I second the OCFD as a good antenna for the C21 or any older rig without a tuner. It's nice to have a no-tune antenna that covers so many bands. I re-worked my original home-brew 40m Carolina Windom into a more traditional 80m 1/3 OCF Dipole a little over a year ago and it's been great to use with my TenTec Century/21. I do have a decent RF choke on the incoming coax to ward off common-mode problems and it works great for me on all the bands I want except 30m. I'm getting better results from the 80m OCFD on its resonant bands than I did from the Carolina Windom.