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

[Wilko Bulte]

hi,

As a FYI:

Over the weekend I have checked 5 of these 5MHz MBF amplifiers. I think I can
conclude that Efratom/Ball has individually matched C41 and C42 to the 5MHz
center frequency. In other words: check what your amp has installed, even 1
capacitor might be > 180pF. Happened to me on one unit.

Sofar all amps I could get centered on 10MHz with 150 or 180pF total
capacitance.

Maybe even better 'peaking' can be achieved with a differen toroid coil but 
I decided that that was too much hassle (these things are attached to the
PCB globs of silicone sealant "goo").

Wilko

Quoting Wilko Bulte, who wrote on Mon, Nov 08, 2021 at 05:43:33PM +0100 ..
> 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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