In search of RF quiet USB charging solution; 2-meters mobile

[Crom]

That's weird, I have two of those Griffin dual-usb chargers, they are both within 12in of my radio and I get zero noise when using them. The only noise I get on my vehicles is from the Rigid Industries Duallys, significant noise at that, and they're at least six feet away from the radio.

I have a general question though, when using ferrite chokes, do you have to use them in the wires of the equipment that emits interference or in the radio's wiring or antenna coax???

Are you using a remote head kit with your radio? My Kenwood body is mounted under the drivers seat and the head is remote and rests by the transmission shifter. When I had the Griffin dual port, it was about 1' from the remote head. I could not hear weak stations, and certain strong ones has significant interference.

I plan to allocate some time to experiment with my setup and try to determine if their is some unique characteristics that my install has that make my situation worse than others.

I'll report back here if I find anything useful.

 

[DaveInDenver]

The remote mounted head helps this make more sense. AFAIK there are no major RF circuits in the face plates, though the connection is not immune to issues. IOW, the face is telling the CPU what frequency to use, maybe bandwidth for filters, etc. So if there's enough interference to cause the VFO to drift a little it would manifest similar to desensitizing the radio. Just speculating. You prolly justed used UTP (which I did, too, Cat5e), but even if you took the time to consider pairs it's all singled ended so susceptible to interference anyway. Shielding is about the only way to protect single ended circuits.

 

[lugueto]

Are you using a remote head kit with your radio? My Kenwood body is mounted under the drivers seat and the head is remote and rests by the transmission shifter. When I had the Griffin dual port, it was about 1' from the remote head. I could not hear weak stations, and certain strong ones has significant interference.

I plan to allocate some time to experiment with my setup and try to determine if their is some unique characteristics that my install has that make my situation worse than others.

I'll report back here if I find anything useful.

Nope, sorry, simple reliable Yaesu 2900R. No remote head (although I would've loved that feature). My 12V chargers are about 6in from my shifter and my radio is on the side of the shifter console. They're seriously close by and no problem so far.

 

[Tennmogger]

This is what I use:

http://www.westmountainradio.com/product_info.php?products_id=rr_4004_c

This Rigrunner distributes power to USB devices, and you can even hook up your HF, VHF, UHF, CB, whatever.

Bob WB4ET

 

[AlbanyTom]

Haven't seen this mentioned before, so apologize if it's obvious. When you add filtering to the dc-dc converter, you probably have to filter both input and output. Reason being, the switch mode converter is coupling common mode noise to everything, you'll get it on both sides.

Someone else suggested ceramic disk caps, and I agree, I'd go .1uF, and on each side between + and -, and both + and - to ground, so 3 caps for input and out, total of 6. Poly caps have higher RF impedance than ceramic, so they make worse filters. Run input and output through big ferrite beads. Recycling ones from computer equipment cables would be perfect. If you can loop them through 2-3 times it would be better. Both caps and ferrite as close to the device as you can. You're trying to choke the signal before it gets to the "antenna", where the cables are the antenna.

You want the whole package to be as small as possible, say less than 3" on a side...the closer it is to 2m, the better it'll radiate, the more noise it makes. Search for stuff on "rf noise reduction" and "compliance engineering", because that's what you're trying to do.

I don't know if you have yet, but if not, try looking for a name brand device. That's more likely to be FCC compliant, and less likely to make noise in the VHF bands.

If you haven't tested it yet, consider that maybe your device, when charging, is actually making all the noise. It could be behaving differently when charging than not. Try plugging an USB LED flashlight or something into the USB charger to make sure you're really seeing the noise from the charger.

I don't think wrapping in aluminum foil would help any. But a real shielded box might. The issue is sealing it up so the joints are continuous conductors. A little box made of copper flashing, soldered up with just little holes for the cables would work. But my guess is that most of what you're seeing is radiating from the cables, caused by the switching in the device...and that you have to choke/filter that.

If you fix it or find a clean charger, let us know...and best of luck!

