[time-nuts] RAPCO 1882M-2 autochangeover distribution amplifier

[Paramithiotti, Luciano Paolo S]

Hi Nigel,

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. 

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.

One additional note and that the original PSU also generates a lot of interference to the external power source.

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 have the operating manual of the Rapco. I think will be very difficult  to have the schematic diagrams of this equipment.

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). 

Ciao, Luciano

Luciano P. S. Paramithiotti
IZ5JHJ


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of GandalfG8 at aol.com
Sent: domenica 24 ottobre 2010 2.14
To: time-nuts at febo.com
Subject: Re: [time-nuts] RAPCO 1882M-2 autochance over distribution amplifier

 
In a message dated 22/10/2010 14:09:13 GMT Daylight Time, luciano.paramithiotti at hp.com writes:

I bought  a distribution amplifier Rapco model 1882M-2 auto changeover on ebay. This  distribution amplifier was intended to be used in conjunction with a GPSDO to  distribute 5MHz and 1PPS.

It has two inputs for 5MHz and and two for  1PPS, and have nr14 5Mhz outputs and two 1PPS. Switching between the two  couple of input is automatic. 
Normally each master input works, when the the  master drop,the input source is switched to the second input.

This  equipment uses wideband amplifiers  with ft100 MHz and I verified that it  works perfectly with no attenuation at 10 Mhz. The gain of the Rapco is 1 and  is not adjustable.

I noticed, however, that without the input signal,  at the exit, there is noise due to the two internal switching regulators that  generate -6 and +11 volts from +24 vdc input. The noise at the 5 Mhz output is  60mV pp(sum of the two switching noise).

I reduced the noise to 10mVpp,  cuttingin two tracks on pcb, from power output from the switchings and  inserting an inductance 300uH (.8 A)than putting an electrolytic 470UF 16V.  from inductance to ground (respecting their polarity).




---------------
Hi Luciano
 
Thanks for the information, I'd been planning on replacing those two switching regulators with linear but that's not so straightforward for the negative supply so might experiment with your suggestion.