Electrical noise

[KX5JT]

So I never had this problem before.  I'm getting things back on the work bench and working things back on the operating desk.   I just put up a 135 ft doublet over the last couple weeks.  This weekend I was able to put a respectable signal on 80 meters AM again.  It felt great.  

BUT.  Here's the but....   I had to operate with my computer turned off... AND unplugged.   I don't have boat anchor receivers out of my storage yet.  I'm using the ICOM R75.   I suppose I need a lesson in ground loops maybe?

With the computer power cable simply PLUGGED into the back of my computer tower.... I get a buzz/hash at 15 db over 9 on 80 meters and S7 or 8 on 40 meters.  The computer doesn't even have to be turned ON.  I noticed this when I unplugged my computer this weekend to move something around the noise floor dropped and all these signals were there.    

Because this occurs simply making the connection, not even powered up.... is this the infamous "ground loop" I always hear about?  It's so very convenient to be able to surf while operating.   I sure would like the capability again.

Any direction or indication of what to do next would be awesome.   I thought maybe running the receiver on the Variac (thinking it would be isolated) might help but it did not.

[w4bfs]

make a rf 'sniffer' and use with yer rx to find noise source(s) .... a simple one is a few feet of coax cable with pl259 on one end to go to the receiver and the other end can be as simple as a few inches of center conductor without shield.... experimentation is the name of the game ... yer computer switching ps is likely radiating and this shud help you find where and then some filtering may be applied ...ymmv

[W3GMS]

So I never had this problem before.  I'm getting things back on the work bench and working things back on the operating desk.   I just put up a 135 ft doublet over the last couple weeks.  This weekend I was able to put a respectable signal on 80 meters AM again.  It felt great.  
BUT.  Here's the but....   I had to operate with my computer turned off... AND unplugged.   I don't have boat anchor receivers out of my storage yet.  I'm using the ICOM R75.   I suppose I need a lesson in ground loops maybe?
With the computer power cable simply PLUGGED into the back of my computer tower.... I get a buzz/hash at 15 db over 9 on 80 meters and S7 or 8 on 40 meters.  The computer doesn't even have to be turned ON.  I noticed this when I unplugged my computer this weekend to move something around the noise floor dropped and all these signals were there.    
Because this occurs simply making the connection, not even powered up.... is this the infamous "ground loop" I always hear about?  It's so very convenient to be able to surf while operating.   I sure would like the capability again.
Any direction or indication of what to do next would be awesome.   I thought maybe running the receiver on the Variac (thinking it would be isolated) might help but it did not.

What you are hearing is the "keep alive supply" within the main supply.  Computers today are turned on with a low level control signal.  To use this type of scheme requires the power supply to generate a voltage to keep the control circuit alive.  Same goes for a lot of electronics today such as TV's, radio's ...etc.  This supply is typically a small flyback supply which operates off the incoming line.   It sounds like the EMI filter within the supply is not doing its job.  It's probably a line conducted issue turning into a radiated issue.  You could try a second line filter and put it as close as you can to the standard IEC connector on the power supply.  Another thing that may work is to put the line cord through a toroidal inductor and wrap several turns through it.  They also have line snap on filters which may help.  In reality, as cheap as ATX supplies are these days I would just try a different brand power supply and your problem will likely go away.

Joe GMS          

[N2DTS]

Some computers are better then others, or maybe the noise is on different frequencies.
Ground the computer case to a good ground, try grounding it to the receiver as well, you never know what works best.
Why have the computer in the shack?
I use one for SDR rigs/band scope, but if its not needed, leave it out of the shack.
I hear people on the air who seem like they are on the web rather then paying attention to the qso, which is rude.

My laptop power supply got into one sdr receiver, but not the other, and it was fine on battery, who knows.
The clamp on ferrite filters work ok if you use a lot of them.
I also do not connect the keyboard on the computer, just the mouse as its another antenna to radiate hash.

[w5gw]

Joe has the right answer.

[Jim, W5JO]

The power supply sound defective, they usually have a line filter at the AC input.  I would replace the power supply to see what happens

[N2DTS]

Its not so easy to replace a DESKTOP computer power supply and have it be any better, who knows that the one you go out and buy is going to be any better?

Clamp on ferrites, ground the case, or leave it out of the shack.

[K3ZS]

I had to replace a power supply on a desktop because the keep alive supply was shot.   A common problem in lightning areas where the computer is plugged in at all times.   Power supplies are very easy to replace and usually also very cheap.  A simple switched power plug strip would eliminate the noise and protect the supply.

