Modify a "Talking House" part 15 AM transmitter

[jr_tech]

"RF Hum"... Could you explain what that is or what causes it? I have heard some SW signals that appear to get re-radiated by nearby power lines that have 60Hz hum... is that a similar phenomenon?

jr

[wa2ise]

Originally Posted by jr_tech

"RF Hum"... Could you explain what that is or what causes it?

This web page explains it http://www.northcountryradio.com/Articles/humred.htm
Seems that the transmitter RF current takes several paths in and around your house, and these paths may include rectifier diodes. These diodes are switching on and off at 60 or 120Hz, and also switch on and off to the RF current. This will result in an AM modulation to the RF signal, thus the received hum. I generally try to avoid these current paths, by inserting coils that look like a high impedance to the RF but allow DC and low frequency AC thru. Another approach is to put 0.01uF caps across the rectifier diodes (use caps with voltage rating more than the PIV of the diodes).

[jr_tech]

THANK YOU!

In the past, several posters have mentioned "hum bars" when transmitting in house with the various Blonder Tongue TV transmitters... same deal perhaps? Perhaps the same cure (caps across rectifier diodes or installing chokes/caps) would apply there as well?

jr