[Linrad] Linrad network connections

[Joe Taylor <Princeton.EDU; joe@xxxxxxxxxxxxxxxx>]

Today I've been playing with the Linrad+MAP65 combination, in 
preparation for making some demonstrations at the EME Conference in 
Florence.

I noticed something that may be interesting to others on this list.

You'll recall that Linrad serves as a "front end" to MAP65.  Digital 
data in the Linrad "timf2" format, taken after the first inverse FFT, 
are sent over an ethernet connection to MAP65.  The default Linrad code 
does this transfer in the form of multicast UDP packets.  Multicast 
means that there is one source of packets -- Linrad -- and in principle 
there may be many receivers.  Many months ago I changed my working copy 
of Linrad (version 02.34) so that instead of multicast it uses 
"unicast".  That is, data are sent explicitly to a single IP address, 
that of the machine running MAP65.  This resulted in more reliable data 
transfer -- and also, even more importantly, it prevented swamping my 
local network with Linrad traffic so that my wife could not use the 
network to check her email, etc.

Today I discovered another big advantage of sending unicast rather than 
multicast packets.   On my network, at least, multicast transfers make 
*much* more RFI.  Every packet transfer is clearly audible on an HF 
receiver tuned to the 30 m band.  I don't hear anything at all when I 
switch to making transfers to a single IP address.

	-- 73, Joe, K1JT

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