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The feed line is a limiting factor when designing a home HAM system. The further the antenna is placed from the transceiver, the greater the cost and attenuation. Is there a way to solve this with an SDR? If the DAC/ADC occurs close to the antenna, maybe the rest of the process could happen anywhere on the LAN. SDR over LAN idea

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    $\begingroup$ A Raspberry Pi next to the SDR with rtl_tcp sounds like what you want. $\endgroup$ Commented Apr 3, 2022 at 23:40

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You can do this currently with any network connected SDR that is capable of streaming raw or IQ samples, and run an SDR application remotely from anywhere there is a network connection, over LAN, WiFi, WAN, optical fiber, etc.

For receive-only, one can plug one of many makes of USB SDR receivers (RTL-SDR, Airspy, SDRPlay, Lime, Colabri, SunSDR, etc.) into a Raspberry Pi (or other small server), and stream IQ data over ethernet or WiFi from the Pi to something that can run an SDR app (PC, tablet, iPhone, etc.) See: rtl_tcp, hfp_tcp, rsp_tcp, et.al.

There appear to be network connected raw ADC's as well, but the full RF bandwidth at the ADC sample rate requires more expensive networks connectivity (optical, etc.), So most of the more affordable SDR receivers decimate to IQ data at a lower sample rate, either for network streaming over consumer-grade LAN, or for transferring data over USB-A, thus requiring a USB to ethernet converter (Raspberry Pi, Beaglebone, et.al.) to pass the data to a network.

Several digital transceivers can stream IQ data bidirectionally over an included network port, including older models of Apache Labs Anan's, OpenHPSDR Hermes, Hermes Lite 2, Red Pitaya, Afedri, Ettus, et.al. The rest of the SDR radio functionality (DSP, user interface GUI, or knobs and buttons, speaker and mic) can happen on some other box (or boxes, or tablets, or iPhones) anywhere there is fast enough network connectivity (not just LAN, but WAN).

Some receivers are small enough that, with a Raspberry Pi Zero W and small battery, one can place them right at (within a few centimeters) the feed point of the antenna, completely eliminating any feedline. Or with a Pi WSPR hat, you could transmit as well. Using WiFi or BLE for control point access.

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Certainly it's possible, and hotpaw2 points out that there is hardware available (besides the options listed there, FlexRadio is also well known for making transceivers that would be suitable).

Some things to consider:

  1. You will need an enclosure / telecom cabinet / small shed to house the radio and keep it safe from moisture, dust, extremes of temperature, and animals.

  2. You will need to get power to the radio, and you might want a means to remotely turn the power supply on / off.

  3. A long copper Ethernet run can act as an antenna that brings noise to the radio. You might want to look into ways to mitigate that, including shielded cat6 (with the shield grounded appropriately), chokes, isolators, fiber optic, or point-to-point wireless.

  4. Consult your electrical code to find out whether you will have to ground the coax and/or power feeds to your radio box / shed, and bond that ground to your existing service ground.

Usually the bands where people have antennas furthest from the shack are HF, where the coax attenuation really isn't that bad, and it's cheaper and simpler to buy a few hundred feet of really good hardline than to do all of the stuff I outlined above. But if you have a really big property, or really particular interests (microwave EME, perhaps?) then it's certainly an option.

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