Combo generator review and improvements
What is your oppinion about this combo generator (attached) powered by the RF signal itself and output level adjusted?
Could be considered a good simple circuit and what would you do to improve it?
If this is a harmonic generator, I don't see the reason to give DC bias to the harmonic generator diode.
An un-biased diode generate more harmonics than a biased one.
To verify this, just connect to the ground the low end of the choke inductor, and measure the harmonics at the output (2nd and 3rd). They will be at least 10dB greater.
The author of the original circuit states that the point of using bias is for the harmonics level adjustment. I thought that it might be useful. http://lea.hamradio.si/~s57uuu/astro...mgen_w_rtx.htm
If you adjust the potentiometer completely towards the ground point, will it be the same as connecting to the ground the low end of the choke inductor?
A diode (and a transistor the same), less bias current have, more harmonics generates. A Class-C transistor with zero quiescent current generate much more harmonics than a strong biased Class-A transistor.
The site you sent is on agreement in this regards. He got highest level of harmonics for zero volts bias, and minimum level of harmonics for highest DC voltage.
I don't know what exactly happen if you adjust the potentiometer in your circuit, because you do not have the same situation. Your DC bias voltage also varies with RF input power, not only by changing the value of the potentiometer.
that is because the rectification diodes are oriented to provide a REVERSE bias on the multiplier diode. The more reverse bias you apply, the more RF drive power you will need. If I read that right, and you have 1 watt drive level, yeah, you might want to reverse bias the diode a little to keep it from smoking! But if you drive it with low power, in that circuit the best bias would indeed be 0V.
Maybe if you told us what you were up to? A very fast digital gate circuit might work better than than one. And those leaded diodes can not take too much RF power.
these might help.
Thank you for the documents, especially the first one I found it very useful.
I am trying to build a simple harmonics generator for antenna measurements (so high efficiency is not needed) using a VU handheld transceiver (0.5-1w) as the signal source, which is very convenient for field testing, without any external power. Using a BPF for the desired band after the harmonics generator is mandatory for selecting the appropriate signals.
oh, I have more articles if the first one made you happy! The old hp app notes are hard to find.
some more papers
Hello,
I am sorry I am digging out this old topic, but I would like to ask if I should better use germanium diodes instead of the 1N5711, to achieve a lower voltage drop?
Sorry to digg out this old topic.
1. What if I negatively bias the diode instead of connecting it to GND? will I be able to increase the level of harmonics?
2. Also what if I leave the bias point (low end of coil) unconnected instead of ground it? Will the harmonics level be like grounding this point?