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Thinking about increasing the amount of information one receives beyond that from one's own 1090 MHz ADS-B in receiver when following aircraft as a hobby, is it perceivable and possible to operate a low power primary radar? What limits exist on emitting power and what must one be aware of?

In general, it would be interesting to know about this from the technical and legal feasibility perspectives of EU countries such as Germany and France or others like Switzerland.

In this paper, the concept of using a smaller primary radar while airborne is explored without mentioning the regulations/legal requirements to do so.

Martin
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    Welcome to Aviation.SE! Are you asking about technical feasibility or legality? If legality, please add which country you are asking about? – Bianfable Sep 14 '21 at 09:53
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    Many people operate primary radar-like devices, they are found commonly on small pleasure boats. However I'm not sure what information radar will give you over ADSB, many airports are ditching primary radar for secondary systems... – Ron Beyer Sep 14 '21 at 10:49
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    Government-operated PSRs operate in the 1.4GHz and 2.7-2.9GHz ranges,which have been set aside for aviation use by the FCC and international bodies. You will have to get licensing approval for your device to operate it in those bands, or use an unlicensed/general-purpose band like 2.4GHz (which will cause problems with your WiFi setup!). 1090 and 978 ADS-B receivers do not have this problem because they are RX-only, snooping on information the planes are broadcasting already. – randomhead Sep 14 '21 at 12:34
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    @randomhead No way you can legally use the ISM ("WiFi") bands for radar. Any public use of those bands is limited to low power transmission which is incompatible with the entire idea of a primary radar. A radar needs a powerful transmitter and a super-sensitive receiver, because just a minuscule fraction of the transmitted power gets reflected back. Good luck picking up that faint echo in a horribly noisy band. – TooTea Sep 14 '21 at 12:48
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    @TooTea I did say it would cause problems... and I would also say "Good luck getting the regulatory body to approve your home-built device that probably interferes with existing radars because it uses the same band." The point I was making is that frequency bands are a limited resource and the answer to OP's question is likely "no, it is not permissible." – randomhead Sep 14 '21 at 13:08
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    @mins, I'm not sure how that is helpful to OP. Obviously devices using those bands must be properly licensed and certified, as I said, whether they are land-based or airborne. – randomhead Sep 14 '21 at 13:39
  • And @TooTea, you are incorrect about "public use of those bands being limited to low-power transmission" (at least in the US). 14 CFR 18.305(a): "ISM equipment operating on a frequency specified in § 18.301 is permitted unlimited radiated energy in the band specified for that frequency." – randomhead Sep 14 '21 at 13:45
  • @randomhead I was thinking more about WLAN and less about microwave ovens. I don't have the slightest clue how the US regulations tell those apart, but there are radiated power limits for WLAN in 47 CFR 15.247. – TooTea Sep 14 '21 at 14:17
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    This is a radio regulatory question rather than aviation. If this question gets closed as off-topic you may try https://ham.stackexchange.com/ - don't post on both at once as it's considered impolite, but if this question is declared as "not aviation-related" then you may ask there. – user253751 Sep 14 '21 at 14:46

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In most countries, including the US and in Europe, it is illegal to operate any self-built RF transmitter without a license. That includes the ISM band. ISM transmitters are exempt from the need for an operating license, but building transmitters for this free band is still restricted. The builder or manufacturer needs to certify that the device indeed respects ISM specifications.

Someone with a Radio Amateur license may build and operate RF transmitters under certain restrictions. The Radio Amateur license might cover radar experiments at least in some countries, see this question on StackExchange for Amateur Radio: https://ham.stackexchange.com/questions/14650/can-i-use-a-amateur-license-to-experiment-with-radar.

Universities and companies that do research on or development of radar, and need to test radar equipment in the field, require some sort of license for their organization.

In any case, your question seems to be about operating existing radar units, rather than building one yourself. The situation should be somewhat similar for aviation and marine radar. If you buy a (legal) aviation (or marine) radar unit, this device will be certified, and allowed to be operated by a certified user. That user will require a pilot license (for planes, or radio license for boats). The device certification only covers operation in the intended environment, that is built into the plane (or the boat), but does not cover land based operation, away from the plane (or boat). You may find discussions about that in the internet (like https://www.reddit.com/r/amateurradio/comments/7zu3x5/does_anyone_have_experience_operating_a_marine/).

bogl
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