question about a radio circuit ?

[patric44]

hello guys

i recently made a SW radio using a **broken link removed** radio ic using the circuit below and it works but ( not as expected )

i have been able to listen to SW brodcasts from china - greec - even egypt !

but the circuit has the folowing problems :

1- most of the stations are mixed together (i can hear more than one station at a time )

2- the signal has a fading issue ( when i listen to a station and its clear ! after 10 sec or so the signal fade and i hear
another station and the firsts station may or may not come back) even that the IC has a AGC on pin 16 ?!
the ic are supposted to be a dedicated AM /FM receiver !?

so is there a way to improve the reception of that circuit?

 

[Nigel Goodwin]

Where are all the rest of the parts? - there's a distinct lack of any selectivity in that partial circuit, haven't you looked at the datasheet you linked to?.

 

[patric44]

i already saw the schematic on the datasheet but the circuit seemed relativly complex and its AM+FM reciver
so i saw that circuit online and made it .

so my question is :
apart from the datasheet circuit is there is any improvment that i can make for this particular circuit
or if can give me a much simpler circuit(than the data sheet one) AM only. i would realy appreciate that

 

[Nigel Goodwin]

You can obviously make an AM only radio with that IC, but you still need all the AM parts to make it work - as it's a superhet you need a local oscillator, IF, and front end tuning.

Note that the 'circuit' you copied says it's for MF (and a crap performer at that), altering it for short wave will make it even worse.

 

[MikeMl]

That is the schematic of a real shortwave receiver. If Kenwood could make and sell a decent one with as few parts as the one you showed, why do you suppose they would sell the one above?

You get what you pay for...

 

[patric44]

MikeMI , ok i get the idea.
but nice schematic tho i defenitly should try it hhhh

i understand that i get what i pay for but the circuit i posted is not a simple crystal radio circuit
or a one transistor circuit or something you know what i mean , the ic i am using is supposted to be a complete AM/FM reciver it has the mixer
the oscillator ..... even AGC . so what i don't understand why it works so poorly ?

i made that circuit below while ago its an FM receiver with the tda7000 (notice that the circuit has much less component
than the keenwood one ) and it works great ! the voice is crystal clear the selectivity is good and manged to pick all the stations !

so is there a radio ic for the Short wave band (insted of the tda1083 that you don't like )
with a much more simpler schematic (than the keenwood one you posted) ??

 

[Nigel Goodwin]

the ic i am using is supposted to be a complete AM/FM reciver it has the mixer
the oscillator ..... even AGC . so what i don't understand why it works so poorly ?

I've already explained why, you left out most of the parts that make it work - you're using it as a crystal radio with a little amplification.

 

[patric44]

first thanks all of you guys for helping. i realy apprechiate it.

ok Nigel Goodwin , i get it ( i have to stick to the datasheet circuit )
but as you can see the circuit looks relativly complex ( with all of these
LC tank circuits ) . i think it could be modified to be much more simpler one
after removing the parts that was intended for FM , but iam having a little hard time doing that
so can any one help with that , (what i wanna do is make a reduction process for that circuit
in return of giving up FM receiving ability and may be some of the selectivity (just a resonble SW receiver).

 

[audioguru]

"Simple" means poor performance that you do not want.
The TDA7000 radio IC is obsolete and had terrible performance. An newer version is the TDA7088 that is in a "radio" sold for one dollar at The Dollar Store and it also has terrible performance. But they are simple.

 

[patric44]

"Simple" means poor performance that you do not want.
The TDA7000 radio IC is obsolete and had terrible performance. An newer version is the TDA7088 that is in a "radio" sold for one dollar at The Dollar Store and it also has terrible performance. But they are simple.

thanks audioguru.

but simple not necessary means poor (at least not in all times).

i don't know what you have against the TDA7000 (its a good dude ) may be against all the TDA series. i tried the TDA7000 circuit my self and its
far from terrible you can say it a relativly decent circuit the audio is clear , no hissing , no noise , the selectivity is good also (after putting a varicap diode )
i don't know what you want more than that !!?(its a radio it doesnt suppose to do any thing else ) perhaps you have a very high standerds

iam sorry but most of you guys are judging the question i asked (reduce the data sheet circuit for more simpler one )
insted of helping me in the question it self ??

