bcd325p2 computer interference on railroad

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briskattivo

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#1
I just recently purchased a bcd325p2 and I have been trying different bands and systems with it. Most work just fine. But for railroad, which I really want to listen to, the whole band goes silent when I turn on my home build desktop computer which I built a couple of years and has a top of the line video card, processor, case, power supply etc. I don't really get great reception even when it's not off, but the computer just seems to kill it. I have a Diamond RH77Ca antenna as well as a VHF150-162 Professional Portable BNC Antenna from scannermaster, as well an RG6 cable with a femaletofemale adapter that is suction cupped to my window for reception. I know the easy solution is to move the scanner to a different room or get an outdoor antenna, but I live in a shared living situation that limits my scanning to my first story bedroom with a 5 star view of the neighbor's vinyl siding 5 feet away. I have thought about RF couplers for my cables, but I can't see how that would help. I have been considering a TrainTenna Blade Indoor Antenna (DPD Productions - TrainTenna Railroad Voice Band & ATCS Antennas) but I don't want to get one if it's just going to be a waste of money.

Any ideas?
 

W8RMH

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#2
An antenna stuck to a window doesn't have a ground plane which will affect reception.

I have a 325 as well as a 396. The 325 does good on P25 but on aviation and VHF is is deaf compared to the 396 using the same antenna setups.
 
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#3
Sounds like you didn't add top of the line noise suppression on the PC, or chose components that are RF-noisy.

I would start with the power supply for the PC. Switching supplies can be really noisy.
 
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#4
Sounds like you didn't add top of the line noise suppression on the PC, or chose components that are RF-noisy.

I would start with the power supply for the PC. Switching supplies can be really noisy.
Check on palomar-engineers.com for ferrite noise suppression for computers and modems, ect.
 

briskattivo

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#5
I abandoned the suction cup rig. It seemed like it was making a difference, but after a while I realized it wasn't, even though somebody else said it worked for them. I believe I have isolated the problem to the switching power supply as suggested. If I unplug everything but the power cable, the railroad channels still go dead when the system is turned on. I even tried replacing the corsair 750w psu I had with an old 500w psu, and it was the same. I realize I could have also tested the power supply alone with no connections, but I am pretty certain that it is the source of the problem. It's not exactly easy to go RF noise testing every component in the computer, which is why I will wait on the following possible solution to see what happens. I guess I never considered the logistics of gaming machines versus scanner reception before I invested into all of this.

So, I was reading this very helpful article: Computer on the ARRL website. The article, too, suggested to use a ferrite core for power supply cables. I ordered a Fair-Rite brand Toroid Ferrite FT240-43 Core. Should arrive some time this week. I will update when I get a chance to test it. If it doesn't work, I guess I will be doing some reverse engineering to identify what the problem could be.
 
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#6
Something else to consider would be your video card. I assume since this is a home built computer that you installed a dedicated graphics card. Some cards are really bad about putting out a lot of noise if they are getting power even when no cables are connected to it. Hopefuly the cores will help but if not I would check this next.
 

briskattivo

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#7
Got toroid/ferrite core today. I didn't have too much trouble looping the power supply through it. I am confident that the power supply is not the issue now though. When I turned on the system with a looped core there was no difference, so I eliminated that as the cause.

So I went to the graphics card. It's an NVIDIA GTX 750 Ti, a somewhat high benchmark dedicated card, at least it was when I bought it. I basically just took it out my comp and put it in an antistatic bag and turned the system on without it. NO INTERFERENCE! So, it is definitely the video card causing the problems. I was afraid of this.

Unfortunately, I don't have an integrated card to hook up to, one of the frugal sacrifices I took when buying the motherboard. I tried experimenting a bit, simply moving the video card to a different PCI-Express slot on the motherboard. It worked for about a minute. After that the card started to overheat, because I guess it was close to the power supply, so I moved it back to the original slot. So, right now I'm faced with the choice of buying a different video card or giving up. I have no idea what kind of video card to buy. I don't even know how to find out. What say you, gurus of the forums?
 
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#8
It is surprising how poorly shielded these aftermarket cases are. I have a Lian Li case that is pretty well shielded. However, some aluminum duct tape was necessary around the front of the drive bays. My son bought an knockoff Lian Li case and most of the front bay is plastic so no good there. My wife bought a black steel case that looks pretty well shielded, except that it is 100% painted where the panels overlap and the screws are painted, the drives lock in with plastic cams. So it is not a very good "Faraday" box.

Personally, I would start by being creative and see if I could run some RG6 quad shielded cable to the rooftop and install a discone antenna on a side bracket, chimney bracket or tripod. You WILL have to ground this antenna with a green # 12 wire down to the ground level. Ground with an 8 foot copper clad rod and make sure that the rod is grounded to a metal water pipe or the service entrance ground rod. Put a cable TV type lightning arrestor where the coax enters the room and use another #12 wire to bond to same ground rod. What I described is a pretty low profile installation if you are clever about where you run the cables.
 

briskattivo

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#9
I think the case is a likely candidate for reasons why the video card RF noise might be leaking so much. I have an NZXT Phantom 410. It's about half plastic half aluminum, drive bay and top parts both plastic. I really like the case cosmetically, especially when it lights up my office/room at night. I imagine it has very poor shielding though. I will check out the Lian Li cases. It would be sad to see the NZXT go but it's just a case, although awesome otherwise.

