On 6/12/2012 6:27 PM, Jeff Liebermann wrote:
On Tue, 12 Jun 2012 04:49:35 -0400, "Michael A. Terrell"
wrote:


Name CISCO DPC2100R2
Modem Serial Number 224656807
Cable Modem MAC Address xx:xx:xx:xx:xx:xx
Hardware Version 2.1
Software Version dpc2100rx-v202r1256-110513Uas-TWC
Receive Power Level -4.9 dBmV
Signal to Noise Ratio 37.7 dBmV
Transmit Power Level 41.5 dBmV
Cable Modem Status Operational

I only edited the MAC Address, for security reasons.

Veddy strange. SNR usually isn't expressed to 3 significant figures
and should be in dBm, not in dBmV. The firmware scribblers seemed to
have goofed. Oh well.

Some tests I did on Telemetry systems were to four places, and had
to match to within .01 dB in diversity sysems.

SA probably didn't bother to review the design, since it's rarely
seen by anyone. Most who would look have no clue what a Decibel is, or
that there are multiple references.

I was never impressed by SA designs. Their C band receivers were
noisier than even the cheapest Microdyne. They reverse engineered a
Microdyne receiver for their only Telemetry product, and lost the court
case for using a patented method. It was a slam dunk case. They bought
a couple receivers, and a year later they release their design. The
only real difference was they replaced the LED displays with a bad LCD
display. Most of the units we repaired had failing or dead displays,
and had to be modified to use a better panel.


I had trouble teaching some techs to use the 'relative' function on
a Fluke 8920 True RMS Voltmeter, and that you had to make sure you used
50 or 75 Ohm cables and terminators that matched a particular board or
module. We used them on the video amps, with up to 20 MHz video outputs.


Directional couplers provide better isolation from the garbage sent
upline by crappy TV tuners.

Huh? The FCC demands that anything connected to an antenna have very
low LO radiation. That transfers to the cable TV connection when the
F connector is attached to the cable instead of an OTA antenna.


You might be surprised at the crap that can come out of a damaged
tuner, or one with a damaged F connector. The backmatch was horrible on
some brands of splitters I tested. Some were over 20 dB off spec. It
seemed like the fancier the label or plating the cheaper the inside were
made. I peeled the back off of a lot of them to see that the soldering
was substandard, and in some cases, they missed some joints.

We blacklisted multiple sources. When you buy them 1000 at a time
and drop cable 50,000 feet at a time, it was worth the pre-screening.
Our plant was the only one in the corporation with a lab & repair shop
so we arranged the supplies fr all the locations.


This is kinda old, but covers the topic:
New Measurements and Predictions of UHF Television
Receiver Local Oscillator Radiation Interference
http://h-e.com/sites/h-e.com/files/tech_docs/rw_bts03.pdf
With 40dBmV (or about -9dBm @75 ohms) transmitted on the return path,
even a lousy LO radiation of maybe -40 to -60dBm in the return channel
isn't going to do much damage.

I'm used to using a Fireberd to measure the BER on digital
communication systems.

The Acterna (JDSU) Fireberd is a nifty gadget. I had an Acterna
HST-3000 but didn't have the CATV plug in or software. I did have a
BERT but it maxed out at T1 rates.


I wasn't working in CATV by that time. We used them to test error
rates for Telemetry systems.


FPQSK was real fun when we first added it to our
telemetry products. The units are those selected by SA, long before
Cisco bought that divison. At one time we built the SA Telemetry
receiver that they had cloned from our 1200 series.

I think you mean FQPSK.

Yes. We used it in the RCB2000/DCR2000 series, but that was over 10
years ago, and just before I became disabled. I'm lucky to sleep a few
hours a day anymore and miss technical typos.