[Skimmertalk] Notes on the N1GP dongle server

[John Ackermann N8UR]

This morning I built N1GP's "librtlsdr" package on a Raspberry Pi 3.  It 
seems to work fine, but I found a couple of tweaks were necessary so 
thought I'd document them here in case anyone else wants to use a bunch 
of $20 dongles to drive a Skimmer Server.

1.  A previous message on this list referred to the "rtl-hpsdr" package. 
That version has been deprecated and Rick points you to "librtlsdr" 
(https://github.com/n1gp/librtlsdr) instead.

2.  To build on the Raspberry Pi 3, one adjustment is required.  After 
cloning the repository, go into librtlsdr/src and edit CMakeLists.txt. 
Search for this line:

set(INTRIN_FLAGS "-DINCLUDE_NEON -mfpu=neon -mfloat-abi=softfp 
-ftree-vectorize")

and change so that it reads "-mfloat-abi=hard" instead of 
-mfloat-abi=softfp". Save the file.  Now do the normal build procedure.

3.  The librtlsdr repository does not include the sample rtl-hpsdr.conf 
file.  You need to grab it from the old rtl_hpsdr repository.

4.  I'm not sure what causes this, but unless I specify the IP address 
of the ethernet port, the rtl_hpsdr program reports that its IP address 
is 127.0.0.1, and while the Skimmer half-way connects it reports strange 
errors like "too many receivers specified."

Using the -i command line option, like "rtl_hpsdr -i 10.73.10.56" makes 
it work properly.  (You can probably add the IP address to the 
rtl-hpsdr.conf file, but I haven't yet worked out the syntax.)

After learning these things, I had no trouble getting the Skimmer to 
connect to the dongle server.

Hopefully this info will be helpful.  I'm looking forward to getting our 
VHF RBN site up and running -- we plan to listen on 50, 144, 222, 432, 
and 1296 MHz from a high spot in southwestern Ohio.

73,
John