RF Buffer Design

[AV]

Lets try and start a discussion!<br>
If I wish to design a buffer to isolate an oscillator from a counting circuit, what options do I have?<br>
To be more specific this is a Hartley type oscillator running at a nominal 100MHz whose output I wish to count. So I want to use the frequency to clock a high speed counter. What I don't want is any effects from the counter (or the buffer) to be propagated back to the oscillator.<br>
My experience at these sort of frequencies is limited. <br>
I'm hoping this will develop into a discussion of high speed buffers in general!

 

[Gail]

Hardly worth the effort now adays... HP, Minicuicuits, Triquent all have MMIC's that cover this requirement for under $2... these parts are in surface mount for direct PC mount. <br>
<br>
Check Mini-Circuits web site... and HP's web site for complete specification... <br>
<br>
Typically they MMIC's will have 15 to 20 dB Gain and 30 to 40 dB Isolation and work from 50 to 500 MHz.<br>
<br>
Regards -Bob Griffith -

http://www.engineers.com

 

[adc]

The ARRL Handbook (hams still do hardware---sometimes) is published yearly and has distilled information on rf circuits and techniques.

Still one of the best desert island books on electronics.

Any library has one--my first exposure to hamming was a 1948 edition in the high school library about 1954.

&quot;Rolling your own&quot; is a good way to learn, even if not the cheapest or fastest way to do something.

 

[jbartos]

Suggestion: It appears a properly designed notch filter will meet your specifications and safeguard Hartley Oscillator.

 

[johnday]

1.. MMIC type amplifiers are rarely suitable for providing this type of isolation and buffering. The input impedance of the buffer should be high to prevent loading of tha oscillator and the buffer stage should have good reverse isolation (S12) specs.

2.. A discrete buffer using a single FET as a source follower (common drain satge if you prefer) or a bipolar transistor as an emitter follower will be more appropriate.

Suitable JFETS wound be 2N4416, 2N4859 or any similar moderate Idss RF type. You could also use the same device you have in the oscilator (you dont mention what it is).

What type of counter circuit are you planning to use? That may affect things as well.

John Day
Technical Director
Words & Images

 

[nbucska]

Use a line receiver e.g. MC100EL16 to translate it to ECL
or PECL.

<nbucska@pcperipherals.com>