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.
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.
For good selectivity you need proper RF design, with decent high-level double-balanced mixer and a quality LO with low phase-noise - single chip solutions will never perform very well by comparison.
However you may be able to enhance the performance with a good tracking pre-selector.
However you may be able to enhance the performance with a good tracking pre-selector.
Your answer made me think of the various ex government forces valve communications receivers I have ,built like tanks but having 2-RF stages -separate oscillator -3 IF stages and a host of other stages to help stability including competent noise reduction - bandspread etc .
When solid state models first came out they were criticized as not up to the same spec. as the older valve units but those old sets are safe from atomic radiation air blasts which (I am told ) is no longer a danger to solid state designs.
When solid state models first came out they were criticized as not up to the same spec. as the older valve units but those old sets are safe from atomic radiation air blasts which (I am told ) is no longer a danger to solid state designs.
Looking at the block diagram for the chip last night, I only saw a couple of spots for selectivity in AM mode: the antenna input, and the mixer output.
As stated, instead of an untuned input, you could use the traditional loopstick tuned by one of the tuning capacitor gangs. That would also give you some directivity from the antenna. A tracking preselector would be difficult for an inexperienced builder to homebrew, but would be even better.
You could use a better filter at the mixer output, either ceramic or a Collins mechanical, or make a crystal filter. An audio filter can also help some. Edit: or make an LC filter from 455 KHz IF transformers, they are still available and inexpensive and should have less loss than ceramic filters.
The AGC only controls the one IF amplifier, so AGC range may not be very good under any circumstances. A really fast AGC is typically used with AM; reducing the value of that AGC capacitor might help some.
Looks like a fun project!
Edit: about the red oscillator coil, can you measure the RF voltage? The sensitivity may be changing because the oscillator does not have constant amplitude output. You may need to adjust the coil for constant output, or as close as you can get to it.
As stated, instead of an untuned input, you could use the traditional loopstick tuned by one of the tuning capacitor gangs. That would also give you some directivity from the antenna. A tracking preselector would be difficult for an inexperienced builder to homebrew, but would be even better.
You could use a better filter at the mixer output, either ceramic or a Collins mechanical, or make a crystal filter. An audio filter can also help some. Edit: or make an LC filter from 455 KHz IF transformers, they are still available and inexpensive and should have less loss than ceramic filters.
The AGC only controls the one IF amplifier, so AGC range may not be very good under any circumstances. A really fast AGC is typically used with AM; reducing the value of that AGC capacitor might help some.
Looks like a fun project!
Edit: about the red oscillator coil, can you measure the RF voltage? The sensitivity may be changing because the oscillator does not have constant amplitude output. You may need to adjust the coil for constant output, or as close as you can get to it.
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Hello! The radio bought has a loopstick antena and dual variable capacitor for both AM RF and LO and FM RF and LO.
Someone gave me in the same time some advices like:
-to pick a station at the low end of the band and adjust the red LO coil so that the station is correctly located on the dial;
-then slide the winding on the ferrite rod for maximum output
-then go to the high end of the dial and choose a station and adjust the LO trim capacitor on the back of the variable tuning capacitor so that the station appeared at the correct position
-then adjust the front end trim capacitor on the back of the variable capacitor for maximum output
I tried them step by step and the result was the following:
I have a TCM radio with electronic tuning and display and another radio with traditional scale with CD2003GP.
When I tune the TCM radio to 972KHz, the radio with traditional scale using CD2003GP stopped at 1427KHz.
The list of the station should be: 603KHz regional radio with strongest signal, 1053KHz another radio station but from a different county with a lower signal here, 1179KHz other radio station with lower signal, 1485KHz - RVS with good signal here, 1494KHz - Radio Moldova with lower signal, 1530 KHz a radio station with weak signal.
In Europe the radio stations have a bandwidth of 9KHz.
After the adjustments from last night the radio with CD2003GP can tune up to 1427KHz as I recognised today. Below 603KHz I can tune the the rest of the band.. between 1400-1600KHz.
P.S.: It could be a solution replacing the ceramic filter with an IF coil with primary and secondary but the problem is that between those pins 4 and 7 and the V+ the ceramic filter could act like a capacitor and I think that the coil could short the circuit in a way. Maybe an ideea would be to isulate the top of the primary and secondary of the coil via a capacitor of maybe 51pF at both ends to pin 4 and 7 for not creating the short circuit and the common wire to be soldered to V+
Someone gave me in the same time some advices like:
-to pick a station at the low end of the band and adjust the red LO coil so that the station is correctly located on the dial;
-then slide the winding on the ferrite rod for maximum output
-then go to the high end of the dial and choose a station and adjust the LO trim capacitor on the back of the variable tuning capacitor so that the station appeared at the correct position
-then adjust the front end trim capacitor on the back of the variable capacitor for maximum output
I tried them step by step and the result was the following:
I have a TCM radio with electronic tuning and display and another radio with traditional scale with CD2003GP.
When I tune the TCM radio to 972KHz, the radio with traditional scale using CD2003GP stopped at 1427KHz.
The list of the station should be: 603KHz regional radio with strongest signal, 1053KHz another radio station but from a different county with a lower signal here, 1179KHz other radio station with lower signal, 1485KHz - RVS with good signal here, 1494KHz - Radio Moldova with lower signal, 1530 KHz a radio station with weak signal.
In Europe the radio stations have a bandwidth of 9KHz.
After the adjustments from last night the radio with CD2003GP can tune up to 1427KHz as I recognised today. Below 603KHz I can tune the the rest of the band.. between 1400-1600KHz.
P.S.: It could be a solution replacing the ceramic filter with an IF coil with primary and secondary but the problem is that between those pins 4 and 7 and the V+ the ceramic filter could act like a capacitor and I think that the coil could short the circuit in a way. Maybe an ideea would be to isulate the top of the primary and secondary of the coil via a capacitor of maybe 51pF at both ends to pin 4 and 7 for not creating the short circuit and the common wire to be soldered to V+
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.
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.
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.
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.