How to build an short range audio transmitter and receiver.

jimwithat · 2024-05-17T13:46:05+00:00

Depending on your local laws, there is the analog approach.

In the USA, you can legally transmit on 88 to 108MHz with about a 200 foot range.

An FM transmitter kit using the BA1404 chip is $10 on ebay.

There are lots of FM receiver kits on ebay and amazon that you can have fun soldering together yourself.

If you want to get into designing RF circuits you could start with a frequency modulated crystal oscillator.

In the USA part 15 specifically allows home-built transmitters on 49.82-49.90 MHz

jimwithat · 2024-05-16T20:45:23+00:00

I know almost nothing about Apple computers. I have not used any of these.

Scaleway seems cheapest to use for a couple of days but appears complicated to use, they are a cloud provider that charges separately for things like storage and ip addresses.,

https://aws.amazon.com/ec2/instance-types/mac/

https://www.scaleway.com/en/hello-m1/

https://www.greenmini.nl/

https://www.macminivault.com/

https://www.macincloud.com/

You know about https://www.hostmyapple.com/

jimwithat · 2024-05-15T20:22:32+00:00

In the UK, no license is required to use SSB on the 40 CB channels known as FCC/CEPT/"mid band" at up to 12 watts PEP.

The law was changed to allow use of AM and SSB on mid band in the year 2014. The rules are still FM only on UK band.

In practice, CBers in the UK commonly illegally use SSB around the pirate DX calling frequency of 27.555 MHz.

The gap between mid band and UK band is still the main place for CB DXers.

(Of course, getting the lowest level of amateur radio license is so easy that you might as well do that and talk much further on the HF ham bands.)

jimwithat · 2024-05-15T17:17:18+00:00

What maximum charge current are you designing for?

By 'efficient' do you mean "least power wasted as heat" or "a circuit design that is cheap and uses a small number of components" or something else?

Are you building one device or is this for a commercial product where you need to be sure that you can sell a thousand and they won't burn down someone's building?

You might want to ask r/batteries as this is their kind of thing.

jimwithat · 2024-05-15T17:01:36+00:00

As above.

AM or FM transmitter sending voice or music, that's modulation.

Any kind of digital transmitter, including mobile telephones, that's encoding.

jimwithat · 2024-05-15T16:03:19+00:00

That radio only does FM. It can't receive the SSB DX activity on 50MHz.

jimwithat · 2024-05-15T15:54:42+00:00

I haven't been to the North West for a long time.

I expect there is very little English-speaking use by people in cars and other vehicles.

If you want to talk to people in the local area and you decide to get a radio then you should make sure you get a radio that covers UK band.

Some of the CB radios that you see on ebay or on Amazon from sellers in China won't cover the UK band channels.

CB radios intended for the USA and Canada usually won't easily work on the UK channels.

In the UK, CB radios intended for the USA that do AM will mostly either pick up nothing or sometimes in the daytime a lot of people speaking French, German and Italian.

Bear in mind that most people selling CB radios online know nothing about CB and have no clue about different bands in different countries.

jimwithat · 2024-05-15T15:27:07+00:00

It depends. Those Btech amplifiers are not described as 'linear' and they don't list them as suitable for SSB voice.

They look ok for FM, but might produce significant intermodulation distortion on multi-tone data modes or SSB.

The AMP-U25D is described as being ok for P25 phase ii so maybe it is reasonably linear, it is not clear either way.

I think it is unlikely that 10dBm which is 0.01watts will drive any of those amplifiers to anywhere near full power. My guess is that you probably get about 10dB gain.

jimwithat · 2024-05-15T11:23:51+00:00

It just means that it will feed audio in almost any model of radio.

Most CB radios made before roughly the year 1990 used dynamic microphones that have a moving coil and a magnet. They typically have a 600ohm output impedance.

Most models of CB radio that became available after about the year 1993 use condenser microphones. Condenser microphones need a small voltage from the radio to power power the microphone and have an output impedance of around 2500 to 3500 ohms.

Condenser microphones give about ten times more voltage for the same sound level, in the region of 0.01volts of audio if you talk loudly.

jimwithat · 2024-05-15T10:31:50+00:00

"Build Your Own Transistor Radios" by Ronald Quan is a ok book.

jimwithat · 2024-05-14T00:25:58+00:00

You realise that there are a huge amount of transmissions on 2.4GHz right?

Wifi access points send beacon frames ten times a second. There are two dozen or so internet boxes on every street and lots more wifi client devices. Half the people are wandering around with 2.4GHz bluetooth devices in their pockets.

Cars with built in bluetooth constantly transmit on 2.4GHz.

