LimeSDR as a Amateur Radio Transciever

So, i am a total noob on these things. Just got my technicians license and working on my general license.

I see a lot about using the LimeSDR for receive, especially in HF, but not so much on transmit. Is that an option? are there specific problems that need to be overcome to transmit in HF/VHF( also, i see Power Output (CW) = 10dBm but, what does that mean?)

Anyway, I am interested in creating software for this on android, learning about radio and SDR, and using it for QRP with my cellphone/tablet as the external processor.

Thanks for any answers…

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First, let’s tackle the easy questions - - The LimeSDR does support TWO channels of transmit in a full duplex configuration (meaning, the two receive inputs are not shared with the transmit and can be tuned anywhere from the transmit outputs) and their power output of +10dBm means that the output power is 10mW (0dBm = 1mW, +10dBm = 10mW, +20dBm = 100mW, +30dBm = 1W and so on…). With 10mW of power you can use the LimeSDR in its native state for such modes as WSPR (which you can use with your General License when you get it), or even PSK31. With a little transmit amplifier that can be boosted to power levels of up to 5W or more - I’m actually working on a transmit/receive amp for the LimeSDR, too, for Amateur Radio use that will have an output power of 1 - 5W in the HF region (1.8 - 29.5 MHz). Developers are working on the transmit functionality and Simon Brown’s SDRConsole V3.0 will be one of the Windows applications that can support the LimeSDR for receive and transmit. Other apps will be out there, too, but there hasn’t been much buzz on this forum about it and I’m even waiting to hear more.

Here’s where it gets tricky…The LimeSDR CAN run on USB 2.0, but to get the ‘full fidelity’ of its features you’d need to run it at USB 3.0 - - the Android USB connection is generally USB 2.0 compliant and there are a handful of newer phones that support the SuperSpeed USB 3.0 - but not very many of them. Also, the drivers that are out there (especially the SoapySDR pieces that make integrating this much easier with the LimeSDR) are suitable for PCs running Windows and Linux, but I don’t think they’re compiled or written to be compliant to an Android environment yet. If you have a stout heart, PLEASE dive in and do it…! You’ll no doubt get A LOT of interest on this (including from me) if you can make it happen.

The best place to learn anything on SDR is from three sources I know:

1.) This forum, or MyriadRF in general
3.) …and the best one —>

Just from those links (and those on their sites) you’ll learn enough about SDR to be dangerous. Especially look into the OsmoSDR website - that was the cradle of all things SDR related for the Ham and Hacker community

Let us all know if you need further info - glad to see you on the forum, and good luck in your endeavors for LimeSDR…!



Will the LimeSDR TX at HF frequencies ?

Yes in hardware this should not be a problem, but you will still need an appropriate antenna for the frequency that you wish to transmit (with a good VSWR). At the moment, as far as I’m aware, this option is not available, but software is being written right now to tune the configurable parameters within the board to transmit (and receive) at low frequencies.

What does 10dBm mean ?

10dBm is the power ratio in decibels (dB) of the measured power when referenced to one milliwatt (1 mW). Put “dBm to Watt calculator” into your search engine of choice, if Watt is a more familiar measurement of power to you.
I like
(You should probably watch Michael Ossmann excellent video to learn more about dB, dB’s are very useful. )

10dBm is 10mW, and you are probably thinking that is a bit low, but people have been able to send their callsign over 2299 km in the 20 meter band using a 10 meter center fed dipole antenna in their attic and only 15dBm of power with no external amplifier. ( ). Ok, WSPR is a special digital mode where you are only sending 50 bits which are encoded with lots of error correction and transmitted over a 2 minute timeframe :slight_smile: , but it still counts.

Almost all (general purpose) SDR hardware sold, which can TX, does so at such low power levels. This is so that they qualify as test equipment and fully comply with “FCC 15.103 Exempted devices” under section C “© A digital device used exclusively as industrial, commercial, or medical test equipment.” Otherwise, because of their extremely large frequency range, which cover bands that it is illegal to transmit on, the hardware could not be legally sold, at least not in the US and probably a good few other countries as well.

