CB transmit sets off MAX 360c laser detection

ljh505

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Just a note that when I key up my CB radio, sometimes, more often than not, the MAX 360c "rear" laser detection goes off. CB antenna is at the rear of the car on a trunk lip mount. Antenna SWR is about 1.8:1 so there is probably some RF running around on the coax and back to the CB radio. CB and radar detector share a cigarette lighter receptacle for power via a Y-adapter. Waiting for a proper power cord from Escort to give the detector it's own direct power.

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thesilverbullet

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PhilP

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Not unusual. My ham radio in my truck will do the same to my 360. CB is going to be a much lower frequency and power level, but I suspect these things aren't shielded all that well.
 

ljh505

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if you think you have problems check these guys out
:) I had no idea such competitions existed.

Running a bone stock Midland 1001LWX at ~3 watts carrier into a Larsen NMO27 screwed onto a Diamond K400 trunk lip mount on a small car. So nothing that's going to heat metal to its melting point, or arc weld the antenna to the trunk lid.

Not unusual. My ham radio in my truck will do the same to my 360.
Good to know. Haven't tried GMRS or amateur VHF/UHF yet with the MAX 360c in the vehicle.
 

LinuxD

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Try to match your SWR better. at 1.8 to 1 you are losing alot of power, Ideally you want it lower than 1.5. Xmitters can be hell on other radio equipment.
 

MASI

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Its likely an RF feedback issue. RF is getting into the RD through the power wires.

1) Wrap the DC power cords of each device through a circular or snap on toroid of the #43 material. (Available from E bay or Amazon for about $ 5-10). Wrap the DC cord through the toroid 6-10 times. Do this as close to the CB as possible. This will cut down on the amount of RF traveling along the CB power cord. Same for the RD.

2) Try to tune the antenna for a better SWR.
 

ljh505

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Try to match your SWR better. At 1.8 to 1 you are losing alot of power.
The trunk lid of this compact vehicle is small, so I tried running a ground strap from the mount base to a hard point in the trunk of the car, about a 12" or so run, but the SWR shot up to > 3:1. The antenna resonates at 27.150 MHz or thereabout, according to the antenna analyzer. The mount seems to want more capacitive coupling to ground maybe? I removed the ground strap, and am running an old MFJ QRP tuner I had lying around for the time being, so the transmitter is seeing 1:1 and I'm running the coax at 2:1. A 2:1 match is about 11% power loss, not that much but big enough to be annoying. I'll see if I can play with the tuning at the antenna base some more, maybe a capacitive switch box in the trunk to find a better match.

Its likely an RF feedback issue. RF is getting into the RD through the power wires.

1) Wrap the DC power cords of each device through a circular or snap on toroid of the #43 material. (Available from E bay or Amazon for about $ 5-10). Wrap the DC cord through the toroid 6-10 times. Do this as close to the CB as possible. This will cut down on the amount of RF traveling along the CB power cord. Same for the RD.
I can try some toroids on the power cables, but my guess is the culprit is common-mode RF coming back down the shield of the coax. Where the coax comes into the trunk, I took 3 turns of coax through some mix 31 beads to try to get rid of the RF on the shield. Three turns through one bead wasn't enough, so I added a second bead. This seems to have improved things as the laser detector isn't going off as much anymore (or I already fried the laser detector diodes, ugh).

2) Try to tune the antenna for a better SWR.
Antenna is resonating at 27.150 MHz or thereabouts according to the antenna analyzer, so it is just the match at the antenna base that needs improving.
 

DC Fluid

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On my older Escorts I got repeated laser alerts when I had a shaky power connection.
Any power fluctuations could trigger some sort of alert.
Try separate power circuits for CB and detector.
 

gwing

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Grounding is my guess. Unless there is a really solid ground for the CB, ie not a cigarette lighter but body ground, I think you'll get these anomalies. You could check the resistance between the battery ground cable and the antenna and the same with the CB ground.
 

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