[time-nuts] RAPCO 1882M-2 autochangeover distribution amplifier
GandalfG8 at aol.com
GandalfG8 at aol.com
Mon Oct 25 16:51:31 UTC 2010
In a message dated 25/10/2010 14:09:08 GMT Daylight Time,
luciano.paramithiotti at 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:-)
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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
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