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Author Topic: How much white noise is too much white noise?  (Read 6668 times)
K8KPO
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Posts: 8




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« on: May 03, 2013, 12:58:43 PM »

Ok, a few things off the bat.  I am very much a newbie to ham radio.  I know very little.  The question I'm about to ask may in fact be an extremely stupid question to ask, but I don't know enough to know how to figure out the answer on my own as my google searches are not turning up anything.

The local club doesn't have much to do with newbies, so I really have no one else to ask other than to post here.

For backstory, I'm one of those used-to-be CBers that a lot of hams hate and am trying to teach myself about amateur radio, so much of my guesses and assumptions about HF are based on my 11 meter experience.

So, with all that out of the way....

I have an IC-718, and a G5RV jr dipole.  My issue is that basically no matter where I tune (which is just through 10/20/40m bands) I have a constant white noise of about 7.5 or more s-units.  Obviously, this means signals have to be pretty dang strong for me to pull them out of the weeds enough to understand what's being said.

Now back in ye olden days of 11m I never dealt with constant white noise of that high of a level.  Either the frequency was dead with nobody keying up and noise would be MAYBE 2 or 3, or skip would be rampant and every channel was a constant 9+ of signal.  But I never just had (literally) months of nothing but 7.5/8 s-units of plain white noise while only hearing the very strongest of stations.

So my question is what am I doing wrong?  I ran the radio straight from battery to make sure it wasn't from the power supply and no change.  There is no pulsing type noise like I would have guessed would be indicative of power line noise, or was that a wrong assumption on my part?  Does anybody else's HF always have that high level of white noise?

Again, sorry for the questions due to ignorance, I just have had this radio for months and am nearly frustrated to the point of selling off and going back to CB because I can't figure out what's wrong.
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WB6BYU
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« Reply #1 on: May 03, 2013, 01:11:00 PM »

There are many sources of noise, and not all of them have a distinctive pulsed sound.

But first, make sure that the RF gain is turned up full on your radio:  that will cause the
S-meter to read high if it is backed off.  A quick test is to unplug the antenna lead from
the radio and make sure that the noise level drops to zero.

The next step is to put the rig back on the battery and turn off the main circuit breaker
to your house:  if the noise level changes, then there is something connected to your
electrical system that is causing it.  Might be a TV (even if turned off) or flourescent
lamp or a battery charger or a touch lamp or any of a number of the myriad of electronic
devices that now fill our homes.  If you find something, then track it down by turning
off the individual branch circuit breakers one by one, and unplugging each device connected
to the offending circuit in turn.  There may, of course, be several offending devices.

If that doesn't find it then the source may be a neighbor, HV transmission line, faulty
streetlight, etc.  Those can be more difficult to get fixed when they aren't on your
property.  If the signal is coming from a single source you might be able to use an
antenna with a sharp null aimed at it to reduce the problem, or one of the noise
canceller devices that are on the market, but they don't always work as well as
one might hope.
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WH7DX
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« Reply #2 on: May 03, 2013, 01:41:32 PM »

K8KPO,

Ask all the questions you need.  Maybe put them in a list as one message etc..

All the previous comments are right on.  I forgot about the RF gain - good point.

If that's not it.  I'd take the rig to a friends or relatives (empty spot on a hill..  joking.. you're in Ohio - Wife's joke.. from there etc. :-) and throw the antenna over a little tree or something to check it out.   If you need to drive away 5 miles to a spot near nothing.. I'd do it if necessary.

You want to rule out an electrical issue near you, but first check your equipment settings and coax condition.   

Try a simple dipole like a 15M or something.

I bet some of those guys in the club would be more than willing to help..

Just walk up and tell them... "HEY OLD MAN!  I need some help, I'm a newbie and I have a question!"   Grin Grin

I'd make sure the Coax is good.  Did you buy it.. make it etc..

Get back to us and congrats for moving into the real world of radio  Grin
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K5LXP
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« Reply #3 on: May 03, 2013, 02:06:03 PM »

If you're having a constant noise level of S7 all the way up to 10M and it's not the RF gain, chances are excellent the source of noise is very close by.  Most noise sources (example, wall wart power supplies) will diminish as you go higher in frequency.  In order to have significant noise at higher frequencies you (your antenna) typically has to be pretty close to the source.

