[hfsig] WSPR board

John C. Peterson jcp at eskimo.com
Tue Mar 7 15:46:48 EST 2017

On Tue, Mar 07, 2017 at 04:38:09PM +0000, Bob Cutter wrote:
>  My unit is still transmitting at same measured power, shack receiver
> shows a signal, but it has stopped getting Spots.?? Also I am now getting:
> "Warning absolute ppm value is greater than 200 and is being ignored".
> Attempted to download a new program but get "error resolving
> host gethub.com/JamesP6000....."
> Any suggestions?
> Bob KI0G??

Hi Bob,

It sounds like you are probably transmitting OK, but out of the frequency
band. It's only 200 Hz wide, so if you are outside that small window,
nobody is likely to decode your transmissions.

The WSPR program by James Peroulas uses NTP (network time protocol)
to keep the frequency of the RPi CPU clock properly conditioned. In a
non-radio context, the frequency of the CPU clock can be off by a lot,
and won't cause any problems. The crystals are rarely temp controlled
so they also drift quite a bit. NTP solves those problems quite well,
but requires a healthy internet connection to work properly.

Something else might be going on, but I would place a small bet that
your internet connection is suffering degradation or other problems.
(The inability to resolve the IP address of github most definitely is
due to that). I have seen that sort of thing myself on rare occasions,
usually when downloading huge files that saturate my internet connection.

With regard to staying in the WSPR +/- 100 Hz window, I made a small
change to the James Peroulas version of wspr.cpp. I changed the value
assigned to the WSPR_RAND_OFFSET macro to 50 (was 80). When using the
-o option, the random offset will be +/- 50 which makes it more likely
you will be in band if your clock frequency is a bit off. Here's a
context diff;

$ diff -u wspr.cpp.orig wspr.cpp
--- wspr.cpp.orig       2014-10-26 18:27:17.000000000 -0700
+++ wspr.cpp    2016-10-17 22:34:57.576348338 -0800
@@ -62,7 +62,7 @@
 #define WSPR_SYMTIME (8192.0/12000.0)
 // How much random frequency offset should be added to WSPR
 // transmissions
 // if the --offset option has been turned on.
-#define WSPR_RAND_OFFSET 80
+#define WSPR_RAND_OFFSET 50
 #define WSPR15_RAND_OFFSET 8
 #define BCM2708_PERI_BASE        0x20000000

John C. Peterson, KD6EKQ DM12ju
mailto:jcp at eskimo.com
San Diego, CA U.S.A

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