Transmitter side specs

I have a few hardware questions:

  1. Can each TX port run separately, different frequency, different modulation, different power ?

  2. Can I have a continuous signal on one TX port and some other modulation on other TX port ?

  3. Is +10dBm maximum power on the TX port that can be run 24/7 ?

  4. What is the power range level I can adjust on the each TX port ?

  5. Is there a DC bias-t on any RX or TX port and specs. (voltage and max current) ?


Hi @MadMax, since you did not specify, can I just confirm that you are talking about the LimeSDR?

Hello Andrew,

sorry about that, yes, the question was related to LimeSDR.

Thanks, moved the topic to the LimeSDR category.



No, but people have used external bias T with a GPS antenna.

@zack, could you comment on 3 & 4?

Hello Andrew,

thanks for the answers.
Meantime, I download the LimeSDR diagram and LMS7002M datasheet and found some answers on my question. So the max RF output is 0dBm and taking in account the transformer and the rf switch the best case can be -1dBm. I think somebody mention +10dBm on the forum so I was confused a bit.

Hello Andrew,

I just read some facts that a bit different from your “alternative facts” regarding my questions #1 & #2.
The answers on questions 1 and 2 should be YES WITHIN THE BANDWIDTH and not just yes.
Digging deeper through the LMS7002M datasheet we can see just two separate PLL, one for the RX and the other for the TX part. This is a 2x2 MIMO device but within the bandwidth of 61.44 Mhz.

That means that I can not use the LimeSDR, let say for the simultaneous transmission on 150 MHz and 450 MHz if I want to build the satellite that is transmitting on two bands. The maximum gap can be not more than 61.44 MHz.
Same for the reception.

I do not blame you as you said that your technical background is not so profound, and mainly the RF designers should point that out in my questions.

This may be useful information for the others planning to do something similar I plan to do.

Is that 61.44MHz also common between RX and TX ?

background info (From page 5 and 6 of the LimeSDR v1.4 schematic)
TX1_1 and TX2_1 optimal performance 30 MHz <-> 1.9 GHz
TX1_2 and TX2_2 optimal performance 2 GHz <-> 2.6 GHz
RX1_L and RX2_L optimal performance 700 MHz <-> 900 MHz
RX1_H and RX2_H optimal performance 2 GHz <-> 2.6 GHz
RX1_W and RX2_W optimal performance 700 MHz <-> 2.6 GHz

To simplify my question I will just assume that the antennas are connected to ports that support 2.4 GHz and call them RX1, RX2, TX1 and TX2.

So what I’m asking is if TX1 is tuned to say 2450 MHz, then TX2 must be within 61.44MHz of 2450 MHz ?

And is the same concurrently true for the two RX channels RX1 and RX2 ? That they must also be within the same 61.44MHz of 2450 MHz ?

And I’m not asking about the LMS7002M chip, I’m asking specifically about the LimeSDR. Because just because the chip can do something does not mean that it is allowed to with the default hardware configuration shipped within the LimeSDR.


Yes, you got it right.
If one of the TX is tuned to 2450 MHz the other should be within 61.44 Mhz, same for the RX if the one is tuned to 1545 MHz the other should be within the 61.44 Mhz.

The gap from the TX and RX may be anything within the declared range 0.1. - 3800 Mhz

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MadMax : since one of my planned uses is for satellites also, I felt I had to comment on your comment. If you wanted to use the LimeSDR to work a satellite with either a V/U or a U/V transponder, you would be simultaneously transmitting on 145 and receiving on 435, or transmitting on 435 and receiving on 145 MHz. Either of those would be possible with the LimeSDR, given the independence of receive and transmit frequencies.

Why would you want to be transmitting on both 145 and 435 MHz at the same time to work a satellite? I understand the rationale of sometimes transmitting on 145 and at other times transmitting on 435, but not both at once.

73 de W0JT/5


maybe I just have a wider perspective and more ideas where such device can be used. One of the idea is transmitting on two bands at the same time. I understand your basic idea using the standard V/U transponder, but we do have already such posibilites.
You probably heard about phonesat. Well one of idea is to have a LimeSAT where some data will be transmitted on one band and the other data or traffic on the other band. Another idea is to make the same on the HAB (baloon) one band using to transmit voice and the other video or telemetry, data, position.

There is another “why” I asked for the two independent TX channels but I will publish that when I test the add-on gadget that I have the parts and prototype design on my desk at the moment.