A 3.7m Prodeline dish for Astra 2D

[pjgregory]

I understand what you are planning to do BUT my concern is that invacom feed neck will not have enough play to move forward/backward in your machined Prodeline part when fine tuning the focal point...

Iceman - I see what you are getting at.

I think I will have 1-2cm of focus motion. The Prodeline dish also has adjustable bolts holding the 4 struts to the dish. I plan to use them to get the focus set according to the book, then adjust the position of the Invacom horn for fine focus.

From your picture, I see that your scaler plate seems much larger that the Invacom version. Is this the fabled "Cyprus" feedhorn? Is it worth trying to get one?

PJG

 

[iceman]

Iceman - I see what you are getting at.

I think I will have 1-2cm of focus motion. The Prodeline dish also has adjustable bolts holding the 4 struts to the dish. I plan to use them to get the focus set according to the book, then adjust the position of the Invacom horn for fine focus.

From your picture, I see that your scaler plate seems much larger that the Invacom version. Is this the fabled "Cyprus" feedhorn? Is it worth trying to get one?

PJG

well...if the struts have height adjustment built into them you are OK..
The scallar rings on the feed you see is larger than Invacoms feed and there is another model slightly larger than the one in the picture...Thats supposed to be better but i have not got round to fitting it on my dish..
Attached is the three feed's..center one is the one on my dish,Invacom feed is on the right and on the left is the larger model....and yes the larger scallar ring models work better than the invacom feed...

 

[pjgregory]

The scallar rings on the feed you see is larger than Invacoms feed and there is another model slightly larger than the one in the picture.....and yes the larger scallar ring models work better than the invacom feed...

Where can I buy them?

PJG

 

[iceman]

Where can I buy them?

PJG

As far as i know only in some stores in Cyprus...

(I will be in South Garda,Italy between 15th-21st..Is it anywhere near you)

 

[pjgregory]

Lake Garda is in the north of Italy, I live in the center 80Km south of Florence, so its not practical.

If you could give me a price for both sizes plus courrier delivery from Cyprus, I could transfer money to your account either in the UK or Cyprus. Any little improvement helps so it will be worth trying both on my larger dish.

PJG

 

[pjgregory]

I got the modified Prodeline feedhorn back from the engineer shop today - a good 10 euros worth. Now the Invacome adjustable feedhorn slides inside and is secured with two set screws. I have about 15mm of focus adjustment, which should be OK for fine focus.

Next week I should get my laser pointer so I should be able to continue with the installation then.

PJG

 

[pjgregory]

Now that I have my green laser pointer, I can mount the feed horn. I wrapped the laser in two places with a thin layer of sticky backed foam followed by layers of clear packing tape until it was a slide fit into the waveguide.

For the Invacom ADF-120 adjustable feed horn, the protursion of the wave guide in front of the scaler ring is given as 5mm for a 0.35 f/d ration dish which is the value specified by Prodeline. I used a little "Locktight" to secure the ring.

Now a question. When installing the assembly onto the dish, do you measure the focal length from the front of the protusion or the front surface of the scaler ring? As these are 5mm apart, it could make a difference.

PJG

 

[patmos]

Great post. I t makes me dream. I could not make my 3.4m prodelin work to perfection. It encourages me to reassemble it. Bonne continuation.

 

[pjgregory]

On Thursady, I finished the stand that allows me to work inside the dish. It is made of 30mm steel L section angle, with the base and supports bolted down to the concrete pad. Two wooden boards on top allowed me to keel or stand inside the dish to attach the feed mounting arms. (042.jpg and 043.jpg)

With no respose to my earlier question about the correct position to use for focal distance measurement, I opted for the front of the throat, cutting a length of plastic conduit to the 1372mm (54") specified by Prodeline. I used this a guage to adjust the distance of the feed horn from the dish. (044.jpg)

Then with the laser inserted in the feed horn tube I checked the aligment of the feed horn axis with the center of the dish, rotating the laser by hand in the tube to trace out circles on the base plate. This proved more difficult than I had imaginged as there was some "play" in the machined mount. Tightening the two grub screws could alter the spot position on the base plate by 1-2 cm.

I then found it impossible to fix the LNB onto the fixed feed horn as I coiuld not get the screws in place. In the end, I put a layer of clear tape aroung the feed horn tube to make it a tight fit in the mount before uncrewed the scaler ring, attaching the LNB nad then putting it all back together again. Not perfect, but I am fairy sure that I aligned the axis to within 1cm of the center.

