There is no need a separate antenna for Tamiya tanks with RC hobby quality radios. These radio systems were mainly designed for airplanes that fly hundreds of feet overhead and may be 1/18 to 1/4 of a mile away. If we ever got that far from our tanks, we probably wouldn't be able to hear it or see what exactly it is doing. As a rule of thumb we are rarely more than 125 feet away. When I used to fly RC we always tested our planes radio range before flying for the day. Or else you risk crash damage or injuring someone. The cheap radios included with the tank (WSN/ Trumpeter, Heng Long/Mato) have very poor range. Just try to run a HL w/o the spring loaded antenna. The receiver in the tank needs a "external" antenna. The Tamiya RC Kubel also has a primitive radio Rx and need and antenna. I run only Futaba radios. None of my tanks have external antennas and most of my ant. wires from the Rx are coiled and bound next to the Rx.

Helpfull Hint: Do not go crazy mounting components like DMDs, MFs, Recievers and such in the hull with the double sided tape that Tamiya gives you. While it is very high quality it is VERY strong. It is very had to get DMDs and MFs apart or easily to relocate or temproarily remove them. In almost all Tamiya tanks (NOTE: this doesn't apply to the M26 Pershing) 3M Velcro is a much better choice. Test fit with the velcro before peeling of the glue shield tape. The velcro is a bit thicker. That is why the caramped M26 can't handle it. I can remove a DMD and MF from my tanks in under one minute for test, repairs or hull interior cleaning. I also like very neat and tidy wires. I call it "Wire Hygiene". I makes the tank look and run better. I hate a "birds nest" of wires. Clear scotch tape is very usefull. Cover your motor and keep the battery wires away from gearboxes. If the are pinched in the gears, a fire WILL occur.
Good Luck, Bob