EMRFD Message Archive 6256
Message Date From Subject 6256 2011-05-06 09:39:47 Pete N6QW Driving two DBM's from a single LO I am working on a project that might require the use of several DBM's and want to drive two devices (ADE-1L's, TUF-1's or SBL-1's)simultaneously. Aside from the different power levels that might be required for the DBM's (ADE-1L is a +3dBM device)any problem with just lifting the circuit from EMRFD Fig 6.132 and using the configuration of T8/T9 and the 2N3904 to do that task?
Thanks in advance
6258 2011-05-06 10:35:02 Wes Re: Driving two DBM's from a single LO No. The Fig 6.132 T8/T9 scheme is not for driving two double balanced mixers simultaneously. Rather, it is a T/R scheme where LO or BFO energy is switched in and out of the mixers.
What you want is a hybrid of some sort. The "Magic Tee" of Fig 3.81 is used throughout the book, although I guess we didn't use that term. Take a look at Figures 6.150, 9.21, 9.22, 9.29, 9.40, 9.62, 9.83, 12.48. I'm sure there must be many more places where the same circuit is used.
6259 2011-05-06 13:34:31 RadiosRUs Re: Driving two DBM's from a single LO Hi Wes,
It looks like figure 3.81 will do the trick.
To match to the 25 Ohm input if the hybrid, I believe if I used 10 Turns on a FT37-43 and tapped that at 7 Turns above ground, I think that would provide a 2:1 transform from the 50 Ohm output of the LO to the 25 Ohm input. In doing some further research I think KK7B used something similar for one of his direct conversi
6260 2011-05-06 19:06:15 kb1gmx Re: Driving two DBM's from a single LO 6261 2011-05-07 07:00:55 ha5rxz Re: Driving two DBM's from a single LO Generate your LO signal at twice the needed frequency and feed it into a divide by 2 flip flop. The Q signal goes to one mixer and the NOTQ signal goes to the other, both via a suitable matching network. This method has the advantage of generating a perfect 50/50 mark-space ratio which will reduce unwanted signals.
6264 2011-05-07 10:50:43 Wes Re: Driving two DBM's from a single LO Pete,
The reasons to use the hybrid are to preserve termination for the two sides, even if the other load (mixer) disappears and to isolate the two load sides. The isolati
6265 2011-05-07 22:25:48 victor Re: Driving two DBM's from a single LO In some cable TV splitters they discard the resistor too. I guess they depend on the ferrit bead loss to represent the between outputs resistance close to 150 Ohm.
Victor - 4Z4ME
6373 2011-06-06 13:48:55 jallade Re: Driving two DBM's from a single LO