From owner-freebsd-wireless@FreeBSD.ORG Wed Aug 27 22:54:00 2014 Return-Path: Delivered-To: freebsd-wireless@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id C0FB7BE8 for ; Wed, 27 Aug 2014 22:54:00 +0000 (UTC) Received: from mail-qa0-x22f.google.com (mail-qa0-x22f.google.com [IPv6:2607:f8b0:400d:c00::22f]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 82C5437F8 for ; Wed, 27 Aug 2014 22:54:00 +0000 (UTC) Received: by mail-qa0-f47.google.com with SMTP id x12so186729qac.20 for ; Wed, 27 Aug 2014 15:53:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:sender:in-reply-to:references:date:message-id:subject :from:to:cc:content-type; bh=peXhwR0Sd1DxsBlk5z7P1YqmQXQ+0Q+Q424HBaQsvkw=; b=IbZ5kkB5ei0nfg7pIn59q4dboUBjpQ4GJqXDANZZmWtw7nF0kJm+PPpxZs7zFSXfmp 7A/aPS6nKP683z3KalDHZwFysdzPwge84C5xdGW2VB1giJkoVPEtwdNU5vTO6CS0DrEv yduIFLwM8GDaQkLTJMluFwUsTWJyZKuHHb8/T8J/KmhSZxPxuO8gaU2VlDcDXkyob+y8 40HPRJixn1bQo+2iZVVR84kyYZkAw88cwc/Ikm9R1fG1R8aIz2iJaoL79bnqcIZsRjRY p/JNdwSfC4udQEpldFSKmbXA5AsA69vmrNWP5A4EDvJEnHxfPBO9/trZMC8hg2JZq3Fn uXPw== MIME-Version: 1.0 X-Received: by 10.224.46.8 with SMTP id h8mr430979qaf.6.1409180038349; Wed, 27 Aug 2014 15:53:58 -0700 (PDT) Sender: adrian.chadd@gmail.com Received: by 10.224.39.139 with HTTP; Wed, 27 Aug 2014 15:53:58 -0700 (PDT) In-Reply-To: <53FE5CF4.1000901@bartk.us> References: <53FE5CF4.1000901@bartk.us> Date: Wed, 27 Aug 2014 15:53:58 -0700 X-Google-Sender-Auth: iUkbLO19rmpFuuVj-gXBbkaPmUg Message-ID: Subject: Re: FreeBSD TDMA: Legalizing 440MHz 802.11 modems From: Adrian Chadd To: Bart Kus Content-Type: text/plain; charset=UTF-8 Cc: "freebsd-wireless@freebsd.org" X-BeenThere: freebsd-wireless@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: "Discussions of 802.11 stack, tools device driver development." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 27 Aug 2014 22:54:00 -0000 Hi! So, I'm not sure if we can underclock it _that_ far. The 5/10MHz channels are implemented by underclocking various parts of the chip, which results in everything being some fraction of 20MHz (or 2x clocking it, resulting in 40MHz.) Bringing it all the way down to 200KHz is a pretty tall ask. I know people have gone down to 2.5MHz on these chips, but I don't know of anything lower than that. The OFDM subcarriers start being way too narrow and I doubt you'd end up with anything sensible. It's likely that you'd want to create a custom DSP based solution to do 200KHz side stuff at that symbol rate. -a On 27 August 2014 15:34, Bart Kus wrote: > Hello, > > I'm wondering if you can tell me if it's possible to modify the FBSD TDMA > code to make this card: > > http://www.doodlelabs.com/products/radio-transceivers/sub-ghz-range/420-450-mhz-dl435-30/ > > legal to use in its intended spectrum. By default the card violates two > Part 97 rules: > > 1) Emissions are limited to 200kHz bandwidth > 2) Symbol rate is limited to 56kSym/s > > Is it possible to slow down the subcarrier symbol rate in that Atheros chip? > Is it also possible to then space the subcarriers tighter together to > respect the 200kHz emission bandwidth limit? They'd have to come closer > together anyway to uphold OFDM subcarrier orthogonality. > > Thanks for any clues, > > --Bart > > PS: I'm asking in the interest of the HamWAN.org project. We're trying to > find a more mobile solution, which penetrates through forests and some > buildings. 440MHz seems to fit the bill, but hardware is really hard to > come by. > > _______________________________________________ > freebsd-wireless@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-wireless > To unsubscribe, send any mail to "freebsd-wireless-unsubscribe@freebsd.org"