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Re: I originally asked: good source & non-expensive url for Attenuators


 

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Dumb question here....

You guys are trying to check the output from your transmitter, right?
Don't you have enough RF in your shack that you could just us the tinySA antenna
to get enough signal to check it?? It is a form of inductive coupling, no?

If you are checking a qrp rig, maybe wrap a wire around your dummy load to get
more coupling.
73,
Gary
WB6OGD


On 1/14/2021 8:36 AM, Miro, N9LR via groups.io wrote:

Hi Dennis!
inductive coupler still requires dummy load, and if you have one, then your resistive attenuator does not need "large power absorbing resistors".

In another thread in this group someone posted this link to the excellent article on theory and practice of inductive couplers ()

Article in your comment is quite misleading if not wrong - inductive coupling is done by means of current transformer. If you leave secondary side of current transformer "open" (no terminator with resistor), in theory potential at it's ends will be infinite value and in practice can reach thousands of volts!

Also, reflected impedance in primary will be quite high and will cause significant voltage drop and dissipated power in turn. Simply said, current transformer MUST be terminated on the secondary side at all times!

The "fix" is surprisingly cheap and simple - just have properly designed resistor :)

Also, number of turns and selection of toroid material is not a random effort - just check the link above, and if you desire to learn even more, check the link in that document that takes you here?

I still don't know what are comparative advantages/disadvantages of "resistive vs inductive" high impedance taps. Resistive are easier to make and have wider bandwidth (when done correctly), inductive gives you galvanic isolation, but not sure if there is anything else.

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