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Low band noise problems...

30. prosince 2006 v 23:35 | Petr, OK1RP |  Technical topics
Noise flooding in suburban areas
In this world of microprocessor-based toys and gadgets, there are many sources of RF noise that find there way into the best shortwave receiver setup. While having a good quality receiver and antenna system is a great start, it will be well worth the effort to locate and reduce any local RF interference that you have control over.

Modern homes are flooded with devices that generate RF signals. Many small electronics devices are passed by the country Regulations for emmisions but they can still radiate RF for a short distance at levels your quality receiver will pick up. Here is a list of possible sources of noise:

* Florescent Lighting
* "Touch" Lamps - Even when the lamp is off, the control circuitry is still operating in the background and can generate RF noise.
* Automatic Outdoor Lights
* Automatic Indoor Night Lights
* Standard Light Bulb that is going bad
* Holiday / Christmas Tree Lighting
* Electric Blankets
* AC Powered Smoke Detectors
* Kitchen appliances
* Bug Zappers or Electronic Pest Control Devices
* Standard Electrical Switch that has bad contacts
* Televisions
* Radio / Police Scanners
* Bad Insulators on powerlines
* Computer Systems and Accessories
* Anything with an AC wall adapter - sometimes these wall adapters are poorly constructed and the diodes inside for DC conversion generate RF noise.
* Portable Games / Electronic Kids Toys
* If you live in an apartment, any one of the above mentioned items may be your cause.

Another source of noise not normally considered is the grounding in your antenna system. It is very convienent to have a ground rod mounted right next to your home but this may also be a source of noise coupled into your receiver. The above mentioned items may transfer noise into the AC wiring in your home and couple down to the ground rod you are using. This is especially true if your radio ground is in close proximity to the AC mains grounding system. You may want to consider mounting your ground rod as far from electrical noise sources as possible. Also it is highly recommended to use coax to feed your receiver from the longwire. Further improvements are to use a matching device like a longwire antenna match to improve reception.

The list goes on and on, but hopefully this will give you an idea of what to watch out for to enhance your listening enjoyment. These sames items also apply to the AM broadcast band as well.

You can make a simple detector by the use of a battery powered AM pocket radio set where there is no station (loudest background noise). When you get close to the noise source, you should here an increase in the background noise of the radio. Some noises are too small to detect this way and require a more sensitive detector to find the source but this is a good way to find most culprits of RF noise.
73 Petr, OK1RP
 

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