Motorcycle mounting Comet CSB-75a

Discussion in 'Mobile Radio Systems' started by HBOOTHE, May 9, 2019.

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    HBOOTHE QRZ Member

    Hello, All. I have a Comet CSB-750a I attach to a Yaesu FTM-10R (50 watts) which I ran on my motorcycle. For a few years, across three different motorcycles, I ran this combination. The antenna was mounted on a Comet cable assembly (like the Comet 3D4M, but I forget exactly which model I had) which was mounted through an aluminum disc about 10 inches in diameter (to act as a ground plane). That aluminum disc was electrically shielded from an aluminum mast (via plastic spacers/isolators) which was about 30 inches tall, putting the aluminum disc/antenna pairing above my head when seated on the motorcycle. It looked goofy but it worked well. The motorcycle got stolen, the thieves stripped my antenna mast/mount off, and all the other gear I carefully assembled on the machine for the volunteer work I use the thing for, and dumped the motorcycle. I got the radio (under the seat and left) and the antenna (not on the motorcycle at the time it was stolen).

    I'm outfitting yet another motorcycle with this radio/antenna pairing but now without the cabling and mounting I had used before. This gives me a chance to review my mounting of the antenna and consider if there are better options. That process brings me here to ask for thoughts/ideas/suggestions, please.

    I'd like to use the CSB-750a; it worked well and the ridiculous look actually is well-remembered by some of the cyclists who have commented on it to me. I'll entertain other antenna ideas, of course, but would prefer, if possible, to keep it. Should I use a plate-style ground plane (like the aluminum disc I described above), or maybe a set of wire radials from a small disc or maybe a panel mount? I've read the wire radials can be bent down from perpendicular to tune the impedence of the antenna...I've read a lot of stuff; would it matter?

    Thank you for your time.

  2. KA3TJI

    KA3TJI Ham Member QRZ Page

    I wish that Comet antenna used an NMO mount as I would like to try it on my setup. I am very happy with the performance on the Larsen.

    Here's what the old V71a looks like on the bike. Control head is on a custom made slide mount that electrically connects when inserted. PTT under left grip. Coiled microphone/speakers cable plug into the bike via waterproof RJ45 jack. Antenna is a Larsen NMO-2/70B Black antenna mounted on homemade and sealed half wave grounding mast with "N" connector on bottom. Antenna/mast assembly is easily removed via three set screws and the LMR200 cable is safely stored on the female "N" connector after unscrewing protective cap. All connections are waterproof.

  3. N8YX

    N8YX Ham Member QRZ Page

    Different Valkyries ('99 Tourer and '01 I/S) but the same radio as the OP (FTM-10SR).

    I used a 2" SO-239 bulkhead adapter in place of Honda's stud mount arrangement which was used with the accessory CB antenna and mounting arm. The stud was removed from the arm, the SO-239 adapter fitted and secured then a length of LMR-400 was equipped with PL-259s - soldered on one at a time - and these were used to connect the transceiver body to the antenna. Rubber weather boots were used on the connectors, and coax routing was done as per OEM layout. The Comet antennas I use can screw on to the upper side of the SO-239.

    The CB antenna was moved to the AM/FM radio mount (left side of the trunk) and a splitter routes signals to the OEM AM/FM stereo or to the accessory CB.

    My Concours 14s required a little more work. One of my coworkers machined a set of mounting arms for me that attach to the rear of two trunk-mount-plate risers, which he also machined. A variety of interchangeable hardware that attaches to the arm ends allows for the installation of a number of antennas. At the moment, a 3ft base-loaded CB whip is installed on the left sides of the bikes via a Diamond mount...while the smallish dual-band antenna which Yaesu offered as an accessory for the FTM-10 series is installed on the right. No splitter needed here, as the CB handles only CB and the FTM-10SRs incorporate AM/FM BCB coverage.


    'TJI - if you're a member of the Valkyrie Riders site, you've probably seen pics of my handiwork posted from time to time.

    HBOOTHE QRZ Member

    Thanks for the reply. In your setup, if I understand it correctly, that mast supporting the antenna in the air, is the ground plane? That is, the shielding of the coax is connected to the support mast with the center conductor attached to the radiator (Larsen) at the top, correct? I've seen, from several sources, that the angle of radials used as ground planes to the vertical radiator affects input impedance; what is that setup you have doing to the input impedance?

    Last edited: May 11, 2019

    HBOOTHE QRZ Member

    Thanks for the reply. I think I've pictured it correctly, you're using the bulkhead connector as a mounting connection for the antenna, just passed through electrically. But there's no isolated or special-purpose ground plane that I'm discerning in that setup. Do the rubber weather boots keep the whole bulkhead connector/antenna/cable electrically isolated from the frame/components of the motorcycle? Have you considered the need, or lack of need, of a ground plane for the antenna?

  6. N8YX

    N8YX Ham Member QRZ Page

    The trunk mounting assembly is steel. In turn, it bolts to the fender rails (steel) which are secured to the frame (more steel) by the shock stud and fender rail mounting bolts. Thus, the entire bike acts as a ground plane.

    I used a similar method with both Concours 14s and bonded their trunk mounts to the subframe attachment points with straps. The subframes are anchored to the top of the crankcase.

    The weather boots merely exist to keep moisture out of the connectors and cables. I ride year-round, in all sorts of weather - so I engineer the running gear appropriately.

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