RF CKT Matching Question

You can just put them together, without an extra resistor. The 50 Ohm resistor would actually cause a mismatch.

However, if both devices without the matching network are on the same side of 50 Ohms, it might be better to make a single matching network to match the actual impedances of the adjoining devices to each other.

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--Larry Brasfield
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Larry Brasfield
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I have to connect the output of a SAW filter to an amplifier input. The SAW filter output is not 50 Ohms and the amplifier input is not either. But the manufacturer of the SAW and the amplifier provide matching network schematics assuming 50 Ohm termination.

My question is do I need to put an explicit 50 Ohm resistor between the two matching networks or can I put the two matching networks together directly?

SAW -> match1 -> 50 Ohms -> match2 -> amp

or

SAW -> match1 -> match2 -> amp

Thanks,

Reply to
Jack J

Fred Bloggs" wrote in message news: snipped-for-privacy@nospam.com...

(Responding to the question: I have to connect the output of a SAW filter to an amplifier input. The SAW filter output is not 50 Ohms and the amplifier input is not either. But the manufacturer of the SAW and the amplifier provide matching network schematics assuming 50 Ohm termination.

My question is do I need to put an explicit 50 Ohm resistor between the two matching networks or can I put the two matching networks together directly? )

[pointless name-calling cut]

of broadband resistive termination.

The SAW filter does not depend on broadband termination for its selective frequency response. The amplifier with an input matching network will have broad enough real input range to permit the filter plus its matching network to see the load for which it was designed, in the vicinity of its passband. At frequencies where the filter load becomes significantly complex, well outside that passband, the response will be different than if a resistor was the load, but it should still reject.

If the OP wants stop-band response that looks like the SAW spec sheet, he will have to insert either a broadband matching network or a 50 Ohm attenuator. But if he cares that much, he would more likely take my suggestion about devising a custom matching network.

So, Fred, what is your constructive suggestion?

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--Larry Brasfield
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Larry Brasfield

How can you say that, pretentious retard? All the device characteristics, especially the filter, are defined in terms of broadband resistive termination. Looks like RF is another area you know damned little about.

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Reply to
Fred Bloggs

My constructive suggestion to the OP is to not waste time listening to you, you obviously have no clue what you're talking about.

Reply to
Fred Bloggs

Most amplifers don't care much about what they "see" at their input. However most SAw devices do care about what they see at their output. You need to design a matching ckt that converts the amplifers input impedance to the provide the load impaedance that the SAW wants to see. Don't worry as much about what the amplifier sees. Depending upon what these values actually are, i.e. uif the amplifer input Z is very high, it may be helpful to add a resistor somplace in the network to help to define the Z.

Mark

Reply to
Mark

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