Eliminating Hum and choosing ferrites?

[RedPenguin]

I have a question about ferrites and even though I researched them on the Internet, I am not sure if they will help in the following situation or if I need something completely different.

I have a BR330T (plugged in with stock AC adapter in power strip) which while NOT receiving anything, records a constant noise no matter what computer or sound card it's hooked up to. It uses a Diamond RH77CA antenna.

I am wondering if I should just snap ferrites on the plug but how do I choose the type of ferrite?

So far, I've seen the following:

Snap-Together Ferrite Choke Core - RadioShack.com (Snap-Together)

Snap Choke Core - RadioShack.com (Snap Choke)

Would I even need a ferrite in this case?

I thought it was interference on my whole house AC lines but my BCT15 does not get it at all.

Here is a recording what the interference is I seem to be picking up, that I never seem to hear when I don't record and just listen to the scanner itself.

http://adam.250free.com/sound.wav

I'm kinda lost because I don't know if it's actually electrical, connection between scanner and PC (audio cable) or what. Is it just normal? If not, will ferrites even help in this case?

EDIT: I have tried the Radio Shack Ground Loop Isolator and even the Attenuating Cable, nothing seems to help this situation except I never tried ferrites, though I should, I know I have a snap on one I got from a PC item (I forget what it was) I was got rid of.

 

[smason]

I wouldn't call that hum, hum I'd normally call the 60hz or 120 hz you get from poorly filtered power supplies.

A few questions. How far is the antenna away from the computer/other possible sources.
What kind of coax (a longshot, but if it's cheap Radio Shack 40% sheild stuff...)

Have you tried unplugging/powering off potential sources (computers, TVs etc)

 

[w8jjr]

Ferrites will help if the noise is getting into the recording line. Listening to recording it sounds like 60hz. SMASON may be on to something. Does it do it if power supply is unpluged. Also do you have 2 prong or 3 prong on AC outlets? Lighting, dimmers?

 

[N_Jay]

Sounds like a ground loop.

Ferrites will not help a ground loop.

Actually ferrites wont help with any "hum" unless it is somehow getting in as RF and being demodulated.

 

[RedPenguin]

Well....

Sounds like a ground loop.

Ferrites will not help a ground loop.

Actually ferrites wont help with any "hum" unless it is somehow getting in as RF and being demodulated.

Well if that is true, why does a group loop isolator from Radio Shack seem to do anything?

EDIT: I feel stupid, apparently completely unhooking the PC Cable all together silences this noise completely. Kinda annoying though because I like being able to use bcTool every now and then. Any ideas on how to fix this? Also, why would my BCT15 not care that the PC cable is in going to the same computer?

 

[prcguy]

Try powering the scanner from a 12v battery and have nothing connected to the scanner except the battery and maybe a rubber duck antenna, no wall transformer and no external antenna or coax that may be grounded somewhere else.

If it still hums its not a ground loop. Everyone has had good advice so far and ferrites will do nothing for ground loops. I'm not sure what the ground loop isolator from RS is but the 600ohm 1:1 audio transformer they sell can fix ground loops with computer audio cards.
prcguy

Well if that is true, why does a group loop isolator from Radio Shack seem to do anything?

EDIT: I feel stupid, apparently completely unhooking the PC Cable all together silences this noise completely. Kinda annoying though because I like being able to use bcTool every now and then. Any ideas on how to fix this? Also, why would my BCT15 not care that the PC cable is in going to the same computer?

 

[RedPenguin]

Thank you....

Try powering the scanner from a 12v battery and have nothing connected to the scanner except the battery and maybe a rubber duck antenna, no wall transformer and no external antenna or coax that may be grounded somewhere else.

If it still hums its not a ground loop. Everyone has had good advice so far and ferrites will do nothing for ground loops. I'm not sure what the ground loop isolator from RS is but the 600ohm 1:1 audio transformer they sell can fix ground loops with computer audio cards.
prcguy

Well, I will have to look in to that, but like I said in my previous reply/edit, simply unhooking the Programming Cable gets rid of this problem completely.

