Renato
My next project is an LC-controlled oscillator. It will be the test source for an 80m handheld radio direction finder build. Output will cover 3.5 - 4 MHz, adjusted with a home-brewed variable capacitor. A step attenuator (not included in the schematic) will provide the range of signal strengths encountered during a foxhunt.
The Hartley oscillator from Art of Electronics is below. I'm working through the analysis required to assign component values.
#hamradio #electronics #homebrew #oscillators
Oct 22, 2025 at 11:50amWeb
Show threadRue MohrOct 22, 2025
@phasedelay Hmm ,I usually see CF go to the collector, and RE would have a bypass cap on it too...
I'm really bad at RF, tell me if I'm close!:
RE set for a current of about 3mA?
Show threadRenatoOct 27, 2025
@RueNahcMohr I'm slowly working out the details, I haven't chosen a transistor yet. I think CF is blocking DC in this configuration?
Show threadRue MohrOct 28, 2025

@phasedelay hmm, sorry, I'm not really up on their operating mode.
uh, the loop gain is more than 1 at the frequency the filter hits 180 degrees on....

yea that....

Show threadMarcoDOct 26, 2025

@phasedelay
Ciao Renato,
sono incuriosito dallo schema e dal dimensionamento dei componenti.
Per dimensionarli dovresti imporre dei requisti del segnale:
potenza in uscita: 10 mW ?
carico in uscita: 50 ohm ?
VCC tensione di alimentazione: 5 - 9 V ?

Io dimensionerei " a naso" i componenti come segue:
RB1 = RB2 = 10 kohm
RE = 1 kohm
CB = 1 nF
CF = 100 pF
CV = 100 pF
L = 20 uH (50 spire avvolte su diametro 2 cm) ?
F = 1/(6,28 x Radq(LxCV)) ?

Che valori metteresti ?

Show threadMarcoDOct 26, 2025
@phasedelay
Se riesco inserisco uno schema alternativo. Avevo montato il circuito che funzionava e accendeva debolmente una lampadina 12V 1W. Non รจ detto che funzioni meglio del tuo.