146.790 Fairfax City Repeater

Revised June 15, 2008

The “79” repeater covers the south and west portions of the Washington metropolitan area.  When fully configured, remote receivers are located in the Beacon Hill area of Alexandria, at the Tyson’s Corner repeater site, Ashburn, VA and at Alexandria Hospital.  The Beacon Hill site is currently off-the-air while its equipment string is being renovated.  Each remote receiver uses a crossband repeater to relay incoming signals to Fairfax on the 420 MHz band, where a LDG RVS-8 voting system selects the best audio signal for retransmission on 146.790.  The main site consists of a Vertex VX-5000 repeater feeding a Vocom  commercial grade amplifier, a Wacom duplexer and a Sinclair collinear 6db-gain antenna for a total of 250 watts ERP.  The repeater controller and autopatch controller is a CAT-1000 repeater controller.     

All of the remote receiver link transmitters have PL encoders installed.  The PL tone on the links serve dual purposes.  The first is to eliminate interference on the link frequencies and in the link receivers.  The link receivers were upgraded from Motorola Motrac receivers with 4 pole front ends to Motorola Micor receivers with 6 pole front ends.  The improved front end of the receiver combined with the PL tones effectively removes the possibility of link frequency interference in the link receivers.  The second purpose of the PL tone is to mute the link receiver as soon as the remote receiver's squelch closes on loss of receive signal.  This eliminates the squelch tail on the remote link, which makes for quieter repeater operation.  The process using PL to eliminate the squelch tail on the links is called "Reverse Burst"

The 146.9100 and 146.7900 repeaters feature digital voice recorders, DVR,  that allow you to send a test message and then have the DVR read back what was recorded so you can hear how you sound into the repeater.  To access the DVR, identify yourself clearly and enter the last two digits of the autopatch code followed by the star (*) key on your DTMF pad.  (The autopatch code is found on the back of your NVFMA membership card) The repeater will then say, “Start Test Now”, key up and send up to 8 seconds of audio.  When you are done, un-key , and the repeater will read your audio back to you.  The main purpose of the DVR test is to maintain quality autopatch communications and antenna testing for communications quality.

Single transmissions are limited to a maximum of three minutes.  When the incoming carrier drops, the repeater will identify itself if it hasn’t done so within the last ten minutes, sound a courtesy tone, and reset the timer.  If the timer expires while a carrier is present, the repeater will announce “Repeater Time Out” and shut down its transmitter.  Once the incoming carrier is dropped, the transmitter will be re-enabled and the repeater will announce “Repeater Time Out Canceled” and return to normal operation.

To properly activate the repeater’s special functions, the DTMF tones generated by your radio must be recognizable by the controller.  If you are having difficulties with a tone-activated feature, your tone pad can be tested by the repeater by identifying yourself clearly and sending a 5 followed immediately by up to 32 digits.  When you release your PTT switch, the repeater will read back everything it recognized after the initial 5.  “Sierra” is read back for * and “P” is read back for #.  To check a key for intermittent operation, send it several times.  The repeater should read back the digit once for each time it was pressed.

Random noise and ‘kerchunks’ are filtered out of the repeaters through the insertion of a slight delay in the audio path between the controller and the transmitter.  In addition to preventing the repeater from being brought up by spurious signals, this feature also permits full muting of incoming DTMF tones during autopatch and other operations.

For more information, please Contact us at the addresses provided.

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