But if you are licensed radio amateur there is nothing stopping you, other than common sense, from adding amplifiers and filters to bring this up to the maximum legally allowed (1,500 Watts 61.76dBm is the peak legal output power for a fully licensed ham radio station in the US/200 Watts 53dBm Peak envelope power for Technicians in the US).

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Sorry for my late response. Life, things…

In regards to USB 2.0: Im in total agreement, I knew that initially that I would suffer from bandwidth issues, but with the LG-G5 and the HTC-10 having 3.0USB, and the new phones soon to be released before the holidays, im sure we will get some more 3.0/3.1.

The drivers… that indeed will be the toughy. But I figured it would be a fun project!

Thanks for the links and the information! It was very much appreciated!


Thanks to both of you for clearing up the 10dBm question I had.

Its funny, because I had no power reference, i didnt know that 0dBm = 1mW. Ive messed around with audio in the past, and knew that dB’s were dimensionless. I kept seeing that 10dBm number as 10dB’s and it meant nothing and was senseless. lol

But i definitely now understand how that is really useful in describing a transmitters output!


Yeah, as long as you keep 0dBm in mind (1mW) then everything from there is pretty simple to know how much gain you need to get to a desired output power. Also, in RF, you double the power output every 3dB. An example of this is if you start with 0dBm (1mW), +3dBm = 2mW. Likewise, +6dBm = 4mW, and so on… For Audio, the power doubles every 6dB.

With the LimeSDR starting out at 10mW output power (+10dBm) if you wanted to build an amplifier to get to 4W of power with a LimeSDR, it’s just a matter of determining the gain of the amplifier you need. An example of this is: Desired = 4W = +36dBm. LimeSDR = +10dBm output power. (+36dBm Desired) - (+10dBm LimeSDR Power Output) = 26dB gain required for the amplifier to operate at the desired output power of 4W. So one would find a suitable driver and final amplifier set of bipolar transistors, or MOSFETS, to obtain at least 26dB gain…and then set out to design the amplifier appropriately.

Play with it for awhile and you’ll eventually be able to do all this in your sleep, too…! :slightly_smiling:

Keep in touch and let us know how you do with the SW effort on a mobile platform,


Here are a few more newbie questions.

Let’s say I’m interested in 10 meters waves (28 MHz). According to the picture in this discussion:

… on this frequency LimeSDR gives about 16 dBm output power on TX1. Can I use LNA4ALL on output to gain a signal (21 dB according to this table)?

It means that LimeSDR will be turn into 37 dBm (or 5 W) transceiver, right?

Also could you please recommend a software that can transmit and receive ham radio signals, preferably Linux compatible?

LNA4ALL, as the name suggests, is generally a Low Noise Amplifier, meant to be used on RX side. Of course, you can also use it on TX side, but need to be aware of its maximum output power, which according to the blog post you have given will be around 21 dBm (or 125 mW in a linear scale):

Beside the LNA purpose the same component can be used as a small driver amplifier capable of delivering +21dBm of output signal thanks to high P1dB value.

So no, you cannot get 37 dBm from it.

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@afiskon - Alex,

The following link will provide an HF to UHF amp that drives at 0dBm (you may need an attenuator ahead of the amp from the LimeSDR) and provides 3.2W of power - enough to drive a significantly bigger RF PA:

73 de Marty, KN0CK


I already got myself on off these and there is one thing you need to be aware. The ground of the power supply is connected to the ground of the coax shielding so your pc and the power supply need to have the same ground or something will make you trouble. so always test the ground for offset voltage and then fist connect ground than power.


@afiskon - Alex,

Here is the PA board I have from EBay and I bought the heatsink separately (also on EBay). This PA drives at 0dBM and provides 45W of power on HF. Here’s are the links:

HF RF Power Amplifier:


73 de Marty, KN0CK


@martywittrock Thanks a lot! BTW great videos ( LimeSDR Operates with LattePanda Win10 64-Bit with SDRAngel ). I googled them just today but didn’t realize you are the author at first :slight_smile: Also I’ve played a bit with SDRAngel. It works great on Linux.

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Using the LimeSDR as a Amateur Radio transceiver is a very interesting idea. I’m loving using SDR + gqrx for listening, but feel like I’m in the stone age when using a regular radio for TX.

