SLM284,
I'm glad you are digging knowledge on the Interweb, It will make you only better. But one should not be ignorant to specifics of applying such knowledge to real life.
Little knowledge is a dangerous thing!
This is very academic description you've found. Nothing wrong with it. In reality, in application like present SlingBox, inductance of these common mode chokes is so small it affects only very high frequency. The purpose of this choke is to eliminate leakage and radiation of high frequency from the box into the air (power cable as antenna). The source of high frequency is high speed digital circuitry on SlinBox's main board. In present case the C.M.Choke is NOT to protect box from power supply interference.
Radiated emissions measured, according to FCC only above 30MHz. So this choke have to work for these frequencies. No reason to put larger one for lower frequency.
The link you referring to is for vacuum tube amp, where it is used to reduce power ripple / hum. In new, switch mode power supplies power input ripple reduced through comparing output to reference voltage and high gain negative feedback controlling the output voltage through varying PWM duty cycle of switching pulses feeding pulse transformer and rectifier. (ok, this is pretty academic too). Everything done usually by single little chip.
Enough with generic info.
If without this choke you have interference on the picture (probably only from analog inputs, ATSC RF input probably produces clear images), most likely your power brick has problems, and probably with similar caps just like the couple of 470uF on the main board. External power adapter should not produce any high frequency interference. If it does - change caps in it too or get new power supply.
I'm running SlingBox 300 without common mode choke and without PTC with zero interference on any input.
And legal disclaimer: I'm not advocating to remove c.m. choke from Box's power input, it is there for a reason (FCC compliance). I'm stating that without, c.m. choke, for the end user, there is no difference if choke is there or not. Oh... even that must be corrected: without this choke your cell phone or radio or TV next to your SlingBox might stop getting clear reception of intended signals, because of coincidental interference, though chance are sooo slim, it is practically nothing.
Cheers!
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Trust me, I'm a professional! ;-)