frequency ??

[Linga]

Hi all,

Help me in calculating the frequency of LC circuit at pins 5 and 6.
http://web.telia.com/~u85920178/rx/tda7000.htm

Thank you

[Daniel7866]

Hi all,

Help me in calculating the frequency of LC circuit at pins 5 and 6.
http://web.telia.com/~u85920178/rx/tda7000.htm

Thank you

Hi,

Here is part of answer http://en.wikipedia.org/wiki/LC_circuit .

Since C total varies between 6.5pF and 14.6pF and L1 is unknown, you can't compute f.

Daniel

[Acetronics]

Hi,

What about a look HERE : http://www.search.philips.com/search/search?q=TDA7000&s=semi&l=global&h=semi

Alain

PS ... with little patience: http://web.telia.com/~u85930032/ta7000d.zip

[Linga]

Hi,

Here is part of answer http://en.wikipedia.org/wiki/LC_circuit .

Since C total varies between 6.5pF and 14.6pF and L1 is unknown, you can't compute f.

Daniel

Dear Daniel,

I understood this formula!!

according to datasheet L=56nH, To me confusion is arround capacitors.... so many cap.... all forms ( series and parallel), it is here I am finidng difficulty, my calculation shows VH frequency (arround 150MHz) but the receiver works in the range 1.5MHz to 110MHz???. That why I want to know how to f in this case......

[Eric_N57105]

Dear Daniel,

I understood this formula!!

according to datasheet L=56nH, To me confusion is arround capacitors.... so many cap.... all forms ( series and parallel), it is here I am finidng difficulty, my calculation shows VH frequency (arround 150MHz) but the receiver works in the range 1.5MHz to 110MHz???. That why I want to know how to f in this case......

The layout of the caps is shown in the illustration below. The 22p and 18p caps are in series and the 4p cap is in parallel with that.

THIS circuit doesn't tune from 1.5 - 120 mhz. The TDA7000 is CAPABLE of tuning that given the appropriate LC circuit (or resonator) at pins 5 and 6.

Looks like your calculation of the resonant frequency for this circuit is about right.

Eric
www.ke6us.com

[Linga]

Hi Eric,

In the following picture, Can you please suggest the values at 5 and 6 pins for 72MHz.

[Eric_N57105]

Hi Eric,

In the following picture, Can you please suggest the values at 5 and 6 pins for 72MHz.

First, what is it you are trying to accomplish. Are you trying to build a 72 mhz single conversion receiver? If so, you need spend a little time with the TDA7000 datasheet and AN193 Application Note:

http://www.semiconductors.philips.com/acrobat_download/applicationnotes/AN193.pdf

The application note provides info on designing the crystal oscillator.

You should probably look into some other receiver circuits. Most use the TA31136 chip, but you will gain valuable insights for using any of these FM detector chips.

Quite often you can recalculate given LC values for another frequency by first calculating the reactance of the L and C components at the published frequency, then calculating the new L and C values at the new frequency so they have the same reactance. It's often a good starting point for quickly arriving at experimental values.

Eric
www.ke6us.com

[Linga]

Hi Eric,

I have seen circuits using all these IC, mc3361,TK83361, TA31136 etc.... They require filters more over mixture input should be 10.7MHz.... etc I don't like these IC...

TDA7000 circuit is so simple.... only capcitors..... I like this kind of simple circuit. That's I selected.

[vintage1]

Yes, but the TDA700 uses an IF down arond 5Khz, which means that it will use a completely non standard crystal. It will also have an appalling image problem at 10Khz away - just where the next channwle is in RC.

The only things you need to change for 72Mhz operation are these around the crystal oscillator. Inclduing a non standarrd TRANSMITTER crystal which you MAY be able to pull enough to get the thing in tune..