AM reflex receiver on 2 germanium transistors

Cool project. Respect for sharing at a time when there are thousands of schemes available on the internet and only some of them work.

acctr wrote:

The headphones are connected in series, which causes them to operate in counter phase, so I reversed the polarity of one of them.

I usually treat the operation of one headphone in counter-phase of a mono receiver as an additional feature rather than a disadvantage, as this introduces a pseudo surround to the received sound. Then the sound comes from different directions, rather than from the top of the head as in mono. I know this doesn't suit everyone, but it's good to know that it can still be done.

For me it's great. For a receiver on two transistors it plays quite nicely. I think I only have the famous ASY37s left of the germanium ones.
For winding this toroid I think elongated double-sided forks would be better.

You wrote that the description lacks information on the transformer . For that, your your description from the book is missing two pages

You do not hold firmly to the standards of years 60 those (PCB) , then I suggest using Li-ion batteries instead of AA



✅ The advantage is that they are free from the donor after the electric cigarette. If on one 3.7V would not want to play, then you can give two in series 7.4V will probably still play louder

Btw If you don't mind I've removed the paper from the pages 😇

These days, unfortunately, it's more of a curiosity.

_ACeK_ wrote:

Btw If you don't mind I removed the paper from the pages 😇

Well you just ruined the vibe of the old books

@gps79, @efi222 thanks, it's nice that someone likes it.
The winding of the tray could probably be improved, I didn't pay much attention to it, I just took what I had on hand, i.e. a plastic stick, which I easily wound with a wire from some coil with the help of a drill.
Germanium transistors are a good bargain at the moment; when such a TG50 NOS classic is priced at under £10 a piece, it's a good bargain. The aforementioned book also gives the parameters of the most popular transistors of the time, and you can compare to the current ones.
As someone already mentioned the missing description I add it. There is a fairly detailed description of the receiver operation, number of antenna and transformer coils, etc. You will find that the transistor in the first stage is TG20 (7 MHz) and not, as I wrote, TG5 (0.8 MHz), which was in another receiver from this book and is in the same housing. The reflex circuit requires faster transistors because of the need to amplify two frequencies.



@_ACeK_ keeping the electronics alone in a 60's climate is completely sufficient for me, if the whole thing was done as described, the case would have to be made of wood and the assembly of the components spatial - I didn't particularly care for that. The use of a rechargeable battery is rather pointless, the voltage is too low, there is a need to recharge, with two you need to add a balancer. Probably after some time of disuse it would fizzle out and would have to be replaced, the expected use is one hour of playing per month anyway and the batteries will last for years.

More about germanium transistors and reflex receivers
RiK_1964-10, page 242
https://publikacje.r-kobus.eu/TEWA/TG5.pdf
https://publikacje.r-kobus.eu/TEWA/TG2.pdf

Thank you for the additional pages 👏

🤔 If it would be possible, could you insert a fast diode Shockley diode for a test



One like the one in the picture I soldered out of a sat tuner, the conduction voltage is 0.178V 😎 I wonder if it would be better than the germanium one 🧐

🤔 Are all the coils wound with the same diameter wire?



In electronics from fluorescent lamps there are sometimes toroidal cores, are these suitable?

😊 Attached PDF paperless books 🙃

Polish Radio Programme 1 broadcasts on AM?

E8600 wrote:

Program 1 of Polish radio broadcasts on AM?

IN AM. That's amplitude modulation, not range (bandwidth). It broadcasts and is doing well, probably as one of the few stations in Poland. I was listening yesterday, PRI is doing quite well from the transmitter in Solec Kujawski;

_ACeK_ wrote:

I wonder if it would be better than germanium

I've done experiments on several receivers with replacing a germanium diode with a Schottky diode (because that's more what you meant). Schottky worked in the detector, but unfortunately worse than germanium diodes (which is a pity, as they are more available). Out of luck you could use Schottky diodes, but with the knowledge that the receiver could play better.

As for the photo of the compact fluorescent light driver, I solder a coil on a straight ferrite core, which is usually between 2 and 5mH, which is ideal for an HF blocking choke in super-reactive receivers.

E8600 wrote:

Program 1 of Polish radio broadcasts on AM?

It broadcasts both on AM and FM, but is the only nationwide station broadcasting on longwave (225kHz).

