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I recently received MultiConnect Gateway (GW) + MTAC-LORA-H-868 but the problem is that I didn't receive any antennas. I need to setup LoRa Gateway ASAP. I'm new to LoRa and I have a few questions.

  1. Is it safe to run a GW without + MTAC a or antenna? (I mean, can I damage GW if run without antenna?)
  2. Will GW work without an antenna?
  3. Is it possible in principle to use another type of antenna (like WiFi) instead of a LoRa antenna?

I mean that for testing purpose I don't need long-range connectivity. An antenna will arrive in few weeks which is very bad for me.

  • Have you got any components to fabricate an antenna from? Any antenna designed for 868 MHz +/- 10% will be OK (if not perfect). – Sean Houlihane Oct 31 '17 at 8:28
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These are mainly very general answers that apply to all receiver/transmitters not just the LoRa gateway.

  1. As a rule you should not run transmitters with out an antenna attached (or a dummy load) as the transmit energy is effectively reflected by the open socket and can damage the equipment. You may be OK to run the gateway without the expansion card if there other things you can configure while waiting for a suitable antenna.
  2. Very unlikely since it will have no way to send or receive transmissions.
  3. No, antenna are tuned to a specific range of frequencies, (WiFi is 2.4Ghz or 5Ghz,LoRa is a number of frequencies 166Mhz-915Mhz) using the wrong antenna means it will not be able to pickup (or transmit) signals in the right frequency range.
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Formally, you should indeed have a matched antenna when operating a radio transmitter, and antenna matching is indeed frequency dependent.

That said, (permissible unlicensed) LoRa RF power levels are relatively low, and the potentially lasting issue with mismatched antennas is from the reflection of transmit power back into the transmitter. The lower the power level, the less the issue. The multitech linecards already tend to run fairly hot, as they use a linear voltage regulator to drop a fairly large difference.

But even aside from the damage concerns, you'll get horrible performance without an antenna.

Fortunately, an antenna need not be complicated. It would be a relatively simple thing to design a vertical dipole for the center frequency of the subband you are using. Take a look at ham radio sites for specifics - you basically want something similar to what would be used on the 33cm ham band, only a little longer as you are on the European LoRa frequencies which are lower in frequency.

Of course, to make such an antenna you'll need an RF connector that matches the device, and a bit of coax (you don't actually need a balun, especially for a vertical dipole). It's possible you might be able to salvage this from some other type of UHF/microwave radio antenna, but do note that wifi typically uses "reverse" SMA or TNC connectors, in contrast to traditional gear which uses the traditional form. A cheap mag-mount antenna intended for RTL-SDR use could even be decent, if placed on a cookie baking pan and with the whip length adjusted per calculations.

If using an antenna in which you have limited confidence, you might see if you could configure the gateway to operate the radio at a low power level only.

An additional (and especially "polite") option if you are doing only "across the bench" testing would be to use a connectorized 50 ohm dummy load in place of an antenna. At the frequencies involved it's critical that this be a non-inductive resistor, so preferably something sold as a dummy load for frequencies of this range or higher. Power levels (especially time averaged) will be low, so it won't need to be a large device. You could even use a high ratio attenuator - as the unterminated impedance match would be only slightly off. Of course with a dummy load, your actual radiated power and pickup will be due entirely to leakage in the shielding, so range will be very short!

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  • Even a 3dB attenuator will probably be OK as a pretend dummy load - but an antenna (on the right band) looks as cheap. – Sean Houlihane Oct 31 '17 at 8:25

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