 

[N_Jay]

You have to look at EACH connection referenced to ground.
Typicalkly;
computer end of audio cable, (Computer power supply ground)
Radio end of audio cable (typically radio power supply ground, but can be radio antenna ground)
Radio end of antenna cable (typically radio power supply ground, but can be radio antenna ground)
Antenna end of antenna cable (whatever ground connection it happened to make)

It sounds like you have a programming cable is rather then a audio cable, but the issues are the same.

Trick is to isolate each point and see when the hum goes away.

 

[RedPenguin]

Well...

You have to look at EACH connection referenced to ground.
Typicalkly;
computer end of audio cable, (Computer power supply ground)
Radio end of audio cable (typically radio power supply ground, but can be radio antenna ground)
Radio end of antenna cable (typically radio power supply ground, but can be radio antenna ground)
Antenna end of antenna cable (whatever ground connection it happened to make)

It sounds like you have a programming cable is rather then a audio cable, but the issues are the same.

Trick is to isolate each point and see when the hum goes away.

Well to begin with, I had all 3 hooked up, the AC adapter, the audio cable to the PC, and the serial cable to the PC. When using bcTool the last two are both needed. The audio cable by it self does not produce noise, but the instant the serial cable is plugged in, boom noise. So it doesn't seem to be anything with the antenna or audio cable, because right now it is recording with no noise at all and everything is of nice quality, without the serial cable plugged in.

 

[N_Jay]

Does the audio cable have ground continuity?

 

[bagmouse7]

The ferrites won't help, but a ground loop isolator like this will fix the hum:
Ground Loop Isolator - RadioShack.com

 

[N_Jay]

The ferrites won't help, but a ground loop isolator like this will fix the hum:
Ground Loop Isolator - RadioShack.com

Not if the ground loop is on the other cable.


(Maybe reading the whole thread will help)

 

[RedPenguin]

I don't think...

Does the audio cable have ground continuity?

Well, I don't believe so, it was just a regular every day 3.5mm male to male cable that I got off the Internet at a site that must have closed up shop now.

If it has anything to do with the audio cable though, why would the fact that the serial cable is unplugged make no noise or interference at all? I mean to me, seems like it doesn't like the serial cable at all.

Also, does it hurt the ground loop isolators to have to convert both ends to 3.5mm for obvious reasons? I wondered that when I tried used it.

 

[N_Jay]

I think the outer conductor on the 3.5mm plug is at ground. Probably at both ends.

I would think the data cable also has a ground.

I don't know why, but to find out what you have to go slow and check ALL combinations.

Make a chart, keep notes, be clear about what you are doing.

 

[AlmostHandy]

(typically radio power supply ground, but can be radio antenna ground)

Hey N_Jay, Are these ever the same? Or, what I mean is, is the antenna ground connected to the power supply ground inside the radio anywhere? Ever? Does it depend on the radio, or are they always isolated?

/highjack

 

[N_Jay]

Hey N_Jay, Are these ever the same? Or, what I mean is, is the antenna ground connected to the power supply ground inside the radio anywhere? Ever? Does it depend on the radio, or are they always isolated?

/highjack

Ohmmeter time.

 

[AlmostHandy]

Ohmmeter time.

lol. Ok.

So I checked my pro97. One of the ground leads to the battery pack has no continuity with the antenna ground, and reads nearly 6MΩ (5.94M&#937. The other ground lead to the battery pack has continuity with the antenna ground, and reads ≤2Ω.

What does that mean?

 

[N_Jay]

It means your power and antenna grounds are common, probably with your audio and data grounds, hence the cause of the problem.

 

[RedPenguin]

More Tests

I tried my BR330T on a different PC using both the same and different serial cables and I still get the noise.

I even tried it on the same PC but just plugging it in a different port.

I then using the different PC simply unhooked the serial cable again and the noise vanished.

I even moved the scanner to a different location and used another PC again and still the noise only when the serial cable is plugged in.

It doesn't seem to matter at any point if I'm using batteries vs AC.

Even using a USB to serial adapter with the programming cable is no relief.

Just as a wild trial and error though, I hooked in the serial cable then left the computer end unplugged, this produces no noise though.

 

[N_Jay]

Can you try to explain what is hooked to what in each case when you get and don't get the noise?

Don't leave anything out, don't leave anything to the imagination of the people reading.

Think back to writing a lab report in highschool science class.