Also, you don't say what the input caoacitance is. In my modeling, with an
assumption of about 4pf for chip and strays, the voltage gain is about 9
(19db), the resonance is a little below 400 mhz and you'd be about 10 db
down at 434 mhz. I agree with Tim...tune it.

Joe
W3JDR


"Tim Wescott" wrote in message
...
David wrote:

I am having trouble matching to the input of a SA605 at 434 MHz.

If I apply a sig gen directly to pin 1 via a 1n cap I get around - 95Bm
sensitivity. I then add my match and the sensitivity drops more than
10dB. I am expecting 10dB increase in sensitivity when input is matched
correctly.

First I tried matching to 800R as per input impedance listed in the
Philips APP note. I then noticed most applications matched to 1k5.

My current circuit is C-Tap (33pF to ground and series 5p6 to inductor).
18.5nH inductor (Q = 100) across input pins 1 and 2.
10n decoupling cap from pin 2 to ground.

Any help much appreciated.

Regards

David

You don't mention any adjustable components -- you _are_ tuning this
thing, right? Your circuit will have a loaded Q of around 5, so you
should see a pretty broad peak, but you will have to tune out all your
stray capacitance.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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