The Tricycle Trailer

3 min read
Trailer Internal

The Tricycle mobile is engineered in a similar way to the Pedestrian Mobile and consisits of a modified Alinco DX-70TH which runs on a 22Ah gel type battery the Alinco is set to run low power (5W) and its output is fed into a modified KL500 linear amplifier,the amplifier is powered from an additional 50Ah deep cycle gel battery mounted under the wooden boards. The output of the system is continually adjustable to power levels down to 10mW on low power to a maximum of 250 Watts on high power, however the battery life is limited when running maximum power output so I usually run it at 100 Watts maximum output power this provides me with around 3 hours use with the amplifier switched on, but I can increase the power if needed.

The antenna is either a modified MFJ-1979 telescopic full sized quarter wave mounted on the rear of the trailer and is used for all bands from 10M to 20M (by length adjustment) or a 10M long fibreglass pole (with a spiral wire) that fits into the rear of the bike for 40M operations, however the 10M long pole is only viable for use on calm days!

The headset is connected via a bluetooth link to the radio behind me which makes operating on the move easier. The radio is connected via a bluetooth sender/receiver so that the radio is a totally hands free operation on the move.

The ground system is a little unusual; the system needs to be truly mobile and as I am usually near to the sea when I operate, the ideal ground-plane already exists, its just a matter of getting a low impedance RF connection to the sea (more information under ground tuning)

This low impedance ground connection is obtained by isolating ALL the radio equipment from the metal chassis of the trailer and connecting the ground line from the radio chassis via an LC series tuned circuit that has linked coupling to an RF ammeter.

When the antenna is resonated the LC tuned circuit is tuned for maximum RF ground current, this has the action of producing a very low impedance not just to the chassis of the trailer but to “true ground”, therefore creating an efficient ground-plane for the vertical antenna to work against.

I have made several comparisons using radials instead of the ground tuning units (GTU) and in reality the ground tuning produces better performance due to the fact that the ground system with radials means that the ground current distribution stays “within” the radials rather than making a connection to true ground (which in my case is the seawater)

This effect is also proved by taking near field radiation levels using the GTU and directly comparing the results with a set of radials above ground.

Lots of RF toroid filters are used to eliminate RF feedback problems, (especially when using the amplifier) this is because the antenna is only a short distance away from the transceiver. A band switch-able quarter wave coiled up coax line is used between the radio and the input to the amplifier to achieve good RF stability.

It is also vital to get a perfect match into the antenna and make sure that the GTU is optimised to achieve a clean RF signal with no RF feedback and good harmonic suppression.

Night Rider

It’s my “Shack-on- a-Bike” and when operating close to the sea it competes well against much bigger home stations.

I would encourage anyone who enjoys bike riding to give it a try, its amateur radio and it helps to keep you fit! and to tell the truth, I don’t think I’ve had as much fun playing radio since I first got licensed. Here’s the best part; lots of stations say “I’ve been a ham for 30 years or more and this is the first time I’ve talked to a guy on a bicycle.” Keep on saying that guys please!

Alongside Blackpool Trams

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