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LCD frequency Display for FM transmitter

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fasti

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Hi Everybody,

I want to make a Frequency Display for my Analog Fm Transmitter.
Would a couple of 4060 ICs do the trick?
I need aprox. 100M division, so two 2^14 divider ICs would do.
But would they work if the input is the ANALOG fm signal?
Must I give them a digital input?
and how do you turn their count to a Number for the LCD/7seg?
Should I count them in a BCD counter and add a BCDto7seg for the display?
and if so, do i have to reset the counter every 1 sec to count correctly?

...isn't there a SINGLE IC that does that?
(but without a transmitter, cause I want to use mine...
and without a Programmable IC, cause it's not fun...).

thanx for any response... :)
 
Assuming this is a 'toy' bug type transmitter you're just wasting your time, they drift all over the place.

But what you're looking for is a frequency counter!.
 
The 4060 has a maximum clock frequency of about 12Mhz, so they will not work at 100Mhz (I assume by "FM Transmitter", you mean something which transmits in the VHF broadcast band).

There are many circuits available for frequency counters, do a google search.

JimB
 
that didn't really answer my question...

Yes, well, thanx for your fast response,
but.. that didn't really answer me..

so, would a frequency counter be able to "read" an FM signal from the tank circuit even though it's not digital (can it work with a sine)?
(and I can't seem to find a frequncy counter/divider that works in the 100MHz area... please if anybody already knows one...)

And you didn't tell me, how does the frequency divider/counter make the 7seg value?
the output just goes up and down...
In a BCD counter, does it reset itself every 1 sec?
So wouldn't the display show the counting? 0,1,2,...100,000,000....
 
fasti said:
Yes, well, thanx for your fast response,
but.. that didn't really answer me..

so, would a frequency counter be able to "read" an FM signal from the tank circuit even though it's not digital (can it work with a sine)?
(and I can't seem to find a frequncy counter/divider that works in the 100MHz area... please if anybody already knows one...)

They are usually ECL, TTL is too slow, you usually square the signal before feeding it to the counter.

And you didn't tell me, how does the frequency divider/counter make the 7seg value?
the output just goes up and down...
In a BCD counter, does it reset itself every 1 sec?
So wouldn't the display show the counting? 0,1,2,...100,000,000....

You count only for a certain time, depending on frequency and resolution. EPE have recently done a 50MHz PIC based one, which is by far the simplest and cheapest method.
 
digital freq. counter counts pulses during gate time. when gate is off, counted value is latched and displayed and counter is reset. this is repeated over and over. all user gets sto see is "static" latched values. gate time can be anything but 0.1, and 1 sec are not unusual.

once you have counter, it's time to think how to interface it to particular source of oscillations. if the frequency of the source is higher than what counter can do, it is common to simply add prescaler (divider).

if the prescaler divides by 10 or 100 or even 1000 you don't need calculator to figure out what is input frequency, just shift result in your head by appropriate number of places. if prescaler is going to be permanent part of the freq. counter, instead of dividing by 10, one could simply divide by 16 (or any other binary number) and adjust gate time.

if the signal is weak, it needs to be amplified (well you don't want your counter to be significant load to the circuit anyway). atenuation plus amplification is usually good enough as "conditioning" because overamplification results in clipping anyway making signal more or less similar to square....

here are some nice links:

https://www.qsl.net/n9zia/pre/index.html
 
thanx a million...

really man, thanx a lot.

Thank you all for your help.

so, should the prescaler or counter (the one I choose to use on the tank circuit) affect the carrier frequency?
Need I add anything to prevent frequency change?
(I'm hoping that the answer is 'no', or 'just add a capacitor'...).
 
Last edited:
Anything that connects to or even gets near the tank will change its frequency.
 
fasti said:
really man, thanx a lot.

Thank you all for your help.

so, should the prescaler or counter (the one I choose to use on the tank circuit) affect the carrier frequency?
Need I add anything to prevent frequency change?
(I'm hoping that the answer is 'no', or 'just add a capacitor'...).

You need a buffer, and even that will affect the 'bug' type transmitters.
 
A prescaler with a buffer might even stop the oscillator in a simple bug FM transmitter.
 
If you're going to go to all this trouble then why not just build a propper PLL transmitter so you can set it to an exact frequency rather than messing aroung tuning it.
 
You don't mess around tuning an FM bug.
You simply move it near something or let its battery voltage run down a little to change its tuned frequency.:D
 
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