CABL Forum - Re: Return Amp

Well I'm no expert but I treat it as though it were a proportionately lower forward frequency (even though at 5-40 the sweep is going upstream). I am useing a Wavetek 2-way meter with a rack mount counterpart in the HE (I forget the model). of course the trick is in the padding / splitting in the head-end to hit the sweep reciever (for rev.) and the cable modem terminal at the proper levels. In the plant at the trunk forward output I run 31 @ ch. 3, 35 @ ch.70, and 29-30 @ 30MHz. I have a mix of 750MHz C-Cor flexnet gear (that works great) and a bunch of Jerrold Starline 450 gear streached to 550. On the C-Cor gear with the Wavetek I set the forward pilets to 3 to 31dB, 70 to 35dB, then the return (30Mhz) to 29dB. Of course on the test point (-25dB) this is 6db, 11dB, and 5dB fior the return. I don't pad or EQ the feeders individually but on certain legs that have not had internet customers yet there are 99dB pads that essen tialy block the return from that leg. As far as LE's go I try to re-establish unity gain at each one but there are many LE's in my system that have no reverse chip so sometimes the reverse only passes through an LE. That shouldn't be a problem but if you have a internet customer right next to the "passive" LE the high tap value will get you and the modem will have to run wide open to overcome the loss of the splitter, drop, tap and feeder (which could easily be 45 - 50 dB). This becomes less of a problem as you get further from the LE where cable loss (miniscule at those freqs) becomes more of a factor and tap value becomes less. Just remember when all else fails set all trunks and as many LEs as possible for unity gain and fine tune the levels in the head end, the modems will adjust themselves. If you have modem analysis software you can tell where your troubles are by weather the modems are running wide open or within range (ours max at 55 to 58dB).

Also as mentioned in a nother post it is very important to have proper impedance matching, make sure every port is hooked to another 75ohm device through good cable OR IS TERMINATED. Also if you are working with gear that doesn't have -20 to -30dB test points (like our Jerrolds) use the proper SPD-30 probes or your meter will have a significant impact on your reading.

You also mentioned feeder levels, with the C-Cor gear I am familiar with the reverse signal is mixed evenly reguardles of weather it's comeing in the trunk or one of the feeder legs, so set your trunk first, then start setting the LEs that hang off of the trunk stations.

I also HIGHLY recommend putting reverse traps on EVERY port that does not need it.

Any questions feel free to e-mail me as I don't check the board very often .

Good luck.

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Re: Return Amp