FM/AM Tuner

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#81
Hello everybody,

I am looking for ideas concerning FM decoder(s).

I have seen some circuits about this with tubes and transistors. I don't know the quality of electronic.

But I can find it. I am sure I have it, where???

Jerome
 
#83
There used to be an ambitious product in the early 80's by the late Orion radio factory in Hungary, the ST-240 AM/FM tuner. The designers incorporated every advanced circuit solutions of that time (discrete MOS-FET front end, TOKO linear-phase LC IF filters, LC phase discriminator FM demodulation, LC multiplex filters, etc). The result was an ugly monster that is still the reference of many fellow-countrymen of mine...

Here is some description and pictures (sorry it is Hungarian only):

http://oldradio.tesla.hu/rajzok/radio/orion_st240_tuner/orion_st240.htm

And the full circuit diagram, it is possible to get some ideas from it:

http://oldradio.tesla.hu/rajzok/radio/orion_st240_tuner/fmtuner.jpg
http://oldradio.tesla.hu/rajzok/radio/orion_st240_tuner/fmkf.jpg
http://oldradio.tesla.hu/rajzok/radio/orion_st240_tuner/programvalaszto.jpg
http://oldradio.tesla.hu/rajzok/radio/orion_st240_tuner/fmdemod_muszerek.jpg
http://oldradio.tesla.hu/rajzok/radio/orion_st240_tuner/dekoder_kimenet_am_tap.jpg

The linear phase filters were also available in electronic parts shops over here. Linear phase in FM domain is amplitude linearity in the audio domain. I have a Marantz tuner with simple ceramic filters, and I replaced them with those linear phase LC blocks (on a small PCB with some additional circuitry). I understand they were also used in the Klein + Hummel high-end tuner "Telewatt FM 2002" and also by Rohde & Schwarz. Now it sounds good!
 
#85
IF and Stereo circuit

Hi everyone!

I have a few questions about my simple design. I want to build IF circuit with CA3189 and AN7470 (stereo MPX).

I want to start with typical application from the datasheet and connect it to a RF+PLL module. Also I have a kit with RDS, but my simple question is where's the pin with mpx signal?

I have CF filters and polish Coil with these parametres:

An externally hosted image should be here but it was not working when we last tested it.

frequency:10,7 MHz
inductance: 2,43uH
Q>=75
I winding: 8+7 turns
II winding: 2 turns
internal C: 82pF

The TOKO coils are unavailable here in Poland in a small quantity. Would it work out with this one?

The main question is which transistors should i use to gain IF? Any ideas or another application circuits for CA3189 would be very helpful.

TIA, Przemek
 
#87
incomplete application

This application is incomplete, I'm asking what transistor (Q1, Q2) should I use? There is also note 'bout coil (TOKO one).

I see, that I just have to try different transistors. Maybe Mr. Kiraly have some info about this circuit?

Heh, look what pretty tuners they build:

http://larsholt.dk/Brochurer.htm

I can see, that CA3189 and LM4500A (TCA4500A) were very popular in the late 80's Hi-Fi receivers.

If this project fails (with universal PCB), I must try something different. I build the complete HiFi system, and what's funny, in my country there's no kit available to build a good tuner.

I need complete IF + MPX circuit, maybe I can do it another way?
 
#90
Mr. Kiraly had suggested to me BF240 ("F" denotes High Freq.) for Q1, Q2.

But as mako1138 suggested, in this place (IF=10.7MHz) almost any modern small-signal transistor will work for Q1 and Q2. Even the humble not modern BC109 will do. See some data sheets on the links.
Look for ft (in MHz).

I have used BF240 (readily available) and works fine.

http://www.pira.cz/pdf/BF240.pdf
http://www.datasheetcatalog.org/datasheet/kec/BC546_7_8.pdf
http://www.datasheetcatalog.org/datasheet/siemens/BC109B.pdf

Best Regards
George
 
#91
I found a 22 year old article on building an FM tuner in my files and they use 2N3563 transistors as the IF amps. The tuner has two 2N3563 IF amps and three ceramic IF filters after the RF section. Don't know what the European equivalent of the 2N3563 is.

I wanted to scan the schemetic and attach it, but the scanner isn't working right.

