Lets take a quick look at what to expect via some easy to monitor targets as single discrete frequencies:
- 1030 MHz ( ADS-B Interrogator)
- 1090 MHz (ADS-B/1090ES)
- 1176.45 MHz (GPS L5 & GLONASS L5OCM & Baidou B2a & NavIC L5)
- 1191.795 MHz (Baidou B2a/B2b)
- 1202.025 MHz (GLONASS L3OC)
- 1207.14 (GLONASS L3OCM & Baidou B2I/B2Q)
- 1227.60 (GPS L2)
- 1246 MHz (GLONASS L2)
- 1248.06 MHz (GLONASS L2OC & L2SC)
- 1268.52 MHz (Baidou B3I/B3Q/B3A)
- 1294.0 MHz (Amateur Region 3 FM Calling)
- 1294.5 MHz (Amateur Region 2 FM Calling)
- 1296.1 MHz (Amateur Region 2 CW/SSB Calling
- 1296.2 MHz (Amateur Region 1 CW/SSB Calling
- 1297.5 MHz (Amateur Region 1 FM Calling)
- 1381.05 (GPS L3)
- 1420 MHz (Hydrogen Line)
- 1544.5 MHz (COSPAT-SARSAT)
- 1561.098 MHz (Baidou B1Q)
- 1575.420 MHz (GPS L1 & GLONASS L1OCM & Baidou B1C/B1/B1A)
- 1600.995 MHz (GLONASS L1OC & L1SC)
- 1602 MHz (GLONASS L1)
- 1691.0 MHz (GOES-10 WEFAX & MeteoSat & GMS)
- 1685.7 MHz (GOES-10 GVAR PDUS & GOES-12 GVAR PDUS)
- 1694.1 MHz (GOES-16 HRIT/EMWIN & GOES-17 HRIT/EMWIN)
- 1698 MHz (NOAA-16 HRPT & NOAA-12 HRPT)
- 1702.5 MHz (NOAA-15 HRPT)
- 1707 MHz (NOAA-17 HRPT & NOAA-14 HRPT)
There is much more more beyond the above list worth looking at, but to do so, you need the right receiver and the right antenna to get started.
Your first L-Band Receiver
This is the easiest part to buy, but will get more complicated later on.
Purchasing an inexpensive software defined radio USB dongle like a genuine RTL-SDR v3 will offer the most flexibility to experiment with for L-Band monitoring. Why?
- Costs less than $40 USD
- Can be repurposed for monitoring frequencies outside of L-Band
- Can resolve signals up to and between 2.4 MHz and 3.2 MHz bandwidth
- Relatively stable accuracy across entire tuning range thanks to its 1 PPM TCXO
- Has a low power DC bias injector needed for some external amplifiers or antennae
- Easy to locate closer to antenna or computer depending on application because of its USB and SMA connectors.
Many of the signals found in L-Band are data communications versus voice modes like N-FM or SSB, so using an SDR is the best way to get started.
Your first L-Band Antennae
This is a tough thing to address since an antenna at L band frequencies will have different benefits or shortcomings depending on what you wish to monitor.
With most applications for L Band focused on directional or space based communications, a pre amplified or passive patch antenna is a good way to start out as well as to try a single plane Yagi antenna.
Currently my "favorite" antenna for a large and interesting portion of L Band is made by the same folks who make the popular RTL-SDR V3 USB device mentioned above.
While the nice suction and gripper base are included with the antenna, I found them personally a little annoying so instead for portable demonstrations, I am using this inexpensive tripod that extends up to almost 4ft tall and collapses down very small. And, it comes with some other accessories that made it an even better deal.
There are many other options for specific portions of L Band to consider especially if you are interested in ADS-B aircraft signals at 1090 MHz or the amateur radio portion of the band from 1240 to 1300 MHz but we are not going to focus on those in this article.
Your first L-Band Software
There are so many options, but here is a list of the top options worth having on hand.
General Purpose: SDRangel - This great and under appreciated software offers a lot if you are interested in L-Band monitoring. Built in mapping for ADS-B at 1090 MHz plus some helpful satellite prediction and visualization tools along with digital television options are a few examples.
Amateur DATV: SDRangel - This program is great for many reasons, but one area to use it for is decoding different analog and digital video signals. A typical DVB-S2 signal is less than 300 kHz wide and using the 23cm amateur band using a Lime SDR or HackRF is a great way to experiment along with DATVexpess to transmit with, and use SDRangel to receive.
This article is not meant to be an exhaustive how to article, but to raise awareness of L Band and for the amateur radio crowd, to see how in demand this spectrum is and to find ways to utilize the 1240 to 1300 MHz allocation in the United States before commercial services further try to purchase this spectrum.