For the weighting elements why not use a binary switched attenuator. At low
frequencies, FET switches onto a tapped constant impedance resistor ladder
will give you constant impedance and exact attenuation steps and will have
good strong signal handling capability
You can get the precise sin/cos values from a look up table. Use a
processor (which could be as simple as a PIC) to make the look up from
sin/cos data stored in EEPROM based on input from your interface - voltage
from a potentiometer, rotary shaft encoder or whatever you like.
Andy G4JNT
-----Original Message-----
From: Johan Bodin [mailto:[email protected]]
Sent: 2001-11-15 21:39
To: [email protected]
Subject: LF: [Tech] Electronic Goniometer?
Dear LF group
Does anyone have an idea how to design an electronic goniometer?
Imagine a "black box" that is fed with two signals from a
pair of orthogonal
(for example N/S and E/W) untuned loop antennas, let's call
them X and Y.
The output from the box should ideally be X * cos(A) + Y *
sin(A) where A
is a control signal which could be a simple DC voltage, a
digital control word
or whatever.. Such a "black box" could be very useful for
direction finding
without the need to rotate a loop physically.
When combined with an omnidirectional antenna and a phasing
circuit, the
resulting cardioid pattern can also be used to null out
interference, just like
a K9AY antenna does, but better - with steerable, instead of
fixed, null
directions. My two loop / eight nulls (modified) K9AY is
doing a nice job
but I miss the ability to put the null in ANY direction...
The "black box" could be a pair of attenuators with ability
to switch the phase
180 deg's. In its simplest form it could be just two
potentiometers and two
switches (and phase reversal transformers). This would be OK
to manually
null out interference but to make accurate D.F. measurements, precise
sin/cos behaviour of the attenuators is required.
Any ideas? (besides making a "physical" goniometer)
73 de Johan SM6LKM
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