PILGRIM FM-ATV REPEATER

WA1YFV/TV (915 MHz Rx/1252 MHz Tx)

The startup date at present is anybody’s guess, but we hope to get it going.  Technicians needed.

àTHIS ATV PAGE GROWS ALONG WITH THE PROGRESS OF THE PROJECT.ß

The captioned pictures below describe each stage in the building progress of the ATV system.

The antenna array comprises 4 log periodic antennas (LPDAs)  mounted on a 17.5” X 21” backplane.  The array has a 14 dBd gain with a beamwidth of 90 degrees at the -3 dBd half-power points.   The bandwidth of the array is from 900 to 1260 MHz.  The ERP will be about 350 watts.

Mounted on the back of the backplane from left to right are the cross-band duplexer (green box), power divider (center box), and a 18 dB preamp for the 915 MHz Rx input (right box).

This is the LPDA VSWR plot from 900 MHz to 1400 MHz.  The two markers (pointers) on the trace show the SWR at the center of the 915 and 1252 MHz Rx and Tx frequencies.  About 1.3:1 at 915 and 1.6:1 at 1252 MHz.

The antenna system was designed  by Dick Austin, K1QIZ, design engineer and former owner of Austin Antenna.  Dick, the master himself,  is shown here checking the bore-sight toward the reference LPDA mounted in the foreground.

The 90 degree beam pattern is designed to cover all of Cape Cod as shown.  Side lobes in the pattern will cover the Provincetown, Wellfleet and Eastham areas.  Receiving stations at the maximum range of about 38 miles will require a pre-amp and high gain antenna for a P4 to P5 picture.

This is the interior of the cross-band 915/1252 MHz duplexer.  The 1252 input is on the left, the 915 output is on the right and the connection to the quad-LPDA power divider is at the top center.  Designed by Dick Austin.

This is a plot taken using an HP8722C Network Analyzer of the duplexer.  The 915 MHz reject is down 70 dBm, the 1252 reject is down 65 dBm.  The insertion loss  for Tx & Rx is about 1 Db+/-.

ATV antenna array was installed on the water tower location on 5/12/01.  It provides the beam pattern illustrated above to cover the entire Cape Cod region.

It awaits the installation of the repeater, hopefully soon.

This is a a close-up detail of the ATV array shown above.  The elements of a Yagi beam can be seen on the opposite side of the ATV antennas.  This is the packet antenna which provides emergency communications to MEMA Area 2 in W. Bridgewater, MA.

An open view of our locally designed and built 915 MHz interdigital RX filter.  The rods, box sides and ends are milled brass.  The top and bottom covers are made of FR-4 copper clad PCB.  The dimensions were calculated using graphs in the ARRL UHF/Microwave Experimenter’s Manual pgs. 6-38 to 642.

The 915 MHz RX filter assembled, tuned,  and ready for installation.  A similar filter for 1252 MHz has been designed and constructed.  It has similar characteristics to the 915 MHz filter.  We built about 4 different models before deciding on this design.   Making one of these things work properly takes a lot of time and sweat.  Of course, that’s just my inexperienced opinion. (W1PY)

These are the network analyzer plots showing the VSWR curve at top of the display and the bandwidth/insertion loss curve at the bottom.  The VSWR is 2:1 or less across the 12 MHz bandwidth with an insertion loss of less than 1.5 dB.  With a preamp gain of >18 dB at the antenna, a Heliax loss of 1.4 dB to the receiver, the insertion loss is negligible.

More photos will be added as the project progresses.

One of these days we might actually get it on the air.