On 08/31/2018 04:50 PM, Joe Puma wrote:
Yes were talking about the same thing, not the 115V
usb square (apple) or what ever usb ac adapter you might have.
Plus I meant that its a great use to use a SDR radio on a laptop
around the car to check for RFI. but having a SDR installed in
the car is nice idea too :).
I have these nice little 5v usb adapters for the 12V
lighter plug and anytime I use them it takes out my radio in the
car. Heck, now that I am thinking about it, I have a terrible
problem with my car remote which operates around 300mhz, I'm
wondering if the adapters are the culpret. The phone has to be
plugged in charging for a load to be put on them for them to
work. Without phone attached and charging the car radio is fine.
Either way using a SDR and Console around the car to
troubleshoot is a great idea, you can use a little yagi to
direct your reception.
I surrender! I suppose I should have started my testing in the car.
Joe and crew are correct! The adapter DOES create interference on
the FM band. I am going to try and find out why, which means
that I will have to crack open the shell and find out what's inside.
Probably will not be able to put it back together with whatever fix
is required, but I hope I'll figure out what's causing the noise.
I do know that it does not seem to make a significant difference
whether the phone is plugged into the cable or whether the cable is
plugged into the adapter. (Of course, the socket in the car
is not rated for an actual cigarette lighter; you're not supposed to
smoke anymore!) I tried ferrites on both ends of the charging cable
without result. Apparently the noise is getting back into
the car's wiring and radiating into the radio from there.
Well, I sawed the housing apart, and sure enough, there's a little
oscillator circuit inside, with a tiny coil, several SMD resistors
and capacitors, and a chip from CHN, (China
marked HC8816 and T746. I can't find HC8816 in a quick search, but
it is obviously the oscillator/regulator device.
A crude and clumsy fix would be to obtain a lighter plug with no
electronics inside, and a lighter socket with no electronic inside,
and wire them together with ferrites on the wires, and some
decent capacitors across the wires at the input and output
sides--around 47 pF would probably be a good starting point. It
would then probably be necessary to put ferrites around the
cable to the phone and the SDR input wires, right at the USB
outputs. You would obviously need to shield and filter this
contraption. If I am going to ever try and solve the problem for my
own use, I would just build a linear regulator with a 7805 and, if
necessary, a pass transistor, and the necessary bypass and filter
caps on a little board, put it in a little box with a lighter plug
on one end and one or two USB jacks on the other. If you are going
to want to run your SDR from the car, you will need to do something
like this. If you just want to charge your phone,
do it while you're having dinner, or something, assuming the lighter
socket is still alive when the key is turned off. Or just remember
to charge your phone at home!
On 08/31/2018 01:42 PM, Joe
I haven’t seen a usb charger that didn’t take out my
radio in my BMW X5. Great idea to use a SDR and
console in the car. I may take a look at my situation
but does anyone recommend a usb charger that is clean.
I found some nice flush one that don’t pop out of the
cigg lighter power, too bad the buggers are noisy.
Joe, If you notice my first message in the thread,
you'll note that I am using ONLY the charging cord
supplied with the phone, NOT the 115VAC charger. You
don't need that. What you need is a charger
CORD that has a USB male plug on one end, and a mini
plug on the other that fits the phone charge jack, AND a
USB adapter for your lighter socket that puts out 5VDC.
The one that I have tested is described
fully in my FOLLOWUP message in this thread. In this
case, there is no device that is creating RFI. I can't
say where I bought the lighter adapter plug, but most
likely Amazon. The adapter comes either in white or
black. Since the adapter puts out 5VDC, and has two USB
outlets, for a total current rating of 3.1 amps, I'm
pretty sure your SDR could plug into the other port.
On 08/31/2018 12:27
PM, doug wrote:
> I have a 4 port charger that makes
listening to FM barely hearable and totally
wipes out AM. I had never thought of using
SDRC to track it down.
> 73 Rick N2AMG
I am sort of surprised that your device
contains a switcher when all you need is 5
Volts DC from a 12 to 15 volt cigarette
lighter socket. I would put a 5V series
regulator in the charging device and it
would make no RFI at all. Perhaps there is one
made like that. I have a two-port lighter plug
with USB jacks on it. I will take a look and
see if it generates RFI. And my phone came
with a separate
charging cord compatible with a USB jack,
which the AC charger has on it. (And IT is a
switcher of course, sind it plugs into
In the meantime, Does the device you have have
a built-in charging cord that goes to the
phone, or do you use a separate USB to phone
cable? If it's a separate cable, then
disconnect it and see
if the RFI goes away sufficiently to listen to
the radio. If it does, then get some ferrite
snap-on RF chokes and run the charging cord
thru about three of them right next to the
If that doesn't work, you will have to find a
charger made with that series regulator.