Brakelight/Tail Light EMI

FLYTYER · 09-30-2011, 11:29 AM

While running 30 watts PSK31 on 20 meters using a screwdriver antenna mounted on the rear hitch, the newly installed super bright LED brake lights turn on and off in sync with the transmitter keying. Nearby RV'ers noted it and wondered what was happening.

The SWR was 1:1.2

I guess ferrite chokes are needed on the wiring for the lights, but there is no space for such a choke....

Any ideas other than antenna relocation??

RandD · 10-01-2011, 08:41 PM

I am thinking that the "D" in LED is doing its job due to the close proximity to the RF field from the antenna. They are rectifying the RF and the resulting DC is lighting the diode - the "LE" part.

If moving the antenna up as in to the top of the ladder so the RF field is basically clear is not possible and there is no room for chokes, you might try what works on audio amplifiers. Try a bvpass capacitor across the LED. You may need to play with the value, but a .1 or .01 uf disk would be a good starting place. The closer to the LED, the better. The idea is to short the RF to ground (-DC wire) so there is nothing to be rectified by the diode.

I am about to start switching all of my marker and tail lights to LED and am in the process of installing an 706 and my Tarheel in my RV although the antenna will be mounted high up on the ladder so the coil is clear of the roof. I would be interested to know if bypass caps do the trick.

Good Luck and 73!

Randy

FLYTYER · 10-02-2011, 10:06 AM

Quote:

Originally Posted by RandD

I am thinking that the "D" in LED is doing its job due to the close proximity to the RF field from the antenna. They are rectifying the RF and the resulting DC is lighting the diode - the "LE" part.

If moving the antenna up as in to the top of the ladder so the RF field is basically clear is not possible and there is no room for chokes, you might try what works on audio amplifiers. Try a bvpass capacitor across the LED. You may need to play with the value, but a .1 or .01 uf disk would be a good starting place. The closer to the LED, the better. The idea is to short the RF to ground (-DC wire) so there is nothing to be rectified by the diode.

I am about to start switching all of my marker and tail lights to LED and am in the process of installing an 706 and my Tarheel in my RV although the antenna will be mounted high up on the ladder so the coil is clear of the roof. I would be interested to know if bypass caps do the trick.

Good Luck and 73!

Randy

Randy thanks for the idea about the cap. My brake light assembly is a sealed 10 LED red light bar. The cap will have to be attached at the power connection of the whole assembly.
However, by moving the antenna up onto the ladder and above the light bar, the problem was eliminated. Before the antenna whip was only 2 feet away.

Ted WB2LOU

RandD · 10-02-2011, 04:09 PM

Hi Ted - It is never easy with RVs, is it. I am glad you found a resolution to your un-intentional light show. With the antenna up on the ladder, I bet it load and tunes a bit better assuming the ladder is grounded to the chassis and box frame.

I _think_ I have seen your call on 20m psk. I work from home and have my radios next to my desk (Flex3000 and FT817) and typically am listening around 14.073-.075 for PSK and Olivia signals above all of the masses - that is when I am not on 18M. I will keep my eyes open for your call!

Randy WB5TEY

wa8yxm · 10-03-2011, 10:34 AM

You should see what happens with 100 watts on SSB and a Slinky looped over the roof

Yes, the long wire from the front of the coach to the rear IS, in fact, a 20 meter quarter wave or close enough to it to light 'em up. Frankly.. I'd use the chance to explain.