Cheap, low-power autonomous rig. Thoughts?

[BlackBeard]

Some months ago I discovered this project on YouTube: (pirate radio throwie).
The idea was quite nice: Using the Raspberry Pi Zero (10€ here) and a power bank to broadcast a low-power signal including RDS + Stereo. Major problem: The absolutely bad signal quality (sprogs etc.).

Nevertheless I was curious if it would be possible to basically do the same thing with a better and stronger signal. This would be a self-made "pocket FM" if you remember that project (http://www.pocket-fm.com/). I would pre-record the broadcasts and just play them back.

Components:
Transmitter: https://dutchrfshop.nl/en/diy-kits-pcb- ... -watt.html => one of the dutch ones

Power supply: A solar-powered power bank with 24000mAh. Generates 1w per hour (5V 200mAh). But this won't be enough to feed the transmitter probably. Costs 35€. Additionally some kind of power adatper for the transmitter would be necessary.

Audio signal + MPX generator: Raspberry PI zero (10€)

Antenna: Something small and portable. Didn't think about this yet.

I'd then just deploy that package on a high tower here and let it there until the power bank would be empty

Any thoughts?

[SD-E1102]

Whilst you might still get sprogs you could get one to those 1w or 5w rigs fron China. Some of them come with rubber duck style antennas. With power I would stick with permanent power if possible.

[nrgkits.nz]

It's using digital synthesis, hence the rubbish it generates - don't amplify it. Albert has posted some really good schematics on here over time, use one of those and you'll have a clean output.

[Maximus]

Doesn’t look much like a bomb!?

[Albert H]

A friend of mine is using cheap, simple, frequency -agile autonomous rigs for a project that's going to tour the UK over the summer. They're all 12V powered and run around 20 Watts in stereo with RDS. Programmes will be pre-recorded and played from USB memory sticks or SD memory cards. The aerials are designed for concealment and are flagpoles or designed to be put up trees.

The designs are simple, and we plan to make the PCBs cheaply available through one of the Far East PCB makers. All the components will be cheaply available, and construction will be easy. It's a "no-tune" design and will work first time of you can correctly identify the parts and solder neatly. If carefully constructed and housed correctly, the specifications are excellent.

[radionortheast]

I once thought of doing this, would be interesting to string a transmitter up in some woods and try to tune to in back at home, theres nothing to listen to, align radios too, going beyond flea power would be hard thought, guess its interesting to think about thought, i'm seen a video on youtube of someone who had a transmitter which auto played music from a card, think people said the transmitter was rubish.

Also a guy in sweden or some where years ago went up in the mountains had a little transmitter on a timer he would listen to on his boat..the other thing to think about is finding some where with line of sight, there are 2 wooded areas within a mile here

[Albert H]

Back in the 1970s, tree sites were quite often used! RFL had an "H" aerial pointing into London from the forest near to Keston Mark. You had to use a car battery (or two) for power.

A friend of mine operates at weekends from woods near his town, using a big, ex-burglar alarm battery that supplies enough power for the 40 hours he does each week. Pre-recorded programmes come from a USB stick, and he has a cheap Chinese USB mp3 player built into his rigs. He uses 4-element vertical Yagis to give the shaped coverage he wants, and the antenna gain is useful too. He covers the town of ¾m people in stereo with a good signal.

[radium98]

He seems brillant as you my freind.

[Albert H]

I showed him how to do it! His first couple of rigs were the RDVV kits from Holland, running about 8 Watts. He then asked for my help to redesign the board a bit to allow for a more powerful FET output (instead of the original 2SC1971). The board was re-worked to allow the use of the Motorola 145170 PLL IC with a little 8-pin PIC that loaded the data into the PLL chip at power-on. His latest boards are mostly surface-mounted parts, and he's changed the PLL chip he uses again (due to availability issues).

It's a neat, single-board rig that gives around 25 Watts from a fully charged battery, dropping to about 22 Watts when the battery is almost flat. The board includes a stereo coder (switching type), audio lowpass filtering, and a basic level limiter to handle the sometimes over-enthusiastic levels of some of his programme-makers! The unusual bit is that he includes battery voltage monitoring to turn off the rig if the voltage gets too low!

[Ignite]

A friend of mine is using cheap, simple, frequency -agile autonomous rigs for a project that's going to tour the UK over the summer. They're all 12V powered and run around 20 Watts in stereo with RDS. Programmes will be pre-recorded and played from USB memory sticks or SD memory cards. The aerials are designed for concealment and are flagpoles or designed to be put up trees.

