Here is your first step to figuring this out, read:
What you want to see is if a -band pass filter- NOT in that frequency range makes the signal disappear or at least attenuate down by quite a bit.
Basically we have been over this and the article I wrote was to address just this, if you are unwilling to do the work to hook up band pass filters for the bands you want to use and are unwilling to properly shield the hell out of this little wonder and make sure even power supply noise can’t get at it then what you will have is a noisy little reciever that show up tons of unwanted signals all over the place and has a noise floor that makes weak signal work impossible.
So if what you are into is watching the noise generated by thousands of cheap LED and flourescent lamps around your house, the RF from your refrigerator supply and all the electrical noise of every car, motorcycle, airplane, power pole, WIFI router, cordless phone and lawn mower in your nieghbourhood please ignore what I am suggesting.
If however you are truly concerned with what that spike is and where it is because you want good performance begin with shielding and filtering, until you do at LEAST those two things your reportrs of noise are just that: noise…