RF Sampler/ AM Demodulator

[KX5JT]

So now I have a 40Mhz dual trace scope.  Whoohoo!  Obviously besides troubleshooting and experimenting I'm going to want to monitor my AM signals.

Enter this project: http://amfone.net/ECSound/RFsampler.htm

I see that the signal is being sampled off the main path... how beefy should this main path be to handle legal limit carrier?  (Not that I have that YET but if I'm going to build this thing, I might as well build it one time with the future in mind.)

And are the components specified in the sampling part beefy enough for legal limit (I understand they will only see a small inkling of the singal, but I have to ask!)

I can't see spending 139.95 for the similar device rated @ 200 watts... (so it has a potentionmeter on it too.... I can do that!)

http://www.cleanrf.com/products.html#RF-D



KX5JT

[K4TLJ]

I use a short loop of wire from the scope input to ground. The wire picks up enough signal for a good display. Cost $0.00

[KX5JT]

But can you hear your audio picked off and demodulated from your output signal on the way to the antenna?

[ka3zlr]

Good Day,

 I have found that the less mechanics involved in the transmission line the better and choose inductive coupling for monitoring.

 The Simple off air monitor does a very nice job coupled with a good clean linear audio amp, and in this situation you can then design any number of Taps further down the chain for headphones, recording etc, all the while maintaining Broadband capability..and no possibility of Waveform Distortion is impressed on the carrier OM..

73
Jack.


 

[W1AEX]

Hi,

I built this circuit for AM monitoring purposes and it works very well indeed. As Jack indicated, it produces a very fine audio sample of your transmitted signal. However, it will not tolerate high power. I left it inline with my dummy load by mistake one evening while tuning up a kilowatt amp and quickly smelled something burning. It was one of the resistors in my little AM monitor, built from the schematic you are considering. You might want to examine the comments by Stu, AB2EZ, and others, regarding component changes for high power use in the thread below:

http://amfone.net/Amforum/index.php?topic=15743.0

The circuit as it is, seems to handle power up to 50 watts without any problems at all.

73,

Rob W1AEX

[ve6pg]

...i do the same, but different....for monitoring audio, i have a diode, with a rfc, mounted in a small plastic pill bottle...1/4 inch headphone jack mounted on the screw-on cap....out of the bottom of the pill bottle, a small hole, which allows a wire (about 1 foot long), which is attached to an alligator clip...i clip on to my receiver toggle switch, or whichever i choose..lots of audio in the headphones...basically, it is a crystal radio...

...for the scope, i mounted a small rca type female connector on the back on my dx100...it has a stiff wire, about 6" long, near the transmitter output so-239...this then goes to the 'scope...you could do the same, with an antenna tuner...

..sk..