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Author Topic: Inverter RFI  (Read 2746 times)
KF5FNP
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Posts: 1




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« on: May 16, 2013, 06:25:14 AM »

Greetings,

Our club had an EmComm exercise last weekend.  The day before, I picked up a Black & Decker 800W Inverted to power my laptop.  When I powered up the inverter everybody could hear the RFI and see it on their waterfalls.  So now I'm in market for an Inverter that does not generate any RFI.  Any suggestions?

Thanks for your time.

73
Glen Thibodeaux
KF5FNP
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KD4EXS
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Posts: 8




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« Reply #1 on: May 16, 2013, 02:27:35 PM »

Glen, you have brought up a problem that I have had an interest in as well.  ‎

Back when inverters first became common in the retail market (80’s?) I also noticed that some of them ‎produced a surprising amount of RFI.  As a general rule, the cheaper the unit, the worse the RFI, but that ‎is not always the case.  This goes for true sine wave inverters as well.  You just have to try them and ‎see, or as you have requested, ask people what works for them.  ‎

The route that I have chosen is the elimination of all AC devices when I am setting up remotely.  I know this approach is not for ‎everyone, but it can be easily done.  For example, I have purchased DC box fans, 12v LED ‎flood lights, and I even found that many models of laptops use 12 volt or 24 volt power. I can run my ‎entire setup from storage batteries.  With the exception of my radio the portable setup is perfectly quiet ‎except for the whir of a box fan.  Love it!‎

I will be watching this thread to see what inverters others are satisfied with.  I would like to know which ‎ones are quiet as well.‎

John Breland
KD4EXS
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KB8VUL
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Posts: 132




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« Reply #2 on: May 16, 2013, 08:18:48 PM »

I have a samlex in the truck that run a service monitor on.  I don't have issues with doing that. 
I have seen other units that were really noisy though.  I am thinking that QST or one of the other ham rags did an article on
this a few years back and found some really high prices units that were noisy into the UHF region and some cheapies that were quiet even on HF. 

Here's my overall thought and experience.  Get a unit that is double or triple what you need.  The less the unit has to work, the less noise it will create. 
Older UPS units that were 12 volt are a good option and are practically free if the batteries are dead in them.
UPS units are typically very quiet as far as RFI creators.

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K1CJS
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Posts: 6034




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« Reply #3 on: May 18, 2013, 05:45:10 AM »

One thing you stated was (to me) a red flag right from the start.  "Black & Decker."  Ever since the brouhaha years ago about their fair trade practices, the one thing they've been known for is how they can sometimes cut corners.  Just my opinion, but you should avoid most of their stuff like that inverter although their power tools are still pretty good.  Of course, YMMV.

I believe Belkin has a small 100 watt inverter--just enough to run a laptop computer--that is said to be fairly noise free.  I have a Delco-Remy inverter, 120 watts, that also does pretty well in the no noise department.  Both these units plug into the cigarette lighter/power outlet sockets in a vehicle.  Just my .02875 (inflation adjusted!)  73!

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KF7VXA
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Posts: 459




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« Reply #4 on: May 25, 2013, 12:26:52 PM »

The new HRO catalog has a couple of pure sign wave inverters for sale, one is 600 watts at $189.00 I have no idea as to the noise of these units.
Maybe a call to HRO would get an answer.
In the mean time, I have six, six volt golfcart batteries, several large solar panels and a Honda inverter generator. Between all of these, I can stay on the air quite a while.

I'm also looking into getting a 20 and 40 meter travel radios from MFJ (used if possible). 12 watts of SSB transmitt power with 1.2 amp draw when transmitting. These units just might do the job with a good antenna to conserve on power when conditions are right.

My Best, John
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KK4RDD
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Posts: 3




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« Reply #5 on: May 28, 2013, 09:13:11 AM »

As far as laptop adapters go, I exclusively use DC→DC converters on the road for efficiency.  They can be had from online (search "laptop car adapter") or local big-box stores for around $20-$30. While I don't have a scope to test for RFI or how clean the supply is, the only interference issue I've noticed is when I'm feeding audio output to the stereo of the same vehicle.  No matter where the power comes from or how it's connected, I'll always get alternator hum unless the laptop's powered from it's own battery.  I don't hear the noise when I'm using headphones or external speakers, so I think it might be a ground-loop issue. I'll have to try it out on a deep cycle battery and see if the noise goes away.

I have taken one of these puppies apart and most of the space is taken up by a large toroid coil, so it's just a DC buck/boost converter.  Mine is rated for 80 watts but the machine I use it with only draws 70W max when charging and under load.  Also has a ferrite core clipped on near the laptop connector, but most AC adapters have that too.

I feel the DC-to-DC converters are way more efficient than making an AC signal just to have it rectified again, and the RFI appears to be more manageable.
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K1CJS
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« Reply #6 on: May 29, 2013, 05:11:33 AM »

DC to DC inverters are fine--to a point.  They're also pricey as h*ll.  It makes little sense for someone who uses their laptop charger unit in a car two or three times a year to spend the money for a DC to DC inverter when they may well have the need for 110 volt AC in their car for other things.  Also, if they get another laptop, there is no guarantee that the old inverter will power the new computer.

As an example of other 110 volt needs, I use an inverter to power my soldering gun when I'm splicing wires or other soldering in the car because its less time consuming than running an extension cord out there.  Others use a vacuum off an inverter, etc.  It makes more sense to use a 110 volt inverter in those instances and then use the laptop 110 volt power supply if the computer needs to be powered.
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KB2FCV
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« Reply #7 on: May 29, 2013, 07:53:32 AM »

In the past I was able to find power supplies for my laptop that would plug directly into the cigarette lighter. It met the power / voltage requirements for my specific model. At the time I think I found them on ebay and they were pretty inexpensive. I haven't needed one in a while, though.. I probably still have one that fits an older laptop I have. You may want to take a look around ebay and see what is out there. Nowadays for portable  110v needs I have a Honda Eu2000i.. but those are much more costly!
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