Make brine
In a small saucepan, combine apple juice, salt, sugar, cardamom, and pepper.
Bring to a boil, remove from heat, and add the ice to cool the liquid. An ice bath can further speed the chilling: place the bottom of the pot in an ice bath and chill to below 70°F (21°C).
Trim the tenderloins of excess fat, if any, and silverskin.
Tie the tail end under the rest of the tenderloin.
Place the tenderloins and the brine in a large zip-top bag and refrigerate for 1–1 1/2 hours.
Heat your smoker to 250°F (121°C) with the wood of your choice. (Apple is great for this apple-laden dish.) Use the Pro-Series air probe attached to your RFX GATEWAY to monitor the smoker temperature.
Remove the tenderloins from the brine, pat dry, and season with the BBQ rub.
Insert RFX MEAT into the very center of the loin, being sure to hit the minimum insertion depth, and set the high-temp alarm for 145°F (63°C).
Smoke the tenderloin, monitoring the smoker temperature with RFX GATEWAY's other input channel. (Set the high alarm for 275°F [135°C] and the low alarm for 225°F [107].)
When the high alarm on the meat sounds, verify the temperature with your Thermapen ONE. Remove the meat from heat, cover with foil to allow to rest, and make your sauce.