Irad: Thanks for the advice. I tried changing the USB-D command from 600 through 610. The rig did cycle through all modes, but it did not switch to USB-D. As a workaround, I eliminated mode control from the CAT.INI file so the rig doesn't switch out of USB-D when changing bands. I will let you know what the folks on the X6100 reflector come up with. Thank you! Tony -K2MO

Hi Irad: Yes, the x6100 uses USB-D mode for digital operation. Using standard USB tends to cause audio artifacts not to mention a loud "pop" from the internal speaker during transmission. I received the reply below from the X6100 reflector. Thanks Irad. Tony -K2MO All CAT interface in method CivDevice::slot_rxPhase - https://github.com/strijar/x6100_ui_v100/blob/main/x6100_ui_v100.c But I don't want to dig into it just yet.

Gary et al: I checked the VarAC CAT file and the USB-D command for the X6100 appears to be identical to ICOM. Seems Xiegu decided to use ICOM commands. The USB command shown below works, but the USB_D command returns LSB. Maybe someone can shed some light on this. Tony -K2MO ICOM / XIEGU ModeUSB=FEFE70E00601FD ModeUSB_D=FEFE70E00608FD

Awesome Chat mode Irad. Thanks for creating VarAC! Thanks, Tony

Gary: Just received word from AF3K. He was using his Flex (6700) at the time of our QSO which explains the latency issue. He was also using the latest version of VARA and VarAC. If other Flex users aren't having latency issues with the current versions then it must be the settings within the rig. I know that sharp filter settings add latency and Flex does recommend using wide filter settings when working ARQ modes in order to reduce latency during the demodulation processes. According to Flex, a filter setting of 500 Hz or less adds 85ms while a filter greater than 2K only adds 11ms. My guess is that the overall system latency is higher and that could be cutting it close when you consider the fast TX/RX timing of the VARA modem. It could also be something simple like having the delay (break-in) slider set to high although I'm not sure if it functions in USB-D / LSB-D modes. Tony -K2MO

thank you Irad. Tony -K2MO

Rich: Glad to hear things are working for you. You mentioned your rate jumped 80% so I'm assuming you were still having latency issues with VARA 4.5.5? I guess all is well now since you've tweaked the driver issues and VAC? Tony -K2MO

Gary: Apparently, the issue still exists and my guess is that it could be an SDR setting that's causing the problem. I tried to work AF3K today without success and it was clear that he was having latency issues with his SDR. I emailed him this afternoon and will advise when I receive a reply. I was running my IC-7300 at the time. I've worked with Jose in the past to fix latency issues I had with my Flex 6600M which showed up while running Winlink. His tweaks worked for the most part, but there are times when I experience a collision or two. I'll have to try my Flex with VarAC and see how things go. Tony -K2MO