I am using a simple Baofeng H6 dual band radio and I programmed weather channels. Well, on frequency 161.77500 I am actually picking up WGN, a local tv network. This frequency should be reserved to transmitting weather, no? Why can I be picking a TV signal in this frequency?
161.775 isn't a frequency reserved for weather broadcasts in the US, no. CMB is a Canadian service; the same allocation doesn't exist in the US. NOAA All Hazards Weather Radio stations are on channels from 162.400 to 162.550 MHz.
According to RadioReference, WGN-TV has an IFB channel at 161.74875 and a remote audio channel at 161.77250. These are channels that broadcasters use "in the back-end" for studio monitoring and for transmitting audio over short distances; they aren't part of the actual broadcast product, but anyone with a narrowband FM receiver capable of tuning those frequencies can listen in. You're probably hearing the latter one — a small tuning error doesn't affect an FM signal very much.
Probably, not sure, WGN is very strong at your location. Tuned to 161.775 the oscillator of the Baofeng is 172.475 MHz. The third harmonic of the oscillator is 517.425. That results in a low sensitivity for unwanted signal at 506.725 (WGN frequency I assume) and 528.125, not of interest for now.
I do not know that type radio, Baofeng H6, and single conversion with IF of 10.7 MHz is an assumption for lower-cost equipment.
Added- Jan 26 - My explanation is probably not correct. Baofeng makes use of a different frequency conversion system: one-step conversion to a low IF frequency, almost baseband. Measuring the spurious signal reception of Baofeng UV3R and UV5R I found many spots that can't be simply explained without taking into account RF distortion. In older documents this effect is also known as repeat-spots. I give up. I think the explanation here below makes more sens.