CB Radio makes rear light flicker with PTT?!

[lsyorn]

I ride with a group of Goldwing riders in Indianapolis and they all use CB radios to communicate. I purchased a handheld CB radio and attached it to a ram mount on the handlebars. I run the radio off of AA batteries in the radio itself. It is not attached to the Ryker electrical system. After several "not perfect" attempts at communicating with the Wings I contacted Sierra Electronics for CB for Bike info. According to them the only way to get good range on a CB is to attach an external antenna to the bike in place of the rubber ducky antenna on the radio. Eventually I would like to hook everything up to Bluetooth but don't want to spend the money until I know it will work. The external antenna, a 24' Firestick works great and dramatically improved both clarity and range. The antenna is mounted to the bike and grounded thru the bike frame. Now the problem. Today a group of us went for a nice 190 mile ride and I was able to communicate with all of the bikes. The bike behind me however noticed that every time I pushed the talk button on the radio my right rear tail light would flicker. When I got home and checked it does this every time the button is pushed. Any ideas...

[SportsterDoc]

RF interference?
Where is antenna mounted?
If radio is independent of your Ryker, why ground antenna to frame?...instead of antenna plug on CB?

[lsyorn]

The antenna is mounted to the rear right side of the Max Mount. The antenna has a 9 foot long cable that I ran under the mount to the handlebars. It's plugged into the top of the CB. The instructions with the antenna said it should be grounded thru the frame of the bike. I currently have the antenna grounded at the attachment point on the max mount. Should i insulate the mount point and and just go the radio?

[Snowbelt Spyder]

If you used standard coax cable to connect the antenna to the antenna plug on the handheld, then yes, the antenna is properly grounded to the handheld. The RF power radiating from the antenna is simply inducing small voltage spikes in your tail light circuit. The wiring is acting like a receiving antenna. That’s why you will sometimes see RF filters in the power wires to devices. Easy enough experiment to insulate the mount. But my thought would be that it has nothing to do with it, would hurt your range and not make a difference with the lights. Maybe be worse. But, try it and see. Another question is if you have checked the SWR or done any tuning on the antenna. You could be in danger of killing the transmitter in the handheld. Curious that the original antenna on the handheld wasn’t working well enough for just riding in a group unless you’re all REALLY spread out. What was the make and model of the radio?

[lsyorn]

The radio I am using is a Cobra 50WXST. The group I ride with often numbers 12 to 20 riders and is sometimes very spread out. Setting the SWR on the Firestick has been done and am currently at a 1.2 reading. I believe I may have solved the issue by borrowing another radio, a Midland 75-822, from one of the other riders. Again tuning the Firestick to a reading of 1.2 on the Midland radio the flickering taillight goes away. Re-hook the Cobra and the flickering taillight returns. Again the Midland and no problem. I chose the Cobra over the Midland initially because of the easier to read blue backlit display. At this point I see a Midland 75-822 in the near future.

Snowbelt Spyder:
Maybe I won't need that Midland radio after all. After replying to your post I went back to the garage and tried the Cobra radio again. Once again the right taillight flickered when the PTT button was pushed. The next time I pushed the PTT button I held my free hand under the antenna base which is above the taillight. This time no flicker at all. As you stated, I believe the RF power radiating from the antenna above the light is the culprit. I think I'll look for a way to insulate this before making a radio purchase. Thank you for the suggestion.