[k7iou]

I had a similar problem with a 2 pronged cord on a transmitter if I plugged my external mic preamp and equalizer into the same circuit. Fortunately when I wired my office I used 2 separate circuits. If 2 pronged cord on TX check which one is hot & neutral and label it. Hot goes into right side of outlet (narrow) neutral into left side (wide). If that is not your case then try a different circuit (not outlet). A different circuit with a different circuit breaker. If issue is still there then the computer power supply may need replacing.
73
k7iou

[W7TFO]

Ubiquitous cheap-ass power supplies are the nemesis of anyone on HF

73DG

[KB2WIG]

My wife's chiner cabinet has one of the touch switches. I don't mind when it turns on when I'm on 10 or 15 meters. She doesn't get the connection (sri) as most of my 10 & 15m operating is daylight. I didn't get the connection until I switched it off and heard the frying egg sound on the Hammarlund drop about 15dB. This crap is everywhere, I put up with my cellphones call home/handshaking for a long time until I figured that one out.

Yas gotta pull one ckt at a time and snoop.


klc

[WD5JKO]

  John,

   If you look for another PC power supply, try to make sure if it power factor corrected (PFC). These put a lot less trash on the AC line than the prior generation switch mode power supplies.

   Your Icom R75 is known to pick up nose from the DC power cable feeding the receiver. I recall some posts on the Icom R-75 Yahoo group that OM's were taking apart the big power brick, and put bypass capacitors across the rectifier diodes. Those supplies put out about 18 volts too, so the regulators in the radio run HOT. A different source of 13.8V might be of benefit to you.

Good Luck,
Jim
Wd5JKO

Send me a PM to see if we can hook up on 75m..or 40m sometime.

[KD6VXI]

I had the same problem.

It is not the pin 1 problem.

Ground the case of the pc to your station ground.

Run mouse and keyboard,  as well as any USB device cords through ferrite.

Buy a real power supply.   Inwin is a good brand.   9 out of 10 times,  this is a power supply issue.   Probably 9 out of 10 of the rest of the times,  it's keyboard or USB mouse related.

--Shane
KD6VXI

[W1RKW]

Agree with Shane. Had the same problem. The computer case should be sufficient in most cases to shield the noise. there's always that one situation where it does not work.

[n1ps]

As noted earlier, add a ferrite to power cable.   I like to use 2" donuts with 43 or 31 material and with as many turns as possible or reasonable.  Other mixes work.  The donut wants to be located right at the point where the power cable plugs in to the power supply.  Almost all electronics today are switch mode types and are full of crud frequently.  Part 15 where did you go?  

[Jim, W5JO]

Just remember to fix the problem not treat the symptoms.

[W6TOM]

  I have my PC on a power strip, printer and DSL Modem are  all on the same strip, it gets turned off when the PC isn't in use, saves power too. I also put my TV (when I had one) and my stereo which has a remote control that draws some power  when off on a power strip to.

  It made a small but noticeable difference in my electric usage.

  Snap on ferrites on the line cord might help, email Palomar Engineers for advice on their products, the owner is a Ham, AK6R.

[KX5JT]

This is why I love this community.   Such great responses and experience in here to be found.  Joe GMS seems to have hit the nail on the head, at least just from reading.    I might try a cheap torroidal solutions but as W5JO said, make sure to fix the problem not the symptom.  Of course if torroidals do the job then great. 

So many are pointing  to a "cheap" power supply and I know there are so very many out there that deliver the power needed for the computer but cost-cutting measures have them ignoring Part 15 FCC.    I "upgraded" just about my entire computer last  year to an i5 with all the latest low-power consumption but powerful stuff.   The case was another item that was upgraded and of course it comes with a power supply.   I need at least 450 watts to run my stuff but I do plan on adding some hard drives so if torroid ferrites don't do the trick, I'm considering this ...

http://www.amazon.com/Rosewill-630-Watt-Certified-Supply-RG630-S12/dp/B004GL8UO2/ref=sr_1_sc_1?ie=UTF8&qid=1423622345&sr=8-1-spell&keywords=power+factor+corrected+power+supply+atx

It's a "power factor corrected" supply as WD5JKO suggested.   I will get to the bottom of this one way or another.   Taking my computer out of the shack does not make sense to this old school/new school generation X'er.   Sorry but I consider it part of the station and my hobby.   It's integrated to the SDR receiver, all the riceboxes are controlled by it and heck, I just love to be able to surf and look stuff up while listening to people mention stuff.  QRZ, logging, AMfone..... nope, defeat is not the answer.  They MUST live together happily!


John

[Opcom]

Go in and kill the standby supply and install a little linear supply based on a filament transformer. It can mount on the outside of the power supply case facing front, or buy a tiny transformer for the few mA and put inside.  If you are sure that is the only culprit inside the PC..

For a thrill do some probing on your ethernet wiring. What a racket it can make. All a good exercise in interference hunting.

I use a Corsair 850W power supply. The standby portion is not offensive, YMMV.