• FM Transmitter

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FM Transmitter site

1. FM Transmitter site
   1. Location, phone
   2. Access
   3. Engineers
   4. Block diagram
   5. Remote control
   6. Transmitter Log
   7. Troubleshooting
   8. Maintenance

Location, phone

1955 Washington Ave
Louisville, CO 80027-1136
map

303-673-0540

• South Boulder Road east

• Up Davidson Mesa

• Go through 1st light (McCaslin)

• 2nd light is Washington, make a left

• Continue to end, you'll see the tower

• Take dirt road between earthen dam and Water Treatment plant

• The transmitter is in the 1st container, door closest to you as you arrive

• Avoid Frank Patete, the owner of the land, who lives in the house just ahead

Access

We have 3 keys:

• Davide 303-413-1500 <1davide AT IGNORETHIS att DOT net>

• Doug Grinbergs 303-665-7086 <saule AT IGNORETHIS pobox DOT com>

• At KGNU. See the SecretInfo page.

The Boulder Sheriff Dept shares that space, so they too have access:

• Dean Scott, 303-910-3248

The key to the fence surrounding the tower is the container where the transmitter is, hanging on the wall just inside the door.

Engineers

• Davide

• Mike Pappas 303-988-0976 (W), 303-807-5619 (C) <mpappas AT IGNORETHIS qwest DOT net>

• Doug Grinbergs

Block diagram

 MicroWave antenna -> STL receiver --> FM transmitter --> FM antenna
                                           ^
                                           |
             phone (303-673-0540) -->  Remote Control

Remote control

The transmitter is controlled remotely through any phone. The controller UPS powered, so you can call and find-out if there's any AC power. You dial in touch-tone codes, and the controller responds with a synthetic voice (shown as 'response' below).

• Dial 303-673-0540

• 'Enter'

• Enter the secret code: see the SecretInfo page

• 'kgnu transmitter site'

• Enter codes to do readings

  • 00 for Plate voltage: 'Channel 00 3.70 KV'

  • 01 for Plate Current: 'Channel 01 408.0 mA'

  • 02 for % of power: 'Channel 02 99.9 % power'

  • 05 for temperature: 'Channel 05 73.2 degrees'

  • 06 for AC power OK: 'Channel 06 normal'

• Enter codes to control functions

  • 03# to turn on the transmitter

  • 03* to turn it off

Transmitter Log

The Transmitter Log tells us what the history of the trasmitter is. It is a notebook by the clock radio.

• Always write on the log

  • What you did

  • When

  • Who you are

Troubleshooting

The most likely cause is lack of AC power from Xcel.

• Call the transmitter and ask the remote control if there's AC power (see above)

• Check with Xcel about power failures:

  • 800 895 1999

  • You'll need to provide the phone number at the transmitter (303-673-0540) or its address (1955 Washington Ave,

Louisville, CO)

• Just wait for power to return

• We do not have a back-up transmitter

Most failures fall in one of these:

• A very short duration power failure locks the transmitter's logic

  • Turn off the Filament, wait, turn it back on

  • Turn on the Plate Voltage, wait, the plate will come back on

• Near the end of the tube's life, there can be Plate Voltage Faults

  • Push the button to clear the fault

  • Flip the Auto Manual power switch to Manual

  • Press the Power Down switch for 30 seconds to lower the power to the minimum

  • Turn on the Plate Voltage

  • Continue operating a low power until you can replace the tube

• Rarely, the HV circuit breaker trips

  • Flip it back on

  • Turn on the Plate Voltage

• The interlock detecting insufficient air flow trips

  • Try cleaning the air filter in the back, low down

  • This is intermittent and self healing. I never figured out what causes this

• Replacing the tube

  • LETHAL VOLTAGES! Don't skip a step.

  • There should be another tube on the floor in a cardborad box, along the north wall. It may be used but with some life left.

  • Turn off the HV breaker (in the lower middle of the cabinet). The fan will stay on

  • Wait some 10 minutes for the tube to cool down

  • Turn off the LV breaker. Everything will go off

  • Open the top door, on the right (2 knurly knobs)

  • Loosen the pipe clamp around the bottom of the brass cyclinder (with a flat blade screwdriver)

  • Loosen the pipe clamp above the brass cyclinder

  • If the cyclinder is still too hot, wait for it to cool down, or use a rag to handle it

  • Lift the cylinder, lock it in place with the top tube clamp

  • This exposes the tube (ceramic body surrounded by metal fins)

  • Use the screwdriver to short between the metal of the cabinet and the C-clamp on top of the tube (a white wire is connected to it). This is just for extra insurance that there's no high voltage left

  • Slip the C-clamp off the nipple on top of the tube

  • Twist the tube a bit counter-clockwise to free it from its socket

  • Pull up the tube up from its socket

  • Drop the new tube down in the socket

  • Turn the tube clockwise until it stops to lock it into the socket

  • Slip the C-clamp onto the nipple on top of the tube Don't forget this step!

  • Make sure the bottom pipe clamp is around the tube

  • Loosen the pipe clamp that is holding up the cylinder and carefully lower the cylinder

  • Carefully slip the brass fingers, at the bottom of the cylinder, into the narrow slit surrounding the tube, letting the cyclinder go as far down as it can

  • Tighten the bottom pipe clamp

  • Tighten the top pipe clamp

  • Close the door and lock-it shut with the knurled knobs

  • Turn on the circuit breakers

  • The transmitter should go on the air automatically within 1 minute

  • Tune the transmitter (see below)

• Always fill the Transmitter Log

Maintenance

• Always fill the Transmitter Log

• Let some nitrodrogen in the antennal line to purge it

  • Open the valve at the nitrodrogen bottle

  • Open the valve at the bottom of the antenna line

  • close both valves

• Filament voltage

  • For new tubes, ajust the filament voltage to 5.00 V (to degass it)

  • After a week to a month, reduce the voltage (to extend the tube life) until you see an increase of Plate Voltage (Auto mode) or % Line current (Manual mode), then raise it back up a bit. Don't go below 4.9 V.

• Tune the transmitter, especially if the tube is new

  • Log the inital values for Place Voltage, Plate Current and Percent Line Power

  • Flip the Auto Manual power switch to Manual

  • Press the Power Down switch for 30 seconds to lower the power to the minimum

  • Use the Tune and Load switches to maximize the power

  • Flip the Auto Manual power switch to Auto

  • Log the final values for Place Voltage, Plate Current and Percent Line Power

• For tower maintenance, call Pete at GRB Construction, 303-417-2219