Inspired by Mark W4CK, Chris K4EFZ and Del W8KJP, I am also sending my experiences with HF mobile CW operation.
Since May 2002 when I bought my new toy MX-21S CW/SSB 2 W QRP transistor receiver/transmitter from Mizuho, I am experimenting with HF CW from the car even with QRP power. I live in Kostica, a small town about 45 miles from Prague, where I work for MIRACLE Network Ltd. as an export manager of sales of microwave connections. Since I commute this distance twice a day, I spend about 2 hours a day in the car. As Mark W4CK said, I'm now spending this time quite productively on bands!
For operation I use a Mizuho MX-21S for 15m CW/SSB with a maximum power of 2W, which has a built-in VXO, RIT, ATT, 4 crystal IF filters - all in a practical size, including a battery if required. Charging batteries via built-in circuits is not a problem. I use a DC-DC adapter connected to the car's main battery, of course fused.
The second receiver I use is Dave's awesome Small Wonder Labs SW-20, K1SWL. I built this famous receiver from the original construction kit. It operates as a mono frequency superheterodyne on 20m, 3 crystals at 9 MHz IF, uses a NE602 IC in the mixing stage with a tuned bandpass preamplifier. I only set the output to 1W due to battery consumption in portable operation, but the PA can handle 3W output. (Many thanks for all the mods emailed by Fraser, G4BJM!)
Antennas are simply homemade vertical mobile "whips" mounted on a magnetic base in the middle of the roof. I mostly use about 1.5 to 1.8 m long "whips", originally intended for CB, which are fine-tuned in the car with a manual tuner and an SWR meter. I know it's not an ideal electrical solution, but due to the company rental car it is not possible to use a fixed configuration with regular tuning. I tried several times the telescopic "whip" from Mizuho with a 1.5 m radiator tuned with a coil in the base. In my case, there wasn't much difference between these configurations.
I was really impressed how both radios work even with very simple antennas when I tested the operation in hills and mountains. Above all, the reception was so clear and clean that I thought it couldn't be from large industrialized cities. In the months that followed I tried various mobile configurations of both radios with "whip" antennas with varying degrees of success. The main problem was the low power, which never exceeded 1.5 W. I also did not have a suitable paddle ready at the time, so I used an old army pump key during mobile CW operation. Overall, I can say that HF mobile CW is usable even with QRP power, but be aware that many operators will not be patient with your weak signals, and this temporary setup is not suitable for long "rag-chew" conversations.
By mid-November 2003, I noticed a lot QSO since spring 2002. Also some CW club QSOs on 15/20m. Now I'm preparing a little more power for serious mobile traffic, especially when conditions are bad, like a few weeks ago. Mobile CW even with QRP is amazing for longer trips as Del W8KJP/m said… You can be with your best friends over the radio and that time is much better spent and more productive than talking on the phone about trivial things…
73 de Petr, OK1RP/m