This past Saturday, I went to the Columbus hamfest and ARRL Great Lakes Section Conference. It was a disappointingly small hamfest for being on the NE side of the second-largest city in Ohio (full disclosure: that's CITY population, regional population puts them third, behind both Cleveland and Cincinnati). I think I spent one hour there and about $40, including admission.
On my way out, I stuck my 10m hamstick on the truck. I knew there was a QSO party on 10, so I thought I'd jump on while driving. I figured I'd check the antenna (which I've never tuned). I set the rig to low power and CW and pushed the mic button. SWR was great.
Fearing that such a good SWR for a never-tested antenna was too good to be true and not hearing a CW tone, I set the rig to AM on low power to check. Same SWR reading. So I set the power to 2 (out of 10) and checked again. SWR through the roof. I contemplated going back in to buy another hamstick to get the small Allen wrench to adjust the stick, but decided that spending more money without a full understanding of the issue (and wondering if the problem was tuning or common mode current), I figured I would have been putting good money after bad and decided to leave and just listen on 10 on my way home until I got in the area of the repeater.
When I returned home (well, several hours after I returned home), I did a little bit of reading on the mobile HF oracle (k0bg's website) and it confirmed my common mode suspicions. Looks like I need to get an order in for some mix 31 ferrite beads. I need to do some vehicle maintenance, so I may try to do all of it next weekend.
Additionally, I spoke with another local ham on the following Monday that gave me a few pointers courtesy of a friend with a 706, including to put a ferrite on the power leads and to make sure the bonding is done well - he had to strip paint to get a good bond.