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S/N and Vara speed levels

Hi everybody,

I have a general question probably related more the vara modem itself then about VarAC. I have not fully understood the relationship between S/N and speed levels; indeed I had qso's with +10 dB and received +00 dB and maximum level at 88 bps, while sometimes even with S/N much lower i have seen up to 270bps. Can anybody tell me more about it?

73 de Phil, iz1fks

5 comments

5 Comments

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NC3Z Gary

May 07

Of course the non-registered versions are limited in their connect speed.

NC3Z Gary

May 07

Generally the better the SNR the better the speed can be. Here is a good read from the Winlink team with graphs.

https://winlink.org/sites/default/files/downloads/a_winlink_digital_mode_performance_comparison_based_on_the_ionis_sim_hf_vhf_channel_simulator_-_november_2_2020_0.pdf

iz1fks

May 07

Replying to

thanks Gary, nice attachment. I agree, but my experience sometimes looks different and I'm trying to understand which the reason is. Could it be related to registered Vara modem? or to the use of different Vara modem versions at the two sides?

htperry

May 07

Replying to

That comparison paper was very good, enlightening.

irad d

May 08

Replying to

@iz1fks So many variables involved... the VARA protocol accelrate speed if the error correction threshold was below a certain level.. sometimes you can have a good SNR but due to some QRM it can cause a lot of error corrections to happen so it decided to take down the speed.