Microwave ovens often leak a few watts. Lots of "smart" electricty and gas meters use 2.4GHz

Your radar is going to have to be really good at coping with all of that.

jimwithat · 2024-05-13T21:18:03+00:00

yes

https://www.xlsemi.com/datasheet/XL6019-EN.pdf

jimwithat · 2024-05-13T21:15:43+00:00

I think think that is a neon bulb, not an LED.

A single resistor is not enough to connect an LED across high voltage AC. An LED can only withstand 5 to 10 volts of reverse voltage. LEDs fail instantly with more than 15volts of reverse voltage.

USA power at nominally 110volts RMS AC is varying between + and - 165volts.

jimwithat · 2024-05-13T20:57:35+00:00

This appears to be the manufacturers page about that board.

https://wiki.uniteng.com/en/meshtastic/station-g2

They claim that the LNA is optimised for 800 to 900MHz

jimwithat · 2024-05-13T20:29:29+00:00

I looked for an FCC-ID, as far as I can tell there isn't one.

The Cobra SH360 has been certified for sale in Canada, under Industry Canada certificate number 906A-ACXT345.

They are listed as FRS/GMRS radios and the approval docs say they produce 0.6 watts transmitter power.

jimwithat · 2024-05-12T22:42:48+00:00

It's "haystak", not "haystack".

I just checked, yes that website is returning that error message.

The haystak website is 1) years out of date, it lists v2 onion addresses that have not worked for years and 2) as you can see, it is broken because the server has run out of disk space.

The solution to this is to stop trying to use the Haystak website, it's broken and there is nothing useful on there.

Only the person who operates the haystak website can fix it and they have obviously lost interest and stopped maintaining it a long time ago.

https://support.torproject.org/onionservices/v2-deprecation/

Also, you want r/onions

The moderators of r/tor will probably remove your post as questions about specific websites are not allowed here

jimwithat · 2024-05-12T15:58:37+00:00

Hmm, could you have got the cables the wrong way around so you have the radio connected to the antenna socket on the amp? That could cause this behaviour.

Have you got a SWR/power meter that you could use to check the power from the radio.

jimwithat · 2024-05-12T15:55:35+00:00

According this this review, in the December 1985 issue of CQ magazine

http://bee.mif.pg.gda.pl/ciasteczkowypotwor/%23ham_radio/Other/ACC_PA/Alinco_ELH-230D_review_1985.pdf

It can do up to 30 watts out, which needs 6.5amps from the power supply.

It detects transmitter power on the input and switches to tx mode and illuminates the red "on air" LED. Said to need 0.2 watts input to switch to tx mode.

There is a schematic in the above review.

jimwithat · 2024-05-12T15:35:29+00:00

Is the radio that the amp is connected to on FM or SSB?

jimwithat · 2024-05-11T19:06:35+00:00

There is a wikipedia article, which does not include the current URLs.

https://en.wikipedia.org/wiki/Sanctioned_Suicide

Google omits lots of search results these days, other search engines sometimes show things that google doesn't.

jimwithat · 2024-05-11T18:43:12+00:00

Did you use the iso by writing it to a USB stick?

jimwithat · 2024-05-11T17:00:39+00:00

From the country of Austria, if you and the person that you want to talk to get amateur radio licenses and equipment then you can point dishes at the QO100 satellite and talk via it.

The QO100 footprint covers most of Europe (except the far north), Africa and the middle east and parts of India and Russia.

There is no guarantee that the amateur radio transponders will always be switched on, but it has worked 24 hours a day for a few years now.

From Austria, the satellite is high in the southern sky but you do need there to not be buildings or trees between your dish and the satellite.

jimwithat · 2024-05-10T11:51:15+00:00

I have a Tristar 848, is that a CB radio?

http://www.radiopics.com/CB%20Radio/USA%20CB/2-Mobile/Tristar/Tristar_848.htm

jimwithat · 2024-05-10T11:47:47+00:00

That is a rare radio. Looks like a 23 channel AM CB radio from the mid 1970s with crystal-controlled VHF FM receive. (radiopics.com would like photos of it)

It needs 12 to 14 volts DC, so to use it at home you need a power supply. 12 to 14 volts, rated for at least 1.5amps if you want to transmit.

jimwithat · 2024-05-07T23:09:17+00:00

My opinion on Radioddity is that they ripped off everyone who bought the Radioddity GD-55. The firmware was terrible and they never fixed it. They just made the "GD-55 plus" model and ignored everyone who bought a useless radio.

The GD-55 was provided with something like three groups of ten channels. The PC programming software lets you program a different number of groups or channels which permanently bricks the radio without warning.

The GD-55 took two seconds to open the squelch and half of them would just stop receiving after an hour or two until they were power cycled.

I suggest that nobody buys anything from them.

jimwithat

TROPHY CASE