Regards,
Ray
 
#92
The old CA3089/3189 were single conversion IFs, with fairly high gain on one freq.- These chips requires a very well controlled PCB layout not to go unstable. A better solution as such would be a dual IF section, with something like the old TCA120 as a dual slope detector - several schematics have been published, but I think I have lost these old mag's....

European Elektor had two designs of quite good tuners - one I believe in the early 80s and another around 89-90....
I have at least some of the mag's somewhere, but a recent house move have made them inaccesible for at least a couple of months more....🙁

Someone else have these copies??

EDIT:
Just rememberd this one!
A very good article by a very skilled ham radio designer..pinpointing some of the problems for modern world FM tuners......
http://mobiledevdesign.com/images/archive/1000Ryder26.pdf
 
#94
Ah.. I just cruised through the thread without noticing that one....
Found it several years ago cruising around the net with this very same purpose...
The reason for choosing the passive doubly balanced mixer is that these are substantialy better and more true to the actual square law one really wants from a mixer.
Much better in sieving out a weak station in the presence of strong neighbouring ones, without creating lots of unwanted higher order mixing products....
 
#95
no problem Ray! I've bought 2 pure new BF240 for my project, according to gpapag proposition. Also I have a broken Blaupunkt car tuner (legal one 😉 )which RF and IF stage I can use as well, I think. The sensistivity and selectivity of car tuners sometimes (or very often) beat their friends for home use. I need to point that many micro/mini systems have nice functions - MP3, SD Card etc. and they sound good. But, what's wrong the tuner is as shity as it could be. 30-years old radio is 2 levels better or higher...

Some say that building a tuner is something ridiculous. With prepared and ready to use IC's, coils and filters it's a good training and nothing so very hard (excluding getting IC's and especially coils). As gpapag said: you're able to understand that sky is something more than we see each day.

And for those who want easily build complete tuner my proposition is Sony CXA1238. It's a great IC with RF+IF+MPX stages.

Another Chip that you can easily assemble to any tuner is Sanyo LC7265 . It's a digital scale and I have good opinion about this one. I'll send more info/application how to build such a display.

Many thanks to all of You,

Przemek
 
#96
This is one instance when DIY simply will not be worthwhile.

Have a look at the performance offered by reasonably priced second hand tuners, e.g. the Yamaha TX series, and you will quickly realise that no published DIY project will come close.

If you prefer to buy new, try out the Sony XDR F1 HD tuner. Even on analogue FM it is excellent.

Perhaps not the answer you wanted to hear, but I hope it helps you make a sound decision.

s0rce said:
I was wondering what you people suggest for a diy fm/am tuner most of the stuff Ive seen seems very low end...

Thanks,
Lyle Gorodn
Click to expand...
 
#97
There's absolutely nothing wrong in building a tuner!
- And as you say, it is very good practice.

but RF design - and RF PCB layout in particular- follows it's own set of rules, so to speak. Stray capacitance have a tendency to play havoc with even the best schematic, and the higher the frequency the worse the problems.
Building one's own FM tuner for quality reasons is truly a daunting task. If this is the reason, one would probably be much better off looking for a second hand of the classical designs.
For practice reasons, it's a superb excercise! 🙂

EDIT:
Being a licensed amateur, I used to build amateur radio stuff both for fun and for use. One of the major problems I see today, is finding parts. ICs and transistors are easy, but suppliers of single unit coils and filters are getting more scarce by the day, - literally!
If you want a few thousands of each - OK- but one or two - no interest!
 
#100
I don't know (or remember) if AM tuners have been discussed in this thread, but a while ago Popular Electronics published the circuit of a synchronous AM detector. IIRC these are lower distortion than the typical diode detector. The PE circuit used several chips, but AM stereo (at least the kind used in North America) also required a synchronous detector, and did it with fewer parts. There's some web pages dedicated to AM stereo and stuff, if you search. A friend's mid-80s Chrysler K-car had an AM stereo radio in it; one of those shouldn't cost much from a wrecking yard (the radio, although a K-car won't be worth much these days either).

Amateur radio books (like the ARRL publications) will be helpful with the RF stuff, since FM is in between the 6M and 2M ham bands. For AM related circuits, you'll find some elaborate (if antique) tuner ideas in booklets from Modern Radio Labs (MRL). I don't see why you couldn't sub a fancy synchronous detector for a cats-whisker diode and get the best of both worlds.
 
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