Re: Airspy R2: Interferences with antenna disconnected


On 09/13/2017 01:23 PM, Doug wrote:

On 09/13/2017 08:09 AM, Ruben Navarro Huedo (EA5BZ) wrote:
Hello Airspy friends :)

I am doing some more tests with my R2.
Here you have 2 screenshots. Both screenshots are with NO antenna and NO coax. (Only R2 connected to PC).
I am using 4 toroids on USB cable.

One screenshot with Gain 0 and another with Gain 10.

Why do i have these interferences?

Tnx a lot.
This is a series of harmonics of something that is oscillating at about 160 KHz, OR the product of two strong signals that are 160 KHz apart. I would connect a 50 Ohm termination across the input to
your SDR and see if it makes a difference. Since you have no connection to the input, it may be the radio itself that has something oscillating inside it. Or it's even possible that there is something
inside your computer that is feeding back thru the USB cable. Do you have another computer--preferably with a different main board and different video card? See if the signals go away or are at a
different spacing. If you put a few more toroids on the USB cable, does that help? Put them right close to the radio.  Also, what is that big signal about 138.34 MHz? Where is that coming from?
After you terminate the input, try wrapping some aluminum foil around the whole radio and connect it to the outside of the input connector. Make a good solid connection.

--doug, WA2SAY, retired RF engineer.

PS: My connection cannot seem to reproduce the illustrations. Other readers will have to look back at the pictures in your original post.

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