walter shawlee 2 wrote:
There have been many questions posted here about the units, here are a
few answers I have collected:
1. the 8140 can drive up to 25 total downstream 8410T taps on the
combined outputs. The mopdels are frequency specific, and are not
easily changed, 10Mhz is the most common. The front selector provides
TTL divided waveforms from the input rear clock.
2. yes, the taps are needed, as the output of the 8140 itself is a
sinewave and +12VDC. using the tap allows long cable distances, and
provides the extracted, buffered sinewave. long cable runs of RG58 up
to 500 feet are possible, with T-taps all along the way, and all 4
outputs can have long runs. the manual says a capactively coupled 50
ohm load is meant to terminate the line, but I have not found it to be
required so far, as the sine wave drive produces very little ringing.
3. yes, it works WITHOUT the taps, if you add a 0.47uF good quality
cap in series with each BNC output, run distance is then short into 50
ohms.
4. YES, taps are different, if you have a 10Mhz source, you must have
10Mhz taps (8410T10). beware of the 8410TTL10, it has a TTL 10 Mhz
output, not a sinewave.
5. the operating quality of the system is excellent, do not be
deterred by it's modest appearance, it works just as well as the
racal, fluke and hp distribution amps I have and use. Late ones are
much better made (they have black, not blue vinyl tops), if you can
score one.
6. Phasing: my measurements show approximately a 190 degree phase
difference between the input sine, and the output waveform at
10Mhz...not an issue for me, but maybe for others?
7. The system checks for DC output shorts (excessive loading) and loss
of input clock, these drive the red front indicator (output fault). An
option can also drive a sonalert.
8. the taps are not generally repairable, as they are potted with
foam. bummer.
9. System details, and downloads are here at Spectracom:
http://www.spectracomcorp.com/ProductsServices/TimingSynchronization/TimeandFrequencyDistribution/8140FrequencyDistributionSystem/tabid/133/Default.aspx
10. Note, there are no schematics for Taps, if anybody has some to
send me, I'd really appreciate it, just to satisfy my curiosity.
so, if you find one in good condition, it is a great addition to your
lab, for distributing your master reference all around the shop area
to counters, spectrum analyzers, generators, etc. it works with
literally all common clock sources, from 0.3Vrms to 2Vrms, should be a
sine wave.
regards,
walter
Walter Shawlee 2, President - Sphere Research Corporation
3394 Sunnyside Road, Kelowna, B.C., CANADA V1Z 2V4
URL: http://www.sphere.bc.ca E-Mail: walt...@sphere.bc.ca
Phone: +1 (250) 769-1834 Fax: +1 (250) 769-4106
--Home of the Slide Rule Universe--
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Unfortunately it has a relatively high phase noise floor (around
40dBc/Hz worse than the current state of the art) common to most
distribution amplifier designs (eg the SRS distribution amplifier) using
AGC or limiting.
The HP5087 has a somewhat lower phase floor but it is still
significantly worse than the current state of the art.
Bruce
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