[time-nuts] Efratom MBF 5MHz distrib amp schematics & conversion to 10MHz

[Wilko Bulte]

hi,

With many thanks to my ham pal Robert PE1MJA for patiently reverse
engineering it please find attached the schematics for the Efratom MBF 5MHz 
distribution amplifier.

Note that the MBF distrib amps come in different versions, the schematics 
show the 5MHz in / 5MHz out version.

Given that we want to use them for 10MHz a small change proved to be
required: 

- in the 1-st stage removing the 750pF capacitor (center bottom) made the 
center frequency of the amp move to 10MHz. That cap is in parallel with an
180pF cap, leave that one in place. The cap to be removed is marked as C42
on the PCB silkscreen.

The amps are quite narrowly 'peaked' on their design frequency, in its original
form the MBF was not much of an amp for 10MHz.

We have both MBF with BNC outputs, as well as units for internal
distribution via their DIN41612 rear connectors. Both versions have 
slightly different parts values in places.

In two of my own units I found 2 different values for C42. Regardless,
ensuring that the total capacity is at ~180 pF peaked the amp at 10MHz. So,
also do inspect the cap in parallel with C42.

Yet to be resolved is the red Fault LED remaining lit with 10MHz, for now I
am ignoring that one.

Wilko
PA1WBU

NB: I also attached an OpenDocument spreadsheet with the connector pinouts 
for the various modules.
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