The roof rig would be nice. It's unlikely my landlord would go for it though. But that's another story.
 
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#11
Wow that Phantom case has a huge hole in the side of it, Quite a waveguide!

My Lian Li case is the bright aluminum. It is anodized, but has bare aluminum where the panels mate with the frame. I measure zero resistance from the corner of one panel to another. I have used this same case through four systems builds.

Hopefully the black anodized models have bare aluminum mating surfaces. You might ask New Egg or buy locally to see one. You probably will still need ferrite chokes on the cables going in and out as well as aluminum duct tape on any openings. Don't scrimp on any fasteners, if the motherboard has 15 screw holes and the chassis will accept them, use them all and use brass or steel standoffs, not nylon. Be sure all the blanking plates in front and rear are secured. The front ones, I found although aluminum, don't snap in with a lot of contact area so I used aluminum tape to bond to the chassis. The trick with the aluminum tape is to have good overlap between surfaces so that the capacitance of the overlap area chokes off the signal even if the electrical contact through the adhesive layer is poor.

Hopefully the power supply has good EMI filtering or it will have to be changed.

The antenna system is 1/2 of the problem however. You need a good signal to overcome the noise floor. Whatever you do, make sure that the computer, the radios and antenna system are bonded to a decent earth ground using separate conductors for each. This is a "star ground" versus daisy chaining everything along a single ground wire.

When you get it all done, use an AM radio to try and determine if any other cables are radiating. Better yet, if your scanner has an airband (AM) mode, use a length of coax cable from the antenna connector with a short stub of antenna or a coil of wire (inductor) and use to find VHF emanations. Practice on your current setup and get a baseline as to the noise levels.
 
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briskattivo

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#12
I switched to the Lian Li case yesterday. It's a very nice case. Everything I needed came with it. The bezels are a tad annoying, but I think I just need to screw them in. So, right now I'm scanning railroad frequencies with the computer up and running. I can hear them loud and clear, good reception. So definitely progress. The computer connections (my Uniden USB cable and 3.5mm audio cable) seem to create a lot of emi/rfi noise that blocks the railroad signals though. I take it I just need to shield them. Tried to wrap the audio cable through the ferrite core about 5 times though and it is still very noisy. The uniden usb cable actually already has a choke on it so ? I'm not opposed to buying entirely new cables or shields, any recommendations?
 
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#13
Did the new case or your mother board come with a new shield to mate the motherboard connectors USB, video, network, sound card etc to the rectangular opening in the case? If so is it fitting tightly? They can be a pain because the finger stock sometimes don't touch the MOBO connectors.

There are various flavors of ferrite that respond better at low or high frequencies. You may want to try other sources.

Did you ground all the equipment? A star ground? Don't simply ground the antenna, the Uniden to the PC and the PC to earth. Each needs separate ground wires to a common earth ground. Until you do this, the USB cable and audio cable are a counterpoise to your antenna system that happens to have a noise generator (PC) in series with it.
 

briskattivo

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#14
The case did not come with a new shield, so I used the one from my last case. I have to admit it has been a struggle to actually get it into place. I just finagled with it a bit just now to see if I could improve it. It looks like a bulging piece of plastic above the ports. It is possible to go more flush with the case and ports, but that results in the little tabs protruding or blocking in many ways.

So sounds like the grounding thing is going to be pretty essential if I want to hook anything up. I must reiterate again, I live in a shared living situation. Might as well be an apartment on the 20th floor, because I do not have access to anywhere to ground. Would it be possible to use the air vent for the furnace as a ground with some wires? I really can't think of much else. If there are any devices that simulate a ground, I wouldn't mind investigating if it will get my radio working. (It is possible I could drive a long stake into the ground by leaning out my window if it were a simple procedure, not sure if this is doable though)

Also, the railroad band is fairly silent at night, so its hard to test in that respect sometimes.

EDIT: (Did a bit of adjusting to the i/o shield, doesn't seem to have hurt anything, included a pic)
 

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briskattivo

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#15
Just a note. I tried to install a downgraded $30 graphics card today instead of the 750 ti. It made no difference.
 
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#18
I still would be suspect of the PS - as I said earlier.

I guess an obvious question is whether you've tried a different PC with that one unplugged and still have the noise...
 

briskattivo

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#19
Just out of curiosity, what exactly about the PS is suspect? Model? High wattage? Fan position? This is what's in there now: Corsair AX 760 Currently, it's positioned at the top of the case with the fan down toward the exhaust fan in the back of the case.

I have attempted this on my laptop, but the audio port is a digital jack, meaning it is a single port that supports headsets (headphone/mic combined into one plug). I have messed around with it a bit, but no luck.

I ordered a ground loop isolator for the aux cable and a 10 pack some ferrite cores for the uniden USB adapter.

Part of me is tempted to setup a raspberry pi on the other side of the room with the sole purpose of scanning railroad. I'm not quite there yet though.

Also, this Lian Li case is noisier (fan wise) than the NZXT I had, so now I'm pulling my hair out over that too.
 
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