VK3RTV Latest Information

The upgrade to a digital picture being transmitted from the repeater is still on track. The boards are coming from a SR Systems in Germany who are out of stock until Feb 2009. A lot of the work required to interface the new system has been completed, including a new repeater controller. As long as things go to plan the conversion should take place in Feb / Mar 2009 and the repeater should be transmitting a digital picture sometime in March / April 2009. The inputs will remain exactly the same as they currently are so there will be no changes required by users transmitting a picture into the device.

The parts we will be purchasing are, a Minimod, an MPEG encoder for each channel and a multiplexer for the 2 channels.

This is the link to the products that we will be using :

The repeater sound problem has been fixed by replacing the feed line from the audio transmitter to the antenna. The old feed line that had been in use for many years had developed a leak and was constantly filling with water. After replacement it was noticed that the cable had many nicks and holes in the outer covering and had been crushed in some spots. A day of work by Geoff VK3GE, Phil VK3GMZ, and Peter VK3BFG had the sound transmitter feed line replaced with a new run kindly donated by the site owners (Vertel). Measurements show the sound transmitter is working better than ever.

The WIA has funded VK3RTV to the value of $1000.00 for the digital upgrade. It is likely that AR Victoria will provide the balance of the funds required, The upgrade will include a MUX for two independent channels and of course two channel sound. It would be possible to stream 1283 and 1250 inputs at the same time. In anticipation I am redesigning the control system which will include some nice new IC’s from Maxim. One is a video AGC unit that will keep the output at 1 v p-p standard for a 6dB range of input levels. Will keep you all in the loop as the project develops Peter VK3BFG would like feedback on how we could set up the system.

There are still problems with the repeater sound transmission. The heliax cable from the sound transmitter to the sound antenna needs to be replaced as it is damaged and no longer usable. As climbing the tower is a labour of love by some of the ATV users they are waiting for warmer weather to change out the cable for a new one. Swapping the cable is a day long job and tower during winter is usually in the cold, wet, and wind so hopefully the job will be complete in a couple of months.

To make the repeater beacon and signal reports a bit more exciting Peter VK3BFG has installed a DVD player at the repeater. The signal reports are now a short video clip giving you your signal report. The beacon mode also has more content thanks to Peter. There has been no change to the touch tones used to access any function at the repeater.

The sound carrier from VK3RTV has recently been very noisy and low in power. A check found water egress into a cable splice on the sound transmitter cable. The cable had been cut by one of the many others that have access to the repeater site and repaired but not sealed properly against the weather. The join has been sorted out but there is still a small problem in the cable / antenna somewhere. The sound output from VK3RTV is now adequate but a proper overhaul will have to wait for warmer weather.

2007

The 10GHz input to the repeater is working well from the greater Melbourne direction. This input requires equipment that is easy to build and small. Here is your chance to play on the microwave bands without too much effort.

G'day from Geoff VK3JDG, Long between updates on the web page.

We now have a 1283MHz input on the repeater with an antenna pointing towards the Yarra valley.

There is a trial 10410MHz input to the repeater that appears to work well with lots of local building of equipment to utilize this input.

Well the new sound TX is all but complete. Required RF output is achieved and most of the associated wiring is complete. Having increased the output power all the way around, I require another small fan (about 70 MM would do the job), preferably 12V DC, but any port in the storm !!!.

Rob, VK3KOS has sent over a replacement PC for the old crock up the mount. It includes a CD ROM drive that will help out with loading software. It is in mint condition except that one of the regulators has a vastly underrated heat sink. I would hesitate putting the system up the mount in this condition. The easy fix would be (guess what) ... yes another small fan !!!!. Any offers ????

G'day from Geoff VK3JDG, Well Sunday the 20th Feb 2000 was an exciting day for at least 2 local ATVers. Joe VK3TMS and Geoff VK3JDG played with a bit of 10 GHz ATV. Joe was transmitting from near the top of Mt Macedon and was being received by Geoff in Sydenham ( a path of approx 43 Km ). A strong P5 picture was received, the received picture was then uplinked to the repeater on 1250 MHz for everybody ( anybody ) to see. Equipment used was all home brew by Joe, who using 10mw and a 60cm dish for TX and a modified satellite LNB and 60cm dish for RX. Video quality suffered slightly as the tx fell in the rear of the car on a bumpy road up the mountain and field adjustments at 10 GHz is not advised. Received signal was roughly 25 - 30db above a full quietening signal. Joe ( and Tony VK3AAZ a few weeks earlier ) also transmitted and received 1250 MHz signals to and from some of the Melbourne locals who were around. Again it was discovered that minimal power ( < 1W ) can achieve noise free pictures across distances of 50 - 60 Km. Joe was able to get a very noisy picture into the VK3RTV repeater on 1250 MHz, firing through a large plantation of pine trees ( no direct view, and a path of approx 85 Km ).

Sunday 20 Feb 2000 is 10 GHz experimenting day ( well for a couple of us ). The plan is to transmit a 10 GHz ATV picture from Mt Macedon to Sydenham and then uplink that picture to the repeater on 1250 MHz from Sydenham to Mt Dandenong ( if all goes well ). Participants are Jose VK3TMS ( at Mt Macedon ) & Geoff VK3JDG ( Sydenham ). Try watching the repeater to see what's happening, we should be trying from mid morning until mid afternoon.

The system seems to have settled down and is performing well with a number of fans operating 24 Hours/day cooling the PA, PA Power Supply and the Receiver !!! ( RX only has a very modest heatsinking facility )

Rain is still a problem, with the reason for the loss of input signal sensitivity a topic of debate within the group.

I have a friend who has agreed to make a stainless steel box to house the 23 cm input BPF and the masthead pre-amp. Unfortunately he has been a bit busy and has not been able to complete the job to date. Hopefully this will be soon.

I had a call from Peter Mill who is the Vic Division Repeater Coordinator, re the letter I sent to the Vic Division requesting some funds for a new 23 cm antenna system. Apparently the President, Jim Linton is very supportive and hopefully this will go through at the Vic. Council meeting this week.

The new sound exciter is well on the way thanks to donations from Mark VK3JMA ( Heatsink ) and Joe, VK3TMS ( Crystal and SBL1 Schottky Ring Mixer ). I am still looking for the following transistors ....

BFX89 BFW92 and BFW16A. Two of each would be good, one for spares should trouble eventuate. If you have one, pop it in the mail, QTH OK in the Callbook. All donatees are acknowledged on the Website.( Please note Geoffrey !!)

The exciter has an FM Modulator at 33.4 MHz which is extremely wideband and quite 'linear'. It has a discrete PLL which locks the freq. very well. A low level mixer/amplifier board will drive a Mitsubishi Module to about 5 Watts. (only require 3 Watts for -10dB relative to Vision Carrier)

I notice that VK3AOB is building a 18W amp that he is going to mount at the antenna. He may well burn out the GASFET in the Rx front end !!!

Regards Peter VK3BFG

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 comparators which produce a BCD code for the micro-controller.

The report is a bit arbitrary 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 achieved 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 frequency 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 oscillator 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 continuously 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 problems
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 propagation 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, VK3AOB and VK3JDG 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 Tullamarine 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 expenditure 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



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