 

[Crom]

The remote mounted head helps this make more sense. AFAIK there are no major RF circuits in the face plates, though the connection is not immune to issues. IOW, the face is telling the CPU what frequency to use, maybe bandwidth for filters, etc. So if there's enough interference to cause the VFO to drift a little it would manifest similar to desensitizing the radio. Just speculating. You prolly justed used UTP (which I did, too, Cat5e), but even if you took the time to consider pairs it's all singled ended so susceptible to interference anyway. Shielding is about the only way to protect single ended circuits.

The remote head kit I bought came with it's own cable for the head, it's 4-conductor insulated wire terminated with RJ-11 at the head end, and if I remember right RJ-45 modular plug at the radio body. I don't think it's twisted, which is unfortunate (I may look at replacing it). It also came with 1-ferrite cable clip which is attached close to the radio body as the instructions say to do.

The mic has an extension on it which is using a Cat-5 patch cord, and a straight through RJ-45 coupler. I believe I have a ferrite cable clip on this connection as well.

Nope, sorry, simple reliable Yaesu 2900R. No remote head (although I would've loved that feature). My 12V chargers are about 6in from my shifter and my radio is on the side of the shifter console. They're seriously close by and no problem so far.

Consider yourself lucky then! The Griffin chargers were the worst of the lot. They produce considerable noise vs. the others I tested. The design has no shielding. I pulled it apart to see what was making the noise. It turns out it's a ACT4060A microchip. The product datasheet states that is switches at 400 kHz frequency.

The chip on the right is the ACT4060A noise maker!

This is what I use:

http://www.westmountainradio.com/product_info.php?products_id=rr_4004_c

This Rigrunner distributes power to USB devices, and you can even hook up your HF, VHF, UHF, CB, whatever.

Bob WB4ET

Thanks Bob! Those Rigrunner products are nice.

Haven't seen this mentioned before, so apologize if it's obvious. When you add filtering to the dc-dc converter, you probably have to filter both input and output. Reason being, the switch mode converter is coupling common mode noise to everything, you'll get it on both sides.

Someone else suggested ceramic disk caps, and I agree, I'd go .1uF, and on each side between + and -, and both + and - to ground, so 3 caps for input and out, total of 6. Poly caps have higher RF impedance than ceramic, so they make worse filters. Run input and output through big ferrite beads. Recycling ones from computer equipment cables would be perfect. If you can loop them through 2-3 times it would be better. Both caps and ferrite as close to the device as you can. You're trying to choke the signal before it gets to the "antenna", where the cables are the antenna.

You want the whole package to be as small as possible, say less than 3" on a side...the closer it is to 2m, the better it'll radiate, the more noise it makes. Search for stuff on "rf noise reduction" and "compliance engineering", because that's what you're trying to do.

I don't know if you have yet, but if not, try looking for a name brand device. That's more likely to be FCC compliant, and less likely to make noise in the VHF bands.

If you haven't tested it yet, consider that maybe your device, when charging, is actually making all the noise. It could be behaving differently when charging than not. Try plugging an USB LED flashlight or something into the USB charger to make sure you're really seeing the noise from the charger.

I don't think wrapping in aluminum foil would help any. But a real shielded box might. The issue is sealing it up so the joints are continuous conductors. A little box made of copper flashing, soldered up with just little holes for the cables would work. But my guess is that most of what you're seeing is radiating from the cables, caused by the switching in the device...and that you have to choke/filter that.

If you fix it or find a clean charger, let us know...and best of luck!

Thanks for your post. In my experience thus far, many of the products produce RF noise even if there is no load on the DC-DC converter--I'm very sure of this, and was most true with the Griffin product. The foil shield should work, but only if the input and output wiring is grounded to the shield (according to information I recently read.) But, yes a metal box would probably work best.

I hope to enlist a local Elmer on a Saturday so we can work together and solve this issue.

