Daniel, Check out http://www.antennex.com/Stones/st0612/st0612.html starting at "Elliptical Polarization for HF". and http://ecjones.org/physics.html
Ionosphere scatter results in two elliptically polarized reflections with opposite sense, that propagate differently because the skin effect of the ionosphere behaves differently for the two different polarizations and one penetrates the ionosphere more deeply than the other. And thus we get fading from both polarization change and multipath. So, potentially one might get better results using crossed loops and trying both polarizations (or decoding both at once). There's a nice dual loop preamp at http://active-antenna.eu/order-and-pricing.php
that could be used to build a crossed loop and examine this phenomenon.
Thanks
Bruce
On 03/05/2013 08:42 PM, David Rowe wrote:
Hi Daniel, Yes I have wondered if a separate rx with separate antenna might help get around fades. I imagine there needs to be a certain separation (certain number of wavelengths) between the antennas. Some other ways to get that 6dB are coding gain (if FEC can be made to work better) and lower Codec bit rates (if that doesn't make the robustness worse). At the tx end higher average power (reducing PAPR issues) would also help the link budget. Thanks, David On Tue, 2013-03-05 at 20:30 -0800, Daniel Mundall wrote:David, Amazing to see all the work that has gone into getting it where it is. Thinking about that 6db you are looking for, wouldn't it be possible to get that at some point with something like SoftRock with dual tx-rx chains (MIMO)? It may not be practical for the lower bands(antenna size), but when possible it may be one of the easiest ways to get that link budget and possibly even lower the tx power. I found some of the ideas here interesting http://www.sequans.com/pdf/SequansUplinkMIMOWP0608_v2.pdf It may not something for right now, but it looks like something with potential for the future. 73s Daniel Sent from Daniel's iPhone On Mar 5, 2013, at 12:09 PM, David Rowe <[email protected]> wrote:Hello, I have just published a new blog post on making FreeDV robust over HF multipath channels: http://www.rowetel.com/blog/?p=2905 Thanks, David ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_d2d_feb _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2------------------------------------------------------------------------------ Symantec Endpoint Protection 12 positioned as A LEADER in The Forrester Wave(TM): Endpoint Security, Q1 2013 and "remains a good choice" in the endpoint security space. For insight on selecting the right partner to tackle endpoint security challenges, access the full report. http://p.sf.net/sfu/symantec-dev2dev _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2------------------------------------------------------------------------------ Symantec Endpoint Protection 12 positioned as A LEADER in The Forrester Wave(TM): Endpoint Security, Q1 2013 and "remains a good choice" in the endpoint security space. For insight on selecting the right partner to tackle endpoint security challenges, access the full report. http://p.sf.net/sfu/symantec-dev2dev _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
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