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Maybe Lower Power and a Lousy Antenna is Better

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Maybe Lower Power and a Lousy Antenna is Better

AM radio reception in my house is plagued with interference, buzzing from light dimmers and hum from who knows what.  Even my two solid state high efficiency transmitters, one of which is ground mounted outside and capable of 1 mile car radio range, cannot overcome the noise inside the house, but perhaps it is a mistake to think that a strong AM signal is going to overcome electrical noise in a home.

I recently noticed that a 5 kW local station also had noise on a portable receiver in my house but a 5 kW station 70 miles away did not have the usual noise on the same portable in or outside of my house.

Maybe weaker is better since it is known that AM RF can get into things such as wall warts, switching power supplies, and almost anything connected to the AC line.  A weaker signal perhaps lacks the strength to cause mixing and hence noise in devices around the house.

So, some experimenting was in order using my Part15 homebrew tube transmitter.  The transmitter operates with 67 mW final input power and uses a 3 meter wire antenna strung upward from a shelf and along the ceiling joists in the basement.  The range on a portable is about 100 feet so the combination of low final power and the antenna pretty much conspire to produce a pretty puny radiated field strength  Despite this, around the inside and the outside of my house the signal is received noise free on the portable. It also provides a noise free signal to line operated AM radios including a 1962 vintage all american five tube receiver.

It seems from this that noise problems can be avoided by using a reduced power and poor antenna for housecasting.

Anyone else have similar experience?

Neil

 

No Matching Experience

Since 2007 when I rejoined the low power life, having taken a few decades to work in pro radio after those early years with Knight Kits, many new experiences have been come and gone.

If I did something one way there would be hum, if I changed the setup the hum went away.,

The most severe form of "house hum" was a consequence of testing the newly built "Big Talker" shortwave transmitter for 13.50 MHz with the quarter-wave dipole stretched through the house just above head level. When received on any radio indoors it had a throaty hum but simply stepping outdoors with a portable radio in hand the hum did not exist. It was strictly a matter of the house responding internally.

Today the kitchen Panasonic table radio hums across the AM band when the AMT5000 is turned on because the Wi-Fi Audio Receiver connected to the transmitter has a switching power supply that injects racket into house wiring.

If I turn on the toaster oven that hum disappears.

The three CFL bulbs in the ceiling fixture over in that room throw some hum when turned on.

There's an LED bulb in the hallway the fills the long wave band with jumpy trash as viewed on the spectrum analyzer.

But after re-considering everything I cannot say that weaker broadcast signals have ever triumphed over a hum problem, and I often run the AMT5000 at minimum power (34 mW) which I am only able to enjoy because none of the hum problems showing up elsewhere happen to cross paths with the Sangean desk radio used for that purpose.

Carl Blare

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