Backtalk

Letters to the editors Here’s a letter we received in response to Audley Alexander’s feature on drop-in amplifier upgrades in our February issue. Drop-In Upgrade Issues

I would like to respond to your article in the February issue of Communications Technology. It is true that some systems could benefit from an active module drop-in to expand bandwidth. We often perform field walkouts and redesigns for system upgrades, and during those processes, we discover things that a simple module upgrade would neither uncover nor provide a solution for. Examples would be as follows. If our sample system is presently spaced at 450 MHz or even 550MHz, there is a good chance it was designed using tree-and-branch architecture, but the following also holds true in express. By dropping in modules capable of 860 MHz, you can add distortion products due to the expanded bandwidth and higher output levels needed to make up for the lack of respacing and the cascade reduction that would be performed through a redesign. Additionally, more often than not there are considerable return violations in the existing older plant that would be found during the redesign. In many older system designs, the return was not high on the list of importance. And finally, passives that are limited to 450 MHz or even 600 MHz will be a problem. To face-plate change or replace them with higher bandwidth devices, along with a simple module drop-in, but not perform design calculations on the new passives’ cause and effect on the system can also cause undesirable circumstances. One of the biggest reasons a good walkout and redesign is required in older system upgrades is that very rarely over the years have the existing system maps been kept up to date with the addition of plant extensions, new homes, MDU complexes, and commercial or business customer extensions. Many times, the in-house technical and construction staff at the system has been instructed to extend plant, splice and only meter balance, etc. to get a new project working. They are, of course, only compounding the problem of an already out-of-spec and possibly poorly functioning system, adding to pre-existing powering, return, performance and reliability problems. In my view as a 28-year veteran of the industry, a system could perform only a module drop-in. But the potential for continued technical problems and service failures over a five-year period could exceed the costs of a proper redesign right from the beginning. Today’s modern systems demand that the system be robust and functioning properly to handle VoIP, VOD, high-speed data, telephony, etc. This means, especially with older systems where redesign has not taken place over the past seven to ten years, it is vitally important to consider redesign for an upgrade. Keith Auzenne
President, Centerpoint Cad Designers
Audley Alexander responds:
Keith, you are 100 percent correct in pointing out that "drop-in" upgrades cannot be treated too simplistically. The intent of the article was to outline the concept of alternatives and cost-effective upgrades. I wish to point out that my company has successfully upgraded over 45,000 miles of plant in the United States and Canada. We treat each project as a custom engineering activity. We usually perform the necessary evaluation to ensure that our proposals will not be subject to the issues you outlined below. A drop-In upgrade does not in all cases negate the need for proper network design. However, in cases where the network is well designed and operated, we have found from experience that no design is necessary. In such cases, the issue becomes one of providing the proper gain headroom along with the other proprietary modifications we make to the original product. I agree that just dropping in an 860 MHz amplifier does not produce a network that will operate properly at 860 MHz. There are operators and customers that have designed their networks for 750 MHz spacing and operation, but for whatever reason have place in refurbished 550 MHz amplifiers; we have successfully upgraded these to 750 or 860 MHz. A drop-in upgrade may not be cost effective if passives and network conditions do not warrant it. Prior to proposing a drop-in upgrade, we provide exhaustive engineering evaluation to ensure network integrity. We also have customers that work with designers such as yourself to ensure that CableServ‘s solution meets their network performance objectives.