_ACeK_ wrote:

Instead of a germanium diode insert a fast Shockley diode

I'm afraid these are too low voltages for a Shockley diode, unless you had a Schottky diode in mind. I've never tried it, maybe I'll test it in my spare time, although it would be easier to test on a detector receiver, which I can also present.

E8600 wrote:

Program 1 of Polish radio broadcasts on AM?

Yes, almost unchanged and almost uninterrupted for almost 100 years, so that you can build working receivers according to designs from the 20,30, 50 or 60s and enjoy listening to programmes of Programme 1 of the Polish Radio S.A. in liquidation

_ACeK_ wrote:

In electronics from fluorescent lamps there are sometimes toroidal cores, are they suitable?

at least some of them will be suitable. Will all of them? I don't know. It's worth trying.

I once did an experiment and checked if I could use another core found in "junk" instead of the usual ferrite antenna, and it turned out to be yes. I wound the coil on an anti-interference core from a data tape from a printer and surprisingly I was receiving Programme 1 PR on this. The reception was worse than on the longer ferrite antenna, but it was there.

_ACeK_ wrote:

In electronics from fluorescent lamps there are sometimes toroidal cores, are they suitable?

It depends what function it had, if it was an anti-interference choke it would mean the trafko would have more inductance, and if it was a core from an inverter it might mean it was a powder core designed for energy storage.
Whether this would affect the coupling in the reflex circuit is hard to say, but it could be as @gps79 wrote.
In my receiver I used a core from some telecommunications equipment where it worked in a signal transformer.

ArturAVS wrote:

This is amplitude modulation, not range

I know it's about modulation, but is this reception in AM acceptable/comparable to FM? I ask because I have 2 radios with AM range only: one is some sort of portable, battery-operated Unitra, and the other is a Russian Falcon in the original cardboard case.

E8600 wrote:

is this reception in AM acceptable/comparable to FM?

Unfortunately they are very different.
The FM UKF signal is transmitted at a much higher frequency, requires a different circuit for demodulation than AM, and, most importantly, the UKF signal reaches the receiver at up to 1000x less power than the AM long wave signal.
This is due to the fact that VHF transmitters transmit with a power of a few kW, while, for example, the AM transmitter of Programme 1 of PR transmits with a power of 1MW, as well as the fact that VHF waves are more rapidly attenuated in the atmosphere than long, medium or short waves.

Added after 5 [minutes]:

I would also add that for PR1 long wave reception it is possible to make a receiver on 1 transistor, while for UKF reception you already need at least 2-3 transistors. Of course, you need to have a good checked schematic, because there are many non-working ones on the internet.

E8600 wrote:

I know it's all about modulation, but is this reception in AM acceptable/comparable to FM?

It depends on what sound quality you accept. For comfortable understanding of speech, a bandwidth of approx. 2.3 kHz is sufficient ( e.g. SSB modulation, a variation of AM you might say ). 1 P.R. programme transmitted in AM modulation has a bandwidth of about 6 kHz , and the same programme transmitted in FM modulation has a bandwidth of about 15 kHz.
I guess you have a radio with ukf 88 - 108 MHz FM and the ones you mentioned, set to that station and compare.
The rest depends on the workmanship of the receiver, speaker, enclosure.

E8600 wrote:

I know it's about modulation, but is this reception in AM acceptable/comparable to FM?

As others have written, the sound quality is inferior to FM, the carrier f is much lower, the AM characteristics also do their bit. The advantage is the range - when I drive across half of Poland and have 225 kHz set on the radio, the reception does not change at all, just like with FM or DAB.
Anyway, what's the problem with checking? You wrote that you have a radio with LW range.

E8600 wrote:

the other is a Russian Falcon in the original dictky case

I also have a Falcon, but rather in a solid plastic case.

gps79 wrote:

On the other hand, for UKF reception you already need at least 2-3 transistors. Of course, you need to have a good tested schematic, because there are many non-working ones on the internet.

It is also possible to do on one (not counting the ac amplifier), I did on BF214 and it played normally, another example by A. Janeczek (T2 and T3 are ac amplifiers)

acctr wrote:

On one it is also possible to do (not counting the amplifier of the acoustic part), I did on BF214 and it played normally, another example by A. Janeczek (T2 and T3 are amplifiers of the acoustic part)

I don't really understand this bidding. You might as well say that AM requires no transistor, only a diode. If you can't listen, it's not a full-fledged radio. You yourself showed a schematic of a radio with 3 transistors.

