FCC Antenna Regulations?

wesleyterry · ‎11-19-2008

In the General Wireless forum is a topic called: "1250 802.11n Brdiging" where it was suggested that a user bridge with 5ghz Yagi Antennas and then it was mentioned potentially getting a convertor for the rp-tnc so that alternate antennas could be attached.

As far as I know (speaking about US FCC) it is illegal to install an antenna that is not certified for the radio by the manfucacturer/FCC. I believe the is why there is a unique connector requirement in the first place.

Anyhow, upon further reading, it looks like the "law" was modified so that you could attach any antenna of equal type (Patch=Patch, Yagi=Yagi) as long as it had equal or less gain.

Now, my first question is this:

Do you think you could add a connector converter to attach a non RP-TNC antenna to an RP-TNC device? Does the unique connector rule apply at the antenna level or the radio? It would seem to me that the antenna would need to be manufactured with the unique connector and that one could not simply convert the antenna at will.

As I investigated a little further, the bigger problem actually may not be the conversion of the antenna but the attachment of a Yagi to a 1250. The only antennas listed in the 1250 Section of Cisco's Aironet Antenna list are Patch and Omni antennas. This would suggest that Yagi's are not certified with this system and therefor could not be attached to the system even if it had the correct connector.

What are your thoughts on this? Obviously it can be done, but from a "Professional" perspective, at what point is it illegal?

Scott Fella · ‎11-20-2008

I will try to give this a shot... What I know is that you have to stay within the limit of what the FCC states for total Transmit power wich includes the TX power level and the antenna gain minus the loss from adapters, cable and lightning supression. What this is... I can't remember off hand. Now the use of adapters, I find it easier to just have the ends replaced with rp-tnc connectors. I think the issue with Yagi's and the 1252 is that since you now you will be using 3 yagi's instead of usually one and disabling diversity is correct alignment. So if you only use one port on the 1252, I don't see any issues..... now trying to line up 3 yagi's at both ends might be tough and impossible unless to build something that spaces and holds the yagi's in place perfectly.

At what point is it illegal... well just determine the max TX and stay within that limit.

-Scott
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wesleyterry · ‎11-20-2008

Ok well I think I've at least cleared up the antenna part. Cisco's 1250 Q&A states that is it certified with Cisco Aironet Antennas. If you go to the Antenna list, although it has a section for just 1250 antennas, it does mention its use with the other antennas on that page.

So there, even though I still think there is a regulation about only putting antennas that are certified on the equipment, it appears Ciscco has made sure all of their antennas are certified.

The next problem however is still whether or not you can modify the connector on an antenna to make it fit..... But I guess since you are not modifing the Radio's connector and you are just modifying the Antenna, I'm guessing its good...

As for your point on power. I know some Frequencies are a maximum of 1 Watt, but for some reason I think 2.4 and 5.7 are 125mW. I could be wrong though.

I also think there is like a 20 DB Antennuation limit.... but I might have made that up too.

Scott Fella · ‎11-20-2008

Out door the limit is 1W unless that has changed. cisco wants you to use their antennas and that is why they certify it. There are alot of installs out there that use 3rd party antennas, and changing the connectors should not violate any regulations. I think you are right about the connectors on the radio, but not the antenna. If you look at some installs where they need to extend cable, one end might b an 'N' type plug and the other end is rp-tnc that connects to the radio.

-Scott
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scottmac · ‎11-20-2008

It is illegal when you knowingly circumvent the rules ("intent").

If you break the law through lack of knowledge, you'll hear "ignorance of the law is no excuse" (at least in the USA) and the owner and implementer will be fined by the feds, then the implementer will be sued for even more, because they knew better and chose to ignore the law.

My understanding is that you cannot use antennas that are not of the type certified or similar in construction, radiation characteristics, and gain..

If there are no certified yagis for that model of AP, then using a yagi means that you would have to have that system certified (FCC bureaucracy FTW/FTL).

Ask the FCC, in a letter (on paper, a legal record), then follow their guidance. You have much more to lose (as the implementer)if your customer is caught with out-of-spec radiators.

...and for those "You'll never get caught, the FCC has no budget" type arguments ... we are entering (at least) a recession. The Feds will be looking to collect on every possible revenue source; these are no-brainers and easy to collect on.

Regarding the use if "pigtails": I agree with the other poster ... it's better to just replace the connector ***IF*** you are a competent solderer and can properly terminate the connection ... it's harder than it looks to do it right.

Doing it wrong can cost you a radio, doing it a "little wrong" means coat-hanger level performance (that would be a "Bad Thing").

Every connector (along with every sharp bend, crush, twist, or junction...) reduces the power reaching your antenna. Gain, even passive gain, relies on a decent signal-to-noise ration at the input of the antenna. A flaky signal in will give you a flaky signal out.

Also, changing a connector on the feed does not change the radiation characteristics of the antenna, it's permitted - as long as it's not changed for a "common" connector type, but one of the "special" connector types used in 802.11 sty;e communications.

Good Luck

Scott

dennischolmes · ‎11-20-2008

Part 93 of the FCC rules state that the antenna used must be certified by the FCC or an equivalent in design, nature, and output as the one certified by the manufacturer. Basically they only look at power output. Dont exceed and you wont get into trouble.

Rob Huffman · ‎11-20-2008

Hey guys,

Very thoughtful and insightful answers all the way around! +5 points for each of you for sharing your expertise on this subject.

Cheers!

Rob

PS: Scott and Scott, congrats on the new badges! Well deserved for both of you.