radiolocation equipment that works, apparently by measuring time of arrival.They previously had a pseudo-Doppler direction finding system (pictures of the distinctive looking antennas are visible in propaganda photos taken on mountaintops) but now they seem to have recently gotten a much better system and they can locate would be international callers very quickly.And that can and does lead to very very serious disasters for families unable to come up with the money to bribe officials.Its a really unequal situation with the regime using these expensive tools to catch people who are just trying desperately to get money to eat. (they often have relatives in the South who are trying to send them funds but each communication carries this very real risk of disaster for them.. I highly recommend checking out the UN hearings at the link above- if you have the time and energy - its heartbreaking to hear these stories from people who are clearly in many cases really traumatized by them- watch them you will become an expert on the situation)This is a situation where the regime's Achilles heel is clearly outside information. So radios make all the difference, the smaller and easier to hide the better. People are also watching foreign movies which are traded on USB flash drives.But radios are the thing which I think is the biggest need- MW/shortwave radio especially.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: March 19, 2015, 07:34:01 pm
content: Quote from: dannyf on March 19, 2015, 01:34:18 pmA single transistor radio can drive high impedence headphones, and low impedence phones through an audio transformer (which may be hard to find).However sensitivity is poor unless it's made regenerative (ie radiates RF which is a no-no) and an outdoor antenna will almost certainly be required.Selectivity will also be poor unless there are two bulky high-Q tuned circuits in the antenna line.It may be possible to conceal a diode into any piece of consumer electronics with an audio amplifier. A stray wire could extend from that to an externalinductor and tuning capacitor, forming an amplified crystal set.There hasn't been much discussion of antennas though that's also very important if using a crystal set or one transistor radio.A wire on a pole is good but can be seen so is probably impractical. One concealed in a tree might also be risky.A tuned loop antenna may be workable. Potentially it could be made quite large and concealed inside a timber door (which would also make it directional).If there are two or three small metal contacts on the bottom of the door it could be connected to a tuning capacitor and diode for a crystal set.I have made crystal sets this way and they work without an external antenna on the stronger AM stations.

author: mtdoc
author_rank: Super Contributor
timestamp: March 20, 2015, 04:41:00 am
content: For a cheap covert radio - how about Ben Krasnow'sCovert radio pen with bone conductor speaker?

author: richard.cs
author_rank: Super Contributor
timestamp: March 20, 2015, 10:00:41 am
content: A few thoughts:A TRF (tuned radio frequency) design or crystal set + audio amplifier would be best as there's no local oscillator to leakRegenerative receivers are totally out as they radiate, but a one-transistor reflex receiver (where the same transistor is used to amplify at RF and AF) should be OKNon linear junction detectors will work even when the equipment is turned off. Disconnect the antenna and short the input when you're not listening to at least minimise the amount of time it can be seen.A MOSFET or even a triode based input stage might be useful here, in both cases the input just looks capacitive and should be much harder to detect with an NLJD.Edited for spelling

author: LaserSteve
author_rank: Super Contributor
timestamp: March 20, 2015, 12:16:08 pm
content: In a nation that probably monitors battery consumption, attention to power supply issues is crucial too.Fortunately medium wave has a pretty low detection threshold.How many of these radios do you envision producing?Steve

author: ivan747
author_rank: Super Contributor
timestamp: March 20, 2015, 03:19:23 pm
content: I think the important thing here is something that can be hidden in many different ways, otherwise, once authorities discover the existence of the device, they will know where to look out for them.

author: cosmicray
author_rank: Frequent Contributor
timestamp: March 20, 2015, 06:03:21 pm
content: One place to hide it would be in the shell for a USB connector, or even a thumb drive (although thumb drives may be considered counter-revolutionary). The advantage there is that any USB wall wart would be able to power it at will.

author: cdev
author_rank: Super Contributor
timestamp: March 20, 2015, 06:58:45 pm
content: Quote from: LaserSteve on March 20, 2015, 12:16:08 pmI am not in a position to do that, nor would I want to - I don't even speak Korean. I have just been - for a long time, interested in this subject and have at various times tried to convince others that radios are the way to bring about peaceful change -I have - actually many times,written to public entities- for example, legislators, people in government agencies, and NGOs- about radios and NK.How do they get radios - There is actually a channel for them now. they are just too expensive, too limited, and especially, too large. They buy their radios in China- where they are as cheap as one could ever imagine. Traders who are often Chinese Koreans (who have the freedom to cross the border legally) themselves buy them in China and import them. Its not far,just a few dozen feet across a small shallow river (the Tumen River) in some places.Re power, smart meters, energy monitoring, not only are they far from that sophisticated- they are way behind the US, for example, the government also is in an extreme state of dysfunction and cannot even deliver power reliably for a few hours a day. Some areas have not gotten power for months. Mines are closing like crazy because of lack of electricity to pump water out. people are dying because of illness caused by lack of clean water.Cheap AM radios are available in quantity and some cheap shortwave radios sell for as little as $10 in China.They have local markets where things from China including various electronic devices like DVD players, some of which include radios are sold, quietly.They are bought in China and previously they were marked up a great deal but recently the use of one particular kind of DVD like player (compact versatile disk- I think they are called) was made legal because everybody had them anyway.At various points in time, one could almost say that radios were close to being almost tolerated .Cheap Chinese shortwave radios which are popular there, most by no name manufacturers but also models by companies like Degen and Tecsun. Those models are fairly decent. But they are marked up a lot.Their government used to try to jam the main Korean language broadcasters from the South but recently they have been unable to because of the aforementioned lack of electricity. That may also be why they have been generally failing to provide a lot of important things.Radios are important in people's lives - especially in informing people about the world outside- according to surveys done of people who decided to make the difficult and dangerous journey to the South.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: March 20, 2015, 07:17:03 pm
content: Quote from: cosmicray on March 20, 2015, 06:03:21 pmThe amount of RF noise (and potentially supply line ripple) these chuck out make these unsuitable for powering radio receivers.Battery power is much more trouble free and it may be possible to build a radio into a torch.Another possibility is a deodorant, shampoo or drink container that would unlikely to be found by the secret police (POWs built radios in drink flasks during WWII).The most bulky part of a small radio is the inductor. While performance may be compromised a small moulded RF choke of 200 - 250 uH may save space in a medium wave receiver.Piezo transducers are quite sensitive earphones and may be substituted for difficult to obtain crystal earpieces.

author: Zero999
author_rank: Super Contributor
timestamp: March 22, 2015, 08:59:22 pm
content: Yes a simple tuned radio receive would work but the selectivity and sensitivity won't be great.How about using a super heterodyne receiver with a non standard IF and carefully design it so as little of it is re-radiated as possible?