The AM Forum

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.

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.

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

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