usb groundloop

[K5IIA]

i have a pmsdr software defined receiver.

i have a big hump in the middle of the pan adapter that i am pretty sure is a ground loop.

with no antenna hooked to unit. but usb and audio cable ran from pmsdr to pc i see the hump.

when i pull the audio cable from pmsdr but leave to pc hump goes away but when i touch the audio cable with my finger hump comes back. went to ratshack and put in a ground loop isolator on the audio cable. now when i touch audio cable no hump but as soon as i plug audio cable back into pmsdr unit the hump is right back there again with only a very small amount of attenuation.

the hump is around -70db the rca ground loop isolator may have lowered it 5db if any.

my question is how can i do a ground loop protection deal on the usb wire going to pmsdr.

one thought was to have a box that i could bring usb from pc to box. then inside box look up some type of a dc ground loop circuit and run the dc power from usb threw that and then out to the pmsdr box. but that was just a thought and wanted to see if anyone had delt with this issue and knew of a way to fix it.

[flintstone mop]

Unplug the power pak or charger for the laptop.........If it is a desk top or tower then cut the third ground connection or use a three prong adaptor..........to lift the ground from the USB cable.
One of those computer things.
I think I spent an UNgodly amount of money to get isolation transformers for all ins and outs for my sound card interface. That was plain ole audio.....you're dealing with the USB cable.

[KB5MD]

That's one of those south Louisiana camels hiding. lol

[WA1GFZ]

If the injection frequency is the same as the operating frequency you will get a 0hz hump. This is the reason flex runs a 11khz IF into the sound card.

[flintstone mop]

If the injection frequency is the same as the operating frequency you will get a 0hz hump. This is the reason flex runs a 11khz IF into the sound card.

oops forgot about that!!! may not be hum