Re: Antuino - the antenna analyzer

Ashhar Farhan
 

jerry,

i built it so i could stuff it inside the cubesat to measure the antenna. an external spectrum analyzer and its cables were upsetting the RF model hence, i needed something that could read the return loss sitting inside the cubesat. then, i borrowed by daughter's DSLR with a monsterous tele lens and sat 100 meters away to read the the LCD display as it swept through the range. 
the analyzer was removed once we knew the correct dimensions and the actual payload went inside the bird.
- f

On Fri, Dec 28, 2018 at 1:19 PM Jerry Gaffke via Groups.Io <jgaffke=yahoo.com@groups.io> wrote:
Farhan,

OK. so best thought of as a basic spectrum analyzer
Has a return loss bridge up front to measure SWR.
Not weird at all.
But does look very cheap and buildable.

I've been thinking of building a spectrum analyzer along those lines for a couple years now.
Snow on the ground here and it's darn cold, could be a good time for it.

The fact that this thing had to be small enough to fit into the cubesat
suggests it's still in there, flying madly about the earth.
And that you are using it to verify that some 440mhz antenna 
didn't get eaten by space aliens?

Jerry

On Thu, Dec 27, 2018 at 10:28 PM, Ashhar Farhan wrote:
The circuit here uses a resistive return loss bridge. the clock 1 drives the bridge through the R22 to a low level of -10dbm. If the bridge is perfectly balanced (that is, the antenna, R21, R29, R16, all the four are the same ohms), then, there will be no RF developed across pins 3 and 4 of the ADE mixer. 
..........
So, the ADE-1 mixer, Q2, Q1 together form a very simple superhet receiver with 25 MHz IF andCLK2 as the local oscillator. The RF at the IF is directly detected and converted to db range with the AD8307. This simple configuration makes this a very powerful instrument.

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