Cheap, low-power autonomous rig. Thoughts?

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BlackBeard
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Cheap, low-power autonomous rig. Thoughts?

Post by BlackBeard » Tue Jun 12, 2018 6:22 pm

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
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Re: Cheap, low-power autonomous rig. Thoughts?

Post by SD-E1102 » Tue Jun 12, 2018 6:34 pm

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.
Pirate Radio's not a problem, it's a solution

nrgkits.nz
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Re: Cheap, low-power autonomous rig. Thoughts?

Post by nrgkits.nz » Wed Jun 13, 2018 1:19 am

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.

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Maximus
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Re: Cheap, low-power autonomous rig. Thoughts?

Post by Maximus » Thu Jun 14, 2018 9:51 am

Doesn’t look much like a bomb!?

Albert H
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Re: Cheap, low-power autonomous rig. Thoughts?

Post by Albert H » Thu Jun 28, 2018 12:14 am

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.
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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radionortheast
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Re: Cheap, low-power autonomous rig. Thoughts?

Post by radionortheast » Mon Jul 02, 2018 7:20 pm

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
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Re: Cheap, low-power autonomous rig. Thoughts?

Post by Albert H » Sat Jul 07, 2018 1:19 am

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.
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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Re: Cheap, low-power autonomous rig. Thoughts?

Post by radium98 » Sun Jul 08, 2018 10:22 am

He seems brillant as you my freind.

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Re: Cheap, low-power autonomous rig. Thoughts?

Post by Albert H » Sun Jul 08, 2018 1:50 pm

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!
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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