Fair Oaks Repeater - Fairfax, Virginia
Posted by: Groundspeak Premium Member flyingmoose
N 38° 51.451 W 077° 21.767
18S E 294980 N 4303618
One of two repeaters that NVFMA operates and maintains on top of the Fairfax County Public Safety Headquarters building.
Waymark Code: WM14500
Location: Virginia, United States
Date Posted: 04/16/2021
Published By:Groundspeak Premium Member wayfrog
Views: 3

While the repeater can be seen from the ground, it is in-accessible to the public. It and other sensors sit upon the roof of the Fairfax County Public Safety Headquarters building which is one of the higher elevated locations for a few miles. Other repeater locations operated by the NVFMA are located in Ashburn and Tysons Corner.

Information below this line was taken from the Northern Virginia FM Association website.


The following describes NVFMA's 146.790 MHz FM repeater that is sometimes referred to as the "79 Machine."

Call Sign
The 79 Machine is operated with NVFMA's club call sign NV4FM. The call sign is automatically transmitted by Morse code at least every 10 minutes when the machine is transmitting.

Repeater Manager
Bruce Freund (K7BC) manages the 79 Machine.

The 79 Machine and its antenna are located atop the Fairfax County Public Safety Headquarters building, 12099 Government Center Parkway, Fairfax, Virginia. This location is in the Fair Lakes portion of Fairfax County, Virginia.

Transmit and Receive Frequencies
The machine's transceiver transmits on a frequency of 146.790 MHz using frequency modulation with a bandwidth of 16KHz (wideband). It receives with a standard -600 KHz repeater offset. This means that the receiver frequency is 146.190 MHz.

Private Line (PL) Tone Sensing
The machine's receiver responds to a PL tone of 77.0 Hz, so all signals received without this tone are filtered out. A 77.0 Hz PL tone is added to the transmitted signal to support the Continuous Tone Coded Squelch System (CTCSS), if desired.

Remote Receivers
In addition to the main receiver site at Fair Lakes, the 79 Machine is connected to three outlying receiver sites. A voting system is used to select which of the four received signals is strongest and to send that strongest signal through to the 79 Machine's transmitter.

Operational Status
The 79 Machine was relocated to its present site in January, 2018. The remote receiver capability has not yet been restored since the move. Recent antenna and feed line work, tuning of the duplexers, and adjustment of the squelch to increase sensitivity, have enhanced performance (using only the main site receiver) that is assessed to be better than in years, even as compared to the previous Fairfax City installation. The 77.0 Hz CTCSS receiver PL tone was added on September 26, 2020.

The 79 Machine includes a timer that automatically terminates transmissions after any continuous three-minute period of operation. This feature provides the opportunity for the 79 Machine's transmitter to cool down, but it also encourages users to limit the duration of their transmissions to no more than three minutes without a break. The timer is reset when the received signal drops. A station transmitting to the 79 Machine may not realize that their signal is no longer being repeated through when they transmit too long. Operator discipline is necessary.

Repeater Call Sign: NV4FM

Output Frequency: 147.00

Input Frequency: 146.00

Input/Output Tone: A tone is required for input, and a tone is encoded on output.

Club Web Page: [Web Link]

Input Tone: Not listed

Output Tone: Not listed

Output Power: Not Listed

Antenna height (above average terrain): Not Listed

IRLP: Not Listed

IRLP Node ID: Not listed

Echolink: Not Listed

Echolink Node Number: Not listed

D-STAR: Not Listed

Visit Instructions:
Not ham operator: Obtain geographical proximity to repeater site and post relevant picture with log. CAUTION: Observe posted KEEP OUT signs to prevent exposure to high levels of RF emissions. Do not climb towers. Do not trespass. Ham operator: Complete a QSO on the repeater. Requirements: Your call, the other station's call, signal report from other station, your location relative to repeater (GPS coordinates, or bearing/distance), transmit power.
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