Boatanchor TDR

[Bill, KD0HG]

OK, here’s a really cool idea passed along to me by a long time Denver area AM broadcast engineer.

Back in the “old days”, 1930s-1950s before TDRs were commonly used to find feedline faults, they used something equally effective.

When there was a fault in a transmission line, they connected a Neon Sign transformer on a Variac to the feedline, with a fluorescent bulb in between the center conductor of the coax and the sign transformer. Then he could measure within a foot where the line fault was.

Slowly turning up the Variac, the fluorescent bulb would light when the short started arcing over.  He coupled a shortwave receiver antenna input to the fluorescent light. A couple of turns of wire around the light bulb to the antenna terminals of a boatanchor shortwave receiver. Since the arcing point was effectively a short down 1/4 wave of the transmission line., he could tune the shortwave receiver for a maximum peak of broadband noise on the shortwave receiver.

If you knew what the propagation velocity of the feedline was, he said you could easily calculate the distance down the feedline where the fault was occurring by finding the frequency of the noise peak on the receiver.

Neat idea.

[W7TFO]

An excellent method to get a necessary meaurement! 

With average (read my) luck, that short would be either underground, in the tightest corner of an attic, or wayyyyy up in the air.

At that point, one might proceed to kick the tube, breaking it, then dusting your measurement receiver with toxic phosphor, knocking the clip lead off, letting the 15kV from that transformer loose on a stack of expensive schematics, setting fire to them, and in the ensuing fiasco, you knock them off smack onto a freshly-wrinkle painted panel you had to do over 3 times already. 

Then the XYL comes in and wants to know just what you are doing.....

OK, I guess I have committed a "thread hijack".  My apologies.

73DG

[The Slab Bacon]

that is a pretty cool idea (if you dont have an MFJ box)

Alas, what is old is new again!!