tech stuff – Page 23 – Engineering Radio

Nautel V-10 repair

Not exactly sure how it happened, but one of our Nautel transmitters malfunctioned! It is a pretty rare event, so I thought the exclamation point was needed. One of the PA pallets went bad and the transmitter lost 1/2 a PA module. Since the TPO for this particular station is 7 KW, they remained on the air at full power. In the interest of staying on top of things, we fixed it anyway.

Diagnostics were simple:

Fault lights on the front of the transmitter observed
Press the status button to find out faults, which were Module D failed
To to module sub-menu, find Module D and discover Q1 disabled, and Q3 shutdown.
The problem is with Q3, order a new pallet from the manufacture

Upon removing the module, I did not see the damage at first:

Nautel V series FM transmitter PA module

It is board A3, which for this particular flavor transmitter is a Nautel Part number NAPA16-B. Once I replaced the defective module with a new one, I discovered what looks like a symptom of the greater problem:

Over to the left-middle-lower section of the board, R10 and R8 are burned open. These are surface mount 2-watt, 20-ohm resistors. A glance at the schematic shows that these are part of the bias supply. A quick set of measurements with a DVM shows that Q1 seems to be intact and not shorted. Interesting…

The question is: Is it worth trying to fix this board or should I just trash it an buy a new spare?

Update: Schematic diagram as requested:

Middle Aged Iron: Cetec/Bauer 701B transmitter

In service as a backup unit at WALL 1340 KHz in Middletown, NY:

WALL 1340 KHz, Middletown NY AM1A on air, 701B into test load

I believe the Cetec transmitter is from the early 70s. I wouldn’t really call it old, we have much older units in the field that are still in backup service. WALL itself has been on the air since 1942 from this site. The tower out back was replaced in the mid ’90s and is 147 degrees tall. It broadcasts the “True Oldies Channel” and is currently owned by Cumulus, soon to be Townsquare.

The site is also home to sister station WRRV (92.7 MHz) which has a side mounted antenna near the top of the WALL tower. We are currently reconnecting the CCA transmitter as the backup for WRRV. That unit is also from the early 1970’s.

WRRV WALL transmitter site, Middletown, NY

WRRV WALL transmitting tower, Middletown, NY

Computer guys…

Some guy posted this picture on Reddit:

In the comments, he gets blasted for being too neat and using wire ties. I know a lot of IT guys that are not very neat with their work and document nothing. This is a big problem in the industry and does not, contrary to popular belief, promote job security. I have walked into some very messy situations in wiring closets and rack rooms over the years. My solution is always the same; run some temporary wires for critical machines/functions, then get out the big wire cutters and start chopping.

Graphical Network Simulator

I have been working with GNS3 (Graphical Network Simulator) in some of my classes. It is a fine tool with which one can build simulated computer networks using various routers and switches. The software program itself is free, however, the Cisco IOS images are not included and must be found elsewhere due to copyright issues. This detail is a bit of a pain, but not too bad. Once the program is set up and the appropriate IOS images are loaded, the console functions exactly like whatever router is being simulated. This includes running whichever terminal program is preferred, e.g. hyperthermia, putty, or if using the Linux version, x-term, etc.

GNS3 screen shot, topology and router console — GNS3 screenshot, topology, and router console

The advantages to this over something like Cisco’s Packet Tracer program are many. In Packet Tracer, certain functions are locked out and generally there is only one acceptable way to complete any given task. With GNS3, the IOS is fully functional, which means that experimentation and failure are available to play with. Failure is a great way to learn things in any hands-on environment. The advantage of virtual failure is that only you know about it.

For real-world applications, this means that router and switch configurations can be created, tested, and tuned ahead of time and then loaded into working devices, saving downtime and potentially handfuls of hair.

A few things about using GNS3, the PC idle tuning is required. Each instance of IOS assumes that the entire processor is available to use, thus starting several routers can work a PC’s processor to 100% and windows will never fully recover. Secondly, when starting each router, wait 10 to 20 seconds before starting another one. Again, this has to do with the way IOS uses processors. Also, to save time, store the IOS image as a decompressed file. This saves quite a bit of time on startup. Finally, do not forget to copy the running config to startup-config. Even though GNS3 says it is saving the router configs, it does not save the running config unless you issue the copy run start command, just like a real router.