SpyServer Updated: Very Efficient Network Usage with 8-Bit PCM Mode

Over the last month SDRSharp's SpyServer has been updated several times. SpyServer is a streaming server for SDR# which allows you to use Airspy and RTL-SDR radios remotely over a network connection.

The updates brought improvements such as IQ PCM compression at various bit depths including an efficient 8-bit mode, removing the DC spike residual in the 8-bit streaming mode, and recently improving the 8-bit mode to work like lossy compression for strong signals. 

We tested the new 8-bit PCM streaming mode and found it to be extremely efficient with network usage. When streaming at 2 MHz with an RTL-SDR a WFM signal on the older SpyServer versions used to use about 1.2 MB/s without any compression modes, and now with 8-bit compression active it only uses 322 KB/s. A NFM signal used to require 120 KB/s, now only requiring about 38 KB/s. No DC spike is present and no degradation in reception quality is noticeable unless the signal requires over 70 dB of dynamic range, which is unlikely for most signals.

If you've had trouble with SpyServer or rtl_tcp not working well on your slow network connection, then the new updated SpyServer may be the solution for you.

Prog, the author of SDR# and SpySever writes about the update on the Airspy group:

This new development allows you to stream large signals over 8bit and reduce the network bandwidth.

The server will try to pack the useful signals into whatever bit depth you select ensuring optimal SNR for the transport. No manual scaling required.

SpyServer with 8-Bit PCM IQ Compression
SpyServer with 8-Bit PCM IQ Compression
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If I use 8-bit only the strong signals are audible. I works like a squelch. Not very usable for DX-ing. How can I change this ?

Nicolas K

I tried spyserver for some time now.
I get good results with spyserver on Raspberry pi 3 over wifi.
The only drwoback for me, a linux only user is that for now there isn’t any native linux SDR program that is able to connect and use spyserver.
I hope it will change when airspy hf+ will be avaliable.


Is it possible to run it on a RPi1? I’m getting a “segmentation fault” when I try to start it.


Is it possible to enable direct sampling for the server for a RTL-SDR v3?


From todays experience with these new versions, I´m very doubtful of any improvements. Updating both Spyserver and SDR# to this latest release broke my two servers. One, an RPi2 server that is accessed directly via wifi at 65MPS the IF mode results in choppy network connection (11kps max) and total breakdown of audio and waterfall streaming, even at 10fps. Oddly, if I switch to Full IQ mode it “flies” at 5MPS, and much better than the apparently slimmer IF mode. Actually, I get better performance with RTL_TCP at full bore from this setup than from any of the SDR# network modes. I had a friend try out in his much more advanced i5 PC and he runs into the same problem with the IF mode. All these systems were running quite well with the previous versions. Whats up? Anyone else experiencing the same results?

No Pain No Gain

If high network throughput works better than low throughput, this may indicate serious fragmentation problems in your network. Try bigger buffer size.