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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] 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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Kf6 Pqt Sent: Wednesday, December 27, 2006 7:43 PM To: [email protected] 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 -- --... ...-- -.. . -.- ..-. -.... .--. --.- - ______________________________________________________________ AMRadio mailing list List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected] -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.15.28/604 - Release Date: 12/26/2006 12:23 PM -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.15.28/604 - Release Date: 12/26/2006 12:23 PM ______________________________________________________________ AMRadio mailing list List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected] ______________________________________________________________ AMRadio mailing list List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected]
