These are handy little boxes for the money. Unfortunately the outputs are not isolated from each other (galvanically and signal-wise) so be mindful that if you connect/disconnect one port, the adjacent port will be affected. Unless you need to, it is probably best to wire all 3 inputs in parallel (with a single 50 ohm termination) and use only one output from each buffer. That still gives you 3 or 4 channels with reasonable isolation. The next step would be to replace the output BNCs with plastic-body types and install isolation transformers for full galvanic isolation (no ground loops).
Didier On Sun, May 19, 2013 at 3:58 AM, Charles P. Steinmetz < charles_steinm...@lavabit.com> wrote: > Chris wrote: > > I have been offered one of these: >> >> ADA 6 300MX HV HDTV RGBHV 1 x 6 Analog Video Distribution Amplifier >> >> I *THINK* it should meet my needs except the HV bit worries me. It >> seems this means it has not got unity gain, but a gain of 0.7 or 1 >> volt, switch selectable. Could anyone comment if it's suitable to use >> my Trimble Thunderbolt with several pieces of test gear at the same >> time? Thanks. Here in the UK the ADA-3-80 seems a rare find. >> > > "HV" just means that it has an additional sync channel ("Horizontal and > Vertical"). I think "MX" means selectable gain. I have two plain ADA 6's > (no MX, no HV) that I used before I built my own iso/DAs. The gain > switching components are present, but the switch itself is not populated, > so it runs at unity gain overall (the amplifier runs at x2 and each output > is back-terminated). > > My ADA 6's use 6, CLC409 amplifiers and, when modified with 50 ohm input > and output terminations, each section (3 jacks) can drive 3, 50 ohm outputs > to +13dBm with ~1dB of headroom (I generally only fed 2, 50 ohm loads from > any one section). Like any video DA, it should have much smaller coupling > caps installed to restrict its low-frequency response to HF. > > You need 21, size 1206 (SMD) 50 ohm resistors and some 100 nF capacitors > to do the mod (I used NP0 ceramics). You also need a deep socket (9/16", I > think) to get the PC card dismounted from the back panel (it is mounted by > the BNC connectors). > > As supplied, there are 3, 1x6 DAs in the box. You can parallel inputs > internally as desired (deleting duplicate input terminations) to make one, > 1x18 DA or one each 1x12 and 1x6 DAs. You really shouldn't have more than > one HF reference frequency running around inside a DA, so the 1x18 > configuration is probably the most useful. > > I was quite happy with mine for routine distribution of 1/5/10 MHz. > > Best regards, > > Charles > > > > > ______________________________**_________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/** > mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.