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Buffer Amplifier Design for tapping a 21.4 MHz IF Output

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blantonl

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Folks,

Does anyone have an easy to implement buffer amplifier design example for use in tapping the 21.4 MHz IF Output of today's common scanners?

Note: this is different than the discriminator output.

I am interesting in tapping the IF Output of a few of the radios that I own for some special decoding projects, and I need to protect the signal... if someone has a good easy to implement design for a buffer amplifier to accomplish this that would be great.

.. thanks in advance!

Lindsay
 

gmclam

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A couple of devices from a quick search

Hello. It seems with today's communications ICs, there should be lots of stuff out there ready to go. It sounds like what you need is a buffer with a high impedance input, that can drive a decent load, be powered from the receiver you're tapping (low voltage), and pass 21MHz.

My first thought was to check and see what Analog Devices has to offer; and I came back with these two devices. A potential problem with this first one is that it has a fixed gain of 19dB. Perhaps that is not a problem (or something you need) for what you want to do.

ADL5530 DC to 1000 MHz IF Gain Block
http://www.analog.com/en/prod/0,,759_846_ADL5530%2C00.html

This is just a second choice that appears they want to use for video but is rated at 110MHz. You might check out the spec sheets to see if they fit your needs.

AD8051 Low Cost, High Speed, Rail-to-Rail Amplifier (Single)
http://www.analog.com/en/prod/0,,759_775_AD8051%2C00.html

The next places I'd check are Texas Instruments and Motorola semiconductor, but there are quite a few devices out there.

Good luck
 

prcguy

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You can use a Mini Circuits or similar connectorized amplifier, check Ebay item # 280212134814. Its easy to tap off a little 21.4MHz IF using a few pf cap and a short coax jumper to a BNC or SMA connector on the back of the radio. Might be good to terminate the connector with a 50 to 100 ohm resistor just in case the external amplifier is prone to oscillate with wacky loads.
prcguy
 

blantonl

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Thanks Guys... I'm going to take a look at the ADL5530 - app notes show it might be a good fit.
 
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