In a message dated 25/10/2010 14:09:08 GMT Daylight Time, luciano.paramithiotti@hp.com writes: I have two distributors of frequency, one to be mounted in a rack where I have all my frequency reference and the other one in my laboratory to distribute the FX to the measuring instruments. --------------------- Unfortunately domestic restraints here, and the fact that another room is already racked out for equipment and parts storage, means that one room has to contain time and frequency, radio, and computing racks, as well as me, my desk, more shelving and my development/test/calibration area. I've just about squeezed in all I can and it's quite a tight fit, next step might have to be a serious crash diet:-) -------------------- I will limit myself to the described modification for the laboratory one, while in the rack that I'm going to completely replace the power supply with another constructed by me, always well a switching psu but well filtered and in a small metal box that helps shielding interference. ---------------------- I'm on a bit of a crusade right now, trying to eliminate as many switchmode PSUs from the lab area as possible. Radiated and conducted noise is not generally so much of a problem at signal levels normally associated with frequency distribution but it plays havoc at sub microvolt levels as I'm sure you also know only too well. There's a limit to how far I can move antennas away from the house and the noise levels from some switchmode wall warts in particular are horrendous. Even well constructed and shielded switch mode PSUs can play havoc at LF. ----------------------------- One additional note and that the original PSU also generates a lot of interference to the external power source. ---------------------- That doesn't surprise me. I've got some toroidal transformers that might just fit that 1U case and they've enough windings to allow a fully linear setup, so might give that a try. ---------------------- My goal 'to have a noise output of less than 1 mV pp measured without input signal. This' to avoid amplitude modulation that would increase the uncertainty of measurement for the phase noise and TIC. ------------------- I can't remember what the general noise floor was, as opposed to the pulsed interference, and the kit's all unpowered again right now, it was quite hight at LF but I would have expected 1mV to be attainable at 5 and 10MHz. --------------------- I have the operating manual of the Rapco. I think will be very difficult to have the schematic diagrams of this equipment. --------------- Fortunately the input and output buffer stages are highly repetetive so tracing the circuitry shouldn't be too difficult. The biggest aggravation is probably going to be getting at the underside of the PCB, I suspect that will entail an almost complete strip down of the case. ------------------ For radio use, I will recommend this high dynamic amplifier http://yu1aw.ba-karlsruhe.de/bfg135aeng.htm (single +12 VDC) followed by a passive splitter (ex.: minicircuit). ----------------- Thanks for the link. That's not the route I'd normally follow at LF/HF, I have commercial and ex-mil antenna distribution units if I need several signals from one antenna but generally try to just use minicircuits splitters without amplification where levels allow, or with a Norton amp if needs be, but will take a closer look at the device specs later. My antenna tests on the Rapco were really just for a bit of fun, and more out of curiosity than anything, but at least with an outdoor active vertical the LF noise floor was already comparable and, aside from the switchmode pulses, it did better than I was expecting With a decent loop it would probably be a different story. regards Nigel GM8PZR