Thetis sample rate @ 24000

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Kurt V.

Sep 15, 2023, 8:28:52 AMSep 15
to Hermes-Lite
If one of the programmers of Thetis read this message, would it be possible to implement a sample rate of 24000? 
With the Beta 6 for HL2, it is great to see it finally working on a PPTP connection. 
As I get about 3mbits /s, it would be wonderful to bring it down to half of this bandwidth for mobile connectivity. 

Jim Ancona

Sep 15, 2023, 8:37:28 AMSep 15
to Kurt V., Hermes-Lite
Unfortunately, the protocol only supports sample rates of 48k, 96k, 192k and 384k: 


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Sep 15, 2023, 9:44:01 AMSep 15
to Hermes-Lite
For mobile receive only, if you have a colocated Raspberry Pi or other server near the HL2, you can transcode the HL2's 48k Protocol 1 UDP down to 48k 8-bit rtl_tcp format which uses about 1/4th the network bandwidth.  Look for hl2_tcp.c on GitHub.
73, Ron, n6ywu


Sep 16, 2023, 10:21:40 AMSep 16
to Hermes-Lite
Hi Ron,

Is there a pre-complied windows exe of hl2_tcp available anywhere?


Steve Haynal

Sep 16, 2023, 4:34:15 PMSep 16
to Hermes-Lite
Hi All,

It is possible to update the gateware to use a nonstandard sampling rate (48,96,192 and 384 khz are standard for protocol 1). I made a 4khz version once, but it was receive only:

It sort of defeats the purpose of a wide bandwidth DDC/DUC radio to reduce it to 24khz or 4khz.

I agree with Ron that the way to go is to add another computer, even a small SBC, at the HL2 side to transcode down to whatever you like. Quisk does this too.


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