David,

What type of inductor are you using ? SMT can be sensitive with
proximity issues.

Are you 100% sure that capacitor values are as you hoped - SMT can be a
pain to verify.

Note, I did drop the 33pF to 15pF to improve return loss.

The 6.5pF cap is the most sensitive of all parts in the cct.

Any chance of a photo of the input network and signal coupling ?

My current bet is an inadvertently loaded wrong value component. Been
there, done that etc.

Regards,

Mark

===========

David wrote:
Mark,
Yes, that's the circuit I am having trouble with.
Regards
David

MarkAren wrote:
David,
http://www.geocities.com/markaren10/misc/SA605.gif
You had this in mind ??
Mark.

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