[AMRadio] hamfest oscopes


Craig C. Heaton wd8kdg at worldnet.att.net
Thu Dec 28 10:32:53 EST 2006


Still lacking one thing for the trapezoidal pattern. RF from a pickup to the
deflection  plates will give just a waveform pattern.

Gotta get some audio from the secondary of the modulation transformer and
apply that to the horizontal amplifier of the scope in order to view the
trapezoidal pattern. Also needed is a small circuit easily built, its all in
the older 50's & 60's ARRL handbooks. Just one capacitor, one pot, and some
fixed resistance.

Years ago I built in a small project box with two circuits and added this to
a cheap 5MHz scope, a Eico 460. This box contains four tuned circuits using
toroidal cores and an air variable cap. A five position switch selects one
of the cores used with the cap and is resonate in the middle of one of the
ham bands. Adjust the cap to vary the height of the waveform on the scope.
Of course, a small RF pickup is needed.

The other circuit is the voltage divider which gets power (audio) from the
coupling capacitor connected to the secondary of the mod tranny. Flip a
small toggle switch and this is connected to the horizontal input of the
scope and now I can watch a trapezoidal pattern.

So its all in the older handbooks! I mostly watch the waveform because more
information is there. The trapezoidal is checked once, just when warming the
rig. The fifth position on the band selection switch is the OFF position.
The IF output of my R-390A goes to the vertical input of the scope. With the
project box switch in the OFF position, I can watch the other end of the
QSO.

later.......& 73's
wd8kdg
Craig

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net]On Behalf Of Jim candela
Sent: Wednesday, December 27, 2006 7:36 PM
To: Discussion of AM Radio in the Amateur Service
Subject: RE: [AMRadio] hamfest oscopes




Jason,

   You can connect directly to the deflection plates for the audio as you
describe. Most modern (1970's and later Tektronix and others) analog scopes
have a setting called X:Y when the horizontal sweep knob is at max CCW. In
this case Channel A is for the X axis and Channel B is for the Y axis. With
a scope like this you can scale the audio and RF for any convenient level
within the voltage range of the scope inputs.

Jim
JKO

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net]On Behalf Of Kf6 Pqt
Sent: Wednesday, December 27, 2006 7:43 PM
To: amradio at mailman.qth.net
Subject: [AMRadio] hamfest oscopes


For a trapezoid pattern, dont you just send the signals directly to
the deflection plates? So all thats really required from a junker
scope is a power supply, a functioning filament, and some viable
phosphor left on the screen, right?

Jason kf6pqt

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