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5.8 GHz NTSC video transmitters are popular for FPV (first person view) model aircraft flying. However, because the 5.8 GHz band (5725 to 5875 MHz) is also available for ISM (unlicensed) use, it's not clear to me at what point I need a license to operate a transmitter of some given power. I've seen a table that says I can transmit up to 1 W (30 dBm) with a low-gain (6 dBi) antenna.

Isn't the ham power limit for 1.3 GHz and up 1 W anyways? What does having a ham license do in ISM bands?

For reference:

           GHz :  5.650       5.725          5.850    5.875      5.925
      ISM Band :                |<------ 100 MHz ------>|
ITU Region 1/3 :    |<------------------ 275 MHz ----------------->|
ITU Region   2 :    |<-------- 200 MHz ------->|
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2 Answers 2

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According to this site, the maximum allowed for non-licensed ("Part 15") equipment is 1W to the antenna, and the maximum EIRP is 4W.

For point-to-point links, the limit is higher, and the site mentions that on 5.8GHz the maximum allowed would be 53dBm EIRP (30dBm transmitted plus 23dBi gain of the antenna), which is 200W EIRP.

For licensed radio amateurs, I could not find any limit other than the 1,500W regular maximum power limit. Restrictions to transmitting as a 'radio ham' on the amateur bands that overlap with the ISM bands are those of the amateur radio licence. This includes the requirement to send an ident every 10 minutes and the end of the transmission in a mode that can be read by any radio amateur, if you transmit anything at all.

The FCC point us at this link for the latest Part 97 regulations (the regulations that govern amateur radio), and looking in there it states that 1,500W is the maximum unless otherwise stated, and there is no other statement indicating a lower power requirement for the higher bands, unless the operator holds a Novice licence.

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  • $\begingroup$ The band in question is an ISM band. ISM bands have a specific power limit (30dBm + 23dBi of antenna gain) the 1500W maximum power for Extra class licensees can not overrule this limit. $\endgroup$
    – sessyargc.jp
    Sep 3, 2015 at 4:57
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    $\begingroup$ 5,800MHz is a spot frequency usable by ISM, but it falls within the amateur band that goes from 5,650MHz to 5,925MHz. If you are using an amateur licence, you can transmit at full legal 1,500W power, as long as you follow amateur regulations. ISM equipment is licence-free, and has a lower allowed power (30dBm + 23dBi) $\endgroup$
    – Scott Earle ♦
    Sep 3, 2015 at 5:04
  • $\begingroup$ 1.5kW is plausible (if one has the money to build a kilowatt microwave transceiver) but as secondary users of the band, a ham will probably be creating interference that can be received everywhere. A big no-no. $\endgroup$
    – sessyargc.jp
    Sep 3, 2015 at 5:15
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    $\begingroup$ Not causing interference to other users is one of the 'amateur regulations' that I was saying must be followed. The comment still stands. $\endgroup$
    – Scott Earle ♦
    Sep 3, 2015 at 6:11
  • $\begingroup$ For reference, ISM is 5725 to 5875 MHz. $\endgroup$
    – Nick T
    Sep 3, 2015 at 15:13
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Isn't the ham power limit for 1.3 GHz and up 1 W anyways? What does having a ham license do in ISM bands?

This is the latest version of the table. Updated 2014 but I can't see the PDF (the text on the site is not formatted properly) because the FCC is updating the website. https://www.fcc.gov/document/5-ghz-u-nii-ro

From FCC 14-30 linked above:

The U-NII-3 band is allocated on a primary basis to the Radiolocation Service for Federal operation, and is allocated on a secondary basis to the Amateur Radio Service for non-Federal operation.

Actually having a ham license makes it more difficult because we are secondary users of the band. If somebody is causing interference to us, we have to adjust. If we are causing interference to others, we have to adjust out equipment so as not to cause/create said interference. The license doesn't have any effect on the maximum Transmit Power that we can use.

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  • $\begingroup$ Except that you can use any antenna, and up to 1500W power. For ISM use of 5.8GHz, there are restrictions on both power and antenna. $\endgroup$
    – Scott Earle ♦
    Sep 3, 2015 at 6:26
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    $\begingroup$ and as you say, the primary user (which should not be interfered with) is Federal radar and not ISM users. $\endgroup$
    – tomnexus
    Sep 3, 2015 at 8:49
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    $\begingroup$ ISM users of the band also have to avoid causing interference. So besides the general restrictions on part 97 operation (must identify, can't encrypt, etc) I don't think there's any particular disadvantage. $\endgroup$
    – Phil Frost - W8II
    Feb 6, 2019 at 16:53

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