On 9 August 2013 14:09, Bob Camp <[email protected]> wrote: > Hi > > A few observations: > > 1) He talks about using a heat sink on the front panel, but then never shows > it / does it. The fan inside the box is not going to cool that Rb the way it > needs to be cooled. You either need a pretty massive heat sink on the front > panel with no fan or something smaller with moving air.
That was what I thought too. It does not look to clever to me. > 2) If the video amps are set up the way he shows (three outputs per amp) then > when you put three terminated 50 ohm lines on them, the amp is trying to > drive (50+50)/3 = 33 ohms. I suspect it's not to happy doing that. TI rates > them at a >= 100 ohm load resistance …. I don't have the video in front of me, but I thought he was basically making the input a high impedance. 100 Ohms would be fine then if one used a 50 Ohm source impedance and a 50 Ohm load. > 3) If you pick up the TDK power supply he's using, it's marked "air flow goes > this way". He never seems to mention that. (maybe I blinked when he did….. > the video sort of goes on and on). I have my doubts there is enough air there. > 4) If you are going to all that trouble, *and* have a big back panel, why not > bring out the serial lines from the Rb to a DB-9? Then you could tune it on > frequency …. Interesting idea. > 5) An Rb is sensitive to mag field. That should be part of what you consider > when you place the power supplies and the Rb. > 7) If you have that much room, and want to do it right, lock up a OCXO to the > Rb and take care of it's awful phase noise and spur issues. > > 8) I think a cutting disk on a Dremel tool would make short work of the > standoffs that he's so worried about … Yes. > 9) There are many examples out there of why video editing is a good idea. > You could have chopped a *lot* out of that video …. To be fair, not everyone wants to spend their time editing video, and its good of him to put it on the web. > Overall, the heat sink on the Rb is the biggest issue by far. The practical > approach is to put a fan on / near the bottom of the thing. If you are going > that way, servo the fan and control the temperature. My distribution amp arrived today. The more I look at it, the more I think it is best left as a distribution amplifier and the Rb is not put in the box. With no changes, one can put a signal into the first input, and take one of the 6 outputs to the input of the next input. Since there are 3 inputs, with 6 outputs per drive, one could use it as a 16-way unit with no changes at all, and leave the flexibility of using it for something else if the need arose. I personally would find 16 outputs sufficient. I'm tempted to put my Rb in another box, with a linear supply and enough room for a GPS locking device. Then take the output of that other box and feed it into that distribution amp. Sure it is bigger than his, but I don't like the idea of a heat sink on the front, and I can't see how one is going to cool that very well. Maybe it will be fine if you have an air-con unit and have that moving air around the external heatsink, but I don't keep my aircon on all the time. Electricity is quite expensive in the UK - we are subsidizing all the next to useless wind farms. </gripe> > Bob Dave _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
