Analog AM Radio Receiver Without Chip - UL1111 Replacement with BC847CW Transistors

I would try to reduce R6 to a value from 5k1 to 9k1.

Mlody_Zdolny wrote:

reduce R6 to a value from 5k1 to 9k1.

Louder but not better.

Hello
Young_Zdolny wrote

Quote:

Why a divider for a base?

Such a divider is very important, because we need to provide the signal without changing the DC parameters of the stage at T3, note that the signal with positive polarity charges through the base resistance (single Ohms) and discharges only through R5, i.e. 2M. The capacitor will pre-charge and will not be able to send a signal to the T3 base. The divider is so that the signals with negative polarization (exactly the ones whose amplitude drops over time) do not cause changes on the T3 collector, and the signals with positive polarization cause the voltage drop on the T3 collector. For this purpose, the base voltage should be less than the voltage that will cause the current to flow through the base (slightly below 0.7V).

As for the divider, one resistor instead of R5 (2M) should be reduced to a 22k resistor, and the second resistor from the T3 base to ground, with the power supply also of 22k.

I am interested in the value of R3, this resistor, in addition to the polarization, also does the feedback by setting the gain below 2. If the first stage ensures the correct polarity at 100K, then instead of the unfortunate 10K I would give 100K or even more, for me the limit would be 0.85V on the T2 collector.

As for the lack of C9 in the original diagram, I consider it a mistake, it does not change anything in the signal wave, but without this capacitor, we get Darlington and force a large direct current on the headphones, which does not serve them and reduces the battery life.

Generally, this is my favorite receiver, only in my detector it was in the form of a voltage doubler on two diodes, now there is a problem with germaniums, and at this voltage the silicon ones are problematic.
There were "zero voltage drop diodes" on Aliexpress, only the price was knocking down on them the detector on such a radio would be perfect.

PiotrPitucha wrote:

As for the divider, one resistor instead of R5 (2M) should be reduced to a 22k resistor, and the second resistor from the T3 base to ground, with the power supply also of 22k.

It won't work (at least not entirely), I checked.
I connected the potentiometer as a divider (10k, that's the only one I have). I set it up so that it could be heard well, I guess it's better, it's hard to say because it was too loud in the headphones. I heard nothing after changing the battery to the rechargeable battery. You had to turn the potentiometer anew.
So I desoldered the potentiometer and changed 2M to 10M. A similar effect, only no bass compared to the potentiometer.
Bass appears when 1uF is added to C5. I will test it yet.

PiotrPitucha wrote:

If the first stage provides the correct polarity at 100K, then instead of the unfortunate 10K I would give 100K or even more

100k is not suitable. With the "first program" it was waking up, let alone with a close transmitter.
Now 10k and one less than a coil of L2, and the headphones are too loud.

PiotrPitucha wrote:

There were "zero voltage drop diodes" on Aliexpress,

There are probably no such. Well, unless it is about mosfet protection against reverse polarity of the power supply. You can call it that from bida.

Hello
Of course, there are such detectors, it is enough to connect the drain with a Mosfet gate with zero Vth and we get an ideal diode with an almost linear characteristic. In circles of little yellow friends, such constructions are used, but they are quite fleeting because these mosfets do not have gate protection and in addition there are some reservations as to the temperature and length of soldering.

Quote:

In recent years crystal radio hobbyists discovered that some "zero-voltage-threshold" MOSFET such as ALD110800 or ALD110900 can substitute the diodes in crystal radio without using a battery. You only need to add an extra coil between the source and the ground to pick up sufficient current induced from the resonant circuit (aka the tank or the LC circuit) to drive the headphone.
However, ALD110900 or ALD110800 are quite fragile and can be easily damaged by static electricity or extra strong signals. They are mostly used in weak signal detection only. The output volume is also a bit low.

These inventions even make VHF FM receivers with passive power supply. Occasionally you find these pages because they are written in bushes, but the translator is quite good at converting to Polish.
A small sample in English Link

The second method of making a perfect detector is simple, we take an op-amp and make on it perfect rectifier , in the past, you could be accused of heresy, but the medium band ends around 1.6 MHz and operational amplifiers operating up to 100 MHz are nothing strange.
We take such an 8-terminal double amplifier, the first stage is an ideal rectifier with high gain, the second stage is a low frequency amplifier. to the loudspeaker, an antenna with a capacitor and we play
I was hooked on the topic, but the nearby transmitters turned off, the closest medium-wave I have in Slovakia beyond the mountains , I will probably try long waves, but our new 225 KHz transmitter is probably not very powerful and I do not know if it reaches Poland B.

Hah, then I guessed it with that MOSFET, though I didn't know it. So far I have been avoiding energy harvesting.

Is it possible to listen to something like this without a long (> 2m) antenna?

PiotrPitucha wrote:

The second method of making a perfect detector is simple, we take an op-amp and make a perfect rectifier on it

Unfortunately, I set myself a 1.5V power limit.
Maybe if I want the version with a loudspeaker and 18650.

Yesterday there was no electricity and I had the opportunity to test the reception of "Jedynka". Zero distortion, just a slight background noise.
The local radio went out too, so I didn't test it.

Hello
I'm like google pro
I recommend LMV951, 1V power supply, 2.7MHz band.
Already 15 years ago, the Americans at some symposium discussed a new one
product, amplifier with one 0.9V supply and 132 MHz band,
they integrated it with a surface filter .

Ps I haven't checked with LMV951 availability, anyway Mouser does.

I rarely shop in Mousera.
In those which I usually order, they did not have stock or not at all.

I built an FM radio on the UL1496 chip with a young technician.
At school, they admired how tiny it was. It answered on a regular W66 telephone insert.