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Anyone active user of software defined radios ?

Externet

Active Member
Hi.
- Is there any SDR dongle for USB jack with an earphone jack built-in, as to listen to a radio reception ?
- After all applications are downloaded to a laptop and the device is plugged-in and running fine, If you unplug it from the USB; apply 5V supply to the USB plug... Nothing works, right ?
- A USB SDR receiver does nothing if not connected to a computer, or does it ?
- If you set the receiving frequency to your desired/favorite; unplug it from the USB jack for one second, plug it back in. It does not start receiving again, or does it ?
 

Mickster

Well-Known Member
Most Helpful Member
The SDR USB dongles do not contain the mixers, modulators/de-modulators, filters etc.
All those are taken care of in software, hence Software Defined Radio.
So, no, the dongle will not work as a standalone device.

A couple of links for SDR which may help explain far better how it works:
Michael Ossmann's HackRF tutorial videos:

Here, Michael shows the software side of things using GNU Radio Companion.
 

Externet

Active Member
Thanks, Mick.
I would have preferred a SDR being a radio gadget that was programmed for frequency, bandwidth, demodulation mode... while connected to a laptop USB and then unplugged to work standalone. Crap!
So having to carry a compfuser to make it work and keeping it on so it does not forget parameters... no thanks :(

Could be renamed as software driven radio, not as currently.
 

Mickster

Well-Known Member
Most Helpful Member
I would have preferred a .......
So many of us would prefer a ...... to do ...... for <dev cost, but so few of us have the capability to do so, so we buy something made by someone else.
What you want is coming in the future, but likely not soon enough...:D
 

unclejed613

Well-Known Member
Most Helpful Member
- If you set the receiving frequency to your desired/favorite; unplug it from the USB jack for one second, plug it back in. It does not start receiving again, or does it ?
like a lot of usb devices, no it does not.... i hope you don't try this with other usb devices like hard drives, or thumb drives....
- After all applications are downloaded to a laptop and the device is plugged-in and running fine, If you unplug it from the USB; apply 5V supply to the USB plug... Nothing works, right ?
why would anybody do this?
- A USB SDR receiver does nothing if not connected to a computer, or does it ?
yes it must be connected to a computer to work.
a radio gadget that was programmed for frequency, bandwidth, demodulation mode... while connected to a laptop USB and then unplugged to work standalone.
there are such things...scanners, communication receivers, amateur radio transceivers, etc.... they are not as flexible or as inexpensive as an SDR radio because they are hardware radios which don't have the same ability to tune 30Mhz-2Ghz (for the cheap SDRs) or 10khz-6Ghz for the "mid-priced" SDRs. there are SDR based amateur radio transceivers, but they are expensive, mainly because a)they have transmit capability, and b) they have the cpu/memory/DSP code built in that is needed to make an SDR work. there are SDRs that will work with a phone as the "computer"... look into that if portability is your main issue.
 

Externet

Active Member
Thanks, uncle.
why would anybody do this?
Yes, I do have very good reasons to desire a portable software defined receiver in thumb size; not a software driven volatile receiver as currently are. Portability is not exactly solved with a cell phone when the receivers have to be left on mountain peaks for a year+...

Perhaps there is some small gadget named "programmable receiver" instead, that may work on a lithium cell ? Plug it in a compfuser; enter Rx parameters, take it to field, done. :oops:
 

unclejed613

Well-Known Member
Most Helpful Member
when the receivers have to be left on mountain peaks for a year+...
sounds like a very unusual application... if it's being left on a mountaintop, what is being done with the received signal?
 

unclejed613

Well-Known Member
Most Helpful Member
what modulation/mode of operation, what part of the spectrum? is there any information in the signal or is it just on/off switching?
 

Externet

Active Member
Meant to 'repeat' an action, not RF 'repeater'. VHF in, carrier only, no modulation, switching equipment on as remote turn-on. Self-timed-off :rolleyes:
On mountains and sea buoys.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Meant to 'repeat' an action, not RF 'repeater'. VHF in, carrier only, no modulation, switching equipment on as remote turn-on. Self-timed-off :rolleyes:
On mountains and sea buoys.
Carrier only, no modulation, sounds absolutely fraught with problems, particularly as any legal method is going to be busy on that frequency.

Needless to say, the answer (as always) is a micro-controller, along with a radio receiver system, of which there are numerous types offering wildly different ranges - the micro-receives the data, and checks for an identification code, and only then accepts the instruction and carries out what it's told to do. This also means you can have multiple devices in the same area.

I essentially do the same at home, where I have four PIC's with radio transceivers connected to temperature/humidity sensors. My ident codes are simply A, B, C and D. I have an ESP8266 connected to a similar radio transceiver, and this asks each remote unit in turn for it;s readings, them uploads all four via WiFi to a webpage.

Depending on what and where, you 'may' be able to use ESP's if WiFi is available?.
 

unclejed613

Well-Known Member
Most Helpful Member
one thing that is small enough physically that will run an SDR is a Raspberry Pi computer which is about the size of a pack of cigarettes.you could run a Pi and an SDR from battery power, and use solar panels to keep the battery topped off. a Pi-3 would probably be the best tradeoff between number crunching (SDRs do need to do a lot of DSP work with the data stream from the SDR), and power consumption. a pi-4 would have a lot more capability, but requires more current (the Pi-3 comes with a 2A wall wart, the Pi-4 comes with a 3A wall wart). another thing to consider is construction. your device needs to be able to withstand some really nasty weather extremes, being baked in the sun during long hot days as well as getting flash frozen in long winter nights, plus rain, snow, icing, etc...
 

Externet

Active Member
Thanks.
Am dissapointed by the need to have a live compfuser/microcontroller gadget to initialize operation on such a receiver. I have several 'digital' radio cheap receivers for 300m, 3m, shortwave, and when energized, always go to the tuning they were when turned off.

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Protection against weather is of course taken care of; power is solar as you guessed.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Thanks.
Am dissapointed by the need to have a live compfuser/microcontroller gadget to initialize operation on such a receiver. I have several 'digital' radio cheap receivers for 300m, 3m, shortwave, and when energized, always go to the tuning they were when turned off.
Why disappointed?, it's fairly obvious - you're replacing a LARGE part of the radio receiver by the computer, that's what allows the performance you get from something which costs very little (not counting the cost of the computer). The module itself is pretty 'dumb' so utterly useless without a computer.

As suggested, if that's what you require, then use a PI to drive it.
 

unclejed613

Well-Known Member
Most Helpful Member
I have several 'digital' radio cheap receivers for 300m, 3m, shortwave, and when energized, always go to the tuning they were when turned off.
those are actually analog radios with digital controls. the demodulator for FM is a hard wired circuit, same for AM or SSB, this is why a good communications receiver is expensive, you need several different circuits to demodulate the RF signal. analog radios are often constrained to narrow receive bandwidths, listening on only one frequency at a time and very limited tuning range. SDR radios can take in a whole chunk of bandwidth (one of the ones i have can sample a 20Mhz bandwidth), and if you save all the samples to a file, and play it back later, you can listen to everything that went on in that 20Mhz slice of spectrum
 

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