Fox's Mercantile wrote:
On 9/2/20 1:56 PM, Michael_A_Terrell wrote:
One thing that wasn't mentioned. The output level is +35 to +45 dB.

Might wanna look at what ever you were looking at again.
The output as specified in the manual is +40 dBmV. NOT dBm.
The correction factor is -48.75, so the actual output in dBm is
-8.25 dBm. Or, about, 0.15 miliwatts.

I seriously doubt this modulator puts out 31.625 Watts.


I seriously doubt that you've ever built any CATV head ends. I
expressed the output stage gain in dB, not dBm. Working in system
design, you work with gain and attenuation levels, not dBmv, dBm or any
other variation. To get the gain required for a line amp, the module
dissipates real power in Watts, not puny mW. Those modules are mounted
on a heavy bar that is bolted to the amplifier's case to dissipate that
heat. If you overdrive the input on a TV, you can damage the input
amplifier. At the very least, intermod and sync compression happens when
the tuners are overdriven. One system had over 10,000 TVs connected to it.

The systems that I worked with in the Military used Jerrold tube
based CARS to link two channels to every airfield around Ft. Rucker.
That system could also take control of the civilian CATV system at the
point where it entered the base. This was t allow emergency weather
alerts, or disaster information to be sent into the housing areas.

When I built an interface to connect two incompatible Community
loops, our lead tech radioed the office to complain that my design was
off. By just under +0.2dB. Not dBm or dBmv, but dB. Cable losses,
connector losses and insertion losses for passives is what eats up your
gain budget.

I wrote software back n the early '80s to simplify system design.
Our company specification was +10 dBmv at the output port of the tap. In
most cases, that allowed four TVs and the drop loss at the highest
channel. The software stored data for every brand of coax we used for
feeder, trunk and super trunk. It held the specs for every brand of tap
for the feeders, so all you needed was an accurate strand map to design
a reliable and flat system.

The only thing that it couldn't do was stop lazy techs from changing
taps to drive more TVs in some homes. That dropped the signal for every
drop past that point. Johnny Bench was one of our customers. We had
drops to both ends of his home, and one TV was on a floating bar in his
pool.

I not only did system design, I maintained the microwave equipment.
Rockwell-Collins had soaked the industry for a crappy, modified fixed
tuned model that was a downgraded Military design. They ran so hot that
the PC boards would burn, and they refused to repair them. The design
was so bad that they used a 1500uF electrolytic in the video output
stage, rather than a properly designed amplifier that could handle the
DC offset. That series was listed as impossible to use with the
Videocypher II descramblers. I had already removed a trap from all of
them, because they didn't work with any channel carrying a secondary
service as a subcarrier.

The idiot manager freaked out, but he wasn't as smart as he thought
he was. He would set the Sat equipment up to output the 1V of video,
without terminating the Tektronix 528 waveform monitor. Then he had to
crank the modulator gain wide open to come close to 90% of noisy video
modulation. He claimed that Tektronix didn't know how to design test
equipment. Those Rockwell-Collins receivers had a 225 ohm resistor in
series with the output, so he was setting them for .25 volts of video.


For anyone who is interested in this subject, Blonder Tongue
publishes handy reference books. This is an older edition that still
covers NTSC equipment.

That large system had a RCA headend that was miswired at their factor.
When you tried to use the emergency alert system, all the outputs
dropped by just under 40dB. They had wired a splitter wrong. One port
work, the other didn't. Once again, the pointy haired boss insisted that
RCA NEVER made mistakes. I not only fixed that, but I modified it so the
individal Hetrodyne Signal Processors could detect a lost input and
switch to the auxilary IF inputs. These were fed by a single modsulator
with no upconverer. I used a spare video output from a character
generator to display, "This channel is off the air. Please consult your
program guide." During an emergency that message was automatically
switched out for a different video feed. This eliminated a lot of phone
calls from customers, and it only took a dozen 1N4001 diodes.

The line, bridger and extender amplifiers were Sylvania, which was
sold to Tekscan. The original taps were built in Canada by Lindsay. They
were absolute ****. Instead of a cast face plate and water tight seals,
it used cheap chassis mount F connectors which were tinned brass, and
mounted on a pot metal face plate. They corroded quickly in the
Cincinnati area, thanks to road salt. That caused all kinds of intermod,
system leakage and poor signal quality.

https://www.blondertongue.com%2Fpage%2Fmedia%2F2014_BRG_lo-res.pdf


Stick to your used business radios, where you can do that simple job.

--
Never **** off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)