SJAC106.7 fm LPFM low power Community Broadcasting.
Some pictures of the antenna and station set up at St James Church.
Two views of our First antenna
A 5/8th base loaded vertical
with Ground planes and was at 27 feet. The SWR on this was 1.35 to 1 But operated on this for about 1 month while the dipole was made and erected.
This antenna was modified to remove the radials and the SWR came down to 1.3 to 1.
The Dipole still shown here on the right was much better and had an SWR of 1:1. on 107.3 this is at 18 feet Needless to say coverage was much much better.
The latest antenna (tall one is) a JPole with an SWR of 1.1 to 1 and is at 27 feet. The lower angle of radiation and gain of this antenna has increased coverage by about 1 Km to aboput 4 km from the antenna.. This is the antenna we are currently using.(After nearly 11 years the Antenna is still performing well but should now need to be serviced.
The Transmitter we started with was a ten year old InForm. Model 400 with an out put of .5 watt at the output socket. Losses in the coax etc reduced that to about .3 watt. into the antenna. ( Real high power) With the 5/8th vertical coverage was at best 1.5 K. When this was coupled to the dipole, coverage went up to 2.5Km
In Feb 2007 we purchased an NRG transmitter and limiter/compressor with .8 watt out put at the socket and this was coupled to the dipole and with coax losses etc we were getting an estimated Eirp of .61 watt.and coverage shot up out to 3.5 Km. Finally we fitted the JPole now we had to watch the EiRP here as this is a gain antenna. However we have found that with the combined losses in the extra coax and antenna connections we estimate the output at about .55 watt This has increased our coverage to 4 Km . However due to the topography of the terrain the best average signal (readable quality) is closer to 3 to 3.5 Km. Transmitter power has been increased to 1 watt at the transmitter and now with all the gains and losses we estimate 1.2 w EIRP.
For the technically minded.
Station construction details.
We are located part way up the side of Mangere Mountain which limits the signal to the South (Mangere Central).
The Manukau Harbour is to the North of us with Hillsborough, Onehunga rising from there up the slopes of One Tree Hill. So with nothing to the East and west of us (except water) to all intents and purposes we are in an elongated ampitheater. Or similar to a long valley if you like.
This gives us most houses having a long view of the antenna. ( Line of sight. Which is Very good). Census details give us a potential households of around 6 to 7000.. (With new development since station was established household coverage has increased to around 20000. Adjacent stations have crept in whch causes a but of muxh zone where we overlap but not too bad at prasent we still cover the Parish OK).
Antenna number two.
Antenna number three.