[Mich VHF UHF Society] Fwd: Re: [VHF] SDR Play [ NEW SDR RECEIVER. 2 GHz, 8MHz bandwidth under $300 USD ]

Roger Cox rgcox2 at gmail.com
Mon Sep 8 18:49:27 CDT 2014




-------- Original Message --------
Subject: 	Re: [VHF] SDR Play [ NEW SDR RECEIVER. 2 GHz, 8MHz bandwidth 
under $300 USD ]
Date: 	Mon, 08 Sep 2014 12:55:34 -0600
From: 	Patrick Dyer <pjdyer at swbell.net>
To: 	vhf at w6yx.stanford.edu <vhf at w6yx.stanford.edu>



That 8-MHz bandwidth would be more than enough to reveal what is going
on with Es propagation of an entire 6-MHz wide DTV signal as was
tantalizingly suggested in this:
http://www.youtube.com/watch?v=NVam6bmJ7p8 from KOTA-DT-2 Rapid City, SD
in June 2013 using a USB dongle with SDR# (max 2-MHz display).  Similar
results were seen later while KSNV-DT-2 Las Vegas, NV was coming thru so
it's not a KOTA artifact of some sort. (Though, due to the awkward
complexity of my hardware/software setup, I've not made any subsequent
combination videos.)

No one had really expected that there would be those drifting
undulations/ripples across the (virtually flat) emissions of a DTV
channel vs something of a wedge-shaped (or even cliff-like) profile as
the MUF was approached.  K6MIO/KH6 has been working on some simulations
to explain that behavior.

Such a view of an 6-MHz NTSC (analog) channel would be less-revealing as
those energy peaks are concentrated near the audio and video carriers
(and, to a lesser extent, the color burst subcarrier) with lots of
"near-empty" space in between.  It's been a long-observed fact that Es
MUFs are often "sharp" enough to preclude any audio in spite of a very
intense, clean video being resolved on a kinescope (some examples of
which are on my YouTube page, http://www.qsl.net/wa5iyx/YouTube.htm)
while at other times the audio will be present even with relatively weak
and snowy video.

More details of NTSC vs DTV Es propagation are at
http://www.qsl.net/wa5iyx/lovesavd.htm

73, Pat - WA5IYX
http://www.qsl.net/wa5iyx/index.html
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