28 Jan 2000 We try again !!!! VK3BFG, VK3AOB and VK3JDG will conduct an ATV flight out of Moorabbin airport on Sunday 30 Jan 2000, weather permitting. (Should be OK) The expected departure time will be between about 5:00 PM and 5:30 PM. VK3BFG will be the pilot, VK3AOB the camera man and VK3JDG will be the supervising engineer. (He points the antenna out the window in the appropriate direction and makes sure the transmitter does not fall off the seat) The flight will take us over the City of Melbourne (providing a clearance is available) and then on to Mt Dandenong. We will transmit on 1250 Mhz for as much time as possible, depending on battery drain. If you will not be home, set your tape recorders up for 5:00 or so with a three hour tape. Regards Geoff VK3JDG ----------------------------------------------------------------- 23 Jan 2000 As most will now know, the signal report is now working. This function measures the voltage on the AGC line which is then fed to four adjustable comparitors which produce a BCD code for the micro-controller. The report is a bit arbitary as after trying a few different ways of setting up, I settled on the good old have a look and see guestimation. No sig or a very weak sig will register S1. An interesting fact was that Geoff, VK3JDG and Tony, VK3AAZ both had about the same AGC voltage. The S/N of the picture was far better for Geoff than Tony. The difference is the noise inherent in the baseband (video) signal before or during RF modulation and amplification. A second fact was that there was only a relatively small window (compared to AM)between an S1 and an S5.For example, a 3 - 4 dB increase from Geoff or Tony would probably lift them to S5.This could be acheived by stacking beams or may be by the forthcoming mastheading exercise. >From my measurements today I would estimate about 12 - 15 dB is all there is between the extremes. (S1 - S5) I am still looking at a new, higher quality wideband sound exciter with audio AGC to replace the old system which has not transferred to the new lower freq. too well. The cost of this would be for two crystals (one is a common garden CB freq.) a local osc chain and a ring mixer and a low level amp to about 50 mw. The system would be based around a 33.4 Mhz F3 oscilIator with PLL control.It is relatively easy to get good linear deviation at this freq. and the existing video modulation is at 38.9 Mhz, so you can see the reason for the selection. I have a 70 cm Power Amp with a Mitsubishi Module in it donated by Peter, VK3BK . A bigger heatsink would be required to make it practicable. I would think about $80.00 would do the trick. The PCB's and some components can be 'provided' by Swinburne TAFE. Regards Peter VK3BFG ----------------------------------------------------------------- 17 Jan 2000 First minor problem ......... the transmit chain local oscillator has decided to drop out. Not a major drama really, but obviously causes no vision RF output. The system has two similar LO's and multiplier chains (only one currently in use)so there should not be too much of a problem. Will try to get to it in the next day or so. Regards Peter VK3BFG ----------------------------------------------------------------- 14 Jan 2000 The Winersat Satellite Receiver is now in operation. My observations at the repeater end are that the waveform is far superior to the Pansat and that the inbound chroma is about 50% more. The line and frame syncs are also square. (Rather than sloping with poor LF response etc.) The video also has a lot more headroom. The A5 modulator is reaching peak white + now rather than the FM RX. There is no more streaking on the sigs as far as I can see. In Electronics there is nothing you get for free ...... the gain-bandwidth product theory says more bandwidth, less gain and more noise. From what I can see here, the western suburbs stations are not quite as strong as with the Pansat, although we have not had enhancing propogation since installation. My vote is to leave it in operation and see how the masthead pre-amp reduces S/N. I have a friend currently making a stainless steel box to house the filter and pre-amp so it should not be too long. Your observations and responses would be appreciated. The power output of the system seem to be settling at a fairly fixed value to date as measured here under similar weather conditions. There is still a slight fall in output with time. The difference between the old system and the new is that the old design was Class A and continuosly rated and the new is Class AB and intermittently rated. Please give the system a break, particularly when it is hot. I noticed in AR Magazine that there