Digirig I’ve had for a while. I assume “mobile” as it has CAT. FT-857D. WSJT-X. Originally was using non-ferrite USB I got with Digirig (probably two years ago). Cables are Digirig 857 cables with ferrites.
FT8 set up is working fine with WSJTX, but only at about 10W max. Above 10, possibly 15W depending on band, the USB port scrambles and control of the 857 is lost, usually requiring reboot of the PC. This happens across two different brands of PC, each with different operating systems.
This occurs with two different antenna setups. One is an EFHW cut for 80, on a tuner. The other is a 20m dipole, also on a tuner.
So far, I have:
Purchased the newer Digirig USB cable with the ferrites. No change
Added a common mode choke to the coax. Seems a slight increase in power capability before failure
Purchased the Digirig USB isolator - does not work at all. CAT fails with device in line and no settings change
I don’t know what else to try from an RF perspective, and I don’t understand why the USB isolator isn’t working at all. The OS I’m testing on with the isolator currently is Debian Linux. I haven’t tried it from the Windows laptop, but I would have expected an “isolator” device not to have affected the USB configuration.
Any tips or pointers? Anyone else have experience with this isolator? Thanks!
A bit of additional information since I posted. Using just the USB cable, the Digirig is identifiable in the system (still Linux) as a CM108 audio device both for audio input and output.
With the USB isolator in-line however, the system doesn’t even recognize that a device was connected.
I also tried on a Windows machine. The Digirig by itself is recognized as a USB PnP Audio device. With the isolator, it’s not recognized at all.
Do I have a bad isolator, or is there a driver I’m missing?
As far as driver is concerned, there should be no difference with or without isolator.
Please reply to your order confirmation if you want to try a replacement isolator.
When it comes to RFI, the best solution is choke on the feedline. What do you use for that and which side of the tuner do you use it?
Thanks Denis, I guess I’m going to try a different isolator. It’s not working with any USB device let alone the Digirig.
My choke is on the antenna side of the tuner. It’s RG58, six turns each direction on a FT240-43 core.
Edited to add, I bought the original isolator from Amazon. Claimed to be Digirig brand, but no stickers on housing like shown in store here. Returning to them. Ordered one from the actual DigiRig store just now.
I’ll report back when it arrives. The other thing I wondered about is that the USB cable I have is the coiled one with ferrites in both ends. I noticed that there’s a short non-coiled one available. Are the ferrites in the coiled one sufficient or should I consider the shorter straight cable? Or for that matter, some other USB connection option?
Shorter USB cable is less susceptible to RFI, but all of that are secondary measures once RF is allowed back in the shack. The most effective option is to block it from getting there in the first place. It sounds like the choke you use should be sufficient, but somehow it still allows some of the RF through.
Update on this issue. I’ve received the isolator that I ordered directly from DR today. I have not yet had a chance to try the complete setup, but I did try placing the isolator inline with a USB device (a mouse) and confirmed that the device functions with the isolator in line as expected.
Apparently something was wrong with the one I sent back to Amazon, because it would not even do that.
Since my last post I tried using my DIY RF choke on a different piece of equipment with the same antenna I’d been using and discovered I was getting some weird power dependent SWR issues with the choke inline. I’ll report back when I figure out that issue and can test the setup with a known good choke.
I’m not sure how the presence of the choke would affect the “ground plane left”. In the configuration I was using, the choke was installed on the antenna side of the tuner AT the tuner. From there signal was running through 50ish feet of RG8x to the unun connecting to the EFHW. So as to prevent the EFHW from using the coax as it’s counterpoise, there’s a counterpoise connection from the unun to earth ground. In that configuration, I wouldn’t have expected choke placement to have a bearing on RF signal ground. Am I missing something?
You situation may be different, but one of the reasons for adding a choke is to stop the antenna system from using the shield the feedline as part of its ground plane. If the shield of the coax was the primary source of the counterpoise to the radiating element then choking it off may leave antenna more unbalanced.
Right. I understand that, but to use the choke to prevent using the feedline as part of it’s ground plane, the choke would need to be at the antenna end of the feedline. In my case, I installed the choke at the radio (tuner) end of the feedline to prevent RF back to the radio but not substantially affect the feedline beyond that. The antenna’s ground plane is supposed to be the counterpoise attached at the antenna unun (the antenna feedpoint) and not the coax to begin with.
It’s certainly conceivable that what’s supposed to be my antenna’s counterpoise (groundplane) isn’t working and I should try to check that somehow, but where I installed the choke shouldn’t have substantially affected the antenna to feedline interaction only the feedline to radio interaction.