RX signal suddenly drops

Lau · May 3

I am experiencing an issue with MSHV after updating to SmartSDR 4.2.18.
In MSHV, when I run FT8, my RX signal suddenly drops by approximately 15 dB.
When I then adjust the RX level back to 0 dB and transmit (TX), the RX level jumps up to +20–30 dB, and I have to manually reduce it again so the level is back around 0 dB.
Shortly after that — even without transmitting — the same thing happens again.
Before upgrading from 4.1.15 to 4.2.18, I uninstalled 4.1.15, rebooted the PC, and made sure there were no remaining traces of 4.1.15 before my Flex 6600M performed the radio update. Everything completed without any issues.
I have verified that this is not a LAN/network issue. I have also ensured that MSHV is correctly configured with the proper DAX RX and DAX TX settings — everything appears to work fine. However, I cannot determine where, or why, my RX level suddenly shifts between approximately −20 dB and +15 dB.
I am running Windows 11 (latest version and build — same for MSHV) on a Windows 11 Pro system with an Intel CPU and 16 GB RAM, in case that is relevant.
I would very much like to avoid having to reinstall my PC to resolve this problem.
Any suggestions would be greatly appreciated.
This post was translated by Copilot, as my technical English is not optimal.
Kind regards,
Lau
OV2B

Lau · May 3

BTW....!!
INFO… I also have an SPE Expert TAURUS connected to my setup. This is done via a USB CAT cable from the radio to the PA, which may be important information. However, I have not experienced the PA indicating “standby operation” or any loss of connection.

Carsten G0SYP · May 7

I have a similar (but not quite the same issue). It is not limited to MSHV although I noticed it there first.

My DAX audio level on all slices drops less (maybe 5-10dB) at random times. Sometimes at RX, sometimes after TX. It also happens often while my screensaver (screen turns off) is active and as soon as the screen goes on again (after moving the mouse or pressing a key) the level goes back up to normal.

It is only the DAX level going down, the waterfall level stays the same, so I can eliminate any issue on the RF side.

73 Carsten G0SYP

Erik Carling EI4KF · May 8

Near same issue here. Random drops in DAX RX1, using JTDX. But not limited to screen saver activity. This is with both 8400M and 6400M.

I did reinstall Windows 11. That did not help. So I have reverted to the original DAX where RX is always at a consistent level.

As a side point: having reverted to DAX v1, I realised that for RX the gain level is substantially higher in DAX v2. Optimum receive in JTDX 32bit audio version for DAX v1 is a gain level of 35 but for DAX v2 it is 27.

Mike-VA3MW · May 8

Carsten and Erik

Have you taken time to listen to the Audio levels on DAX and see if you can hear it change? Or, could it be a metering issue?

Just a thought.

Erik Carling EI4KF · May 9

I believe that it is a gain issue in DAX v2. I had not listened to audio levels so I made that check. Audibly, it is hard to discern the drops in level but they are there. They coincide with a drop in the RX level indicator in JTDX, approximately 8dB and similar to Carsten.

Using a RTTY program that uses DAX, there are no drops of any note but there are minor fluctuations of a greater amount than with DAX v1. Using SDC on RTTY where DAX is not used, there are no drops or fluctuations at all.

A modulated 8-FSK FT8 signal will typically exhibit variable receive audio levels, even though the transmitted signal is designed to be a constant-amplitude frequency shift keying mode. There is excessive gain in DAX v2 and this accentuates the variations.

At least, this is my contention though I can understand the lack of belief in it that will undoubtedly exist. There are very few reports of this so something else may be at play here.

I am now back on DAX v1, and RX is as it should be.

RX signal suddenly drops

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