Ultra wideband RF detector design challenge

[Inquorate]

Inductance/Capacitance/Frequency DMM - Jaycar Electronics

A meter like this would help define the frequency being picked up which means one can use a variable inductor to one's heart's content, and easily discover whatever frequency the peaks are at.

Love and light

[Inquorate]

Ac/Dc

Anyone know why my Oscilloscope shows ac coming off the transistor's emitter? It's on the dc setting..

[sucahyo]

Anyone know why my Oscilloscope shows ac coming off the transistor's emitter? It's on the dc setting..

Did the scope has common gruond with the circuit?

[Inquorate]

Ground

No common ground, the scope is running off a $200 isolation transformer, and is 'grounded' to the metal sheeting that goes down on the first layer of wall of the house, which is on stilts. The detector (essentially an AM radio tuner) is grounded to a copper pipe hammered into the ground.

I've seen this with avramenko plug configurations off the sec; it should be dc but it's ac.

Got me stumped.

[sucahyo]

Why should it be DC?

[Inquorate]

why dc

Because a transistor allows current (conventional notation) to flow from collector to emitter when the base is triggered, unless the reverse breakdown voltage is exceeded.

The base in this circuit is triggered by a diode, and the current flowing is in the millivolt range. That is not enough to allow current to flow the wrong way, so it should be flowing in one direction; dc.

Even with an avramenko plug is the 'RF' bubble of an sec, the current should be dc (forward - forward), but it shows up on a scope as ac(forward - backward).

[sucahyo]

I see.

Did you have diode at emiter to base or emiter to collector? I see Ainsley and Bedini circuit have it.

I also see some scope output where AC ripple happen at some frequency. I think at higher frequency anything can happen. Maybe the scope detected reverse voltage where the current is lower than the transistor/diode specification.

I think if the scope do not have the same ground as the circuit the scope may not know where the zero point is. I think the scope just confuse the zero point because the scope don't have anything to compare to. I may wrong though.

[morpher44]

old school

Some old school devices to explore RF... fyi

CENCO CATALOG page 1325 circa 1930

[dave_cahoon]

Frequency Domain

A saw tooth wave generator. With, A VCO tuned tuner. (cable tv) Another tuner for the output frequency. With signal strength connected to a scope in XY mode. Run the saw tooth to the VCO and X-channel. Connect signal strength to the Y-channel.

I think most of you will quickly see what this describes.
Here is a guy making them Science Workshop

HaveFun
Dave