The AM Forum

   For a really nice home-brew RF sampler, check out:  http://amfone.net/ECSound/K1JJ8.htm
Thanks to Tom, K1JJ, for this.  I built mine from parts I had hanging around.
   The only change I made is using a BNC for the output rather than an SO239.

   My apologies for this getting separated from the original thread; I don't know how that happened.

Very nicely built!

   Thanks - the mismatched SO-239's would probably disqualify it from the big AM Fone homebrew test gear contest, though.

Looks good!

Unless there's a good technical reason, I think I'd have run the SO-239 line from one end of the
box to the other, and made the pick up with a bend from the side... also I'd have insulated one
or both of the wires in there with some teflon spaghetti, just in case it gets dropped and
bends the wires inside!

                           _-_-

Nice work. That gauge wire is probably large enough to withstand physical abuse. You definitely want loose coupling for AM.

   I figure it's pretty much "six of one/half dozen of the other" as far as placement of the connectors, but insulating the wires in case they bent probably wouldn't be a bad idea.  The wires are pretty stiff, though, and I gave the box some pretty good thumps as a test.

After I posted, I realized a good solution would be to drill a hole and mount a strategically located
stand-off to hold the wire at or near the end! :D


                       _-_-

OK, "dueling modulation monitor" of the day....  I see mine came to life in 2011!!  Works like a charm.  ;D

Tom

The best I ever had for monitoring was the Lenk Demodulator. ;)

Yes, that is a nice, simple design and works FB.  If more outputs are needed, like to drive the SDR to monitor your output transmit signal, mod monitor for audio headphones pickoff and normal scope input (3 pickoffs) , then additional pick-off wires can be added, just like the first.


Since building the original, I later needed three outputs so decided to do the job using toroids. The coax simply goes through the core and a secondary is wound on the core for the output. Use three cores as needed for the entire job. The signal is as clean as the original wire technique. Experiment by adding or subtracting the number of turns to fine tune the individual signal output levels and matches. 63/43 material cores or whatever for HF is fine.

The reason for the SDR pick-off signal:  I like the idea of being able to use my SDR spectrum analyzer to monitor my transmit signal at the amplifier OUTPUT (1.5 KW point) , rather than the internal SDR low level signal which is a useless test and always clean. The real amplifier splatter test is at the high power output point.


Here's the current scope/SDR/AM audio mod monitor RF pickoff.  Built into the "Chassis of 1000 Past Lives."   :-)


T

I have a question. Why uses everybody a capacitive pick-up? One resistor more and you have a directional coupler. All 50 Ohms, no problem with larger cables to the scope or monitor and a well defined attenuation.

   Nice.  I think that's pretty much what Mr. Bear was talking about; straight through with the SO-239's and a nice little bend for the sampling wire.