|
|
A prototype reflectometer with its own oscillator.
This shows how easy it can be to hook up LogProbe to a project.
This page is somewhat temporary. It is probable that I will provide directional couplers alone as attachments for LogProbe as well as the same couplers with an oscillator in the same housing.
In the picture above we can see a small shiny box. It is a VCO, Voltage Controlled Oscillator. This particular one emits a signal from 100 to 200 MHz depending on the control voltage. Since the VCO also generates harmonics (2 x, 3 x … the original frequency, and often only 10 - 15 dB down) that will disturb measurements, a Low Pass Filter is needed. The three red coils are part of a low pass filter. This particular filter rejects signals above 200 MHz.
The two black trim potentiometers sets the basic frequency and the width of the sweep when swept from an external source. An oscilloscope for example, if it has a sweep output.
Just where the cable is attached we can see a smaller white box. It is a directional coupler. It is sensitive to signal coming back in the brown cable on the upper right. If this cable is perfectly terminated, with 50 W , no signal is reflected, and the LogProbe connected on the upper left, will detect no signal. In reality this will barely ever happen. The VCO gives about +10 dBm out, the reflectometer delivers some 0 dBm for a total reflex and LogProbe can detect -80 dBm. The load would have to be incredibly good for to reflect this little. A Return Loss of -30 dB is already a very good load!
|
|
On the Polaroid picture to the left we can see the reflex from a two element antenna swept from about 100 to 200 MHz. Furthermore, I have a 6 dB attenuator on the detector, so even a total reflex has a RL of 12 dB. Just to the right of the middle there is a deep narrow dip. It actually goes 3.5 cm below the mid line. With 10 dB/V and 1 V/cm, from 2 cm above the center line this dip is thus 55 dB deep! The second dip shows a RL of about 14 dB. Sweep speed is 2 ms/cm. To the detector, with a 6 dB attenuator, the 55 dB RL is really 67 dB deep! |
For mail, inquires or orders, please contact us at
