Bicycle Mobile Radio

Introduction

For hams who like to bike, there is an increasing need for bicycle mobile operators at some public service events (PSEs). There are several reasons for this. First, like EMTs and police, hams on bikes provide an easy set of mobile eyes in crowds or spread out events allowing situational awareness to extend beyond a fixed station. Second, bikes can easily plug visual coverage gaps, such as bends in rivers, between fixed stations that would require multiple fixed stations. If your ham community is like mine, it is sometimes difficult to find enough radio operators, and bicycle mobile becomes a force multiplier. Bikes are also a fairly low key way to provide a "Tail End Charlie" for foot races, especially where the path is inaccessible to or impassible for vehicles.

For the ham, there are a couple of benefits beyond just serving in PSEs depending on your motivation. First is the exercise aspect. But if you want aerobic exercise, this isn't going to do it for you. There really isn't a reason to go faster than 10mph in most cases. This is a very leisurely pace for most people. In one instance, I had to bike almost 20mph for the better part of 10 minutes to catch up to another bicyclist participating in the event to provide an unplanned Tail End Charlie. Second, like everything else in ham radio, is the technical aspect. Bicycle mobile radio can be tough to make work well on multiple fronts - antenna performance, antenna attachment, mounting a radio, and safely operating a radio while bicycling to name a few.

Like everything else, there are often many ways to accomplish the same thing. This is how I made it work for me. I encourage you to experiment to find what works for you. To that end, I provide links to other articles on bicycle mobile radio, which I used to help me figure out what I wanted to do.

http://www.arrl.org/files/file/Technology/tis/info/pdf/9303052.pdf
http://www.gobahams.org/how_to_wire_a_bike.pdf
http://www.bikexprt.com/bicycle/antennae.htm

What's So Hard About Bicycle Mobile Radio?

You can't just slap a radio and an antenna on a bike and expect the setup to work well.

First, a bicycle is a lousy ground plane. Although most bikes are made of metal or conductive materials like graphite, the structure of the bike has a vertical orientation whereas ground planes are horizontal and radials are typically bent at 45 degrees. Second, if you think the frame of your bike looks like a radial, it is definitely not the correct length if you are used to cutting radials to specific lengths.

Second, you would think it's easy to carry and mount a 5W HT, i.e. "walkie talkie", radio. While not difficult, it's also not trivial especially if you're not well versed in all of the possible attachments and techniques. While 5W is usually sufficient, especially given the much better performance of the antennas you will be using compared to the rubber ducky antennas, maybe you need the power of a 50W mobile. This isn't out of the realm of possible, especially with modern lithium ion batteries that keep the battery pack light and small while still providing enough amps and energy.

Third, the bike is a moving machine and so is its rider. Bicycle mobile operations really force you to think about how to properly secure everything. You not only need to protect your equipment from vibration, shock, and chafing but you also need to do this in a way that lets you safely operate the bicycle. Providing service loops and securing coax and other cords to prevent entanglement with both you and the bike is paramount.

Finally, there is the issue of operating the radio while also safely operating the bicycle. Most important is the need to be able to operate your microphone in a way that let's you safely control the bike. The radio should also be mounted in a way that's easily accessible for volume adjustments and frequency changes. However, since you'll likely stop the bicycle to make these changes, it is much less important.

Antennas for Bicycles

As mentioned before, bikes make horrible ground planes, radials, and counterpoises. You either need to provide these things as part of the antenna installation or use an antenna that does not require a ground plane. Adding ground planes and radials is not very practical and introduces safety problems because of how they would hang off the bike. Adding a counterpoise is not too difficult and can be done in an effective and safe manner.
5/8 wave bicycle antenna with counterpoise from QST, March 1993
The other option, using an antenna that does not require a ground plane, means finding an antenna that radiates like a true dipole while being end-fed (1/4 wave antennas do but with a ground plane or radials). What you need is a half wave antenna. And there are two types of these. The first is what is colloquially known as a half wave antenna (duh!). The second is the J-pole. Electrically, the two really only differ in the type of matching network between the feedline and high impedance (typically 1500-5000 Ohms) end of the antenna. Each has its pluses minuses.

For the half wave antenna, I use the Larsen 150B HW with an NMO mount. For the mount, I had a piece of scrap aluminum from an airplane project and used a step bit to make the required 3/4 inch hole for the NMO mount. The NMO mount I used was the Larsen NMO thick surface mount, which allowed for some clearance between the coax and bike frame. This particular NMO mount uses a weather resistant housing at the feedpoint and a crimp style connection improving the weather resistance and providing strain relief for the feed point. If you need to be able to get to a backup repeaters during an event, the half wave antenna approach may not work very well since by definition it is only for one frequency, normally in the VHF band, and backup repeaters can sometimes be in the UHF band.

There are other approaches possible using other connectors and mounting styles. Just make sure that whatever mounting style you choose can properly support the antenna while being jostled around on a bike and also take the wind loads.

