Why is my cable not working?

[Claude Greiner]

I was at a commercial job today on a digital HD headend. Couldn’t get anything to come on channel 47 (350 MHz or higher)

I never seen a splitter with such a low rating for passing frequencies.

Needless to say me and the customer replaced this beauty with a 2-way and (2) 8-way 1 gig splitters.

 

[slice1900]

Must actually have filters in it to prevent it from passing higher frequencies. Wonder what the reason was, can't see why you spend money to put filters in there to deliberately limit it to 300 MHz. Maybe it was for applications that would mix in something at higher frequencies like UHF modulators? Or they were worried about signal egress from higher frequency sources?

 

[Claude Greiner]

No filters. I opened it up and it’s literally 3 4 way splitters one circuit boards.

I think it’s atleast 30/40 years old

 

[slice1900]

Why would it have such trouble passing frequencies above 300 MHz then? It isn't like ordinary 900 MHz splitters have a special design.

 

[HoTat2]

Also, pardon my ignorance of CATV systems here. But what actual unit of measurement for signal level are cable techs referring to when they say so many "dbs" (i.e., the plural of "db")?

"dBm," "dbμV", ect.?

They drive me crazy with just loosely using the db measurement for an absolute unit signal level like that, when they're technically a unit-less system of relative measure of course.

And just curious, but how does a tap actually treat a signal going back in the reverse direction from trunk output to input such as the upstream MoCA networking signal from a receiver in a DRE installation or something?

Is some of a reverse signal siphoned off into the tap down port same as a portion of a normal forward signal is?

Or is it blocked from doing this? ...

Just wondering (if anyone knows that is ....)

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[cypherstream]

Some good questions here. I wonder if it’s the wire gauge or circuit trace thickness. Or maybe the materials. Like you wouldn’t expect cheap speaker wire to pass 1 GHz. There must be something to the materials or construction. I’ve also seen 550 MHz splitters, 900 MHz, 1 GHz and 3 GHz.

 

[slice1900]

I think satellite deals with dBM but cable uses dbUv. So cable is looking for inputs in the range of +10 to -10 "db", while satellite wants -25 to -45 or so.

Also, pardon my ignorance of CATV systems here. But what actual unit of measurement for signal level are cable techs referring to when they say so many "dbs" (i.e., the plural of "db")?

"dBm," "dbμV", ect.?

They drive me crazy with just loosely using the db measurement for an absolute unit signal level like that, when they're technically a unit-less system of relative measure of course.

And just curious, but how does a tap actually treat a signal going back in the reverse direction from trunk output to input such as the upstream MoCA networking signal from a receiver in a DRE installation or something?

Is some of a reverse signal siphoned off into the tap down port same as a portion of a normal forward signal is?

Or is it blocked from doing this? ...

Just wondering (if anyone knows that is ....)

Satellite uses dBm, which is referenced to millivolts and is typically used in RF. Cable uses dBmV which is referenced to microvolts. Thus you see satellite receivers usually wanting signals in the -30 to -55 range, while cable receivers usually want signals in the +5 to -10 range. I think the conversion factor between the two is a little under 50, so a satellite signal at -45 "db" is equal to a cable signal that's +5 "db".

 

[slice1900]

Some good questions here. I wonder if it’s the wire gauge or circuit trace thickness. Or maybe the materials. Like you wouldn’t expect cheap speaker wire to pass 1 GHz. There must be something to the materials or construction. I’ve also seen 550 MHz splitters, 900 MHz, 1 GHz and 3 GHz.

Good point, if they used a very thin gauge wire in that ancient splitter it would have greater loss at higher frequencies than "modern" cable splitters.

 

[Claude Greiner]

Good point, if they used a very thin gauge wire in that ancient splitter it would have greater loss at higher frequencies than "modern" cable splitters.

Yes it was very thin wire inside of it

 

[HoTat2]

I was at a commercial job today on a digital HD headend. Couldn’t get anything to come on channel 47 (350 MHz or higher)

I never seen a splitter with such a low rating for passing frequencies.

Needless to say me and the customer replaced this beauty with a 2-way and (2) 8-way 1 gig splitters.

View attachment 141297

Yeah wow ....

That must have been one of the very old muti-outlet taps intended for early analog CATV systems, that only carried the 12 VHF TV broadcast channels 2-13 (54-216 MHz) at the time.

Lol ....

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[Claude Greiner]

Yeah wow ....

That must have been one of the very old muti-outlet taps intended for early analog CATV systems, that only carried the 12 VHF TV broadcast channels 2-13 (54-216 MHz) at the time.

Lol ....

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The place is very old. But before going digital they where running 2-36 analog

 

[slice1900]

When I was a kid our cable system had channels 2-35, with a little box that looked something like this

 

[TheRatPatrol]

We had one like this. My dad had it set up on the end table next to the couch.

 

[Claude Greiner]

We had one like this. My dad had it set up on the end table next to the couch.

We had one of those. My dad found out if you messed with the dial you could get free HBO.

We had a stack of index cards next to our box to keep the dial in between channels to get it to descramble HBO

 

[DWS44]

When I was a kid our cable system had channels 2-35, with a little box that looked something like this

Wow...hadn't seen one of those in years! The earliest cable I remember us having when I was a kid had a box like that, if not the same exact one. I was usually the one dispatched to run the slider between channels.

 

[raoul5788]

I used to have one like this, with a separate inline switch for premium channels.

 

[HoTat2]

BTW;

When Blonder Tougue named that obsolete device a "12 Port Directional Terminated Tap."

Is that because it's actually comprised internally of an asymmetrical splitter as all taps really are. With the twelve -13 db taps sipphoning off a combined 60% of the RF energy from the trunk in total.

And thus with only 40% of the RF energy now remaining in the trunk is simply terminated and thus thrown away as waste heat?

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[Phil T]

I used to have one like this, with a separate inline switch for premium channels.View attachment 141356

That is the same one I had in 1981 with Televents cable.

 

[raoul5788]

That is the same one I had in 1981 with Televents cable.

I had Telesystems which became Dimension, and then bought by Cox.

 

[Claude Greiner]

I had one of these and a device that would put it into “test” mode.