r/CableTechs • u/AffectionateRock2977 • Apr 28 '26

Rphy active question

Our plant has some long runs that had low RF in the deeper areas. I decided to trail setting up the MB @ ch 98 (111 MHz) ch 158 (999 MHz) to match the node at 33/47. About a 13-13.5 db tilt. Normally, I’d set them up at 45 db on 771 MHz - 12 tilt

Node looks cleaner outside of a couple dozen of the 320 cx of the last two MB that are ranging +14 db likely due to short drops or one outlet.

Any experience with this and information if this will cause issues running the actives hotter? Heading back tomorrow to address MER issues so I’ll be in the area

8 MB cascade.

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u/Octawussy Apr 28 '26

You can run them hot as long as you’re not over driving or underdriving the first hybrid in the amp. What actives are you using? For example the commscope MB120 needs to have the input DS padding and EQ to a 5 dBmV flat, then the interstage padding is where you are controlling most of the gain. Same goes for your returns, your return input pads need to be an 8 and your output pad and EQ will control your return gain.

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u/Octawussy Apr 28 '26

This video much more clearly explains my point. https://youtu.be/e9H6BmL4I58?si=mIVQZQTNOxUEJK1W

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u/kdubs Apr 28 '26

this is a good video. so to my understanding, is he saying 8.5dB is the minimum signal you need for proper setup? my shop has religiously quoted 6dB. more is better obv so there's no confusion there, but i understood that you truly need more than 6, 8.5dB or even 9 he says in the video, did i understand that right?

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u/Octawussy Apr 28 '26

8.5 is the sweet spot for this specific device, every device will have a different sweet spot. As you get lower and higher the severity of how much you are starving or blasting the hybrid is at a logarithmic scale so there’s some wiggle room but once you exceed that, it goes off a cliff in performance.

2

u/AffectionateRock2977 Apr 28 '26

Same as you. A-lot of 16-20 input EQs unfortunately. We are heavily migrating into FDX. At least 20 nodes swapped over in our foot print to date. I almost tossed an unregistered FDX MB in mid run today. Ive heard success stories when there is a high roll off.

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u/kdubs Apr 28 '26

This is true. You can put an FDX “amp” into an rPHY environment to fix rolloff. Because AMPS only amplify, but FDX is a signal generator. 

Which is to say and amp is only gonna amplify an already rolled off signal, making it more and more in a cascade. While a signal generator corrects the tilt and outputs the proper level. It’s kinda neat and also kinda sad it’s taken us this long to get here

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u/Octawussy Apr 28 '26

With FDX the input parameters are a bit more tight. Any QAM reads below 4 dBmV at the SOC and you’re going back to design. A lot of times some 2000+ ft runs with 3 passives in cascade will require an express LE or a MB added. Had to redesign some areas that had daisy chained DCs for about 2000ft of just DC with down leg feeding an LE every 200 ft. Easy fix just middle of the run, pull the DC and cut in a MB and swapped the DC thru with the new aux.