For the J-pole, the obvious choice is the roll-up style J-poles made with twin lead because they are light and easily secured to bicycle flags, which are themselves easily secured to the bike. If you are not mechanically inclined and don't want to make your own mount, this is the way to go. The roll-up J-poles that you can buy almost universally come with a short lead of RG-58 and BNC connector all ready to connect to a radio. Be warned, J-poles can be affected by how you secure it. Vinyl electrical tape can change the tuning of the J-pole, and theoretically J-poles don't like anything, non-conductive objects included, to be near the (high impedance) ends. In practice, I haven't found either concern to adversely affect the J-pole performance for the kinds of ranges in normal use at PSEs.

Like the half wave antennas, J-poles will typically only work on one band. However, the DBJ-2 antenna has an ingenuous design that allows it to work reasonably well on both VHF and UHF. For about $30 (2015 prices), you get a very good roll-up J-pole and support the designer's graduate students at the same time! A J-pole on a bike flag also has another advantage right out of the box - visibility - which is very important if you are sharing the road with non-event traffic. You could affix a flag to the half wave antenna, but bike flags already come ready to go!

The performance of the half wave and J-pole antennas on the bike are spectacular when compared with a rubber ducky or 2m whip. I can open a repeater here in Dayton, OH, about 8 miles away with 0.5W on my 2m whip but not with 0.05W. The same HT connected to a half wave antenna with 4ft of RG-400 coax (same as RG-58 but lossy compared to RG-8X or RG-213) will open the repeater with 0.05W! When an organizer for an event says he needs operators with 25-50W (typically mobile) capability at certain stations because of range or terrain, you might be able to get away with a 5W HT with a roll-up J-pole hanging from a pole or tree!

Protecting Your Equipment

Like any vehicles, bicycles experience shock and vibration loads that must be appropriately dealt with to protect your radio equipment. Shock and vibration ultimately lead to fatigue and chafing failures. Very rarely do shock loads result in basic strength (limit load) failures, but it is a possibility. Bicycles experience far more shock and vibrations loads than do cars, so a technique that works on a mobile car installation may not be appropriate for a bicycle environment. A better analog would be a aircraft environment. Be thinking about rubber isolation mounts and feedlines and wiring with stranded conductors such as RG58 and RG400.

Another consideration is that equipment needs to be kept away from moving parts to avoid entanglement. This not only includes the moving parts of the bike but also the moving parts of the person riding the bike! Various attachments techniques using standoffs need to be considered. Personally, I make standoffs out of a pair of aviation style clamps, including Adel and AN742 clamps. Spiral wrap is needed where wiring and coax may chafe with the bike frame or anything sharp unless a standoff can be used. Lacing cord can also be used to secure coax and wiring where chafing isn't a concern. If you use plastic zip ties, they will eventually cut their way into wire insulation. If the wire or coax contacts the bike frame or could come near to a sharp edge, spiral wrap or some other protective measure, including standoffs, should be used to prevent chafing.

Last but not least is providing strain relief between parts that move relative to each other and where connectors attach to equipment. Wiring and coax may need to cross between the bike frame and handle bars to connect to a radio on the handle bars. In these cases, you need to plan for a generous service loop to allow for the range of motion and reduce strain on connectors. To further reduce strain on connectors attaching to HT radios, try to use SMA connectors with wide bases such as the one Diamond produces. Rather than have the connector on the radio side take any bending loads and cause problems with solder joints, the wide base forces the radio chassis to take those loads instead.


Mounting Equipment

Of all of the equipment, the radio is the most sensitive to shock and vibration. There are various methods to mount a radio to a bike, and most involve some sort of cell phone style mount that grips the handle bars or the frame. Ram makes a series of mounts called X-Grip that are designed to grip a smart device as if fingers were grasping it. This ensures that most cell phones and tablets are compatible.


Some HT radios such as Kenwood's TH-F6 are fairly small and do not fit well inside the X-Grip. In those cases, it's best to make an adapter plate out of Lexan or aluminum sheet about the size of a smart phone and use the belt clip holes to attach it to the radio. Kenwood's HTs use 3mm machine screws spaced 30mm apart. The use of the adapter plate also allows the radio to sit higher in the mount allowing clearance above the "fingers" to attach the speaker-mic plug. There are other mounts sold by ham supply companies that directly utilize the belt clip on the back of the HT to hold the radio and optionally use an elastic band over the radio to provide additional security. The only mount I've tried is the X-Grip, and even not having tried other mounts I think the X-Grip is by far the best for mounting an HT. It can even mount the control head for a mobile radio such as Kenwood's TM-G710 series.

I have a dedicated piece of RG400 coax running from the back of the bike where the antenna attaches. I run this to the front of the bike and use the brake cables to run a generous service loop to allow for turning of the handle bars and provide strain relief at the radio. At the radio, I use a wide base SMA connector to provide additional strain relief at the connector.

