TA2003P radio

[andreidaniel]

Hi everybody!

I tried to make a radio with TA2003P. It works very nice on FM, nothing to say wrong about it. The sound is clear. The only problem could be the ceramic filter (BPF88-108) for the antena, it takes too much of the active signal, but if is replaced by a capacitor of around 15pF or by an LC circuit in "T" the problem is easyly solved.

The big problem is for both TA2003P and its equivalent CD2003GP is that while AM working a good part of the band is occupied by a local or regional powerfull radio transmitter. While is centered, the audition seems to be crowdy and overmodulated, depending on the power of the radio transmitter for that area. I changed the coil oscilator or the capacitor either in series with the variable capacitor or in parallel with it but nothing changed. The only thing I can observe is that while adjusting the red coil for medium waves is that a half of the band is more sensitive or the other one. Does anybody know if there is a small artificial to solve the selectivity on the AM? On a commercial radio I saw two ceramic filters put in series through an 1nF capacitor, but even this solution doesn't work. I also tried to use the IC as an IF stage for AM and taking the signal after the mixer stage fron another radio, but, again the sound is somehow overmodulated and the sensitivity is not so good.

 

[Binkman]

Paging @PE9ZZ

 

[PE9ZZ]

Your question is a bit hard to understand. You have a local AM station that overloads the AM section of this single chip AM/FM radio solution? The far away selectivity is made by the ferrite rod antenna on pin #16. The channel selectivity is made by the ceramic filter between pin #4 and #7. So if your powerful transmitter overloads the hapless front end there is not much you can do about it. Which is your "red coil" BTW?

 

[andreidaniel]

Your question is a bit hard to understand. You have a local AM station that overloads the AM section of this single chip AM/FM radio solution? The far away selectivity is made by the ferrite rod antenna on pin #16. The channel selectivity is made by the ceramic filter between pin #4 and #7. So if your powerful transmitter overloads the hapless front end there is not much you can do about it. Which is your "red coil" BTW?

Hello! Thank you for your reply. The red coil is usually the AM oscilator coil. In my case is as shown in the diagram a 3 pin coil, with a tap that is connected to the pin 12. There is a capacitor of 330p in series with that variable capacitor for the local oscillator coil. Otherwise the band would go too down in frequency.

The radio has 2 ceramic filters of 3 pin of 455KHz between pin 4 and 7, instead of just one. The two filters are connected one to each other via a capacitor of 1nF.

For the FM the 10.7MHz ceramic filter is connected through a resistor of 330 ohm. In other designs I saw for the FM two ceramic filters of 10.7MHz in series with a resistor of 100 ohm between them. For making the receiver maybe more precisely on the desired frequency I think.

The question is: to keep the manufacture of the radio design or to modify it as in the datasheet? For example the BPF88108 at the FM has too strong atenuation compared to an LC filter mostly find in comercial radio which are using TA2003P or CD2003 IC.

P.S.: An off topic question. In the datasheet of TA7358 or LA1185 and even on TA2003P are given the same values for the FM 1,75 for the oscillator and 2,25 wires for the VHF. In other magazines there are 2,5 and 3,5 wires but those are calculated for the entire band including japanese band as is written for 76-108MHz. How can I spread the band and make the receiver receiving only 87.5-108MHz? I also made some modules with both TA7358 and TA2003P and both with those values received much more under 87,5MHz.

 

[PE9ZZ]

Hello! Thank you for your reply. The red coil is usually the AM oscilator coil. In my case is as shown in the diagram a 3 pin coil, with a tap that is connected to the pin 12. There is a capacitor of 330p in series with that variable capacitor for the local oscillator coil. Otherwise the band would go too down in frequency.

Maybe that is part of the problem. The local oscillator of an AM (MW) receiver is such a distance from the received frequency that tracking between the antenna coil (ferrite rod) and local oscillator is tricky to set up. Usuallyyou have a set and adjust capacitances at the high end and inductances at the low end for sensitivity. Repeat until you find the optimum.

For the FM the 10.7MHz ceramic filter is connected through a resistor of 330 ohm. In other designs I saw for the FM two ceramic filters of 10.7MHz in series with a resistor of 100 ohm between them. For making the receiver maybe more precisely on the desired frequency I think.

Hard to say. Maybe it's a matching issue or an oscillating IF input that stopped when this resistpr was introduced.

The question is: to keep the manufacture of the radio design or to modify it as in the datasheet? For example the BPF88108 at the FM has too strong atenuation compared to an LC filter mostly find in comercial radio which are using TA2003P or CD2003 IC.

Also hard to say. If the BPF attenuates too much it is kaput. Datasheet?

P.S.: An off topic question. In the datasheet of TA7358 or LA1185 and even on TA2003P are given the same values for the FM 1,75 for the oscillator and 2,25 wires for the VHF. In other magazines there are 2,5 and 3,5 wires but those are calculated for the entire band including japanese band as is written for 76-108MHz. How can I spread the band and make the receiver receiving only 87.5-108MHz? I also made some modules with both TA7358 and TA2003P and both with those values received much more under 87,5MHz.

Those numbers create inductors of a certain value. Their value also is determined by the internal diameter, wire gauge, length of the coil and the presence of a core. These values also depend on capacitor values and the layout. You must calculate the values using a tool like the attached spreadsheet. Also usable for MW.

 

[andreidaniel]

Maybe that is part of the problem. The local oscillator of an AM (MW) receiver is such a distance from the received frequency that tracking between the antenna coil (ferrite rod) and local oscillator is tricky to set up. Usuallyyou have a set and adjust capacitances at the high end and inductances at the low end for sensitivity. Repeat until you find the optimum.