 

[Crom]

One solution I have come up with, although not very efficient, is my truck has a built in inverter. I plug in the little OEM wall wart rectifier from Asus, LG, Etc, and use those in my travels and I have no interference problems. I know those are switching power supplies too, but for whatever reason they don't bother my radio. Seems stupid to have to do this, but for now it's all I got if I want to use my radio and power electronics.

 

[AlbanyTom]

One solution I have come up with, although not very efficient, is my truck has a built in inverter. I plug in the little OEM wall wart rectifier from Asus, LG, Etc, and use those in my travels and I have no interference problems. I know those are switching power supplies too, but for whatever reason they don't bother my radio. Seems stupid to have to do this, but for now it's all I got if I want to use my radio and power electronics.

I almost suggested that, but didn't because it's kinda weird. It does make sense, though, in that I'm sure the truck's inverter is designed to be electrically pretty quiet, as are the oem chargers. That dc-dc above looks like it doesn't have any filtering at all.

If you're set on going to the trouble of taking apart the converters, I'd go back to previous suggestions and just make a linear converter. I'd use a 317 series, or even a pair of them. They're quiet and reliable and easy and inexpensive. Less efficient? Sure, in terms of watts, but if you're talking about a car battery it's pretty small. In terms of time? Linear is pretty darn efficient.

If you're still aiming at doing dc-dc switching, which may be a lot less efficient than you'd expect, consider maybe building your own...you're already on the road to spend a lot of time and learn some stuff, may be easier to build a decent purse than make one from a pig's ear.

 

[DaveInDenver]

Converters often to change characteristics intentionally between loaded and unloaded (or lightly loaded). Part of that is to keep the efficiency high and to prevent stressing the inductor and/or caps with overvoltage or losing regulation as extremely small duty cycle. A common technique is to skip pulses (e.g. change to PFM) under light load. This can be confusing if you're trying to figure out why something is noisy in one condition and not the other. Also they are sometimes only tested loaded, which has the effect of making the load part of or maybe the whole filter. Not to mention even if there is a filter present, if the converter changes mode (e.g. probably the PWM fundamental) the filter only works across one band so is ineffective on the PFM.

 

[Arclight]

FYI, Powerwerx sells a nice in-line filter with Anderson Power Poles pre-installed:

http://www.powerwerx.com/powerpole-accessories/dc-line-noise-filter-powerpole.html

Arclight

 

[Crom]

Found a solution. I made multiple changes, so unfortunately I can't say what the silver bullet was. I pulled the mic extension cord and replaced with CAT 6, slightly shorter than original . Factory Kenwood remote head cable is like 10'. I made a shorter one with CAT6 but unfortunately my crimper does 6- conductor and not 4, so I had to scrap that for now until I can get my hands on a proper tool/die.

I routed the head, mic, cables in a slightly different path.

I also got some new chargers and new USB charging cables, which are excellent. Well built, charges fast, no interference!

Anker® 24W Dual-Port Rapid USB Car Charger with PowerIQ http://www.amazon.com/dp/B00D82O68Y/

At some point I'll try the other DC-DC chargers again just to see if the problem has been solved or not, but for now I'm happy.

 

[4x4junkie]

I recently acquired one of these USB chargers myself.
(this one in particular)
http://www.harborfreight.com/universal-usb-car-adapter-61546.html

As expected, it interfered profoundly with radio reception of all the bands I tried except UHF 440-470MHz (which it did affect also, though only if the receiving antenna was held near the unit). I didn't think to try on the AM-broadcast band beforehand, though currently I don't seem to be detecting anything there other than a weak "birdie" occurring at intervals of approx 350kHz (700kHz, 1050kHz, 1400kHz, and so on), and becomes difficult to detect on a standard SW receiver as you near the lower end of HF (the use of 0.1µF caps instead of 0.01µF might improve things here, though I'm not sure if it wouldn't be at some expense of VHF noise suppression.

Remembering this thread I took some pics of what I did to quiet this thing down. Turns out it was a simple 20-minute project.

Hope it helps.

(should be clickable for bigger)

 

[Crom]

^Thanks! Excellent post!