Noise Filter

[zzdiesel]

I did a search on filters but only found info about front end overload and engine noise. This is about my two scanners here in the house. I'm getting Heterodyne (sp?) off of the power lines & etc. This town was always real bad about it. In my CB days the noise blanker always pretty well took it out. Why can't scanners have noise filters? The noise covers up weaker stations. It's very aggravating.

 

[zz0468]

I did a search on filters but only found info about front end overload and engine noise. This is about my two scanners here in the house. I'm getting Heterodyne (sp?) off of the power lines & etc. This town was always real bad about it. In my CB days the noise blanker always pretty well took it out. Why can't scanners have noise filters? The noise covers up weaker stations. It's very aggravating.

You mean an impulse noise blanker? It's probably cost that prevents manufacturers from adding it.

But a heterodyne from the power lines? Maybe you'd better explain better what it is you're hearing. It's not possible to eliminate the impact of many noise sources at the receiver.

 

[zzdiesel]

I may be wrong about the term, but that's what I've always heard it called. It's like a constant buzz or a grinding noise. The reason we've thought it was power lines & etc is because it usually gets a lot better or goes away when it rains. Then it gradually comes back as everything start to dry.

 

[zz0468]

I may be wrong about the term, but that's what I've always heard it called. It's like a constant buzz or a grinding noise. The reason we've thought it was power lines & etc is because it usually gets a lot better or goes away when it rains. Then it gradually comes back as everything start to dry.

Ok. That's not a heterodyne. It's generally just referred to as 'power line noise'.

ARRLWeb: The Power-Line Noise FAQ Page

 

[zzdiesel]

Thanks for the info. I'm going to check out the link

 

[kb2vxa]

If you're hearing power line noise on FM signals your scanner, the detector in particular is out of alignment. That's not surprising, all the tuned circuits are pre-tuned before assembly so the receiver is never aligned as a unit. Accuracy is a hit or miss proposition, "good enough for government work" as they say.

You COULD deal with the power company but that's another hit or miss proposition, we hams have had rather mixed luck ranging from instant fix to no response at all. On the other hand there is plenty of RFI coming from inside the home, both yours and neighbors that closely imitates line noise so switch off the mains and operate on battery power to determine if noise is coming from something of yours. There are threads all over this site on the subject, search and read.

 

[CCHLLM]

The new screw-in fluorescent replacement bulbs are big producers of noise, and as might be expected, the cheaper they are, the noisier they are.

 

[kb2vxa]

Not necessarily Cecil, I live in a house full of them and nary a problem. Fluorescent lamp noise is the old bugaboo of MW and HF but seldom if ever shows up on VHF and never on UHF the same as any other impulse noise. What I suspect here is not impulse noise but something that often closely mimics it, RF hash locally generated by digital equipment. Anything from a computer to a TV to the clock timer in a microwave oven may be suspect and our homes have quite a collection of these cute little toys these days.

One thing to note when it comes to these offenders, they're never off when shut down, always some part of the power supply is on powering something digital. Case in point; how else could you turn on the TV with the remote if the remote receiver and control board weren't powered up? How could it remember it's programing if it's memory weren't powered up? Unplug it for a few minutes and watch it return to it's default settings and run through auto channel detection when turned back on. That's why when tracking down interference sources the first thing you do is switch off the main breaker to see if it's coming from inside or outside the house. If it's inside you go around UNPLUGGING things one at a time, just because it's "off" doesn't mean it's off.

 

[slicerwizard]

How could it remember it's programing if it's memory weren't powered up?

EEPROM perhaps? Do TV's lose their factory alignment settings during shipping?

Devices don't have to lose their marbles when the power fails. Non-volatile memory and supercaps are simple tech. My Toshiba TV doesn't lose any of the user settings (channel names, etc.) when it's unplugged.