"Amos Keag" wrote in message
...
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


These seem like horrendously large capacitors to use at 45 MHz.


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).

For an unloaded Q of 50, I would shoot for a loaded Q of around 5. If you
plan to put any power through this, try getting the unloaded Q up to around
200, with a loaded Q of around 8.

My guess is that if you remove the 4.7K, the impedance at the other end of
the network will not change all that much.

Tam/WB2TT