as I received several emails with questions about the preamplifier which I am using for my LB external RX antennas like W2PM MiniDiamond loop, EWE loop, K9FD loop etc. I decided to post over here some informations about this unit.
The basic design is inspired with his permission by Larry, W7IUV. The complete article about his preamplifier was published on his web here:
The size, shape and terminals has been choosen according to my alu-case available...
The most important part of this design in my opinion is the transformer and working state of the transistor 2N5109. You must follow the winding rules as same as core material for transformer and finally you must use prescribed current of the transistor in order to reach expected performances.
If you are interested in the suppliers for Amidon, Fair-Rite cores or even you have problem with finding the 2N5109 there are some links which I used...
The heatsink on the transistor is a must. Do not change the resistors in order to decreasing the collector current of the transistor! These conditions are key parameters for high IMD immunity / OIP3 performance...
Testing the assembled preamplifier is straight forward. Before applying power double check your work. The most common problems are solder shorts and resistors inserted in the wrong place. Once you are satisfied you have correctly assembled the circuit place 50 Ohms terminations on the input and output.
Hope it helps.
73 - Petr, OK1RP