Running the rig off of a battery *and* killing the mains to the house is a quick test.  It's not enough to turn off individual items because there may be more than one noise source, or the noise source could be something connected via hard wire circuit (like a climate control or alarm).

As an example, once I had some interference all the way up through 6 meters.  Turned out to be from a cordless drill charger in the garage.  Had I just gone around unplugging or switching things off around the house it never would've occurred to me the problem was in the garage (no "tech" stuff out there) nor would I have believed a drill charger could generate that much grunge.  When you turn off the mains and you catch everything at once.

What your antenna is next to might be a factor.  If it's close to a conductor or piece of equipment that's radiating grunge, you're more apt to pick it up if you're a few feet away vs a few dozen feet away.


Mark K5LXP
Albuquerque, NM
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K8KPO
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Posts: 8




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« Reply #4 on: May 03, 2013, 05:40:34 PM »

Thank you for the replies.

I have turned the radio off with the antenna unplugged and the signal drops to zero.  I forgot to mention that.

The RF gain is turned up.  I did verify what was said about turning it down makes the signal meter go up even though it goes silent.  So yes, that is set correctly.

The noise level on 10m is not quite as high as it is on 20/40m.  Right now it's running about S5 of white noise instead of the S8 I have right now when I switch over to 20m.

If I activate the preamp the level jumps to well over S9 (on 20m).

If I activate the attenuator the level of white noise drops to S6, but of course the good signal drops as well making that no help.

I did not try killing the power to the whole house.  It is too late and dark to do that now, but I will try to do that this weekend.

Thanks for the suggestions and I will report back on this thread with my findings.
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AD6KA
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Posts: 2237




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« Reply #5 on: May 03, 2013, 07:14:11 PM »

Quote
I bet some of those guys in the club would be more than willing to help..

Just walk up and tell them... "HEY OLD MAN!  I need some help,
I'm a newbie and I have a question!" 

That's funny.

Better yet, walk up to them and say "Hey Old Timer!
I'm a newbie and I have a question......and that guy standing
over by the coffee machine bet his buddy $5 that
you wouldn't know the answer"
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KE3WD
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Posts: 5689




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« Reply #6 on: May 04, 2013, 06:33:59 AM »


I have turned the radio off with the antenna unplugged and the signal drops to zero.  I forgot to mention that.


What happens when the radio is ON and no antenna is connected? 

Or is that a typo? 


73
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NO2A
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Posts: 786




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« Reply #7 on: May 06, 2013, 06:56:30 AM »

I`d also try running the `718 from an extension cord to another circuit. Years ago I had a loud buzzing ac type noise in my shack. It turned out the outlet for that room was simply damaged from so many plugging in/unplugging over the years. Replaced the outlet and noise was gone. Wish everything was that simple. Do you have a computer on that circuit?
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WA1GJF
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Posts: 11




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« Reply #8 on: May 08, 2013, 02:40:23 PM »

I had an S-8 noise floor until I tracked down the source, and that was a step down transformer for the kitchen low voltage lighting under the cabinets.  It appears that the transformers are wide open, and most likely not type approved. Tried ferrites on the output wires to no avail.  Now have an agreement with my wife:  When I go on the radio, the lights go off!

However, I still have an unidentified noise at up to S-5 that comes from the outside.  it was still there when our town lost power during the blizzard! (I was on batteries at the time)

Leeds

WA1GJF
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AD0DJ
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Posts: 4




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« Reply #9 on: May 08, 2013, 04:03:25 PM »

When I was MUCH younger (in about 1969 or so) I built a Heathkit GR-64 receiver, and although I didn't ever hook it up to an outside antenna, I could pick up stuff from all over the world with an indoor  wire - the air was really, really quiet back then.  Now, 44 years later, I got interested in SWL all over again (which led to me finally getting my ticket, but that's another story) and I recently got a nice Icom SW receiver and hooked it up to an indoor wire just like I did so many years ago, and I was positively appalled by how much RFI there is to pick up now.  (Nasty hash about every three turns of the tuning dial.)  I did some research on the web and found the likely answer - my house is crammed with RFI generators that didn't exist in 1969...  Cell phones, wall warts, LED lighting power supplies, computers...   Once I get a proper HF antenna set up in the back yard (which I will be doing soon) I'm hoping that most of that will be happening far enough away from my antenna that it won't be a big deal, but then there are other possible issues like the guy across the street who has an Invisible Fence system for his dog, which I understand can radiate a lot of trash throughout the neighborhood too.  Good luck to the original poster - I guess the point I wanted to make is that it used to be a much quieter RF world than it is now. 

