[time-nuts] RAPCO 1882M-2 autochance over distribution amplifier
GandalfG8 at aol.com
GandalfG8 at aol.com
Sat Oct 23 20:13:41 EDT 2010
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
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.
>From the description in the manual I guessed in advance these might be
wideband and took a gamble on that, once confirmed on my first one I bought a
Aside from frequency distribution I was also curious to try them as LF/MF
antenna distribution units.
I knew they were likely to be quite noisy at microvolt levels but there's
quite a bit of noise at LF anyway and the op amp noise actually wasn't too
However, when feeding into a radio with a 30MHz wide spectrum display the
effects of those switching regulators are immediately obvious. They're
running at 100KHz and the harmonics generate a nice picket fence that's clearly
visible up to at least 20MHz.
I'd still like to get rid of those switching regulators altogether but
could really do with a schematic before trying that.
I assume you got a copy of the basic user manual from the seller? If not
let me know and I'll send it to you.
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