EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: dave_j_fan on January 15, 2023, 07:57:36 am
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I surfed the net and no full walkie design is available..
From u tube I have got this regen receiver circuit.
A mid power transmitter I need to club together to make a complete walkie... Which is easy to make.
My plan is to build walkie 2km or 1km
And provide it in open instructible it can be used for rescue teams in poor countries.
1.how is this receiver for walkie
2.suggest easy and mid power transmitter
Attached the regen receiver
And my test proto of part of the receiver
It's work in progress
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Here is the circuit
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I've not seen a 27MHz walkie talkie for awhile. They tend to use 433MHz nowadays.
There used to be loads of 27MHz walkie talkies back in the 80s and 90s. I had a set as a child. I remember opening them up and noticing the number of transistors, a crystal, transformer and many passives. To save cost, the speaker was used as a microphone. I think a regen design was used as a receiver and the crystal only used for transmission. The transformer was used to match the impedance of the speaker, to amplifier.
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I've not seen a 27MHz walkie talkie for awhile. They tend to use 433MHz nowadays.
There used to be loads of 27MHz walkie talkies back in the 80s and 90s. I had a set as a child. I remember opening them up and noticing the number of transistors, a crystal, transformer and many passives. To save cost, the speaker was used as a microphone. I think a regen design was used as a receiver and the crystal only used for transmission. The transformer was used to match the impedance of the speaker, to amplifier.
I too had a pair of those. Cannot remember the exact year but would have been around 1965. I think they had 3 transistors. Think they were or became illegal in the UK. Complaints from radio controlled model aeroplane owners who were legitimately using that band. Stories of planes crashing due to interference from the walkie-talkies.
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CB has always been on 27MHz in the US, but I don't think there's any worldwide standard. Here, the radio control hobby did start on 27MHz, but I don't think it's used much for that anymore.
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CB has always been on 27MHz in the US, but I don't think there's any worldwide standard. Here, the radio control hobby did start on 27MHz, but I don't think it's used much for that anymore.
CB didn't start until long after 1965. RC models using 27 MHz were the norm long before 1965.
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If you want to build this as a fun project and personal challenge go for it, but you can't compete with China for producing a useful transceiver. You can buy a pair of 433MHz transcievers that are nice compact handheld units that will fit in your pocket for around 30 bucks. I doubt you could build something for less even if you value your time at zero once you factor in a suitable enclosure and it will offer inferior performance.
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433 MHz is no good for 1...2 km, 27 MHz will work. And it's much quieter nowadays, as the "Rubberduck" and "Pigpen" truckers use other communication methods today. And the 100+ W walkie-talkie amateurs are mostly gone.
Building such things is no big issue, but alignment and tuning needs some equipment, which fortunately today is much lower price than back then.
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If the country is that poor for this to be viable it is a sure bet they have no access to the parts needed or perhaps even a way to charge it. In the U.S. the 27Mhz part 15 walkies were 100 milliwatt maximum d.c. input to the final R.F. stage with perhaps 60 milliwatts delivered to the antenna. Part 15 rules also stated a maximum antenna length and these 9 volt battery powered units seldom could do better than 1/4 mile. As for search and rescue, Well, a bunch of hacks trying to do search and rescue usually end up needing rescued themselves. Any 'competent' S.A.R. group could surely beg, borrow or steal (as they say) enough money for some FRS or GMRS units for a serious S.A.R. activation. GPS units for the 'leader' of each group would be very useful also. I have participated in S.A.R. missions on Iceland on horseback and with state ranger patrols here in the U.S. At the end of the day, your intent is good but S.A.R. doesn't need any hand built unreliable radio gear that won't be water proof and 10G shock resistant.
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433 MHz is no good for 1...2 km
I disagree. Even the 25 Euro Silvercrest PMR446 pairs that Lidl sell every so often are good for more than that distance. https://stesbintegrationprod.blob.core.windows.net/public/articlemanual/67462728/93835_EN.pdf
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I disagree. Even the 25 Euro Silvercrest PMR446 pairs that Lidl sell every so often are good for more than that distance. https://stesbintegrationprod.blob.core.windows.net/public/articlemanual/67462728/93835_EN.pdf
Yes. If it 's LOS.
But trees or foliage of any kind or a hill will kill that.
Also, the devices you link to are 446 MHz, which is irrelevant to India, and the allowed ERP is 0.5 W, which is irrelevant to 433 MHz.
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433 MHz is no good for 1...2 km, 27 MHz will work. And it's much quieter nowadays, as the "Rubberduck" and "Pigpen" truckers use other communication methods today. And the 100+ W walkie-talkie amateurs are mostly gone.
Building such things is no big issue, but alignment and tuning needs some equipment, which fortunately today is much lower price than back then.
433MHz FRS radios easily do over 2km. I've used them on road trips a few times between multiple cars and they would reach miles loud and clear under ideal conditions. If you want 27MHz CB transcievers are still available, I don't know what other countries they're legal in though. The standard American CB radios are 5 watts IIRC.
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Thank u for great response
Few points I clarify
1) initially it will be POC many places like india and Bangladesh Or African countries China inport is costly. Will help there.. In disasters will help as it will use vv easy parts
2) will be "1st opensouce " 2way thereby helping newbies to try
3) china price can't be beaten but we can have fast repair design. Full board will be plugable.
Wars firres calamity times u can swap bad board with fresh like a gameboy cassate
4) it will ve vintagelike initially. With usb charging.
Lot tx given in utube for long range in 27mhz .
They used normal radio to catch so if my rx is as sensitive it will catch a good range
I will open source
-case making
-battey fitting
Signal tuning
-a semidigital version in second phase will be there to get different channels
Probably will avoid IFTs making simple
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I had CB radio walkie-talkies when I was a kid. Theoretically, the range is better than LOS, but you'll have the wavelength (11m) require _huge_ antennas. Small coil antennas exist but they're all rubbish, more dummy load than actual antenna. The built-in telescope antennas were of course better but too fragile to be actually usable. I don't remember how often they broke, but it was a lot. CB handhelds are completely impractical therefore. 433MHz PMR is the best compromise, really.
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To answer the OP question, here is a couple simple schematics:
https://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/27MHz_Walkie-Talkie.gif (https://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/27MHz_Walkie-Talkie.gif)
https://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/27MHz_3-BJTs_Walkie_Talkie.gif (https://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/27MHz_3-BJTs_Walkie_Talkie.gif)
The site has more versions of different degrees of complexity, as have been said already, the distance is given by the antenna and the terrain configuration, but these designs are very cheap and worth experimenting with, I have fond memories of them ^-^.
https://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Homebrew_RF_Circuit_Design_Ideas.htm (https://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Homebrew_RF_Circuit_Design_Ideas.htm)
Best of luck with your project,
DC1MC
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Do you expect to b able to design and build these units to sell at much less than 1200 Rupees?
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Thank u.. Design uses ift likes but may be useful.
I remember handheld 27mhz cb radio exist with short antenna. However 433mhz may be better option.
Planning to test by jan25 as I am in some other work till then.
Regarding selling cost:
At POC stage we must not think much.
Later we will see how to make lower.
Many situations any good walkie with scrap parts is much much needed. That is one goal.
Using bc548/bd 139 alikes I assume we can.
Thse are available all the places