What frequencys beetween 315 MHz and 434 MHz can I transmitt at safly? - Page 1
Forum section: electronics / rf-microwave

author: rainbain
author_rank: Contributor
timestamp: January 15, 2021, 11:02:55 pm
content: Hi, I am super new to making radio transmitters and receivers and wanted to use the SI4467 to transmit some data between two micro controllers at a frequency between 315 MHz and 434 MHz. I live in the U.S. and wanted to make sure I would not interfere with peoples stuff or get the FCC at my front door. Mainly, what frequency would be the best to experiment with and what is the max power and range I can broadcast at and for what period of time. It should hopefully have an output power of 13 dBm so advice as to what antenna I should use would be awesome. I know my wording is probably super confusing and all over the place but any help or further reading would be amazing. I heard that 315 MHz could interfere with key fobs and garage doors so I was a bit scared tho I am probably over reacting. I also live across the water from an Air Force base so I want to make sure my journey into making a transmitter does not get me in huge trouble.

author: bob91343
author_rank: Super Contributor
timestamp: January 15, 2021, 11:27:36 pm
content: You need to read the FCC document regarding frequency allocations to determine what is allowable. +13 dBm may be too much signal, since most unlicensed operations have very low limits. Further, the unlicensed operation is very limited and I have no idea whether there is a frequency in your desired range that is allowed.Log on the FCC.gov or whatever the website is to find the document. Or just Google unlicensed transmitter or something like that.

author: LaserSteve
author_rank: Super Contributor
timestamp: January 16, 2021, 12:45:19 am
content: If your near AFBs in Florida or California, steer clear of 420-446, Space Tracking RADAR is primary in the band in those locations, with a big exclusion area.Other AFBs use ~380 Mhz for their trunked radio system. Be aware of the National Radio Quiet Zones, as well.420-430 Mhz north of FCC line "A" is a no-no near the Canadian border.200-400 Mhz is Military UHF, your there on a low duty cycle shared basis.Listen before you transmit.Check the local "Repeater Guide".432.1 is the center of the weak signal region for 70 cm, Working near there will draw negative feedback from local Hams.The No Code Tech ham test is fairly easy.US Title 47 Part 15 is your guide.You'll need to know your antenna's design gain as Part 15 is in Volts per Meter, not dBm. There are on-line clculators to help you with your field strength calculations.You DEFINATLY have duty cycle limitations.The FCC will not hunt you in most cases, but Hams and DOD will, and do so easily. Usually you'd get a cease and desist letter long before you get fined. The amateur folks, unless you get a craggy nasty "LID" will ask you to shift frequency or reduce power, and take an interest in your project.Ham Spectrum management in most areas is by "Gentleman's Agreement" and is self enforced. A few places need more active spectrum co-ordination and will have a State or Local spectrum co-ordination council.+13 dBm is probably way too hot. 0 dBm would seem more like it. Take a look at LORA if you want to go the distance without too much resistance.See:https://www.minicircuits.com/app/AN40-012.pdffor knowing what your radiating without much math.I wish they would update this:https://www.ntia.doc.gov/files/ntia/publications/january_2016_spectrum_wall_chart.pdfThere are designated sub-bands and allocations in nearly every box on that chart, it takes quite a bit of learning to know what is going on.This is a good read, with some tables.http://www.arrl.org/part-15-radio-frequency-devices#:~:text=Part%2015%20sets%20out%20the,for%20various%20types%20of%20devices.Steve

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: January 16, 2021, 01:21:01 am
content: Go here:https://fccid.io/frequency-explorer.php?lower=315&upper=434It will give you a list of all the FCC device authorizations with frequency operating ranges overlapping in this range. For each result, you can click on it and find out what it is. This will give you some idea of the kinds of devices and the common frequencies used. You can end up down some fascinating rabbit holes.Also see pp25-28 ofhttps://transition.fcc.gov/oet/spectrum/table/fcctable.pdf

author: LaserSteve
author_rank: Super Contributor
timestamp: January 16, 2021, 01:31:18 am
content: Toss in this if your near an Airfield:The use of the band 328.6-335.4 MHz by the aeronautical radionavigation service is limited toInstrument Landing Systems (glide path).Don't mess with the ILS!Happy Confusion:https://transition.fcc.gov/oet/spectrum/table/fcctable.pdfThat gives me headaches the few times a year I read it.Less Confusion:https://www.ntia.doc.gov/legacy/osmhome/alloctbl/allocmhz.htmlRabbit Holes indeed.Steve

author: Lord of nothing
author_rank: Super Contributor
timestamp: January 16, 2021, 10:14:32 pm
content: Well when you not know where you can transmitt its better to not transmit anything.I heard that in the US its cheap and easy to get an Amateur Radio Licence.I would do that and try it out there.

author: rainbain
author_rank: Contributor
timestamp: January 17, 2021, 12:52:43 am
content: Ok, I talked to a good friend and got a lot of help with armature radios and I am found I really need to expand my range so I am going to try 915 Mhz and before I transmit anything I am going to listen for a day and make sure its good. What do you think of 915 MHz. Thank you so much for the help, I am super experienced in digital stuff and all the experience I have with this is stopping interference between PCB traces.A lot of priceless advice outside of this too. EEVBlog forms are the best.