L-Band: Frequencies and Equipment You Need to Know About

by Steve Bossert (K2GOG)

L-band is defined by IEEE as 1 to 2 GHz and there is a lot going on in this valuable chunk of spectrum that will be of interest to any radio hobbyist, regardless of if you are an amateur radio person or not.

In the United States, the Federal Communications Commission (FCC) visualizes the L-band like this:


For this article, we will dissect these charts into a short list of 30 discrete frequencies that are worth exploiting/exploring, but first let's look at the basic equipment you will need to monitor terrestrial or from orbit L-band communications.

Your First L-Band Receiver

A receiver for L-band is rather simple to acquire and you may already have one in your possession if you have heard of USB Software-Defined Radio (SDR) dongles.  For under $40 USD, you can purchase this multi-use 24 MHz to 1766 MHz device such as the RTL-SDR V3 which has one feature that makes exploring/exploiting L-band spectrum a little easier.

A receiver like the RTL-SDR V3 includes a feature called a 4.5-volt bias-T which allows low-current, low-voltage to be sent over the antenna port to power external preamplifiers with minimal fuss.

While a high-gain antenna can be used which would not require a preamplifier, sometimes a smaller antenna for covert monitoring is a better idea and, therefore, having the option of the bias-T built is helpful.

To turn on this function in your SDR, a simple batch file needs to be run first to turn it on to be used with some software like SDR#, whereas some more advanced programs like SDRangel include a simple button to turn this on which is rather nice.

I won't go into super deep details on other devices you can use, such as the more expensive Airspy R2 which also has a bias-T, or the transmit capable infamous HackRF, its clones, or the Lime SDR family, or ADALM-PLUTO devices.

These later mentioned devices would work great for L-band monitoring but will require an external DC power bias-T to inject power over feedline to power downstream amplifiers.

So, therefore the RTL-SDR V3 is a nice gateway into the world of L-band monitoring.

Having access to the appropriate receiver is the important thing to stress here.  Most signals will be narrow, which is fine for the 2.4 MHz bandwidth of the RTL-SDR, but other devices with wider bandwidth like the pictured Lime SDR Mini or HackRF Blue offer 10 MHz to 30 MHz of spectrum reception at one time, which may appeal to some of the astronomy-focused use cases in L-band.

You Need Three First L-Band Antennas!

If you already have an RTL-SDR V3, please take the included telescoping antenna kit it came with and please lose it fast.

These antennas will not be useful for L-band, regardless of what any marketing language says.  There are three different antennas you should consider if you really want to get the most out of your L-band monitoring activities.

The first antenna you will want is one capable of operating on our first frequency of interest of 1090 MHz, which is where you can find ADS-B based aircraft transmissions.

A simple "mag mount" antenna would be fine for your portable kit or something a bit larger like a collinear if you plan for fixed L-band monitoring.  Being able to monitor your local air traffic (civilian and military) makes for lots of interesting data to be analyzed.

Consider this antenna as your general-purpose antenna for terrestrial and aeronautical monitoring that does not need a directional focused application.

As a bonus, sub-GHz monitoring is possible for both the 978 MHz UAT aircraft tracking standard, along with many public service and ISM targets, not part of this article.

The second antenna to consider is a little more variable but would be some form of wide band directional antenna such as the PCB based log-periodic antenna designed and sold by Kent Britain (WA5VJB).  These will cover almost all the L-band and work for terrestrial and signals floating above you.

Another option to consider which you can build is the HASviolet Project antenna designed by this article's author, Steve (K2GOG).

Both offer polarized reception across a wide tuning range and pack up flat for easy storage.  Construction and technical dimensions can be found in the links at end of this article.

The third antenna you will want and may even wish to prioritize is what is called a patch antenna.

These are broad band and directional, but a little more specialized for satellite reception since this type of antenna offers what is called left- or right-hand circular polarization.  This type of antenna offers more stable reception compared to the single plane directional antennae mentioned earlier.

Some patch antennae also include a built-in filter and preamplifier which can enhance reception even further for certain frequencies.

The patch antenna pictured works from 1525 MHz to 1660 MHz as an example and is very flexible when paired with a small tripod.

Doing Stuff Now That You Have the Hardware!

Let's finally talk about what you can do now that you have some fancy equipment which will also require the use of either a Linux or Windowz computer, depending on what may interest you.

Here is a short overview of some use cases and related frequencies:

Perhaps you may find some secret spy satellite since L-band is possibly considered the most valuable spectrum available, due to how well it works in all weather compared to higher frequencies which sometimes get blocked during storms.

Ethics of L-Band

It's worth mentioning that with so many important things taking place in L-band, you need to be careful with what you do with this information once you receive it with your inexpensive monitoring system and it's why some details are not included in this article.

If what you read intrigued you, there are many details available on the Interwebs for further reading.  So, here are the frequencies you may wish to get started with:

Frequency (MHz)Description
1030.0ADS-B Interrogator
1176.45GPS L5 & GLONASS L5OCM & Baidou B2a & NavIC L5)
1191.795Baidou B2a/B2b
1202.025GLONASS L3OC
1207.14GLONASS L3OCM & Baidou B2I/B2Q
1227.60GPS L2
1246.0GLONASS L2
1248.06GLONASS L2OC & L2SC
1268.52Baidou B3I/B3Q/B3A
1294.0Amateur Region 3 FM Calling
1296.1Amateur Region 3 CW/SSB Calling
1296.2Amateur Region 1 CW/SSB Calling
1297.5Amateur Region 1 FM Calling
1381.05GPS L3
1420.0Hydrogen Line
1561.098Baidou B1Q
1575.42GPS L1 & GLONASS L1OCM & Baidou B1C/B1/B1A
1600.995GLONASS L1OC & L1SC
1602.0GLONASS L1
1691.0GOES-10 WEFAX & MeteoSat & GMS
1698.0NOAA-16 HRPT & NOAA-12 HRPT
1702.5NOAA-15 HRPT
1707.0NOAA-17 HRPT & NOAA-14 HRPT

Antenna Links

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