Added after 22 [minutes]:

There is a 50uV signal coming out of the UKF antenna and a 50mV signal coming out of the AM antenna, hence the need for at least one gain stage more for UKF reception.

@E8600 Such a comparison, it's closer to a wire tape recorder aka cassette recorder. Completely different frequency response.

AM transmitters at long and medium wave cut the HF band to 4.5 kHz. UKF transmitters with FM modulation (there is no other in this range as far as radio broadcasting is concerned) have a bandwidth of up to 12 kHz, so there is necessarily more treble. In addition, the higher frequency and FM modulation move interference away from the broadcast. Unfortunately, Chinese products also sow interference in the UKF range. The AM modulated bands (long, medium, short) are more susceptible to interference from converters. It is fortunate that these converters operate at increasingly higher frequencies, moving interference away from long wave. Nobody reports the bugs, so they are imported from the far east and interfere.

gps79 wrote:

I don't really understand this bidding. You might as well say that AM requires no transistor, only a diode. If you can't listen, it's not a full-fledged radio. You yourself have shown a schematic of a radio with 3 transistors.

I could nod or deny that "for UKF reception you already need at least 2-3 transistors", but I have made more than one reaction receiver that consisted of only one transistor, so there is no bidding here, just facts. Anyway, in the post >>21721982 I inserted a schematic where there is a receiver on a single transistor, T2 and T3 form the ac amplifier, without which the receiver would also work.

gps79 wrote:

From the UKF antenna comes out a signal of the order of 50uV, and from the AM antenna of the order of 50mV, hence the need for at least one more amplification stage for UKF reception.

How much signal you get from an antenna depends on the antenna and the distance from the transmitter.
In general, the claim that such and such modulation requires so many and so many transistors makes no sense, as there will be those who will prove that this is not the case, e.g. the famous case where a Soviet spy room used a piece of metal as an eavesdropper in a foreign embassy.
Here are examples of FM radios with and without transistors on one transistor





Here an explanation of this type of FM demodulation

acctr wrote:

What signal you get from an antenna depends on the antenna and the distance from the transmitter.

Let me say more - the power of the transmitter, the distance/propagation and the antenna will determine the *power* of the signal the antenna can deliver to the receiver. And the voltage you get at the antenna depends further on the input impedance of the receiver. A receiver whose input stage is based on a parallel LC resonant circuit has a very high input impedance at tuning, hence the voltage from the antenna can be quite high - orders of hundreds of mV (and that's why it's possible to demodulate it on the diode at all). BTW: respect for a working project!

acctr wrote:

In general, the claim that such and such modulation requires so many and so many transistors makes no sense, as there will be those who will prove that this is not the case, e.g. the famous case where a Soviet spy room used a piece of metal as a wiretap in a foreign embassy.

That's right. I'm building an AM receiver for the umpteenth time now and, paradoxically, my impression is that while AM is trivial to demodulate by-no means (on a diode), such a simple demodulator is very poor - it has terrible linearity, high signal loss and, on top of that, can't cope with selective carrier fading (matters rather more at HF when using a reflected wave). Building a good AM detector is paradoxically perhaps even more complicated than an FM detector and requires at least a phase-coupling loop to extract the carrier.

LEDówki wrote:

Also, the higher frequency and FM modulation move interference away from the broadcast.

You are right that there is generally less interference in the FM radio band than in the lower bands - all those pulse chargers don't get that high. However, it is not quite so with this modulation - FM modulation is somewhat less susceptible to interference in radio broadcasting, because it uses a much wider bandwidth - and the same information is encoded redundantly on many frequencies (the spectrum of a signal modulated by a single tone has many widely spaced striations, in AM there are only two). In the FM radio band you could fit 2,000 AM stations into a standard 4.5 kHz audio bandwidth, or about 500 stations, assuming full bandwidth up to 16 kHz. However, if you were to set a level playing field and compare AM and FM at the same bandwidth, I already have considerable doubt that FM would be better.

There is also a second reason: many popular portable receivers have the AM band treated negligently. For example, the very fact of using a simple envelope detector already means that you have an SNR 3 dB worse than with a synchronous detector. A great deal also depends on the characteristics of the filters.

