My attachments were more than 100kb, so my message got sent back source
forge. Here it is without the graph attachments.
Hi Bruce/David/Barry,
I totally like the idea of diversity, and what really needs to happen is
actually testing some links to see how much it helps. I am going to see
about getting some antennas setup here for experimenting.
The receive seems like the easiest to work on, using something like MRC
(using the data from the antenna with the best SNR on a frame by frame
basis.) Doing that would insure that you had the best possible RX between
the two antennas. 2RX = ~3db, 4RX = ~6db
Maybe .8 wavelengths would be a good spacing?
http://www.jpier.org/PIER/pier64/02.06062401.Khaleghi.pdf
It also looks like something like STD (sending every other frame through a
different antenna can gain a little bit more) Might be possible with a
STDP RF switch and only one radio? Gain: ~2db
Bruce, thanks for the links! Very interesting. Now I just want to try it! :)
David, maybe it's just me, but FEC (Reed Solomon) seems kind of pathetic
for the amount of code word vs correction ability.
I think it was something like 35% data added for 7% correction. And going
up from there data wise. But then again it might be possible to optimize it.
One other thing I was thinking about, and I am sure you guys and already
talked about this in times gone by, but would it be possible to narrow the
carriers to something less than 75Hz and keep the symbol rate the same? It
would allow for more power output, right?
Anyways, thanks for your thoughts guys, maybe I can try a link with one of
you some time using receive diversity. :)
73s
Daniel VA7DRM
Sent from Daniel's iPhone
<image.png>
<image.png>
On Mar 6, 2013, at 4:33 AM, Barry White <[email protected]> wrote:
An effective fade reduction antenna is to have one vertical and one
horizontal antenna. Due to changes in the ionosphere the signals can
arrive with constantly changing polarisation.
Barry VK2AAB
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
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