Finally the moment of truth.

I connected my Satlook spectrum analyser to the LNB, set the elevation to 37.5 degrees and rotated the dish in azimuth to lock onto a strong low band Astra 2 transponder - 10964H. After a few minutes of trying with the wrong satellite (Arabsat at 30.5 degrees east), I got a lock on Astra 2D and peaked the signal in both elevation and azimuth. Then set the LNB tilt to 9 degrees.

Back in the house, connected to the Pace Skybox, I had Radio 4 on 11954H, but NO BBC1,2 or ITV!

Disaster - after all this work and care what a let down. My wife went very quite.

So there must be something wrong. I checked the signal strength on 10964H and found that I was getting 71.2db on the meter. I removed the LNB, put it back on the 1.2m Channel master dish and measured 75.8db.

That was enougth for the day. Corviello, who has posed about his own experiences with a 3.4m Prodeline disk is visiting on Friday, so I will try again then.

PJG

 

[pipino]

On Thursady, I finished the stand that allows me to work inside the dish. It is made of 30mm steel L section angle, with the base and supports bolted down to the concrete pad. Two wooden boards on top allowed me to keel or stand inside the dish to attach the feed mounting arms. (042.jpg and 043.jpg)

With no respose to my earlier question about the correct position to use for focal distance measurement, I opted for the front of the throat, cutting a length of plastic conduit to the 1372mm (54") specified by Prodeline. I used this a guage to adjust the distance of the feed horn from the dish. (044.jpg)

Then with the laser inserted in the feed horn tube I checked the aligment of the feed horn axis with the center of the dish, rotating the laser by hand in the tube to trace out circles on the base plate. This proved more difficult than I had imaginged as there was some "play" in the machined mount. Tightening the two grub screws could alter the spot position on the base plate by 1-2 cm.

I then found it impossible to fix the LNB onto the fixed feed horn as I coiuld not get the screws in place. In the end, I put a layer of clear tape aroung the feed horn tube to make it a tight fit in the mount before uncrewed the scaler ring, attaching the LNB nad then putting it all back together again. Not perfect, but I am fairy sure that I aligned the axis to within 1cm of the center.

Finally the moment of truth.

I connected my Satlook spectrum analyser to the LNB, set the elevation to 37.5 degrees and rotated the dish in azimuth to lock onto a strong low band Astra 2 transponder - 10964H. After a few minutes of trying with the wrong satellite (Arabsat at 30.5 degrees east), I got a lock on Astra 2D and peaked the signal in both elevation and azimuth. Then set the LNB tilt to 9 degrees.

Back in the house, connected to the Pace Skybox, I had Radio 4 on 11954H, but NO BBC1,2 or ITV!

Disaster - after all this work and care what a let down. My wife went very quite.

So there must be something wrong. I checked the signal strength on 10964H and found that I was getting 71.2db on the meter. I removed the LNB, put it back on the 1.2m Channel master dish and measured 75.8db.

That was enougth for the day. Corviello, who has posed about his own experiences with a 3.4m Prodeline disk is visiting on Friday, so I will try again then.

PJG

i would check the dish if its assamble 100% its impossible to have a 3.70m monster underperforming that way !!!specialy when you did the difference with your 1.20m ,few years back i had similar situation with a petalised "alcoa 1.80 dish" , setting it again properly saved me the day,,in the other side i would ask advise from guys like Prodelin them self(regarding how to check the assembling) or david roman from slovakia as he have the exact same dish like you

ahh one thing what LNB are you using for your tests ??i saw a single invacom before in one of your fotos..if so Change it for inverto C120 or invacom Quad ,single invacom is total rubbish
..good luck ..regards

 

[Channel Hopper]

Back in the house, connected to the Pace Skybox, I had Radio 4 on 11954H, but NO BBC1,2 or ITV!

Disaster - after all this work and care what a let down. My wife went very quite.

So there must be something wrong. I checked the signal strength on 10964H and found that I was getting 71.2db on the meter. I removed the LNB, put it back on the 1.2m Channel master dish and measured 75.8db.

I think you need to carry out a shakedown of the reflector.
Put the dish back to the (absolute) horizontal, string it in the four positions between the reflector panels, undo all the bolts - by two turns - holding the reflectors and the support struts (long and short) , and give the dish a good shake. Then retighten.

