LimeSDR input ESD (static) protection

Does LimeSDR have input ESD protrction against static when connecting an antenna? If so, are there any protection diodes or is this realised differently?

Also, can anyone confirm that the max input (rx) power (before damage) is really 12dBm?

I just want to be careful and not damage my future SDR with my 10W ham radio station.


All the inputs to the LimeSDR are transformer coupled from the U.FL connectors and there’s a fair amount of conditioning and decoupling post-transformer. I’m attaching a schematic that shows this. I would think it’s going to be nearly improbable that any ESD would propagate to the LM7002 to cause damage.

Hope this helps,

Marty, KN0CK

Which power amplifier are you willing to use?

I would like to use LimeSDR as the foundation of a portable radio station but struggling to find a good portable PA


There is a 50W PA that I just purchased and took delivery on from EBay that accepts 0dBm (1mW) and provides +47dBm (50W) of power output. Here is the link to that PA:

The LimeSDR outputs +10dBm (10mW) so you’ll have to attenuate the output of the LimeSDR to obtain the 0dBm input requirement to the 50W PA, but that’s easily fixed with a small SMA attenuator like this:

That’s how I’m going about getting the LimeSDR up to power. All this also considers that you have a Low Pass Filter at the output of the PA very much like the TAPR LPF that will eliminate any transmitted harmonics from going over the air because of any non-linearities of the PA to the feedline and antenna.

Also, this assumes that you’ll be running the LimeSDR in the HF band. If you’ll be running the LimeSDR in the VHF, UHF or SHF band, there are comparable RF amplifiers out there for those services that you can find reasonably cheap, too.

73 de Marty, KN0CK

Let’s say someone wanted to put some ESD protection on just in case. What would the part be called? An attenuator? A limiter? Can you recommend some parts?

Diodes are usually used for ESD protection.

I do not know what values you would need, I’ll leave that to the EEs in the forum.

Search around, and you should be able to find out how to solve the problem of what kind/type of diode to use.

You should search for “Low Capacitance ESD Protection Diodes for rf usage”

There are others, application specific, eg for usb or other devices. But searching in that way you will get the ones good for rf.

Just an example:


This is my device schematic, used like standard HF input for all SDR RX
Can be useful from 400 kHz up to 130 MHz but best performances are 1,8 to 50 MHz
diodes are 1N4148

  • optional
    Bourns 2057-07 Series Light Duty 2-Electrode Miniature Gas Discharge Tube (75 V)

Picture (early one w/o Gas Discharge Tube)

RX1 and RX2 outputs are not protected from damage in case of TX
power on any of them.

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Thanks for the 50W PA link! Please keep us posted how this HF PA plays with LimeSDR.

There is also the $15 kit of this PA if anyone is adventurous to couple two of these for 2mW IN, 100W OUT.

$15 50-W PA Kit:

$47 100-W LPF:

Here is the PA advertised output:
3.500MHz 54W
7.050MHz 56W
10.000MHz 57W
14.270MHz 55W
21.400MHz 41W
24.000MHz 37W
28.100MHz 25W
29.600MHz 20W

73, Rob KK6IOZ

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That’s actually the PA that I purchased, but they offer it with a heatsink attached and that’s the one I purchased (assembled and with a heatsink). I’ve yet to strap it to a LimeSDR because I’m waiting for transmit to come along for Single Sideband (SSB, as in USB and LSB voice…There are no apps that support that yet).

More to follow on my results as I have that - stay tuned,

73 de Marty, KN0CK

I was thinking of something inline. The key with effective searches is to have the proper terms.

This helps, I will follow this down.

Will follow those links down. How would one apply tx power to rx1 or rx2? Does that require a physical connection or is that possible in software/firmware/gateware?

typical case can be when you connect RX1 to SDR and RX2 to any other transceiver.
Press to PTT (TX on, transmit) means end of life to SDR on RX1.

Therefore sometimes when I use for example FT817 with some of my SDR, mic or CW key
are physically disconnected from FT817 unit.


Hello @hTo137, I was on another site and saw a reference to this:

That seems like what you are looking for.

Do a google search about “static bleed” choice whatever you like you dont have to buy anything most part ready available from junk box.

Seems like the right thing but maybe I do the search like @Ancer suggests for some cheap solution since I am cheap.

I might think about adding this too in between antenna and LimeSDR:

The best lightning protection is removing the antenna from the radio or the card itself that i always do when there is thunderstorm or lightning i dont trust anything else since voltage current or lightning can jump even its 1 inches apart.


Indeed. On the equipment I have permanently connected to external antennas I use N-type surge arresters. However, as with IT security, the best defence possible is to disconnect :slight_smile:


@ancer this one wants to make the disconnect automatic. Works at night or when one’s away.

@andrewback from the hackaday description it sounds like they’re in a high lightning area so seems like they want to disconnect although they mention alternatives. Disconnect is what I do with equipment plugged in.

Back to static, seems like something inline is the best way.

It really is the only way to protect against lightening, the spike itself is so short and intense that any device based protection will only blunt the worst of a nearby hit.
Direct hits are death to anything connected no matter how you protect it.
Lightening? Unplug the antennas, preferably at the mast.