E.g. aviation uses AM en masse in the UKF band because of the *greater* immunity of this modulation to interference.
You can hear AM even if you have noise stronger than the signal and you can hear something there. If two are transmitting on AM simultaneously, you'll hear both of them too. FM has the disadvantage that if you have a signal too weak, you won't hear anything, and you'll only hear one of the two superimposed transmissions.

LEDówki wrote:

UKF transmitters with FM modulation (there is no other in this range as far as radio is concerned) have a bandwidth of up to 12 kHz

At least 16 kHz. Limiting the bandwidth to 12 kHz would be silly and just waste bandwidth, because you have a stereo pilot signal on 19 kHz anyway. In fact, you can get as close to 19 kHz as your anti-aliasing filters will allow. As long as you don't interfere with the pilot itself and nothing goes above 19 kHz, it's ok.

gps79 wrote:

and, most importantly, the UKF signal reaches the receiver with up to 1000x less power than the AM long wave signal.
This is due to the fact that VHF transmitters transmit with a power of a few kW, while, for example, the AM transmitter of Programme 1 of the Polish Radio broadcasts with a power of 1MW, as well as the fact that VHF waves are more rapidly attenuated in the atmosphere than long, medium or short waves.

That how? But you know you're comparing a transmitter broadcasting to the whole of Poland and a chunk of Europe with stations with the range of one large city?
Signal strength depends strongly on the distance from the transmitter. On FM UKF transmits with low power, but the distance you have from the transmitter is generally much smaller than for that one Polish station transmitting on LW. In sum, the power of the signal reaching the receiver is similar, unless you live right next to the mast in Solec Kujawski. BTW: I've just checked - the UKF signal in my city is actually very strong - often at -50 to -70 dBm. FM is so strong that until I installed proper decent input filters in my AM receiver, FM stations magically materialised for me on shortwave (via heterodyne harmonics).

The other thing is UKF is not attenuated in the atmosphere, because if it were then aviation would not operate on UKF
UKF has a short range because:
- it penetrates less well through terrain obstacles (houses, trees)
- it does not bend on the curvature of the ground; in practice you have to see the transmitter to receive the signal - a transmitting antenna behind the horizon means no signal - this

W Practical Electronics 11 2025 ⬇️



A series on new radio technologies begins 🧐 There is a description of the modern "crystal detector crystal" without diode

_ACeK_ wrote:

There is a description of a modern "crystal detector" without a diode

You can see that a solid ferrite antenna means reception is good too.
I recently took on a turn-of-the-century tower with LW and MW bands, without the internal ferrite antenna but with an input for an external frame antenna. Whether the reception is better, I don't know.

acctr wrote:

You can see that a solid ferrite antenna means that reception is also good.

It is also worth adding that a ferrite antenna is a directional antenna and should be positioned perpendicular to the direction of the transmitter.

Posted schematic above ⬆️ from Practical Electronics may someone not like it because of © 🤔
It's just in case I made a copy In US you're not allowed to take photos in court 👀 but no one forbids making drawings
✅ To satisfy all cyclists, retros, computer users there are two versions 🙃

⬇️ First with paper 😇



⬇️ Second with colour 😎

The radio itself is for medium wave 700 kHz to 1.6 MHz ⚠️ Coil L1 has 54 coils of wire with a diameter of 0.55 mm 🧐





PCB

---

😊 Back to the diode question Schottky 🙃
⬇️ The one in the photo



There is a rectifying diode 3A 40V where the drop at the junction at 3A is 500mV . Checking with a meter at current probably 1 mA has a drop of only 178 mV so I'm curious how it will behave at higher frequencies 🤔

I also used to mount it on the TG8, TG50 but the problem was colossal interference.

Hello

With a little reworking you could use silicon transistors e.g. BF214 and BC211 instead of germanium transistors for the diagram in the first post.

żarówka rtęciowa wrote:

With minor modifications, silicon transistors could be used

Probably yes, an AM radio can be made in dozens if not hundreds of ways. Here I am just presenting one particular implementation, distinguished by the fact that the design as well as the key elements date back to the 1960s. Otherwise, I would not be motivated to build and present here a receiver on silicon transistors, even made by CEMI.