73's,

Joe AD0DJ   
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K8KPO
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« Reply #10 on: March 27, 2014, 05:33:06 AM »

I'm hoping since this is my own thread I am allowed to "necro" it.  If not, I apologize.

So a year later I'm still working on this problem.  Wife had a baby so I've really had no time to do much monkeying with it for the past few months, but am now trying to get back to it.  I really want to be in the radio hobby but my frustration level is nearing the giving up point.

(Yes, I still know very little, and yes, I'm still very green.  It sure would be nice if getting this HF up and running was as easy at the 2m was.)

So for grins a couple weeks ago I decided to plug my homemade 2m groundplane that I have installed in the attic (works great!) into my HF radio.  I never expected it to tune up, and I never even tried to be honest.  I simply wanted to see if I picked up the same noise with it as I do on my wire antenna.  I didn't.  In fact it was extremely quiet.  So I figured (more like guessed since I'm clueless) that it was so quiet either because the antenna is so short relative to what I'm trying to pick up, or because maybe the 2m antenna is vertical while the wire is horizontal.  I had no idea if polarization alone could make that much difference which is why leaned more towards guessing it was because the antenna itself was so short in comparison.

As an aside, the noise level was so low using the 2m groundplane that I actually was able to clearly understand some people that were chatting on various frequencies as I tuned around.  That told me that there is traffic out there to be heard if only I can get my noise level down far enough to actually hear and understand it.

Now I'm thinking maybe the antenna I am attempting to use is just more susceptible to noise for whatever reason, so I guess I'll blow some cash one more time to try to get this thing working.  So I bought one of these:  http://chameleonantenna.com/BASE%20ANTENNA/CHA%20ZEPP/CHA%20ZEPP.html and yes I realize I could build that as there is seemingly not much to it, but when you know nothing and have nobody to help teach you then you usually end up either having to pay someone else to do it for you or simply give up, and I'm trying so hard not to do the giving up thing.

This thing comes in and I string it up outside, fire up the radio and no noise.  Now you'd think my first reaction would be jubilation, but with all the heartache this thing has given me my first reaction was that something was wrong.

I tune around 20m a bit hear a few very faint voices.  I tune off frequency a bit and figure I'll hit the autotuner and see what happens only to find out that the antenna is untunable and the SWR is sky high.  Awesome.  So I begin unscrewing the coax and as soon as I get the threads off, but the center conductor still inserted, all the sudden the noise is back.

Ok that's weird.  So I start to screw it back on and as soon as the threads touch the signal drops to zero again.  Unscrew, and there's signal again.  So my immediate thought is something is shorted out here.  I grab my multimeter and switch over to ohms and start checking coax which all was fine.  Then I disconnected the "impedance transformer" (this is an unun, right?) and test it and find a dead short between center conductor and shield on this thing.  Surely there shouldn't be, correct?  That has to be the defective part, doesn't it?

So I will try to contact the vendor to have this transformer replaced, and at least fix that part.

But that doesn't change the fact that my noise level is still stupidly high.  I turned off all the power upstairs yesterday thinking maybe it was something in the room or the adjacent bedroom or the attic wiring but that made no difference.  There is a plasma TV in the living room directly below so I'm wondering as I type if that could be it.  I will try unplugging that TV to see if it makes a difference.

This is all just maddening.  I never would've guessed that trying to hang and use a simple wire antenna was going to be so frustrating after how easily I got the 2m antenna up and running.
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M6GOM
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« Reply #11 on: March 27, 2014, 06:07:39 AM »



If I activate the attenuator the level of white noise drops to S6, but of course the good signal drops as well making that no help.


Yeah, that is unfortunately a throwback to your former CB way of thinking.

