Shoshone Falls, Twin Falls, ID

 
Praecom Consulting is a professional services and consulting company with a 35-year heritage as independent consultants. With expertise in the technical and regulatory aspects of electronic communications, Praecom consultants hold certifications and licenses in several disciplines including networking, unified communications, microwave, land mobile radio, and web presence engineering.

 
The explanation of how this works is as follows:
 
Both wires of the circuit labeled Circuit A in Figure 1 become one conductor of the phantom circuit. As the current flow in these two wires is identical and in phase there is no voltage differential across the pairs and no audio is heard in the Circuit A audio circuit. The two pairs of the Circuit B audio circuit work in an identical manner. By taking the center taps of the two transformers and using them as the conductors for the phantom transformer, a third audio channel is derived that is not heard in either Circuit A or Circuit B audio paths. Note: it is necessary that the conductors themselves for each of the two side circuits must be within 2 ohms of each other and ideally below 0.5 ohm of each other. If this is not the case, the side circuit audio and phantom circuit audio will crosstalk.
 
There is even one more circuit that can be derived. By the addition of an additional set of transformers, connected between the center tap of the phantom transformer and ground, an additional audio circuit can be derived. This circuit is unbalanced and can be susceptible to audio hum, however, this circuit can be used as an intercom circuit between the radio equipment building and the dispatch center. This gives four separate voice circuits over 2 copper cable pairs and some inexpensive center tapped audio transformers.
 
A PDF version of this article is available for download in the White Papers section of this website. 
Copyright 2009 all rights reserved.

Generators are no different than an automobile when it comes to engine maintenance.  It’s common knowledge that the worst thing you can do to an automobile engine is to only run it for 15 or 20 minutes and then shut it off. This has to do with several items that affect an internal combustion engine.

First and foremost is the oil.  Oil oxidizes while sitting in the crankcase.  This causes acids to form and chemistry to change.  What removes these acids and normalizes the oil is heat and pressure over a minimum period of time.  15 minutes is not long enough to heat the oil and maintain that heat and pressure to remove the acids that form from the oil oxidation.

Oil and heat has a secondary affect on an engine.  Oil attaches and migrates into the pores of the metal. This limits rust and other contaminates from bonding to the metals of the engine.  The classic example of this is in the form of a cast iron skillet.  Anyone who cooks knows that a well seasoned cast iron skillet will not have food stick to it. The vegetable oil permeates the pores in the iron, thus not allowing things to stick. To maintain this, you must use the skillet regularly, get it hot and allow the cooking oils to penetrate into the iron. A skillet like this also will not rust, and will last for years.

Secondly, moisture affects an engine – particularly the exhaust system.  The engine needs to heat the exhaust system enough to boil all the water condensation out.  Have you ever noticed that during the winter your car exhaust has “smoke” coming out for some time after you start it, but it disappears once the engine gets hot? That’s the water vapor escaping as the system heats up.  A generator is no different, and the exhaust system is critical to proper operation of any gen-set.

It’s important to remember that the engine is only half of the generator.  The other half, the actual generator has its issues too.  It is also affected by moisture and heat.  That is why it’s very important to exercise the system under a load.  This allows the electrical portion of the generator also to come up to operating temperature.

Lastly, the NFPA has specific standards for testing.  The critical section is in NFPA 2010 Section 110, Chapter 8.  The maintenance routine is in Section 8.4. Specifically, Section 8.4.2:

“Diesel Generator sets in services shall be exercised at least once monthly for a minimum of 30 minutes, using one of the following methods:

(2)    Under operating temperature conditions and at not less than 30 percent of the EPS nameplate kW rating”

I will take issue here: I don’t believe that monthly testing is adequate.  In our industry, and for critical sites, weekly is required, with all the above criteria met.

There are several other standards dealing with standby generators, their installation and maintenance. Specifically, NFPA 70/NEC 701, which deals directly with “Critical Operations Power Systems” and the Joint Commission on Accreditation of Healthcare Organizations. I would recommend that if you have not reviewed these standards, that you do so.

So, why am I posting this? A couple of reasons;

First, I know that not everybody pays attention to the weather service, or the news for that matter, and I wanted to “spread the word” in my own way.

Second, I wanted to reinforce maintenance and systems preparedness.

Some of the things that I have come across in my experience that happens during flooding and chronic wet conditions can really create headaches. You really don’t want to be troubleshooting a communications issue while trying to dispatch sand trucks or trying to maintain a switching station.

Things to look for primarily are weatherproofing issues.  Some may be beyond your control.  Water creeps into telephone cables all the time. This can cause noise and cross talk in analog circuits, and can cause errors on T1 lines. While fiber is somewhat immune to the water, the electronics are not. Additionally, if the fiber handholds and electronics are under water, the circuits will fail.

Water also does interesting things to microwave paths. Water has a high reflection coefficient. This is why we design in diversity when paths travel over large bodies of water. These ties back to overall system design.

So, my question is, when was the last time you tested your hot standby systems? Have you recently busied out your T1 and accepted calls on your backup trunks? For that matter, when was the last time you tested your UPS on some of your smaller sites or non-generator systems?  Have you forced a ring direction switch on your fiber or ring microwave system?  If you are running a simulcast system, how does this affect the timing and the system retraining time? Are your people trained and experienced enough to notice and respond to equipment alarms appropriately?

For some of my customers, these items are standard operating procedure, but for some, the network is taken for granted.  Let’s not take things for granted.

OK, so a pithy headline can get anybody’s attention, but when it comes to tower maintenance, it really is about nuts and bolts.

Towers are like bridges – they all need maintenance, but unless they break or are visible, they tend to get neglected. Oh, sure, the big ones, the ones with lights and alarms get some attention, but when was the last time you checked the ones that don’t get painted or lit? Would you be worried if the nuts at the base of your tower were like the ones in this video??

www.youtube.com/watch?v=Ixa1UwE7kuk

OK – so, not fair; this was a new tower. BUT we discovered this during our final punch list.  This tower was lighted, and had all antennas installed.  In fact all the civil was completed.  We only needed to install electronics at the site.

However, this photo

is not of a new tower, but one that is up.  Notice the concrete? Over time, everything fatigues, even concrete and steel.  The forces of heating and cooling naturally work parts loose, and if not checked regularly, could lead to a major catastrophe. The crack in the concrete was found while adding antennas to this tower.  The crack leads right to one of the anchor bolts.  This is a serious repair.

As part of this post, I went out to Rohn, Sabre, and Valmont to try and find the recommended maintenance intervals and practice.  Unfortunately, my search of their respective web sites was not fruitful. I’m sure an email or phone call to them with the model number of your installation would get you quick results.

The point here is to make sure that you include tower inspections and routine maintenance in your budget.  I know things are tight from a fiscal perspective, but like your communications system, a minor failure can multiply, and over time become a real issue.  And we all know that it’s during the critical times that systems tend to break down.

However, this months feature article is on Ethernet over Fiber Optics.  Titled “Demystifying Optical Ethernet Networks” this really gives an excellent basic understanding of how Ethernet works in carrier networks for the uninitiated.

These networks are becoming more and more predominant – particularly for larger customers, or customers in areas that have a better technology infrastructure. Ethernet is becoming a more common access method for everybody.  What I really like about this paper is how it’s broken up in to the PHY layer (or physical) versus native Ethernet and long haul carrier Ethernet over SDH networks.

This is also just a technology paper, not published by any specific vendor. I recommend that everybody go out an take a few minutes to read about Ethernet and how it all works together over a wide area to provide services, and what happens in the middle.