Lrl from Italy

[behnamvp]

good day

Mr.franco Italy
thank you for sharing project and helping others

don't know if someone asked or no but why you don't use ready oscillator
instead of crystal?
because running high frequency xt is a little bit hard at least at no projects i had success
so, i always use ready oscillators except projects that XT runs by microcontrollers.
i think many members that built your L.R.L also couldn't run XT but they don't know

thank you

[FrancoItaly]

Originally Posted by behnamvp

good day

Mr.franco Italy
thank you for sharing project and helping others

don't know if someone asked or no but why you don't use ready oscillator
instead of crystal?
because running high frequency xt is a little bit hard at least at no projects i had success
so, i always use ready oscillators except projects that XT runs by microcontrollers.
i think many members that built your L.R.L also couldn't run XT but they don't know

thank you

You are right, you could also use the "ready oscillators", but I find that the quartz version is the simplest, even most oscillates even without the capacitor between the emitter and the base of the transistor, in the range 2 - 10 Mhz in my opinion is the best choice. The same scheme also works with 20 Mhz, but it is more critical, also because we are at the frequency limit for quartzes that work in fundamental (harmonic). Furthermore it is necessary to have a waveform as distorted as possible, to have many harmonics and a signal of small amplitude in order not to radiate towards the sensor stage.

[Pahom]

Originally Posted by FrancoItaly

You are right, you could also use the "ready oscillators", but I find that the quartz version is the simplest, even most oscillates even without the capacitor between the emitter and the base of the transistor, in the range 2 - 10 Mhz in my opinion is the best choice. The same scheme also works with 20 Mhz, but it is more critical, also because we are at the frequency limit for quartzes that work in fundamental (harmonic). Furthermore it is necessary to have a waveform as distorted as possible, to have many harmonics and a signal of small amplitude in order not to radiate towards the sensor stage.

Good afternoon Franco! Reading about a new project at 20 MHz, you constantly repeat that the waveform at the output of the generator should be DISTORTED as much as possible. Is this so or is it a translation error?

[FrancoItaly]

Originally Posted by Pahom

Good afternoon Franco! Reading about a new project at 20 MHz, you constantly repeat that the waveform at the output of the generator should be DISTORTED as much as possible. Is this so or is it a translation error?

It is not an error, a distorted signal means that it contains harmonics of higher frequency, in our case: fundamental = 20Mhz, second harmonic = 40Mhz, third = 60Mhz, fourth = 80Mhz, fifth = 100 Mhz, always with decreasing amplitude. The L1 / C10 resonant circuit is tuned to one of these harmonics (I think 80 Mhz or 100 Mhz) and this makes the sensor stage more sensitive.

[Pahom]

Originally Posted by FrancoItaly

It is not an error, a distorted signal means that it contains harmonics of higher frequency, in our case: fundamental = 20Mhz, second harmonic = 40Mhz, third = 60Mhz, fourth = 80Mhz, fifth = 100 Mhz, always with decreasing amplitude. The L1 / C10 resonant circuit is tuned to one of these harmonics (I think 80 Mhz or 100 Mhz) and this makes the sensor stage more sensitive.

Thanks! Another question, in the circuit display 1, the capacitor c1 is indicated 10mf is it an electrolyte? The previous version specified 0.22mF.

[FrancoItaly]

Originally Posted by Pahom

Thanks! Another question, in the circuit display 1, the capacitor c1 is indicated 10mf is it an electrolyte? The previous version specified 0.22mF.

C1 is 10 nF, in the previus version was 22 nF, however it is not very important, however too high values, 100 nF and more, can slow down the response, especially if you search with fast scans.

[Pahom]

Originally Posted by FrancoItaly

C1 is 10 nF, in the previus version was 22 nF, however it is not very important, however too high values, 100 nF and more, can slow down the response, especially if you search with fast scans.

Thanks Franco! It remains to find out to what frequency to tune the input circuit L1 and C1, if I understood you correctly, then it should be approximately in the region of 80-100 MHz