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G4SGI England flag England

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Ever since I returned to cycling, I have had a hankering to try operating mobile. I never learned to drive so I’ve never experienced the fun of operating a mobile station from a variety of different locations when on the move. Cycling offered an intriguing challenge that sounded worth taking up. So in July 2007 I took the plunge and fitted out a mountain bike for radio. This is the story of my adventures so far.

The first thing I considered was the type of bike I wanted and the types of radio operating I envisaged doing. I wanted to do both HF and V/UHF, and to operate from the kinds of rural but nearby places I cycle to at the weekend (combining two pastimes into one). Having consulted chapter 7 of The Amateur Radio Mobile Handbook, which is dedicated to bicycle mobile, and various other manuals, I realised I needed either a touring or hybrid bike with a rear luggage carrier to provide suitable antenna mounting points. However, after reviewing a number of bikes I realised that the build quality of a normal road bike would be too poor for the rural places I had in mind, so I ended up using a mountain bike modified with mud guards as protection and a luggage carrier.

The selected bike is of sturdy construction and has both front and rear hydraulic disc brakes because of the weight it would be carrying, however, I deliberately selected a ‘hardtail’ bike with only front shocks to simplify modification for mounting antennas at the rear. The mechanics are much simpler and there are fewer problems with operation of the bike to contend with. On no account can the bike frame be drilled or otherwise modified for safety reasons.

Once I got the bike, I needed to fit it out with antenna mounting points. I did this by fixing a commercial HF mobile mounting plate already fitted with a 3/8 inch mount to the bike’s luggage carrier. The plate just happened to be just the right size and all I needed to do was remove a plastic keyway from the carrier and drill some holes in the plate aligned with some existing screws on the carrier. But before going ahead I carefully drilled a hole for a bulkhead SO-239 adjacent to the 3/8 inch HF mount for a V/UHF antenna. Everything fitted together well and I ended up with a very professional looking antenna mount just behind the saddle. For HF operation, I realised I would want a ground plane when stationary so I put four bolts on the antenna plate to provide attachment points for crocodile clips so that I could quickly clip on radials. I earth bonded the plate and luggage rack to the frame using a short piece of mains earth cable so that the bike frame could act as a counterpoise. The books told me this should work well on the upper HF bands but not so well on the lower bands.

Connection to the antennas was setup using two short lengths of RG-58 coax terminated in BNC sockets. This connector was chosen for fast hook-up, but quick release in case I fell off the bike, in which case not twisting the bayonet on the BNC should make it fall apart easily. I colour coded the cables red for HF using the 3/8 inch mount and blue for V/UHF using the SO-239 bulkhead socket.

Next, was the choice of antenna. I wanted to operate both V/UHF and HF (not ecessarily at the same time). I also needed to take into account the fact that there is no effective round plane on the bicycle. So for V/UHF I used a dual band 2m ½ wave and 70cm 5/8 vertical with excellent results. I also tried a 5/8 over 5/8 colinear (just for laughs) but kept clipping tree branches as I cycled along the country roads. This would prove to be a more serious problem for the HF antenna, as well as its weight. I started with a selection of mono-band HF mobile antennas for 6m, 20m, 40m and a multiband Outbacker antenna. I managed to break the 3/8 mount on the first trip out using the Outbacker because despite my efforts to avoid trees, the antenna still caught on branches and bent the mount. This particular antenna is also very heavy, which did not help. I overcame this problem by fitting a spring to the 3/8 mount – it may seem obvious, but on a push bike weight and complexity are real problems.

There are several ways in which the radio can be mounted. I have tried using a chest harness to hold a 2m handheld connected with a length of cable over my shoulder to the antenna, and a high power 2m mobile radio in a handlebar bag with 2.8AH lead acid battery. The latter was less well engineered because the mountain bike has outsized handlebars, but the bag expected a smaller standard size. I fixed this by lashing the bag’s mount to the handlebar using washing line – not pretty but effective. My favourite way of mounting the radio is to wear a backpack, and this is how I have operated using the IC-703 on HF. The backpack can hold the radio, the battery, a headset and other accessories. This particular radio allows you to mount the control head in a pouch on your belt Using a separation cable, while the rest of the radio sits on your back. This is effective and comfortable while still allowing you to cycle safely.

Over the winter of 2007 I continued to improve the system. I obtained a full face mountain biker’s helmet and fitted it with a motorcycle headset. This allowed me to operate much more conveniently using a Kenwood TH-D7 2m/70cm handheld kept in a chest harness while cycling along. The headset comprises a boom mike that fits snugly inside the helmet and a ‘ring’ type of PTT switch intended for the handlebars. Instead of mounting the PTT on the bike, I wear it on the tip of my left index finger. This allows me to form an ‘OK’ with my left hand while still gripping the handlebars so that I can key the mic. without interrupting the important business of riding the bike. I also retain the single cable connection between me and the bike – my preference for safety. This refinement worked extremely well indeed and I got excellent reports on my 2m FM audio through the local repeater.

I took this one step further and build a small adaptor so that the headset would work with my IC-703. This extended the system to HF operation while actually in motion, previously I had to be static mobile to operate on HF. In March I used the opportunity of participating in the ARRL DX SSB contest to attempt transatlantic 20m SSB QSOs at 5W on the IC-703 while cycling along. The result was an impressive but small selection of QSOs with East Coast American stations in RI, PA and NY as well as Canadians in PEI and ON.

I haven’t perfected logging while cycling – I currently have to stop to write down the QSO details, so some form of voice recording may be the next project. In the meantime, I am looking forward to the 6m sporadic E season as this will be a chance to use the IC-703 for continental contacts while out and about.

Overall, this has proved to be an interesting and rewarding project with lots of promise for further adventures. It’s been real fun at a time when conditions on the bands have been really poor. If you can’t work any DX, you can at least make single skip working a bit more interesting and keep fit at the same time.

Project Update (December 09)

After successfully installing a D-Star repeater for Gloucestershire, GB7GL, I am now operating bicycle mobile using D-Star on a regular basis. Equipment is an IC-E92D with HS-94 headset and modified VS-1L (to allowme to use the finger ring PTT switch). I've found that the best antenna to use on FM is a 3x 5/8 colinear as this reduces mobile flutter considerably. This also works well for D-Star, especially as the repeater is about 20 miles away.

To see where I have been cycling search for "G4SGI-9" on APRS.fi.

Project Update (July 13)

I now alternate between using the original setup I devised (shown in my 2011 video) with the antenna mounted on a modified luggage rack on the bike, and the new setup with the antenna mounted on a Bobblebee backpack (as shown in my 2013 video). There's no significant difference in RF performance between the two.

6321670 Last modified: 2015-07-16 00:30:05, 9476 bytes

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