Read the data sheet for the AD8302. The
module just puts it on a board.
There are two independent multi-stage
log detectors, and a mixer that
multiplies the two signals. The phase
detection relies on the two signals
being close in amplitude (within 30dB,
which limits the depth of a null
you can detect). There is no filtering
at all, so whatever comes out of
the mixer gets detected as phase, even
if the two signals are on
completely different frequencies. Same
deal with the relative amplitude;
it's only *relative* amplitude of the
transmitted vs *all* received signals.
It was designed to recover a video
signal from a clean filtered IF.
I.e. it works ok if you have clean
signals and no interference. When
probing an antenna, that pretty often
just isn't the case; especially
up on a roof where other antennae are
transmitting. A real VNA is
immune to off-channel interference.
> On 30 Nov 2017, at 2:40 PM, Vaclav
> I have not really look at the
schematic / concept details of
> The AD8302 module is coming without
much doc ( as expected from e-bay) , but
from the looks of it the output has some
componets , perhaps filter? I will do
some "reverse enginnering " when the
> I am in hardware stage and as much
as I appreciate your comments I'll use
AD8302 alone for now.
> I need to clean up my spec , I keep
a log of "progress" and it is getting
> Give me couple of days.
> On Wednesday, November 29, 2017,
7:49:38 PM CST, Clifford Heath
> On 30 Nov 2017, at 12:21 PM,
> > I am repackaging VNArduino
> > This is just an amateur
project, not an attempt to reinvent the
> > I am using the original
VNArduino as base - changing some
hardware and controller / processor.
> > This is strictly a fun amateur
project NOT intended to be mass for
> > I welcome anybody who wants to
> I'm doing a similar project at the
moment, and also wanted to
> use the AD8302... until I decided
that I didn't.
> The problem with the VNArduino is
the very limited rejection of
> spurious signals of they AD8302,
which picks up *everything*.
> If you want to analyse an antenna,
you need a more selective
> front-end because you're often in a
> The same problem exists with the
PHSNA, of course.
> The current plan is a bit more
sophisticated and *much* more
> capable. It uses a mixer and a
dual-channel DDS (AD9959)
> that's good to 200MHz. The LPF
after the mixer allows rejection
> of anything more than 10KHz away
from the transmitted signal.
> There's another cunning aspect
regarding phase detection that
> I won't go into here. It involves
digitising the audio off the mixer.
> If you're interested in using the
AD9959, I wrote a library for it:
> In any case, I'd like to see your
> I did look at github and have to
say I am impress with readme.
> It actually contains useful info
instead of usual copies of "open source"
> Clifford Heath.
> > At preset I am collecting
necessary hardware and laying out PCB.
> > I envision to have ability to
use any suitable controller / processor
and associated hardware.
> > I have written short
specification to keep the project from
wondering of the track.
> > If anybody is interested I can
share the spec, but NOT in public.
> > Vaclav
> > 73 AA7EJ