Bicycle Mobile

I’m a long-time avid cyclist and was a daily bicycle commuter when I was first licensed in 1995. My first radio was a handheld transceiver (HT), as is often the case with new hams. As a technical nerd, it was natural for me to mount it to my bicycle for use during my commute. This old photo shows one of the many variations that I had tried. I did well with 3-5 watts, but I still added a 30-watt amplifier and pair of 6.5-Ah lead acid batteries at some point (heavy!). I even rode that setup on an 1100-mile bicycle tour. Today, my options are both more sophisticated and lighter.

I’ll start by sharing my current radio platform, a 2014 Trek Crossrip LTD. In short, it’s an aluminum utility bike (early “gravel bike?”) with 2×10 mountain gearing, cable-actuated hydraulic disc brakes, and racks for panniers. As a retired(?) randonneur, I’m known for carrying plenty of supplies to keep myself independent on the road. That practice eventually led to the nickname, “Captain Overpacker.” My bike weighs about 30 lbs with racks/fenders, 40 lbs with radio equipment, and up to 80 lbs at full load with panniers (an uncommon occurrence). See my somewhat dormant website at CaptainOverpacker.com for details.

Using an HT is an easy choice for battery conservation, not to mention saving space on the handlebar. I carry an Icom ID-51A dual-band D-STAR radio, which consumes less than 100 mA during receive. It lacks Bluetooth; so, I have to use corded microphones. The good news is that it’s not hard to find compact headsets for HTs. I chose an SPM-1430 by Pryme. An HT limits my output power to only 5 watts. That’s sufficient in areas with good repeater coverage. However, not all of my rides are well covered.

I managed to acquire one of the few remaining dual-band amplifiers from Mirage, the BD-35 (no longer in production). The BD-35 is capable of outputting 45W on VHF and 35W on VHF. Of course, it scales back the output power with less input from the HT. This image shows the amp’s graduated output power; my HT’s “Watts In” is in red. The final version is compatible with D-STAR, which allows me to use my HT to its full potential. Best yet, I can leave it turned off when it’s not needed and enjoy very low battery consumption.

Selecting a bicycle mobile antenna is easier than most hams believe. Speaking only about the 2m band, some opt for a compact 1/4-wave antenna while others go for a larger 5/8-wave. Both may work, but performance will be compromised since a bicycle offers almost no ground plane. I think most seasoned members of Bicycle Mobile Hams of America agree that a 1/2-wave antenna is the way to go on a bicycle since it works without a ground plane. Sure, it works better with one, but performance is good without. A twin-lead J-pole that’s fastened to a fiberglass safety flagpole is a top performer on 2m (see photo in the album below). However, most opt for a mobile antenna since they’re compact, readily available, fast to replace if broken, and easy to mount/dismount. I use a Diamond NR770HBNMO, shown above, since I already have one on my car. Selecting an HF antenna for a bicycle is more of a challenge. As with any mobile HF antenna, everything is a compromise, perhaps even more so with a bicycle. I’m using 66 inches of RG-58 feed line; the losses are minimal.

Powering a bicycle mobile radio is much easier today than when I first started because lithium iron phosphate (LiFePo4) batteries are abundant and affordable. My Bioenno 15-Ah LiFePo4 battery weighs just 4.3 lbs, yet lasts four times longer than my old lead acid batteries. Its voltage level stays above 13 volts throughout its discharge cycle, meaning that I could use 50W power for a most of the day. Best yet, it will last about 2000 charge cycles. I also have a 4.5-Ah battery that I carry for local riding.

I admit that 50 watts from a bicycle is insane! I used a 30W amplifier in the 1990s, which was before RF exposure calculators were readily available. I survived my 30-watt days, but ARRL now has an easy to use RF exposure calculator. I’ve determined that 8 watts is about the limit for safe RF exposure for my bicycle on both the VHF and UHF bands when using FM modes (my antenna is 16 inches or 1.33 feet from my hips). Today, I carry only the HT, along with a smaller 4.5-Ah, 1-lb LiFePo4 battery during my routine rides. The BD-35 is small and easy to add for use during rides in remote areas. If I need full power for an emergency, then I can stand in front of the bike to achieve a safe distance from the antenna.