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Running VarAC (actually VARA) with an ANAN Radio

There were two issues associated with connecting and ANAN radio running with either Thetis or PowerSDR software using VAC to a VARA modem.

One was a very isolated corner case when SNRs are high which enable high VARA speeds and VARA enters an IDLE state where neither station is transmitting. With high speeds and in the IDLE state, ANAN VAC timing would cause the connection to drop after one minute. Special thanks to Jose for posting an update to VARA on his website that addresses this issue. This new VARA update does not change the version number. You just need to copy this new version of VARA.exe into your VARA folder.

The second issue is more complex. I won't try to rehash it here. Check this Apache Labs ANAN forum thread for more info. Be prepared to have your eyes glaze over.

https://community.apache-labs.com/viewtopic.php?f=13&t=3901

With both forward error correction and ARQ, the VARA modem is very robust and handles errors caused by digital audio sample rate differences between the radio and computer. I just turn off the resampler without any degradation to packet error rate or bit rate for small chat messages and larger file transfers.

Larry

W6LVP

5 comments

Comments (5)

NC3Z Gary

Sep 08, 2022

So were you seeing issues with the resampler On or Off?

W6LVP

Sep 09, 2022

Replying to

I was able to create a fairly stable setup with the resamplers on (Force boxes unticked). However, it takes a few minutes for them to initially stabilize or after any configuration change. I also had a few situations where the resamplers would destabilize in the middle of a VarAC QSO requiring they be turned off in order to continue.

I use a test setup to connect my ANAN radios to my 7300 using attenuators that enable configuring the receive SNRs at any level.

While there may be speech audio benefits to running the resamplers, using my test setup, I found no difference in packet error rate or maximum bit transfer rates while transferring large files. I also saw no difference using different types of Windows sound drivers from the older MME to newer ASIO. Also no difference with different types of virtual audio cables.

With regard to SSB speech, I use the integrated audio codec in my ANAN radios to connect headphones and a mic to the jacks on the front. Probably not the best for the audiophile but communications audio is much less demanding than broadcast FM that some seem to want to achieve.

I attribute the lack of difference in VARA performance to the power of the VARA modem using its forward error correction and ARQ to deal with minor audio glitches.

When all other things are equal, I believe in keeping it simple. I run with the resamplers turned off. When the resamplers are off, the only VAC parameter sill in effect is the Buffer Size which does impact latency a little but not enough that VARA cares. I set mine to 256.

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