Re: 2n7000 X 3 , Class E Part15 Transmitter Idea

by dare4444 Wed Oct 06, 2021 3:41 am

Don't know, Haha. My OCD! If a 200 ohm LPF is added after the 100n, just wanted a cap but you're right. Here's it's already DC isolated.

by **Ruud** Tue Oct 05, 2021 8:40 pm

6. The 100n capacitor before the antenna circuit seems to be unnecessary if the antenna is a short whip.

Just for protection.

Protection for what?
100 nF in series with 41.5 pF (in the output ciruit) doesn't have any function.

by **Ivan** Tue Oct 05, 2021 7:19 am

dare4444 wrote:
2. The 100n capacitor behind RFC shorts modulation a bit, I would remove it.

Lm386 doesn't like RF at all. Using two RFCs at collector prevents problems. A small value like 100p would do?

3. ..,. Keep RF away from 386.

8. "square wave should have high rise and fall times" - do you mean short ones?

Yes. 74AC74 is around 7nS from 0 to 5 and another 7nS from 5 to 0 volts. Here the transistor is only a switch.

2. 1000 pF seems to be near optimum (it has impedance 16 Kohm at 10 KHz, 160 ohm at 1MHz).
3. Shielding between AF and RF circuit is essential in that case.
8. Certainly, class E is a switching mode circuit.

VBR from Ivan

by dare4444 Mon Oct 04, 2021 8:36 pm

The diode in the LM output seems to be unnecessary.

It is to raise modulation a bit as 386 max swing is 10Vpp at 12v.

2. The 100n capacitor behind RFC shorts modulation a bit, I would remove it.

Lm386 doesn't like RF at all. Using two RFCs at collector prevents problems. A small value like 100p would do?

3. L1 should be a part of RFC (or vice versa) - one coil is enough.

Maybe. I prefer two. Keep RF away from 386.

4. The 100n capacitor before the tank circuit seems to be unnecessary.
Maybe . LPF might be added here.

5. L2 could be probably included into the tank circuit.
Not sure. It's a series tuned ckt, keeps power level stable in class e amps.

6. The 100n capacitor before the antenna circuit seems to be unnecessary if the antenna is a short whip.

Just for protection.

7. The linearity of the E-class modulator should be checked, but it seems to be good at the first glance.

Yes, it is good.

8. "square wave should have high rise and fall times" - do you mean short ones?

Yes. 74AC74 is around 7nS from 0 to 5 and another 7nS from 5 to 0 volts. Here the transistor is only a switch.

by **Ivan** Mon Oct 04, 2021 8:27 am

Hi,
my comments:
1. The diode in the LM output seems to be unnecessary.
2. The 100n capacitor behind RFC shorts modulation a bit, I would remove it.
3. L1 should be a part of RFC (or vice versa) - one coil is enough.
4. The 100n capacitor before the tank circuit seems to be unnecessary.
5. L2 could be probably included into the tank circuit.
6. The 100n capacitor before the antenna circuit seems to be unnecessary if the antenna is a short whip.
7. The linearity of the E-class modulator should be checked, but it seems to be good at the first glance.
8. "square wave should have high rise and fall times" - do you mean short ones?

VBR from Ivan

by dare4444 Mon Oct 04, 2021 2:30 am

Three parallel 2n7000. Why? To increase efficiency.
Input gate drive capacitance is around 65pF.
The 0 to 5V 1MHz square wave should have high rise and fall times, 6nS is okay. Use 74AC04. A 1MHz TTL can oscillator should be able to drive the parallel gates of 74AC04.

I aimed at 70% efficiency but we are using three mosfets in parallel. Efficiency will rise to 80% quite easily if everything goes well.

80mW of carrier rising to 320mW with 100% modulation peaks. How does it sound, awesome right? An AF compressor is a must before feeding the audio to LM386 to maintain high average power. It should give a solid 200m to 400m meters range provided grounding is good. A 200ohm Low Pass Filter before the tapping at antenna coil is a good idea.

Not tested anywhere. It will work? Definitely. Use high Q inductors.

by dare4444 Mon Oct 04, 2021 2:28 am

by dare4444 Mon Oct 04, 2021 2:25 am

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