David,

Be careful of that "Match Efficiency" number read out by the MFJ. I
don't remember what they are showing, but I do remember there was a caution
in their manual about just what it was and that it was a rather crude
indicator. Some over simplified readout.

73, Steve, K,9.D;C'I


"David" wrote in message
...
Amos,

The circuit is passive (R/L/C) only. I would not expect any non-linearity.

I suspect the previous post may have been correct. The match was over a
large ratio of impedance (50 Ohms to 4500 Ohms). I expect the small
value of inductor and reasonably low Q was limiting the performance of
the circuit.

I tried the match again from 50 Ohms to 800 Ohms as a test and found the
MJ-269 showed match efficiency of 90% with SWR dropping to 1.8. These
results are much better.

Regards

David

Amos Keag wrote:
Have you considered that there may be non-linear effects in the test set
up?

The MFJ uses several to ten milliwatts in it's circuitry [+10 dBm].
Sensitivity is generally measured at the pico-watt [~ -130 dBm] level.

AK

David wrote:

Hi,

I have a matching circuit that matches 50 Ohms to 4500 Ohms in
parallel with 2.5pF at 45MHz.

The coil was measured at 147nH with a Q of 50 at 45 MHz.

The circuit is a C-Tap typology with following values.

Tap input to ground = 784pF
Tap to hot side of coil = 92pF
Par inductor = 147nH

My design calculations predict Loaded Q = 26 and BW = 1.7 MHz.

I used a 50p trimmer in par with 68pF cap for top of tap to fine tune.

A 4k7 resistor and 2p2 cap were placed across the output to simulate
the correct load.

The test results show BW = 1.7 MHz and Loaded Q = 24.7 (agree with
calculated values).

When installed on the IF front end, the expected sensitivity is
achieved when tuned. This would indicate most of the signal must be
getting through or sensitivity would be effected due to mismatch.

All seems to look ok but when I attach the MJF-269 Analyzer I get
impedance of 280 angle 35 degrees (240 -j 179) for the impedance, I
get SWR = 6.1 , return loss of 2.8dB and match efficiency of 48%.

I cannot understand why there is such a discrepency between the design
values and tested results (using sig gen, spectrum analyzer and power
meter) compared to the MJF-269.

Is there something I am doing wrong here or is it a mis-interpretation
of displayed values ?

Thanks for any help.