Roelof

Had an opportunity to build 6 of the Amrad CP666 e probes (for a military customer) a while back and measured the following. First column is measurments from the QST article, second column is measurment average of the 6 antennas built (all measured within a dB or so of each other), third column Amrad circuit with single J310 at 12 volts and fourth column single J310 at 24 volts.

Measured significantly higher IP2 than the original article leading me to believe there might have been a measurement error in the original article...or I got a batch of CP666s that were unusally good performers. The fact that the J310 at 12 volts achieved +50 dBM makes me lean toward possible measurement error in the original article.

Hope these columns stay lined up when passing through the reflector! 

                      Amrad article         W1VD built           J310 12volt       J310 24 volt
                       
 
1 dB comp.    +25 dBm                +25 dBm            +17 dBm            +18 dBm
 
IP2                +53 dBm*              +60 dBm             +50 dBm           +60 dBm
 
IP3                +37 dBm                +36 dBm             +32 dBm           +32 dBm

Gain              -16.7 dB                 -16.5 dB               -10 dB              -10 dB

* possible measurement error

Jay, W1VD