Goat Mountain is a reasonable easy summit to access that's not too far from Portland. For anything but high clearance vehicles, the last 1.5 miles to the summit will be on foot, but it's not too far. This site is popular with OHV as I saw seven in two hours on a chilly and damp November weekend.

Start from Molalla, Oregon at the four way stop downtown and go 15.8 miles east on Highway 211. Turn right on Hillockburn Road and go past a group of three gates where the paved road continues through the open gate in the middle.

 When the pavement ends after about 9.2 miles you find a large four way intersection - take a slight right and go up hill from here. After about 1.7 miles you'll come to a T-like intersection with yellow gates to the left and to the right - take the left. After a half mile, you come to the summit access road that will require a high clearance vehicle. The coordinates for a place to park are 45.11995,-122.28394. Usually there would be fantastic views but this day I was inside a cloud - windy and damp. This spot has LOS to the Portland Metro area for UHF and microwave contacts and good places for HF wire antennas - but be careful not to put any wires across a road or trail - there can be a lot of traffic. The RF at the summit was blocking the front end of my Yaesu HT - you might try a yagi or a rubber duck antenna instead of a gain vertical as I was showing about S7 but hearing nothing from callers on 2m FM.
You should also check out the report by N7UN here: http://www.pnwsota.org/node/241.