Hard to say. Maybe it's a matching issue or an oscillating IF input that stopped when this resistpr was introduced.



Also hard to say. If the BPF attenuates too much it is kaput. Datasheet?



Those numbers create inductors of a certain value. Their value also is determined by the internal diameter, wire gauge, length of the coil and the presence of a core. These values also depend on capacitor values and the layout. You must calculate the values using a tool like the attached spreadsheet. Also usable for MW.

Thank you so much, but tell me please what doest it mean "w/pader, trimmer"? With or without?

 

[PE9ZZ]

The padder is the capacitor in series with the tuning capacitor. As you can see in the spreadsheet, both sections of the tuning capacitor are equal. To get the proper range with the local oscillator it has to become smaller. The trimmer is the adjustment for the capacitance at the high end of the tuning range. The low end is determined by the inductor. Please read up on the basics of a superheterodyne receiver (which is what you are attempting to build). You are not the first one who finds this concept challenging in its century long history.

Fun fact: I just discovered that on FM (UKW) you don't need a padder because the frequencies of the RF and LO are much closer together.

 

[Binkman]

superheterodyne receiver (which is what you are attempting to build). You are not the first one who finds this concept challenging in its century long history.

Superheterodyne... a word you don't often read about. I'm not a tuner guy but sure are picking up some knowledge.


OP? got pics? would be nice/

 

[andreidaniel]

Hello!
I fooled the radio and now it works like a charm, undistorted and not covering other stations surround or about half of the band.
I changed the IF of the ceramic filters to a lower one. I read years ago that usually the IF for AM should be somewhere between 430 and 470KHz. So I had another filters like 450KHz.
I also found on the web that different filters have different results on the atenuation. Murata could be a good choice.
Instead of those SFU455B coupled via a capacitor of 1nF, because only one didn't succeed, I used a SFU450B directly coupled with a red filter A450BL.
I measured before the capacity between pins end I noticed that the original filters were inequal at their capacity. SFU450B is equals and also A450BL.
SFU450B has a little bit higher capacity between pins and A450BL has a lower capacity between pins.
I also found on the web last night a diagram with this integrat that is using somewhere a resistor of 75 ohm from the oscillator coil tap through the AM OSC pin of the integrat. This trick i also found on transistored based radios for the AM. There was a tap and from that tap a small resistor of about 22 ohm was coupled via a capacitor to the emitor of the transistor. In my case I inserted a resistor of 100 ohm between the oscillator coil tap and the AM OSC pin of the integrat.
The result is very good. Now I can hear clearly the stations. The top station is a little bit up of 1593KHz, as tested with another receiver making the difference of 450KHz the top should be arround 1600 or 1610KHz. The receiver goes down up to 486KHz. More than enough I can say. There aren't 'image frequencies' or 'harmonics'.
I can even tune nearby frequency arround the 603KHz where is the regional station (whice earlier took me under 500KHz and up too 900KHz), such as 630KHz durring the night or 576KHz. Also on the top part of the band I can easyly tune 1485, 1494, 1350 KHz very sharp, even the 1548 KHz with fadding and the weak station with same fadding 1593 KHz.
I adjusted the coils and the trimmers as someone told me and the sensitivity is almost flat, at the same level, not only a part of the band like before.
So the secret I think for this IC is the quality of the ceramic filters, to have a good separation, maybe two filters like in my design can be a great success and also, if there is an overlap, to change a little the IF of the ceramic filter for not creating other effects.

 

[PE9ZZ]

Glad to hear you got it going! So your filter was kaput.

 

[andreidaniel]

I guess so. But I tried some filters of 455KHz. Maybe one is not enough where is a strong local station, or it should be doubbled. even so, maybe to avoid some acrosage or pinching, I guess we can in some limits to change a little the IF for our purpose. Maybe could also use different filters with different attenuations to be the IF chain as a result, more similar to one made from real LC. We know that the old radios have 2, 3 or 4 stages for AM or at least the modern from the 80's or 90's have a standard : yellow, white, black. Even though they are tuned on 455KHz I guess they have differente impedance.

 

[PE9ZZ]

We know that the old radios have 2, 3 or 4 stages for AM or at least the modern from the 80's or 90's have a standard : yellow, white, black. Even though they are tuned on 455KHz I guess they have differente impedance.

Well, I for one didn't know. LC filters are completely different from ceramic ones. The latter provide much more selectivity in a very small package, something you cannot do with LC filters. They have very different properties necessitating a dedicated design like the TA2003P chip. The whole idea of this exercise is to make the radio as cheap as possible and they did a good job at the time.

 

[andreidaniel]

Do you know if there is any idea of project for using this IC on SW or LW? How many turns should have the coils? A similar IC KA2297 made by samsung also it was used on radio clocks.

 

[PE9ZZ]

Do you know if there is any idea of project for using this IC on SW or LW? How many turns should have the coils? A similar IC KA2297 made by samsung also it was used on radio clocks.

These ICs were intended for use on MW. Some manufacturers may have made an MW/LW version but almost certainly no SW version as the requirements for SW are more stringent than MW/LW. That said, you can use that spreadsheet to calculate those values. Fill in new coil values to get the correct frequencies and the spreadsheet should give you immediate results allowing you to iterate to an optimum solution. That is how I got all those values in the first place. I believe LW runs from 153 to 279 kHz (carrier). So your LO values are 153+455=608 kHz through 279+455=734 kHz. I took the liberty of starting for you (attached). I found I had to remove the padder. You will have to optimize some more, my peak error is 2.8% or 16 kHz at the low end.