is a one year extension on Ch35 for all current users, subject to any interference probs from digital TV experiments. Our move was apparently a bit premature, but I had no indications at all from Vic. Division WIA. The move for us got rid of the Bendigo problem in the western suburbs, increased output power and better propogation due to lower freq. and still primarily within most TV tuners. Also we are still using 70 cm effectively as before. A day or so ago someone was re-transmitting either CNN direct or a video tape. This is not a good idea as we are now much more public than we have ever been. Regards Peter VK3BFG ----------------------------------------------------------------- 6 Jan 2000 Flight over Melbourne did not take place due to potential fuel problems currently being experienced with light plane's. Regards Geoff VK3JDG ----------------------------------------------------------------- 5 Jan 2000 VK3BFG, AOB and JDG will conduct an ATV flight out of Moorabbin tomorrow ( 6 Jan 2000 ) afternoon, weather permitting. (Should be OK) The expected departure time will be between 3.30 and 4.00 PM. VK3BFG will be the pilot, VK3AOB the camera man and VK3JDG will be the supervising engineer. (He points the antenna out the window in the appropriate direction and makes sure the transmitter does not fall off the seat) The flight will take us over the City of Melbourne (providing a clearance is available) and then on to Mt Dandenong. We will transmit on 1250 Mhz for as much time as possible, depending on battery drain. If you will not be home, set your tape recorders up for 3.30 or so with a three hour tape. Regards Peter VK3BFG ----------------------------------------------------------------- 5 Jan 2000 The new 28dB pre-amp and bandpass filter is currently in test operation fitted at the receiver end. It is being powered as a masthead via the co-ax. The BPF is a high quality unit (ex Tullarmarine I think ... ask 3BCU) with a very low insertion loss of less than 1 dB. I have written a letter to the WIA Vic. Division seeking some financial support for further development. VK3RTV has, however, always been mainly funded by donations of both hardware and $'s from the users. To continue development, I think we need to again set up the '3RTV Fund' that has existed previously. I have kept all receipts of expendature over the years with this fund and would continue to do so if a new fund was established. I suggest that an initial donation of $20 - $30 from each user would be a good starting point for this. Donations could also count towards this contribution. Obviously there would be no charge for viewers unless they volunteered. Projects for the future could be ........ New 23 cm Antennas Switchable 23 cm Antennas New PLL controlled high quality sound exciter. Improved graphics capability. 2 Metre graphics upload capability for user framestore. etc etc etc Your response to the fund proposal would be appreciated. Regards Peter VK3BFG ----------------------------------------------------------------- 30 Dec 1999 VK3RTV is now both keyed (Sync Detection) and driven with line video from a SCART Connector at the rear of the receiver. The result of this change is there is no longer any 'blue screen' showing 'no signal'. This means that the repeater will not turn on without composite sync. present. Brett 3AOB is doing a short mod. job on a different receiver to try out. The transformer runs extraordinarily hot, so we need to cool it down. (There does not seem to be any fault other than the transformer design is poor. It may have been designed for 60 Hz which would explain the problem) The receiver is a PLL locked Winersat and as far as I can see, the video quality is superior to the existing Pansat. (Not that the pics are too bad from it at the moment !!) I am currently putting together a 28 dB pre-amp which we will masthead in the new year. (Will also try it 'at the bottom' in the interim) This is a minor task compared to recent tower operations and should result in greatly improved signal strength, especially for those who are struggling a bit at the present. The only remaining project for the near time is new antennas for 23 cm. I have suggested a few options in the past, but perhaps an array of three co-linears may be the best option. I suggest we wait and see how the pre-amp goes. The existing 23 cm antenna will need to be replaced, however, as the current mechanical design will probably not stand up too much longer. I would expect the new 70 cm antennas will be good for quite some time yet. ( A reasonable number of years) Regards Peter VK3BFG ------------------------------------------------------------------