PHASE LOCK LOOPS AND DDS CHIPS

With today's current Technology it has become easier and easier to generate Stable RF Oscillators at low cost.

This is just an insight into what as a Radio and Television Amateur for over 40 years I have found in the about subject and wish to pass on the information to unmask these devices to you. 

Before the semiconductor age came of being down at the audio end of things we had to generate sync pulses by using  ECC81 valve dividers and diode pump dividers all very hot and a long while to stabilize themselves.

Then came along transistors and yet another learning curve going through different types of flip flops and trying all sorts of magic ways to up the speed by adding anti-saturation diodes so that the base of the device only had a little amount of current to turn it on and the rest was bypassed via the diode thus it would turn "OFF" faster. we got up to 70Mhz then along came TTL then CMOS right up to today's state of the art counters at 10,000MHz and beyond.

With the advent of stabile oscillators and the control (tuning) of these by adjustable counters all under u/P control we can now set frequency and even phase to a very high accuracy way beyond what is required for ATV use.

Because of satellite receivers PPL's (Phase Lock Loops) are cheap and easy to obtain such types as TSA5055T that will work up to 2.65GHz direct. This chip is set up with I2C protocol to the u/P (2 wire).

So far I have found the above chip in the G1MFG series of 1.2 and 2.3Ghz RX/TX's

Also the Steath 2.4GHz Video senders and a pair of these TX/RX for less than 100 I have not tried all other units but suspect they use said device.

So having written the software just once it then went into at least 8 units RX's and TX's from 1.2GHz up to 10GHz.

Other frequency generation devices are DDS chips that generate a sine wave from a look-up table and don't rely on counter and comparators and can even set up the phase to a very high degree. But the ones I have seen only work up to 50 or 100MHz but in time I expect these to take over from the PPL system. DDS chips produce a clean sinewave once filtered. One such device is the AD9850

 

 

 

You can divide down from a very high frequency by using counters that are called prescalers and you place these in front of a PLL and work fine.

Such a 10Ghz device is the FMM1103VJ Divide by 8 this only needs -25dbm @ 10GHz drive and it's output can be about +8dbm into 50 ohms.

 This device needs 5V @ about 90m/A Supply.

The above device would make a very sensitive Frequency Counter up to 12GHz and a frequency resolution of about 2KHz. All that is requires is a Div 256 prescaler and a PIC plus an 8 or 12 digit display.

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