Today was spent tinkering with the FM transmitter. I swapped out my initial 150cm half wave wire antenna for a 165cm solid core half wave, fashioned a crude battery pack from two D cells some wire and duct tape. After modifying the battery pack I moved the transmitter to the loft and went and did a little range check. The modifications possibly boosted the signal by 20-30 meters. In total line of sight I think roughly 200 / 250 meters reach which isn’t too shabby. FM needs a lot more power to extend range and I think the circuits good to 12v and is currently running at around 3v will do a little more reading before I start experimenting with different power supplies and voltages, also want to check the data sheet for the transistors.
What is SDR?
S.D.R. stands for Software Defined Radio.
SDR is a combination of hardware and software used to scan/monitor/demodulate/transmit electromagnetic radio signals.
Signals can be used to transmit voice or data.
The most common methods of transmission are FM and AM.
FM = Frequency modulation
AM = Amplitude modulation
FM, modulates the frequency of the carrier wave to transmit a signal.
AM, modulates the amplitude of the carrier wave to transmit a signal.
Both can be used to transmit analogue or digital data.
You will need …
PC / laptop – Laptop preferably for portability, currently running on an i5 2.4ghz 8gb ram pretty smoothly, I did try this on an older atom processor on linux using gqrx but latency was an issue.
SDR dongle – RTL2832U – If you want to follow along with the next few videos grab an RTL dongle you can always decided if you like the hobby enough to invest in more expensive equipment at a later date.
Antenna – You can use the one provided but its not recommended for the next few videos ill be using a cheap airband antenna I bought from ebay.
Realtek DVB-T+DAB+FM Dongle
RTL2832U – Notes: The dongle was never intended to be used for SDR but two researchers discovered the chip used was able to cover a wide range of frequencies (24 mhz – 1766 mhz) and decided to rewrite the drivers. (Antii Palosaari and Eric Fry of Osmocom) Since then the dongle has proved hugely successful with amateur radio enthusiasts.
So what can you do with SDR?
Voice, ADSB, ACARS, digital voice, AIS, POCSAG, FLEX, consumer devices, weather ballon data, HAM internet, DVB-T, GSM, GPS, spectrum analysis, weather satellites, ISS, radio astronomy, meteor scatter, FM/AM radio, RDS, DAB, RNG … probably much more!
Over the last few years lots of researchers and developers have started producing applications and code for the RTLSDR and hopefully many more projects to come as the community grows.
Keep tuned for more SDR fun stuff!
If you get bored in the meantime try googling some of the stuff I’ve listed above and start your own research / project / experiment / learning / hack / etc.