Actually it does help. Yes it does reduce the strength of the incoming wanted signal however the interference drops even more which actually improves the signal to noise ratio of your wanted signal. All it means is you have to turn the volume knob up a bit.

The problem you have is the antenna you're using and where you're using it. It is extremely susceptible to noise and it causes all kinds of common mode issues. Having it indoors just makes matters even worse.

Please do what someone said last year - build a simple dipole for say the 20m band and put it outside. You can built it from scrap wire. If it costs you $10 to build a dipole for 20m you've spent too much.  Grin
« Last Edit: March 27, 2014, 06:12:28 AM by M6GOM » Logged
AA4PB
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« Reply #12 on: March 27, 2014, 06:46:57 AM »

His former CB way of thinking is exactly correct. If you put in 10dB of attenuation both the signal and the noise drop by 10dB so the signal to noise ratio and the ability to copy remains the same.

Baluns (depending on the design) often show a DC short when you check them with an ohmmeter. They are not however, shorted in regards to RF signals.

I have no experience with the antenna you purchased but if the tuner can't match it then it's not right. My suggestion would be to build a simple coax fed 1/2 wave wire dipole on 20M and give that a try. Trim the antenna until the SWR is good in the part of the 20M band you want to operate on. That'll give you a pretty good reference with an antenna that is as simple as it gets.

Often times you have to trace the noise to its source and eliminate it. One trick is to get a portable AM radio and tune if down to the low end in a clear spot where there are no stations operating. Now you can walk around and see where the noise is coming from. Defective power line insulators on the poles are often noise sources but the noise is usually kind of "raspy" sounding (buzz) rather than white noise which is a steady "hiss" sound (what you hear on 2M when you open the squelch with no antenna connected). If you have a handheld scanner that will receive 2M AM (AM not FM) that often is more accurate in identifying the noise source because the noise usually doesn't travel as far at higher frequencies and that makes it easier to pinpoint the source.

I'm not surprised that your 2M antenna doesn't pick up as much noise on 20M because it is pretty inefficient on 20M. It certainly will not make a good transmitting antenna even if your tuner can match it. I'd be a little worried about possible damage to the tuner with such a mismatched load - the tuner is probably going to dissipate a lot of your power as internal heat.

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K8KPO
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« Reply #13 on: March 27, 2014, 07:16:02 AM »



If I activate the attenuator the level of white noise drops to S6, but of course the good signal drops as well making that no help.


Yeah, that is unfortunately a throwback to your former CB way of thinking.

Actually it does help. Yes it does reduce the strength of the incoming wanted signal however the interference drops even more which actually improves the signal to noise ratio of your wanted signal. All it means is you have to turn the volume knob up a bit.

I understand many in the ham community hate CB, but I don't believe my time spent there has clouded my judgment on this issue at all.  If the good signal and the bad noise both drop by the same amount then I'm still left with unintelligible signal, no matter how high I turn up the volume.

At any rate, I can run the antenna completely out of the house with nothing inside but the feeding coax and still have the noise, so I'm not understanding how cutting a new wire dipole will change anything.  The antenna is already pulls in the extreme noise even when the entirety of the radiating/receiving portion is outside.  This is the part that baffles me because it makes me think the coax itself is what is pulling in the noise, yet the coax from the 2m antenna does not pull in the noise even though it runs through the same area.

I wish I were experienced enough to listen to the noise and be able to say it's is this kind or that kind, but unfortunately I'm not.  It is definitely not a humming sound.  But it could be called raspy.  It's so subjective that I'm not sure what to call it.  I've emailed the antenna manufacturer because I just find it hard to believe that the short and inability to tune is by design.  Once I get that sorted I may just take the whole thing outside on a battery and see what happens (if it ever warms up and stops snowing).
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KA5IPF
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« Reply #14 on: March 27, 2014, 08:41:20 AM »

  There is a plasma TV in the living room directly below so I'm wondering as I type if that could be it.  I will try unplugging that TV to see if it makes a difference.

This is all just maddening.  I never would've guessed that trying to hang and use a simple wire antenna was going to be so frustrating after how easily I got the 2m antenna up and running.

Bingo, plasma TV's are notorious noise generators. When you killed power it was to the second floor and the tv was still powered up under the radio. Unplug it and your noise may disappear.
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