Hi As you go to ever narrower filters, the phase shift / group delay of the filter goes up. Just how much very much depends on the filter type, filter order.
With something like a 5 or 10 MHz Rb, narrow filters can get you into trouble as the temperature changes and it. The edge of your output can shift by quite a bit. This degrades the timing accuracy of the signal. With narrow filters, it can impact the frequency stability. Bob > On Dec 13, 2021, at 9:34 AM, Wilko Bulte <[email protected]> wrote: > > 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. > > > > > --- End of quoted text --- > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send an > email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