Prime focal point of the feed is achieved with the distance about 1cm within the scalar rings.

Boresight tool is literally a tool that can be used to look down the feedhorn, and locate the centre of the reflector, be it a stiff stick, or a laser sighting unit. Failing that, measuring the edges of the scalar rings to the outside of the reflector at a distance not more than 3mm should be sufficient.

If all else fails, you may have to take the paint off the reflector.

 

[pjgregory]

I started again Friday morning.

My first concern was the focus. The specified focal distance was 1372mm. First I measured the dish diameter - 3660mm, then the distace from the faceplate to the crossing point of the strings. This was actually 60cm, rather than the 61cm specified by Prodeline. So using the formula

F = Diam * Diam / 16 * Depth

I have a computed focal length of 1395mm, some 2cm more than specified as measured this from the front of the throat. Channel Hopper has now suggested the focal point should be 1cm inside the scaler ring, which would reduce the focal length by some 1.5cm. Adding the two errors together should make me about right, but there is still an uncertainty as to the best position.

Before I could do any more, Corviello arrived. We went through the string test again and the laser alignment. He though they were both fine. He then tried adjusting the LNB orientation with his own meter.

Then he noticed a strange thing. When he climbed the ladder to move the LNB, the signal level rose by about 1 dB. Coming away from the dish, it fell again. So covering up part of the left side of the dish gave a stronger signal (048.jpg). He suggested there could be an error in the azimuth setting.

So we tried moving the dish. But as before, as we shifted it away from the maximum, the signal level fell. Then he moved it even more in the easterly direction. From nothing, the signal suddenly shot up to a peak far higher than before. In my first alignment, I must have been receiving the stronger signals on the first side lobe of the dish.

Now the readings were much more sensible. The output on 10964H was 79.6dB compared with 75.8dB on the 1.2m Channel Master, a near 4dB improvement. (Photo 049.jpg has Corviello on the right and me on ther left). After a little more fine tuning, we went into the house to check.

The Full Montey!

BBC1, BBC2, ITV, Channel 4,5 etc. on all vertical and horizontal transponders. Even by 6pm BST, we were still showing 70%-80% signal quality on all channels. Last night my wife watched Casualty on BBC1 at 9pm BST for the first time in years.

So many thanks to everyone who provided hints and advice and especially to Corviello who took the time and trouble to help me out. Could I do better - possibly as there is still the focus issue. But for now I have just bolted everyhing up light to sit back and enjoy the show.

Strictly Come Dancing - Ahh!

PJG

 

[pipino]

Fantastic!!!!i must thank you very much for sharing your experience with us i´m sure in the future some other members will learn from it...congratulations!!

 

[satelliteman]

Interesting reading and a great result

 

[CROSSBONES]

What a great thread and photo`s! Very nice dish too!:-worship

 

[pjgregory]

Some more thoughts

1. The Channel Master 1.2m dish has a published mid point Ku band gain of 42dB, while that of the Prodeline 3.7m dish is 50.7dB. So I should have an increase of some 8.7dB. The measured improvement in gain with the same LNB etc. at 10964H is only 3.8dB so unless the published figures are wrong, I am still missing some gain - maybe the focus issue?

2. On the question of the focus, while it was easy to simply drill out the supplied Prodeline feed horn to take the Invacom horn, the range of focus was in the end limited to about 1.5cm. If I started again, I would follow Channel Hoppers advice and make a new flat aluminum plate instead with a boss to hold the Invacom horn. This would give me a much wider range of focus positions.

3. Using the modified Prodeline horn also gave another problem. Corviello brough with him a much larger "Cyprus" scaler ring, but it would not fit in front of the mount so I was unable to see if it would improve the signal. Using a flat mounting plate with the four legs spread wider apart would have have allowed me to try the larger ring.

PJG

 

[patmos]

Great job. Its a pleasure to read such a detailed thread. god bless

 

[charly20]

Excellent detailed report.

It was worth the effort and frustrations.

What an inspiration!

 

[denis1501]

Congratulations on your success in getting Astra 2D and thank you for your excellent posts.
I'm south of Rome where Astra 2D remains a no-go area! So my wife and I are really jealous....!!
Well done m8,
regards
D.

 

[rolfw]

Yes, well done PJG.