[Aavso-sid-list] Gyrator II receiver

[Mike Thompson]

Looks like my original reply to this message never got
posted. I had some pictures with it so that might have
fudged things up. Hopefully the links I post will work
instead.

=====================================================
This is probably more info then you need but I can't
help the fact that I love showing pictures of my
equipment:)

There is a total of 5 pictures and they basically show
my progress in order.

http://i219.photobucket.com/albums/cc216/MightyZ0rb/0304080529-00.jpg
Picture 1.jpg, shows my initial setup. Its been some
time since I tried receiving the transmitter in Cutler
MA at 24KHZ so I needed a basic setup to see where I
stood. In this picture you can see my big 6 foot, 4
turn PVC loop. Whenever I start playing around with
loops I usually build one of these since I can use a
capacitor decade box to tune it across a wide
spectrum. I can easily tune this guy from near DC to
about 10Mhz. To the left of the loop you can see my
pair of capacitor decade boxes. Connected to that is
my old Rycom 6010 Selective Voltmeter (My baby). With
this setup I was able to easily get the Cutler
Transmitter with the 6010 set at -80db.

http://i219.photobucket.com/albums/cc216/MightyZ0rb/2.jpg
Picture 2.jpg, shows my slow evolution of the setup. I
needed a loop that was decently effective at 24Khz and
that would fit the bill when it came to mounting it in
a fixed location. For this I came up with a 3 foot
loop. As for the amount of turns, well that can be
anyone's guess. I basically just used up the remainder
of a spool of wire I had laying about. I was sloppy
when I made this and as a result the nulls are not as
sharp as I would have liked them to be, but for the
most part it is still directional. Again I have my
decade boxes and 6010 hooked up to this. The signal
was a little stronger this time around and I could set
the input to -60db. I would imagine the strength
increase was do to the fact that I had more wire
harnessing the signal and less capacitance merely
offsetting what turns the coil was lacking. I used
this setup to get a reading of what sort of capacitor
I would need to fix to the loop to tune it
permanently.

http://i219.photobucket.com/albums/cc216/MightyZ0rb/3.jpg
Picture 3.jpg finally has a glance at the actual
Gyrator II receiver. To the left of this you can see
my voltmeter I have attached to the integrator output.
I tuned the circuit BEFORE I actually hooked
everything up, simply because I did not have any faith
in the receiver to tune from past experiences with
oscillation. I went about tuning by first using the
loop and decade boxes with the 6010 to tune to the
Cutler MA source at 24Khz. Then I took the 6010 into
my workshop and played with a sine generator at -80db
until I got a lock on 24Khz. I hooked the Gyrator II
up to this signal source and tuned the gyrator a bit
until I got the strongest signal at Pin 1 of the TL082
used for amplification. After this I set the Gain to
halfway. 

http://i219.photobucket.com/albums/cc216/MightyZ0rb/4.jpg
Picture 4.jpg is a blurry shot of the capacitors I
used to tune the loop without the decade boxes. I for
one am willing to admit that the better the capacitor
the sharper you’re tuning. These caps have a +/- 10%
tolerance. Not the best but it certainly does the job.

http://i219.photobucket.com/albums/cc216/MightyZ0rb/5.jpg
Picture 5.jpg shows the real meat of the setup. I
purchased the Gyrator II board. The components for the
most part were just parts I had lying around, or that
I bought from Radio Shack. The potentiometers are both
10 turn precision pots. For the gyrator tuning this is
a lifesaver as far as getting precision tuning.
Remember the gyrator circuit was set up to have
roughly a 200Hz bandwidth. A precision pot makes all
the difference. I might get rid of the 10-turn pot
used for gain. It seems kind of silly, and has proven
to be more frustrating then anything else.

When everything was hooked up, tuned, and aligned
properly I could only squeeze 32mVolts out of the
integrator during sunlight and 16mVolts when it was
dark.

In writing this it seems somewhat clear to me that
possibly the loop and the tuning capacitors I am using
are to blame for such a small output. Also I am not
sure (I will have to check) to see if the pot I am
using for gain is truly a 50Kohm pot and not a 10Kohm
one that I tossed in merely to get the thing built.

It has proven to be an interesting and fun project,
however I won't feel any sense of accomplishment until
I start getting daily plots of signal data.

Questions? Comments? Or most importantly SUGGESTIONS?
:)

Thanks for taking an interest
Mike T.


Homepage
http://home.comcast.net/~mikethompson236/index.htm


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