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Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
hey all, as I have long known, my car does not like 40m ham band. The car body resonates at 40m, and I keep repositioning and wiring my grounds hoping to make one suitable for it but to no avail. However, today I was having moderate success in that my car radio stopped going AWOL. the amber lights kept turning on as expected due to an unshielded wire. But, tonight something unusual happened. Something that has caused me so much concern I no longer will operate 40m out of my car unless I have a tripod antenna parked. My car's engine started to rev up as I tuned the transmitter to a good SWR. e.g. Whenever I keyed up, the car went forward assuming it was in gear (I actually tested it in gear after I noticed it while parked, and yes we moved forward quite a bit).
Anyone have any bizarre stories of an unusual situation for a transmitter causing bizarre behavior?
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
I have had some interference situations in the lab. We were getting some really weird results from some testing we were doing on the frontend of a GPS receiver. The gain and phase kept fluctuating all over. Turns out because our testing was so low power, about -70dBm as I recall, another network analyzer across the lab not hooked up to anything but still doing a sweep was radiating enough power to mess with our measurements. Terminating the output of the other network analyzer solved it.
I've been working on some noise measurements lately. And I've noticed, qualitatively at least, that my data is smoother at night when there are fewer people around and less equipment turned on.
Once in a circuits class one of the projects was an infrared audio transmitter. The prof who ran the course noticed a significant 120Hz interference from the lights, so he had to design in a notch filter to kill this interference.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
radiotech wrote ...
Try one of these to measure RF currents in various wires:MFJ 854
well I'd have to buy one if I wanted to
But it would be too complicated trying to track the RF going into the ECU (Engine Control Unit) and accelerator wiring, I think I'll just lay off the 40m Hamstick (well, MFJ clone of Hamstick). I'll just use a tripod when I'm doing 40m, as then the car is no longer part of the antenna system and should act as a Faraday Cage.
@Mattski
I was talking to a friend's uncle yesterday who worked with TI. They, at one point, were short on space so they setup labs in a big warehouse without walls but only partitions between the different work groups and labs. They were working trying to find the intermittent problem with a circuit for 9 MONTHS. It would do fine in all of the tests, then suddenly fail or go haywire. They never knew why. Then, one of the technicians was walking down the aisle of another work group and saw a Negative Ion generator on the desk of a worker. When asked, the worker said he only turned it on Intermittently. This was the cause, all the way across the room!
It's amazing what something can do to something else by reasons to bizarre for people to predict.
Registered Member #16
Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554
DajjHman, I have had very similar troubles, but I've finally got them licked.
In my 2008 Tundra, all HF bands worked great with my bed-rail mounted screwdriver. When I switched to hamsticks after the screwdriver broke, I started seeing serious RFI issues on 20 meters. In my case, it was causing *serious* misfiring and timing issues in the engine, enough so that it was virtually impossible to drive the vehicle safely while transmitting at full power on 20 meters.
In order to eliminate it, along with some other issues, I went back to a completely stock truck, removed *everything* I installed, and started over. I ran a single, 4awg bus into the cab of the truck, fused for 50A. Each device then split from that bus to it's own individually fused line, each with a very heavy duty, homebrew steel core inductor, configured in a Pi network with both large electrolytic caps (several thousand uF) and a couple 100uF tantalum capacitors.
The antennas also got several ferrite beads right at the base of the antenna to keep RF out of the cab. Hamsticks are bad about RF on the coax shield. I also placed some clip-on ferrites on both cable bundles that connect to my ECU (which is under the driver's seat).
This not only eliminated the RFI issues with the ECU, but it also drastically reduced the noise that made it into my receiver.
It was labor intensive, and took some careful planning, but I ended up with a highly reliable, and very safe installation for a number of different devices in the truck including a laptop, 3 ham radios, a scanner, a weather radio, emergency lighting, and a 1kW inverter.
Some info on it can be found in my project thread:
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
Dave Marshall wrote ...
DajjHman, I have had very similar troubles, but I've finally got them licked.
In my 2008 Tundra, all HF bands worked great with my bed-rail mounted screwdriver. When I switched to hamsticks after the screwdriver broke, I started seeing serious RFI issues on 20 meters. In my case, it was causing *serious* misfiring and timing issues in the engine, enough so that it was virtually impossible to drive the vehicle safely while transmitting at full power on 20 meters.
In order to eliminate it, along with some other issues, I went back to a completely stock truck, removed *everything* I installed, and started over. I ran a single, 4awg bus into the cab of the truck, fused for 50A. Each device then split from that bus to it's own individually fused line, each with a very heavy duty, homebrew steel core inductor, configured in a Pi network with both large electrolytic caps (several thousand uF) and a couple 100uF tantalum capacitors.
The antennas also got several ferrite beads right at the base of the antenna to keep RF out of the cab. Hamsticks are bad about RF on the coax shield. I also placed some clip-on ferrites on both cable bundles that connect to my ECU (which is under the driver's seat).
This not only eliminated the RFI issues with the ECU, but it also drastically reduced the noise that made it into my receiver.
It was labor intensive, and took some careful planning, but I ended up with a highly reliable, and very safe installation for a number of different devices in the truck including a laptop, 3 ham radios, a scanner, a weather radio, emergency lighting, and a 1kW inverter.
Some info on it can be found in my project thread:
-Dave
I might give some of that a try, but I have to wonder what changes I'd need to make because I am running the Radio off of dedicated Batteries in the back seat rather than the car, and the charger as far as I know for those batteries should be RF isolated - I guess I could start with shielding/beading that? - also, I realized (as I should have, but originally didn't) is that the vehicle chassis is grounded to the electrical ground (hence why you attach one part of the jumper cable to the chassis rather than the battery negative).
I would like to maintain 40m without a tripod antenna, so I might start installing some of this over a few weekends. Or, get a different antenna!
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Bizarre Electronics Activities due to radios