How is it working for you? What OS and software are you using? Do you have voice and digital modes working? What bands are you using? How hard was it to connect it all up (LimeSDR -> 45 watt linear power amplifier. Anything else needed besides a PC and antenna?

Adding 45 watts comes in stages. In the HF region,
You will see that lower HF output is low. Also, you get about 10Dbm output (10mw) that has to be upped first, filtered, then fed to an amp, filtered, TX/RX switching & bandpass filters for the receive. That is what I am doing for a project.



I haven’t laced-up my LimeSDR to a 45W amp yet, but it’s totally possible to do so since the Lime drives (for the most part) to +10dBm. In those cases when it doesn’t, ALC (amplifier leveling control) would be what I’d use to level the power to a constant +10dBm no matter where I’m tuned in the HF and V/UHF bands.

In terms of the application I’ve been running, check YouTube and look for ‘martywittrock’. There are several videos associated with the LimeSDR running with SDRAngel (the app that I use most for voice and data transceive). Earlier versions of the Lime firmware and earlier versions of SDRAngel work excellent together - - right now there’s been an issue with both the firmware and SDRAngel not playing well together, but the previous versions (one version back) worked very well on HF.

Hope this helps - let me know if you need any further info,

73 de Marty, KN0CK

My sdr is already set up for a drive of 10mW … to an output of 100w HF.
Once the lime is able to switch over and perhapse band select i might make the lime as perminent.

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OK, here’s the somewhat finalized TX chain, copper spreader (Under amp modules), heat sink, enclosure & autotuner.
Since I decided that there was no way possible to fit everything in the 2"X10"X12", so, I discarded the back shell & will be making a new one that gives me 3 1/2 - 4" of depth.

This shows a general picture of the parts (Less LPFs for VHF/UHF.
Output of LimeSDRUSB to HP programmable attenuator, to bandswitching relays.

Another general overlook.
Input to 1 SPDT SMA latching relay, then each output to another. Stage 2 relays A switches VHF/UHF, B switches HF/6M & exterior output.
From the VHF/UHF band relay, comes outputs to each Class AB module, through a directional coupler. The VU OUT latching relay in the middle will get LPFs between it & the amp modules. THen, the common will go to a mutual VHF/UHF port.
In this, you can see the third amp feed, also through a coupler for monitoring, then to the TS-440SAT PA, LPFs, (Not shown BCD board that I have to dremel apart), & the autotuner.

So, there’s the somewhat complete TX chain.
When I get the LPFs in, I will test it out. I still need to get BPFs for VHF/UHF, receive, too.

All ports of the Lime will still come out the back. THe input to the LimeSDRUSB will be KVMd to allow operation from the Udoo X86 Ultra, or, any other PC. Network, DP/HDMI, RS-232, USB3.0 & a GPIO plug for 12-15 connections.

I am sure that there will be more, along the way, but wanted to show what the plan has morphed into.



@AA7QQ - Ed,

Holy SHIZZLE…!! You’re A LOT further ahead of me on this than where I’m at…! When I get my life back in 2 months (I’m working on a renovation project that is my future QTH) I’ll be able to give you my spin on this, too, but it’s in-line with what development you have cooking there…! :slight_smile: !!

Keep on truckin’ on this one, Ed - looks GREAT to see all the pieces come together to make what we’ve all wanted to aspire to…A LimeSDR based broadband transceiver (HF, V/U/SHF).

73 de Marty, KN0CK

My best advice:
Start looking for a TS-2000 or some other “DC to daylight” rig for a donor. Newer serial MKIIGs would be good.
It will save a lot of headaches I am having, due to 3 different amp modules.
But, this is all a learning process.
At least with making a new backshell gives me the room to jam it all in. Also changing to different relays SP4T with 50 ohm terminations for unused connections. They will be on input & output.



@AA7QQ - Ed,

Well, I’ll be looking for a bottle of aspirin because that’s the way I’m doing it, too…Nothing like REALLY rolling your own on this project…! Keep at it and let us know your progress…Once I get my life back from this renovation I’m going to take the dive, too…

73 de Marty, KN0CK