Problems with DIG mode on TX-500

Have a Lab599 Discovery TX-500 paired with Digirig to a Windows 10 computer. I have been happily using this setup for about a year.

Recently, the radio has started “chattering” between Tx and Rx when in DIG Mode, but only when the Digirig is plugged in.

Without the Digirig, its fine (though of course useless) in DIG.

With the Digirig and a dummy load instead of an antenna, it’s fine. But then, with the dummy load it’s not actually receiving anything.

As soon as I take the dummy load off and connect the antenna, it’s starts doing the chattering thing.

On this basis, I figure there is something gone funky with the Digirig or perhaps its cables.

This is actually great, as that is much easier to replace the Digirig than the radio!

However, anyone have any ideas how to narrow the problem down between the Digirig unit itself, or one/more of the cables?

I’d like to replace just the defective part, but I’ll just buy a whole new kit if needs be.

That’s frustrating. The problem seems to be RFI, since there is no problem when using the dummy load. Great troubleshooting! Consider:

  1. 1:1 choke on the antenna leadline to reduce common mode current
  2. better impedance match to the antenna
  3. increase the distance between the antenna and the rig.
  4. ferrite beads on the USB cable and power supply lines if you are not running battery.

73 Constrainted

Thanks for the thoughts, Contrainted.

  1. 1:1 choke on the antenna leadline to reduce common mode current

Worth a try; will do and report back.

  1. better impedance match to the antenna

Two antennas tried, one was 1.8:1 and the other was resonant.

  1. increase the distance between the antenna and the rig.

When problem started, antenna was EFHW about 30 feet from rig with 60 feet of coax (that was the 1.8:1 antenna).

  1. ferrite beads on the USB cable and power supply lines if you are not running battery.

Am running on battery (POTA ops).

If its RFI, why does it only appear in DIG mode? FYI, I run about 5W in DIG but 10W in SSB.

You may be right. Maybe I am not understanding.

Maybe try looking at Topics tagged lab599-tx-500

73 Constrainted

Have done; this is not covered.

The issue is new; was working happily before.

The rig “chatters” between Tx and Rx, kinda like as if one was quickly feathering the PTT button on a handheld mic. But this happens only when all of the following are true:

  • radio is in DIG mode; and,
  • the Digirig is plugged into the radio; and,
  • an antenna is connected.

No problem in voice modes; no problem when Digirig not plugged in; no problems with a dummy load.

What tests would you suggest for diagnosing what part of the Digirig (unit or cables) is causing the problem?

Is your Digirig powered up when this happens?

Assuming the Digirig is powered through its USB cable, the answer is YES.

Results of further testing are as follows:

Equipment:

  • Rig = Lab599 Discovery TX-500 running on BAT500 battery

  • Antenna = 20M resonant dipole, deployed almost horizontal (very shallow inverted-V) at 40 feet elevation, SWR = 1.0

  • Feedline = LMR174 coax, 50 feet long

  • Digirig = “TX-500” type, c/w Digirig brand cables

    • 4-socket cable to CAT on rig and SERIAL on Digirig
    • 7-socket cable to REM/DATA on rig and AUDIO on Digirig
    • USB cable to USB on computer and USB port on Digirig
  • Dummy Load = MFJ-261 Dry dummy load

Configurations tested:

  • Rig + dummy load + mic = no chatter

  • Rig + dummy load + Digirig plugged into computer which is on but no radio software running = no chatter

  • Rig + dummy load + Digirig + Computer running WSJT-X = no chatter

  • Rig + 20M dipole + Digirig connected to radio but not connected to computer (Digirig not powered?) = no chatter

  • Rig + 20M dipole + Digirig + Computer off = no chatter

  • Rig + 20M dipole + Digirig + Computer on = chatter

  • Rig + 20M dipole w/ ferrites + Digirig + Computer on = chatter

  • Rig + 20M dipole w/ balun + Digirig + Computer on = chatter

There is no problem when using dummy load instead of antenna. The problem only arises when connected to an antenna. However, the antenna is resonant (not an SWR problem) and the ferrites and balun seem to make no difference (likely not a common mode problem).

So, I’m still convinced my Digirig (or one of its cables) has given up the ghost.

For what it’s worth, the problem started when I was trying to get into a Winlink gateway. I hadn’t had any success, tried a different gateway, and VARA was “knocking on the door” of a second gateway. About 5 “knocks” in, the rig started this “chattering” thing. I’ve been happily using this Digirig with a number of different softwares (Winlink, WSJT-X, JS8call) for about a year.

1 Like

Bump.

Anyone?

Try activating an attenuator on Digirig. There is a possibility that very strong input audio bleeds into PTT circuit.