I am trying to increase the range of communication between two SDRs to simulate near space communication. The output power of TX is 10dBm but I would need 37dBm for near space communication. That would mean that a power amplifier would be required at the transmitter side. I am wondering if it is possible to do without the power amplifier at TX and instead increase the RX's power to receive a stronger signal by using a high gain antenna for RX? Would it be possible to amplify the signal at RX with an amplifier?

Communication is not a field that I am familiar with. Would greatly appreciate any advice given!


Thank you for the answers given by everyone, I really appreciate them!

I am planning to conduct transmission and receiving of txt file using SDRs. I have decided to utilise a ground station in my university to receive the signal from the transmitting SDR, which is controlled by Rpi. I will be using attenuation at ground station to simulate the environment of near space transmission of 30km. The actual physical distance is across a building

My transmitting set up will be Raspberry Pi 3B+, LimeSDR, LimeSDR antenna, ANT500 Telescopic antenna. I am planning to transmit at 433MHz and 2.4GHz at the same time. I will be using BPSK modulation.

My receiving set up will be a ground station, which I assume that I could adjust the gain of the antenna.

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    $\begingroup$ it's not quite clear what you mean with "simulating near space communication". What do you plan to do? And if communication is not your expertise, that sounds like a problem: How would you know whether what you're simulating is representative of what your near space communication would encounter? $\endgroup$ – Marcus Müller Oct 22 '20 at 18:26
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    $\begingroup$ Hello and welcome to ham.stackexchange.com! $\endgroup$ – rclocher3 Oct 23 '20 at 0:23
  • $\begingroup$ @MarcusMüller I am planning to conduct transmission and receiving of txt file using two SDRs. Have added the additional information in the question. $\endgroup$ – wei Oct 28 '20 at 16:25

Is it possible to do without the power amplifier at TX ... by using a high gain antenna for RX?

It is. You need another 27 dB (37-10) of antenna gain in addition to whatever you included in your existing link budget. You can split that gain between the RX and TX antennas to avoid needing a very high gain antenna at one end. High gain antennas are also highly directional. If the two ends of the link are moving with respect to each other, your real, rather than simulated, system would need to make provision for tracking the antennas. (I see you have an earlier question on high altitude balloons. Does this question also relate to them? What frequency range are you considering?)

Would it be possible to amplify the signal at RX with an amplifier?

That's trickier as receive performance is affected by background noise in addition to amplifier gain. You would benefit from reading up on receiver noise figure calculations (e.g. see W8II's answer here). A receiver pre-amp would need to have a much better noise figure than the SDR receiver if it is to benefit the overall performance. It also reduces the receiver's strong signal handling (by its gain) should that be significant. It's generally better to use higher gain antennas than a pre-amp (unless the tracking is a problem). A specific answer requires calculations but as a rough guide you'd only get another 27 dB system performance from a receiver pre-amp if the SDR receiver had a truly terrible performance.

As with most engineering design communications systems are subject to trade-offs between conflicting objectives. As you mention you are not familiar with this area if you can tell us more about the system you are trying to simulate we can provide better suggestions.


Amplification at the receiver is not equivalent to amplifying at the transmitter. This is because at the receiver, the signal is mixed with signal and noise. An amplifier can not distinguish between the two, and so an amplifier at the receiver does not improve the signal-to-noise ratio.

The only time additional amplification at the receiver improves performance is when a low noise amplifier (meaning, one that adds little internally-generated noise) is added where there was not one previously. For space communications there can be significant gains to be realized here since the RF noise background in space is extremely low, however this requires an expensive cryogenic LNA. You can read more about this at How can I calculate the effects of an LNA, antenna gain, etc. on noise performance?

What you can do is add antenna gain at either end, or transmit with more power. For that, see What is a link budget, and how do I make one?


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