The coax is secured using a variety of methods including avionics lacing cord and aviation style clamps. Lacing cord is nothing more than waxed nylon string. Nylon won't dig into insulation like other methods will (zip ties), and the wax provides some stiction when you have to tie knots, which prevents the knots from coming loose. For small diameter bundles, you use a short piece of lacing cord to first tie a clove hitch, and then you lock it in with a square knot. Additional techniques can be found in various places including aviation's AC43.13-1b. The saddle bag frame happens to use rods whose diameters are small enough to use aviation style clamps to create a standoff to keep the coax away from the tire. The plain metal clamps are used on the rods, and wedge style Adel clamps are used to hold the coax.

Operating a Radio While Biking

When the bike is stopped, you can operate a radio just like you would do without a bike. The real challenge with bicycle mobile operations is being able to safely operate the bicycle while also operating the radio. Remember the first is more important than the second! The problem isn't really manipulating knobs and buttons on the radio because you will probably set that up before start to bike and never touch them again. What's hard is being able to operator the mic and listen to the radio while also operating the bike. Ideally you want to be able to keep both hands on the handle bars and be able to operate the mic. Second best is a mic that allows for one hand to be on the handle bars. A workable, stop-gap approach is to actually hold the HT in your hand. I actually had to do this before in an unplanned situation when I had to chase a bicyclist in a triathlon who desperately needed a Tail End Charlie for their safety. I had already mostly secured bicycle mobile operations, and if I had taken time to set it back up properly there was no chance I was going to catch up. It was workable but only for a short while and only because the last rider was relatively slow.

To keep both hands on the handle bars requires a push-to-talk (PTT) switch that can be attached to the handle bars where you normally place your hands. But it can't constantly get in the way and be accidentally pushed! I put mine near the brake handles between where my thumb and forefinger lie. That allows me to move my thumb to actuate the switch and still be able to quickly pull the brakes. As for the speaker, it either has to be an earbud of some sort or an external speaker loud enough to be heard with road and pedestrian noise, not easy with the speaker power coming out of an HT. The mic that allows you to keep both hands on the handle bars is more challenging. It can be a boom mic or a mic designed to pick up mechanical vibration such as an ear bone or throat mic. Beware! In my limited experience, the ear bone mics have terrible sound quality either having almost no treble, which makes for poor intelligibility, or makes you sound like you're talking in a tin can. Throat mics are better. But it may be a problem with the manufacturer and you get what you pay for not the style of mic. The MFJ ear bone was horrible at $30 (2014) while the Planet Headset mic was awesome at $130 (2015).

There are other approaches that allow one hand to remain on the handle bars. Boom mics often have a PTT that dangles down and clips to a shirt. To activate it requires taking one hand off the handle bars. The MFJ boom mic that I own does not fit securely enough around my ear so is quite loose. It works but requires frequent adjustment and sometimes falls off. There are ear bud speakers with the mic built into the PTT in a similar clip on arrangement. There are the normal external speak-mics that fit in your hand. To safely use these requires clipping them onto something like your shirt. However, a lot of these speaker-mics have less than desirable mic and speaker sound quality. All of my radios are Kenwoods, and I discovered that the KMC-45 speaker-mic for their commercial HT radios not only has the same plug as the ham radios but also has excellent speaker and microphone quality, maybe better than what's in my TH-D72A. The speaker is actually loud enough to use on the bike as-is. This mic is more expensive than its ham radio counterpart at $70 (2015). However, apparently you get what yo pay for. Just be careful because there are $20 Chinese knockoffs of the KMC-45 on eBay and other sites that probably aren't worth $5.

The table below summarizes how I would rank the various speaker-mic-PTT options for bicycle mobile in terms of cost effectiveness with the best at the top. Your mileage may vary.

KMC-45 (best)
  • $70
  • Excellent speaker and mic
  • Requires a free hand
Planet Headset throat mic
  • $109-$130
  • Good vibration mic
  • Excellent speaker
MFJ-284
  • $30
  • Good speaker and mic
  • Loose fit
MFJ-295/296
  • $15-$20
  • Tinny, noisy mic
  • Tinny speaker
MFJ-283 (worst)
  • $30
  • Mic has too much bass
  • Good ear bud speaker quality

One other comment on operating the radio. I've found that it's difficult to converse with a pedestrian with an ear bud with someone talking on the net. Maybe the human brain has trouble taking in two signals through separate ears. I find that its much better to have both ears available to hear both signals (muxing for lack of a better word), which is what an external speaker-mic allows for. Of course this isn't an issue while actively biking. But when I stop there is a tendency for pedestrians to want to converse or for PSE participants to ask questions. If there is someone talking on the net, I usually have to turn the volume way down in order to talk with the person in front of me. Otherwise I can't understand a word they are saying as if my brain were too distracted.

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