Quaote ("Simple" means poor performance that you do not want)

SIMPLE = relativly decent(fine) circuit (it dosent have to be as complex as the keenwood one ) there is a lot of reg.. receivers that work fine
and it hasn't a 10^8 components that you may not find

POOR = rapish noisy circuit.(dont want that )

i dont understand , after removing the FM part from the datasheet circuit the circuit
will became poor at reciving AM !? that doesnt make any sense

 

[Les Jones]

The way you are using the TDA1083 in post #1 is not the way it was designed to be used. It is designed to be used as a superhet receiver which means that the selectivity is provided in the IF stages. The only selectivity in your circuit is one tuned circuit on the input. (Which will have quite a low Q as it is loaded by the antenna and the input of the IF amplifier which you are using as an RF amplifier.) The design in Fig 10 on page 8 of the data sheet is how it should be used as an AM only receiver. This design is for a fixed frequency as it uses a crystal controlled local oscillator. You would need would need to use a variable frequency local oscillator. You would need to use a two gang tuning capacitor so the input tuned circuit was tuned to either 455 Khz above or below the local oscillator requency (Depending on weather you wanted the local oscillator above or below the received frequency.) At higher received frequencies the image rejection would not be very good with a 455 Khz IF frequency. This is just a more detailed explanation of what all of the other replies have said. I think it would be cheaper to buy a ready made short wave receiver. I used to have a couple of synthesised short wave receivers that I took on holiday to listen to the BBC world service which only cost me about £10 each.

Les.

 

[cowboybob]

Removed.

Might have done myself a favor by reading the FIRST post... .

 

[patric44]

The way you are using the TDA1083 in post #1 is not the way it was designed to be used. It is designed to be used as a superhet receiver which means that the selectivity is provided in the IF stages. The only selectivity in your circuit is one tuned circuit on the input. (Which will have quite a low Q as it is loaded by the antenna and the input of the IF amplifier which you are using as an RF amplifier.) The design in Fig 10 on page 8 of the data sheet is how it should be used as an AM only receiver. This design is for a fixed frequency as it uses a crystal controlled local oscillator. You would need would need to use a variable frequency local oscillator. You would need to use a two gang tuning capacitor so the input tuned circuit was tuned to either 455 Khz above or below the local oscillator requency (Depending on weather you wanted the local oscillator above or below the received frequency.) At higher received frequencies the image rejection would not be very good with a 455 Khz IF frequency. This is just a more detailed explanation of what all of the other replies have said. I think it would be cheaper to buy a ready made short wave receiver. I used to have a couple of synthesised short wave receivers that I took on holiday to listen to the BBC world service which only cost me about £10 each.

Les.

thank you so much les jones for the explanation ,

after a closer lock at the block diagram of the ic it became now clear to me that the circuit leves pin 4,5,6 not connected
which are strange becouse these are the most important pins of the ic ( the oscillator - the mixer ) ,
i propaply will stick with the datasheet circuit or buy a SW radio insted

but the ic costs me about 1$ , compared to the high prices of SW radio where i live ,

 

[patric44]

Removed.

Might have done myself a favor by reading the FIRST post... .

no proplem , it seems that that the only circuit out there beside the datasheet one
is the circuit above .

 

[Les Jones]

I am not clear about your location. Your profile shows your location as the United States but in another thread you say it is Egypt. If you are in the US then I would think you could get a short wave radion for a similar price to the price in the UK.

Les.

 

[patric44]

I am not clear about your location. Your profile shows your location as the United States but in another thread you say it is Egypt. If you are in the US then I would think you could get a short wave radion for a similar price to the price in the UK.

Les.

iam from the us but Currently resident in egypt.

 

[audioguru]

thanks audioguru.
i don't know what you have against the TDA7000 (its a good dude ) may be against all the TDA series. i tried the TDA7000 circuit my self and its
far from terrible you can say it a relativly decent circuit the audio is clear , no hissing , no noise , the selectivity is good also (after putting a varicap diode )
i don't know what you want more than that !!?(its a radio it doesnt suppose to do any thing else ) perhaps you have a very high standerds

Of course the TDA7000 produces clear sound without much hiss or noise, it is FM, not AM and it cuts high audio frequencies to reduce its hiss. But it was designed a long time ago with only a single tuned LC circuit when there were few FM radio stations to cause poor selectivity. Its spec's also show horrible distortion and noise.
Here in Canada a half-decent FM radio has many tuned LC circuits so that it can select only one local FM radio station from the 50 or more local stations here. Do you have 50 or more local FM radio stations in Egypt?

 

[patric44]

Of course the TDA7000 produces clear sound without much hiss or noise, it is FM, not AM and it cuts high audio frequencies to reduce its hiss. But it was designed a long time ago with only a single tuned LC circuit when there were few FM radio stations to cause poor selectivity. Its spec's also show horrible distortion and noise.
Here in Canada a half-decent FM radio has many tuned LC circuits so that it can select only one local FM radio station from the 50 or more local stations here. Do you have 50 or more local FM radio stations in Egypt?

ok now i see, a more decent radio IC require more LC circuits for more selectivity with the crowded and mixed stations.
but here in egypt there is only 17 stations at max . so i didnt notice the lack of selectivity of the IC .
ok iam convised , you are right its a slightly rabish IC

 

[audioguru]

Where do you buy the obsolete radio ICs you are talking about?

 

[patric44]

Where do you buy the obsolete radio ICs you are talking about?

i am currently resident in Egypt , and they have here a lot of old electronics stores , surprisingly a two or three stores has that old TDA series
TDA7000 - 7021 - 7088 ......

look what i found also (seems they have a sock of that old oscilloscope )