The designs are simple, and we plan to make the PCBs cheaply available through one of the Far East PCB makers. All the components will be cheaply available, and construction will be easy. It's a "no-tune" design and will work first time of you can correctly identify the parts and solder neatly. If carefully constructed and housed correctly, the specifications are excellent.

Albert, did this project ever happen? If so, where can we get the PCBs from?

Thanks
Ignite

[Polecat]

[/quote]

Albert, did this project ever happen? If so, where can we get the PCBs from?

Thanks
Ignite[/quote]

+1
Fascinating thread. Thanks for bringing it to my attention @ignite

Sent from my SM-A202F using Tapatalk

[Santiago]

ive been pondering doing this again almost 3 years now, I've been collecting a few low power bits for when the time is right.
done it before 15+years ago using a nrg board and car battery ontop of a small block of flats on a hill, we got a good 5/6 miles which covered our small town and.just done the weekends.
since then we've had Kik, fresh, love, impact fm grace the the local towers, with that comes the dozens of self proclaimed "engineers" that were shown how to set up over the years who now, still unemployed are just waiting for something to steal...

[NTRRadio]

I have been experimenting with this method on and off over the past couple of years. I built a low power RDVV connected to a shitty old mobile providing the stream with some sound processing tools installed on it. It was only pushing about 5watts and was all enclosed in a weather proof box and attached to a solar cell and 17amp hour battery. The antenna was a home brue, hidden in a tree. I also had a GPS switch connected to it so it could be switched on and off from a text message remotely. Although low power, it was placed on high ground and the coverage was OK over distance, but would of benefitted from a bit more power to truly cover the area intended. Problem is being topped up with solar too much power drain means that more power means bigger panels which means harder to hide the equipment. Mine got found by a farmer, but the theory worked.

[Polecat]

@Santiago @NTRRadio Thanks for keeping this thread alive. You both mentioned that autonomous rigs can still be found. And taken.

This brings to mind another thread: viewtopic.php?f=6&t=2125&p=26052&hilit=random#p23412 The op suggested putting together a network of low power rigs, transmitting randomly from different locations. It's a similar concept but with the idea that random 1hr transmissions would be difficult to track down.

The focus of that thread is evading the attention of Ofcom. But what about rig thieves? How long does it take to track down the precise location of a signal? I mean from the point where you hear the signal to the point where you turn up at the site. let's say you're 5 miles away from the antenna and have the right equipment.

[NTRRadio]

Problem is FM is really easy to track down, so you have to be prepared to lose the gear to not only ofcom, rig thieves, or just to someone who spots it. My idea was to built the kit as cheap and easy as possible, so if it gets found then you're not hugely out of pocket, one of reasons I went down the RDVV route as you can knock them together pretty cheaply and they give you a nice clean signal over them Chinese cheap sproggers. I did also have the idea of knocking up a few of them, hidden around, but having them all on at once low power to create a network. However I've heard you can get phasing issues if not done right. When the weather gets better, I will start experimenting again. My goal is to produce something cheap enough to lose, but will do the job and a way to get discrete solar to keep it charged for day a whole weekend.

[Polecat]

I get it. Seems a few people have similar thoughts about this. Please uodate with progress.

Did you see a 2w rig on Ebay for about £20? I spotted it earlier. It wasn't Chinese and didn't seem to be chip based but now I can't find it again. Doh.

[teckniqs]

I get it. Seems a few people have similar thoughts about this. Please uodate with progress.

Did you see a 2w rig on Ebay for about £20? I spotted it earlier. It wasn't Chinese and didn't seem to be chip based but now I can't find it again. Doh.

I just did a quick search and this awful thing came up if this is what you mean? I would stay well clear, looks like that thing from the 1980s which used 2x 2n3553 for the oscillator stage and it says the final output is a 2n3866 so it will probably be more like 700 to 800mW than 2w.

https://www.ebay.co.uk/itm//123901184963

[Polecat]

That's the one teckniqs. Good insight thanks.

[Liamashley]

ive been pondering doing this again almost 3 years now, I've been collecting a few low power bits for when the time is right.
done it before 15+years ago using a nrg board and car battery ontop of a small block of flats on a hill, we got a good 5/6 miles which covered our small town and.just done the weekends.
since then we've had Kik, fresh, love, impact fm grace the the local towers, with that comes the dozens of self proclaimed "engineers" that were shown how to set up over the years who now, still unemployed are just waiting for something to steal...

. Used to DJ on impact DJ Legacy UKG!

[Santiago]

yo mr legacy