CB And The Dummy: Yet Another O-Scope Adventure
Unfortunately, I took a blurry photo. My workbench has been expanding. The radio is citizen’s band, an Uniden Bearcat 880 that I thought was broken. Then my new dummy load, and MFJ-264N. It’s a bit hard to tell, but there are 3 power supplies tucked in around the monitor. A soldering station in the background. I have a wattmeter for the CB transmission line, as well as a wattmeter for the DC power supply. And, what you don’t see is my new (to me) Tektronix 2465 oscilloscope.
I found a plug with a cigarette lighter end that fit the Bearcat. I clipped off the cigarette lighter to instead terminate with Anderson Powerpoles. Here is my assembly guide: https://km1ndy.com/how-to-assemble-powerpoles/. I tend to put Powerpoles on all of my DC gadgets. I went ahead and took apart the cigarette lighter just to see what the inside looked like. The circuit was mainly a 1K ohm resistor and a light emitting diode. I added some power and turned on the blue LED. And for giggles, I probed the circuit with my oscilloscope, watching the DC voltage go from low to high as I moved around.
So, as thrilling as it is to watch a straight line on the CRT display of the oscilloscope bounce up and down an inch or two, I really wanted to try to find some RF. After I attached my newly built power cable into a 13.8 amp switching power supply and the Bearcat fired up fine. I clamped the ground of the probe to one of the screws of the chassis. And I rested the tip of the probe against the outer ring of the PL259 connector. My hope was to capture some leaky RF.
After a LOT of pushing buttons and turning knobs, I finally got a signal that appeared to be some sort of sine wave, i.e. AC. In fact, I thought it may just be amplitude modulation. But then I turned off my CB radio and power supply, and you guessed it, the signal was still there.
So, I have no idea what I have captured with the oscilloscope. Stray RF? My coax acting like an antenna? Common mode current? Regardless, I am just starting my journey into understanding this stuff. And I will look back someday and see how far I’ve come….
Yours Truly,
KM1NDY