Melbourne Amateur TV Group
|Live Pictures from VK3RTV streamed via the BATC web site|
Hello all ..
I am just in the first testing stages of the 500 Watt PA funded by donations from Melbourne ATV Operators. It was a bit painstaking to assemble and you are always nervous before the first switch on. I also have to be a bit careful as most of my dummy loads will be sorely taxed by this device. I don’t really have any power measurement instruments for this level of power. I am currently just using a Revex Through Line for this purpose. The gain is quite high as predicted and I can easily get 100 watts out with about 300 milliwatts in. I will need to bring the DVB-T exciter down from the hill soon to interface accurately from a power drive point of view. I will thoroughly test the amplifier before this so VK3RTV should be back on the air the next day. The 50V power supply donated by the EMDRC looks as though it will do the job nicely although it was a bit of an adventure working out how to get it to switch itself on.
I have finished temperature testing the new PA and have it running 100 watts out and quite cool. (Can easily touch the heatsink, only mildly warm). I am waiting on a temperature sensor to arrive and have designed a power supply sequencer that will run the fans for 10 minutes after key off and inhibit any DC power to the amplifier should the temperature of the heat sink rise above a pre set value ( about 50 degrees). When I have all that in place I can bring the DVB-T exciter down from the site to set up drive levels and monitor IMD products at the output. It will be interesting to see what the difference is between QAM 16 and QPSK. Danny, VK4KI and Richard VK4XRL have kindly provided appropriate settings for QPSK. At the same time I am working on antennas to improve Melbourne stations into VK3RTV2 and also a new antenna with better coverage for VK3RTV1.
Regards Peter VK3BFG
** For Melbourne ATV stations, Winston VK7EM will be on 1283 Mhz analogue this summer leaving the transmitter on for extended periods when the band looks a possibility across Bass Strait. You will need an analogue Sat Receiver and probably a pre-amplifier to receive the signal. A very good pre-amplifier is available from Minikits and an analogue receiver from HamTVstore ($56.00) **
Amateur Television (ATV) transmissions in Melbourne are mostly via the VK3RTV amateur television repeater on Mt Dandenong although a number of operators make simplex contacts on both 70cm, 23cm and 3cm. The ATV repeater is in operation 24 hrs a day and provides coverage of the greater Melbourne area.
The output of VK3RTV is a standard Digital TV signal on 446.500 MHz (Not all digital TV's or STB's can receive this frequency - Check the list of known good receivers on the Receiving ATV page and if you have a receiver that works that is not on the list please let us know at firstname.lastname@example.org). Currently VK3RTV1 shows the analogue input and and VK3RTV2 shows the digital input. If no one is being received on the alternate input then the colours bars will show on that alternate output.
Voice contact with other ATV'ers can be made on the ATV liaison frequency 147.400 MHz FM simplex, it is also a good idea to keep an ear out on this frequency when operating ATV. If unable to transmit on 147.400 MHz and require a picture to be put up on the repeater then drop a short note to the email below and I will see what can be arranged.
For more information email : email@example.com