Interference Sources on OTA, Radio, WiFi Signals

[majortom]

Yeah you would think they'd undergo EMC testing, etc. just like motor vehicles, or anything else during the design phase. It would be a far stretch (pun intended). Still would be interesting to sniff as the trains go by to see what the spectrum looks like.
So, general consenseus = multipath it is and a yagi would probly be ur best bet to work around it.
Positive multipath confirmation would be past experience/reports seeing ghosts on ur analog TV back in the day in the same areas only when the trains went by.

From my friend's experience in close proximity, there's not much ur gonna do that's gonna completely eliminate it, to the point he gave up.
Those are some of the choices people have to make when choosing a place to live I guess.

[JamesK]

^^^^
As I mentioned, you can easily "sniff" for interference with a portable AM radio that covers the various frequencies. Scanners capable of aircraft bands operate on AM around 108 MHz. There are other radios that cover the various amateur radio bands (some are almost "DC to light" <g>) and even the old "CB" radios will work at 27 MHz. Grab some equipment, head down to the tracks and see what you hear.

BTW, there are several amateur radio publications that cover locating interference sources.

[BOUVAL]

It could be a mechanical problem.

A train going by at 300 meters from a house can cause some ground vibrations that you may not feel inside and if you have a slightly loose connector or element in your antenna setup, there goes pixelation.

And tilting the antenna is still valid.
.

[RobertPlant]

Hi everybody,

This is a huge thread, so I apologize if this has been discussed previously.

I live on the ground floor of an apartment in Toronto. I use a cheap RCA antenna (VHF/UHF/FM) and I get many channels with decent picture quality, but I am experiencing signal drops and interference whenever a car drives by.

Can I fix this with some kind of notch filter? Is it happening because my antenna is getting overwhelming FM signals from the cars? Should I get a better antenna? Is there anything you can suggest?

I really appreciate any advice.

Thanks.

[Jase88]

RobertPlant, interference by passing vehicles (cars, buses, trains) is a frequent issue for those using antennas lower to the ground.

Many (including myself) have speculated that electrical interference could be the culprit. However, I'm more convinced that multipath is the issue.

Multipath is an effect created when reflections of the signal bounce off surfaces vehicles or structures, creating several "versions" of the signal arriving at the tuner milliseconds apart. In the analog days, this phenomena would create the "ghosting" effect. With digital, in creates dropouts or loss of signal.

It's kinda like talking to someone on a cell phone with bad echo. Like humans, digital tuners have a difficult time sorting out the mess that's received...

In the case of multipath generated by passing vehicles, the resolution would obviously be to get your antenna above the interference source. However, this isn't always possible or practical.

Another option is to use an extremely directional antenna pointed away from or above the interference source. Something like a small Yagi (perhaps an XG-43 by Antennas Direct). Though this may not be enough to overcome the problem.

I hope this helps!

[RobertPlant]

Thanks Jase.

I appreciate your explanation, and suggestions. I'll look into a yagi, and post my results once I test.

Thanks!

-RobertPlant

[balm]

I tested a 2-Bay indoor sized antenna on an analog Tv thru a HD Acess DA converter box, and I receive all the moderate & strong digital channels very well, however I get a constant static noise on all channles (I assume is interference).

The DA converter & cables, and antenna, are new.

The TV does not have any static noise when fed with Cable TV subscription (or possibly Satellite). When testing the antenna I completely removed the subscription cable feed.

The TV is on ground floor, in apartment building, with no other source of interference in proximity which I can determine. It is in a suburban area of 2-3 apt buildings with houses all around. The antenna is looking thru a window towards a line of trees and a field.

I think I noticed a small decline in the noise when using new RG6 coaxial cable from the DA converter to TV, instead of the coaxial provided. But either way the channels cannot be listened due to the overpowering static noise.

Any ideas what might be doing this, or how to eliminate it ?

thanks

[Dave Loudin]

So, the relay to the TV from the converter box is via RF on ch. 3 or 4? If you have an AM radio handy, do you hear constant static on that? If so, then there's a bad transformer in general or ballast for flourescent lighting in particular. If the AM is clean, then I'd suspect a fault in the converter box.

Can you use direct audio and composite video connections between the digital tuner box and the TV?

[roger1818]

balm, Have you:

1. used this TV with cable or satellite at this location?
2. used this DA box with a different TV?

My first guess would be a faulty DA box.

[balm]

Yes, the TV was on satellite, I believe

and no, the DA box was not tried elsewhere.


My next step is to try another DA box.


Thanks all.

[majortom]

Been fixing up some old tube AM and AM/FM radios (40's/50's) lately in my spare time.
Finally got around to isolating what was causing horrendous trash in the AM Broadcast Band throughout my house.
Causing AM reception to be impossible except for the strongest of local stations.
Turns out it was the Switching Power Supply that came with my Prof 7500 USB Satellite TV tuner.


here's a few pics from the spectrum analyzer, 550 Khz to ~ 1600 KHz, input Attenuator is at -30 dB

clean with the prof pwr supply unplugged.
http://db.tt/znZRMVHh

trash with the prof power supply plugged in
http://db.tt/HRf4R7nf

and here's a pic of the problematic switching pwr supply that came with the Prof
http://db.tt/8cIzQWeq

[CanadianRyGuy]

I live on Eglinton and every time a bus goes by which is quite frequently the signal gets all pixeled and its really quite annoying. The way my apartment is situated, i really cant move the antenna too much. Any ideas?

[ProjectSHO89]

Unless you can get the antenna in a location so that the primary signals can get to it without them being blocked by or reflected off the bus, there is no way to fix your problem.

[roger1818]

What antenna are you using and where is it situated? A higher gain, more directional antenna may help as it will receive more of the desired signal and if reflections are the problem, it won't receive them as strongly.