Stereo shutdown (was HID headlights causing...)

[arctictraveller]

I posed this question in a different thread “HID headlights causing interference” but I ended up derailing the original posters question so I wanted to start a new thread. My question relates to the fact that when I key up my ham radio, it occasionally causes my stereo to go into a “protected mode” that requires a hard reset, which also requires resetting all the parameters.

Originally Posted by Timerider

if the stereo reboots immediately when you "key up", and doesn't continuously remain in some kind of "reset" state while you're talking, then the first suspect in my mind would be a voltage transient on the 12V supply to the stereo. (Any chance your 2-meter / 440 MHz ham rig draws its power from a point that is both somewhat distant from the battery and also fairly close to where the stereo gets its power? Like the fuse block?)
The first test that I would perform is to grab a digital storage oscilloscope (if you have one),
Are you transmitting with more than just a few watts out of your ham rig to punch through the QRM? Sorry for all of the post-scriptum questions, but you've engaged my curiosity - at least a little bit.

It doesn’t happen all the time, but seem to happen more often when on high power. Using a Bird wattmeter, I have discovered that on high (rated at 50w), I’m really only putting out about 25w. The SWR was pretty good though, I don’t remember the exact number but it didn’t cause any concern at the time . Most all the time, I run on low power (5w?) and don’t seem to have the issue then. Power for the rig is drawn from a dedicated circuit that is connected to the battery combiner, rather than any factory wiring harness points like the fuse block. The location I tapped is under the hood, probably 4 feet from the start battery and the house battery’s all the way in the rear of the van. While the engine is running, the batteries are combined, and that’s pretty much the only time I use the radio while on the trail. As for putting a scope on the circuit, my duel channel storage scope was murdered a few years back when I had it stored in a shipping container which leaked, and also got crazy hot inside in the summer. I sold it for parts when it refused to work despite my best efforts.

Originally Posted by Wowbagger

Have you checked your antenna's VSWR? because symptoms like you describe are usually due to RF coming down the outside of the cable due to a mismatch. If so, tune your antenna and/or put ferrites on the cable to choke the RF off the shield. Also make sure that where you mounted the antenna has a good ground to the chassis - a lot of the metal elements on the van aren't well bonded to ground.

As mentioned above, I did check the SWR and it was reasonable, but power output was only half of rated. I never looked into it because I rarely run high power unless I’m out of contact with someone far down the trail. If I were to install some ferrites, would they go at the antenna end of the coax or the radio end? Meanwhile, I’ve relocated the antenna and will have to recheck the SWR.

Originally Posted by REDOVAL

Where is your ham radio power lead connected to? I assume you are using the factory wiring for the audio receiver in the dash correct?Scott

To expand a little, I ran a wire from the battery combiner under the hood, on the house circuit side (just a relay energized when the key is on) That 12ga wire runs to a fused terminal block located in the void behind the cup holder on the dog house. At that point, there are connections to my scanner, usb chargers, volt meter, ham rig, road camera and probably more. The stereo gets it power from the factory radio harness. There’s an amp buried under the dash too, I forget where it’s powered from, but I’ve never had any issues with it.
So, I’m interested in any further ideas, thanks…………..

[Wowbagger]

The ferrites go on the antenna cable as close to the antenna as possible.
25W vs 50W is only 3dB, which isn't much, but I still would be very suspicious of that - either the voltage is sagging or the radio is folding back due to VSWR. Since you are using a reasonable tool to make the VSWR measurement, check the voltage while you are keying up, and see if it's dropping.

[Orv]

You can have low VSWR and still end up with the coax shield "hot" with RF -- which can also make the radio's foldback circuitry unhappy. What kind of antenna is this and how is it grounded? If the mount doesn't provide a good ground, and the antenna is a typical 1/4-wave or 5/8-wave, the antenna will ground through the coax, with unhappy results. Magnetic mounts often fail to provide an effective ground; gutter or lip mounts can do OK *if* they pierce the paint.

If you need to mount to fiberglass I suggest using a 1/2-wave whip. I did this because I wanted the antenna to still be above the roof when I had the pop-top open. It has slightly less gain than a 5/8-wave but eliminates the need to provide a ground plane.

[arctictraveller]

Originally Posted by Orv

You can have low VSWR and still end up with the coax shield "hot" with RF -- which can also make the radio's foldback circuitry unhappy.

Interesting........ The antenna is a Diamond duel band that was mounted on a bracket attached to one of the fender mounting bolts. The hood and roof are both fiberglass though, there was a good connection to the fender, but it's has a very small horizontal surface area. I just moved the mount to the side of some 1.5in tubing that I've run up from the bumper to the roof, so there will be quite a bit more of a ground plane to work with. As soon as I find someone to let me use their Bird meter, I can check the SWR again, but meanwhile, I'll add a couple ferrites on the coax. Thanks for the advice guys..............

[Wowbagger]

Dual band antennas, specifically the Diamond, are 5/8 wave, and need a ground plane to operate. If nothing else, adding some radials at the base will likely help the radiation pattern, and reduce the RF on the shield.

[arctictraveller]

Originally Posted by Wowbagger

If nothing else, adding some radials at the base will likely help the radiation pattern, and reduce the RF on the shield.

Humm, good idea, but not real easy to do. Would round wire do any good?

[Orv]

One issue with a fender mount is, if you have the usual stock FM whip, you're putting your FM antenna right in the near field of your transmitting antenna. This will both induce a pretty massive amount of signal on the FM antenna and distort the transmitting antenna's pattern. In practice this may or may not be a problem -- usually it just overloads the radio front end and essentially mutes it while you're transmitting, but it depends on how robust the radio's internal design is. You can see if this is the problem by temporarily unscrewing the FM whip and seeing if the problem goes away.

[arctictraveller]

Originally Posted by Orv

You can see if this is the problem by temporarily unscrewing the FM whip and seeing if the problem goes away.

I thought about that when I unscrewed the fm antenna about five years ago and never put it back. I'm 100% satellite now, but there are times when I'm far from home and would like to catch some local color so I may put it back. My entire antenna set up is a compromise due to it's low mounting point (helping to avoid getting ripped off by vines or tree branches) and it's sub par ground plane. Fortunately, I rarely need more than a two or three miles of range to keep in touch with travelling buddy's. The bigger issue is the one with the head unit. As long as I run low power, it's not an issue, and at times even high power doesn't affect it, but when it does, it requires a hard reset and i loose all my presets. So, I'm going to try some of the suggestions here, thanks..........
By the way, do round wire radials work?

[Orv]

They should work fine, although as you noted radials are an awkward thing in a mobile setup.

[Wowbagger]

Any wire, round or not, connected to the shield of the coax and arranged as close as possible to right angles to the antenna should help. You could also try putting foil on the back of the body panel the antenna is mounted on.