RELIC HAWK

[mikebg]

Yes, I got the same, but I am not sure if in real world so little difference in power supply can lead to so huge distortion (a little unbelievable for 0.1V only)?
As you can see on second pic, the same happen with I circuit total I(V1).

WM6, when resistors R1 ... R4 are correct designed, the TX can operate with maximal possible undistorted amplitude at very heavy load. My idea is to load the LC tank circuit with a rectifier used to supply RX preamp placed inside search head. The idea is sketched below.
In the original circuit (see formulas in equivalent circuit diagram - post #957), to avoid distortion, we should adjust amplitude Vp no more than Vp = Vbat_min - Vsat = 10.2 - 3.8 = 5.4Vp, ie TX should generate voltage swing less than 10.8Vpp . This amplitude can be adjusted with resistors of voltage divider R6 ...R7.
However when battery voltage is 13.6V, the circuit oprates with very bad efficiency because theoretical possible swing is 27.2Vpp. TX power is proportional to square of amplitude Vp. The large saturation voltage 3.8V of cascode Q2&Q3 is gilti for this drawback. No need of cascode.
My idea is to remove Q3 and to use a reference voltage proportional to battery voltage. In the circuit below, Q3 generates very filtered such voltage. We can adjust R5 so that amplitude will be always almost equal to battery voltage despite its change.

[porkluvr]

Mike, you should remove the components in the red box. Unless I am mistaken, the 68k resistor was put there to isolate an oscilloscope lead during setup. One end is a test point.

The net segment that you labeled "Test" is connected to ground which means that 0V=test in your simulation.

Right click the net, and then "Highlight Net" and you will see what I mean.

[WM6]

Yes, I got the same, but I am not sure if in real world so little difference in power supply can lead to so huge distortion (a little unbelievable for 0.1V only)?

As you can see on second pic, the same happen with I circuit total I(V1).

[Davor]

Ah! Nice catch!
I tried it but supply voltage was not on my checklist. (I assumed that it was taken care of)

[mikebg]

Working under Ubuntu and I can't import your LTSpice file in my Qucs simulator. Depend on your demo for now.

See what happens when battery discharges from 12.2V to 12.1V:
1. LC tank circuit starts to return energy in source V3 because the cascode Q2&3 saturates.
2. Distortion of oscillation becomes remarkable.
3. Efficiency drops because tank pumping pulse has width more than 180 deg. For maximal efficiency we need conducting angle about 120deg (duty cycle about 1/3).
4. Control voltage Vo (the red line) should be very low (TL074 can not deliver such low level).

[WM6]

LTSpice works ok with WINE in Ubuntu.

Thanks Qiaozhi, will try.

[Qiaozhi]

Working under Ubuntu and I can't import your LTSpice file in my Qucs simulator. Depend on your demo for now.

LTSpice works ok with WINE in Ubuntu.

[WM6]

Please make the above SPICE analysis to see what happens when battery discharges from 12.2V with 0.1V only.

Working under Ubuntu and I can't import your LTSpice file in my Qucs simulator. Depend on your demo for now.

[mikebg]

Excellent mikebg, don't stop to early.

Here you have ivconic's version of RH - proven as working:

WM6, I know that it works, but it is incompetent and incorrect designed. Its TX and RX sections will work better if we redesign them. I will post SPICE circuit of RX preamp to show that it also has drawbacs.

I use for simulation of TX a single supply opamp like LM358 and LM324, which operates better than 074 because have small value Vo_min (see post #927). If we remove transistor Q3 and all components forming voltage source V3, the TX starts to operate better until 10.2V battery discharge and with increased power. Please make the above SPICE analysis to see what happens when battery discharges from 12.2V with 0.1V only.

[WM6]

Excellent mikebg, don't stop to early.

Here you have ivconic's version of RH - proven as working: