Oye buddys..

Here's a very simple AM Radio circuit I've designed couple of years ago. Don't know whether anybody listen to AM stations anymore. But I still use it(maybe I wanted to listen to my own built radio lol..). The radio section is wired using a single transistor(BF494) and it was so amazing that an audible sound is recovered at the output which is faint though. It doesn't use any external antenna and the sensitivity/selectivity of the receiver is pretty good. However I used an amplifier(TA 7368P Toshiba, Low voltage) which drives an 8ohm/1W 4" speaker inside a box rocks the entire room with a high fidelity audio that is unbelievable and outperforms Superheterodyne ones in this regard . It is a reflex receiver.

The audio recovered at inductor L is rather strong comparing to ZN414 and free from oscillations.(I've never succeeded in building ZN414 which always give me annoying motorboating and chirping crappy I say!)

Using a flat ferrite bar antenna allows local reception for a pocket radio and a big rod antenna captures stations beyond 200miles! So it doesn't require an external wire antenna, adding it only helps in electrical noise catch.

Only critical part in the circuit is inductor L, its optimum value gives excellent results. Make rf parts close to the transistor. I made it on a 1.5" ultra small pcb. 2 x AA battery lasts very long.

Another important thing is that the radio is absolutely silent in between the stations - means no noise at all if no any electrical interferance which is a plus point over Superheterodyne receivers. It was so amazing to tune it during power failure period. So I'll call it a true radio

Attached Thumbnails

 

 

Please do not say "AM radio" and "high fidelity audio" in the same thread.
they are two completely different animals. An AM radio sounds awful.

A superheterodyne radio has good sensitivity, good selectivity and automatic gain control. Your radio has none of them.

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Uncle $crooge

 

No, it's appalling quality.

Sensitivity should be quite good, but that's all - and it's not even a particularly good example of a reflex radio, using 1N4148's isn't a good idea.

Superhets wipe the floor with them though on all counts.

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Well, from my experience the circuit has better performance than ZN414 in all aspects. Sensitivity is comparable to portable superheterodyne ones but not to that modern high sensitivity IC receivers. I got plenty of distant stations(some are more than 500Kms away) clearly separated during night. Till now I can't figure out any overloading but a strong local station may widen it's space a little . But I'm satisfied on the selectivity from such a little receiver.

Regarding "high fidelity", the radio is capable of reproducing almost the entire audio modulation frequencies unlike superheterodyne ones and it eliminates unwanted IF noises amplified.

Without considering high end selectivity and AGC, this receiver sounds very good. My Philips pocket transistor superheterodyne radio which uses a small bar antenna can receive only strong local stations. So a bigger antenna increases sensitivity of both types.

OA79 germanium diode can be used in place of 1n4148.

(Wow! does anybody think that I'm talking from a century back..)

 

No one ever suggested a ZN414 was much good.

It can't reproduce what isn't transmitted, if it sounds better than a superhet then you're listening to a rubbish superhet.

Right, so you're comparing it with a toy superhet - those are truely rubbish, and don't work well.

And would work far better.

No, only 50-60 years - bit longer if we count valve reflex receivers.

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Using the ZN414 alone does not give you a superheterodyne receiver.

The ZN414 is now obsolete and has been replaced by the MK484.

The ZN414 and presumably the MK484 can be used to make a good quality superheterodyne receiver, see page 11 of the datasheet. I suggest you try building it and compare its performance with the crappy reflex receiver.

Attached Files

ZN414484.PDF (761.3 KB, 217 views)

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I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong.

Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

 

so stupid project

 

thanks I wanna giv it a try..

 

I wouldn't say a 'good quality' superhet - but you can use the ZN414 series as an IF amplifer in a simple superhet as well as for a complete TRF radio.

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I've already seen its datasheet. That is called 'toy superhet'. 455KHz filter may reduce the audio quality. I've seen it on some SW receivers for high end selectivity, but poor quality audio. So I'll call it a crap circuit. ZN414 may work well as an IF amplifier.

BTW, what I wanted to convey is the single transistor radio is performing well within such a simple circuit. The principle is awesome

 

it can be built inexpensively.

what should be noted is the var.-cap is expensive, and can be difficult to obtain, and/or expensive.
recently i have purchased a simple AM/FM radio, for 4.49 Euro's,
that's about 7 dollar.

personally I never understood the principle of these 350pF var.-cap's,
they have six pins i think.
the circuit listed here could be a good starting point.

I have one (new) ferrite rod (for AM) from MAPLIN UK, including coil, but currently stuck where to get one of these var.-cap's, for a good price.
I would not consider to take it from my new radio...

 

Do you have radio rallys other there? (car boot sale for electronic parts), I went to one last sunday, and there were loads of variable capacitors for sale.

If you're buying them at normal retail, expect to pay MORE than your cheap new radio was. Jackson was always the prime manufacturer, and they still make them.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

Hmm i'm not uninterested in the radio topic, i want to increase it in the future, but do not have much experience.

I can get var.-cap's from futurlec, at least 15pF or 30 pF. edit: indeed I have few of them, but yet did not build anything with them.

I am not sure about car boot sales, I've seen some pic's on flickr, from the States.

I guess they can be found for one or two dollar from some chinese source!

i have, after two years search, found a lot of cool parts, such a small project PCBs for just $1, or 1/8W resistors, and low-current LEDs.

never searched for these 350 pF capacitors, only looked sometimes when i found some new supplier website.

unfortunately most chinese suppliers do not sell small quantities, for instance the small ferrite rod including coil.

and personally I do not utilize new devices for parts.

I have one such radio tuner PCB from an old SONY stereo, but maybe it can be used as it is?
I am also thinking eventually to take it apart (but do not really know the TOKO coils, how to use them properly).

so the circuit is interesting for me, eventually I will build it some time.

 

Those cheap 1$ chinese radios have these variable cap. Alternatively you can salvage it from old tuner boards. However this article may entertain some of you enthusiasts which shows how simple is the architecture of a tuning cap: Homebrewed Variable Capacitor

 

Hmm, how would it be to use a stepper motor, and hide it into an enclosure?
would it be neccessary to use a gearing?
or maybe, another, smaller, fine tune capacitor, two steppers, and no gearing.

just had this idea when reading the reply.

I know the cheapest $1 radios often use a digital IC, tuning controlled by a button...