[P12] What's up?

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For some reason we suddenly have solid reception of all the weak channels. Instead of the low 50s. Quality is now in the high 60s. Even as high as 70% on one channel! Signal strength S remains at about 78.

The weather is almost totally overcast but bright. With only occasional sunny periods. After a completely still start and an overnight frost, the wind is picking up to a breeze.

I have no explanation for this sudden change in signal quality. The wind cannot affect the dish very much even when it is blowing hard. Otherwise the stronger channels would disappear along with the weak ones. A large dish demands a much stricter pointing accuracy with its acceptance beam width of less than 1 degree.

I have found a second hand galvanised pipe to get rid of the ugly concrete fence posts which I use to load down the present iron and steel base. A simple pole will be much neater and allow the grass to be mown tighter to the dish.

By the time the new pole is cast in concrete it should provide a much more stable base for the new dish. A flange on the bottom will ensure the pole (and mounted dish) cannot rotate under wind loads. Normally one would have to add rods or fins to stop pole rotation in the concrete base.

A pole set in bare earth, even with added rocks or boulders in the excavation is not nearly stable enough. The concrete greatly increases the surface area of the pole. Thus avoiding the localised pressure a simple pole is able to exert on the soil. An "elephants foot" excavation will avoid the pole lifting due to frost heave or wind storm effects on the large dish. Channel Master recommend a cubic meter of concrete for their 1.8m dishes!

Yesterday's improved reception excitement was short lived. Q had dropped to 53% by 14.30 on most Spot Beam channels without a safe lock possible. Nothing pm, overnight or early morning.

Today the higher signal strength had returned by about 10.30am. S was back up to 80 with Q up to 70%. By 2.30 many channels were becoming only borderline watchable with low 50s% Q. Though some channels were still fine at 17.30pm! A very strange variation in Q across the range of transponders on the UK Spot Beam. 

I found this YT video on checking satellite dish focus using the sun and some small mirrors:

http://youtu.be/TTXvpES1_ZA

Provided the reflections are all equal and all overlap on the face of the LNB (or feedhorn) they must be centred and in focus. I believe the spoken language is an Indian dialect.

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[P11] Bigger AND better?

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As I hinted in my last post; there is the option to go on increasing dish diameter if stable reception is impossible with a smaller one. However there are many obvious and less obvious disadvantages to up-sizing. Not least is having a huge round object cluttering up the garden. Then there are the inevitable problems of wind drag literally tearing the dish from a weak support. "Hoist the spinnaker!"

There is the increasing narrowness of the field of view or signal acceptance angle. This problem is severely exacerbated by any wind movement in the mounting of the dish. Massive concrete foundations and thick walled pipe of requisite diameter to suit the dish size and its mounting are a must.

Dish flexure, or that of the feed support arms, is very possible in very high winds.

Sturdy stands (usually of tripod or four-legged construction) are available to allow the adjustable mounting itself to be bolted down. Usually onto buried concrete footings. Though these stands may also be bolted own onto flat, concrete roofs if necessary. The emphasis here must obviously be on absolute strength and stability in extreme wind speeds. Nothing else offers the level of public safety required.

Or the dish can be attached to a massive aerial mast as seen here in abundance. (These are all high quality, Channel Master/Andrews (now Raven) offset dishes except for the very top one which is prime focus)

The bottom one is about 6' or 1.8m in diameter at a guess. It is very difficult to judge from below and impossible to reach with a tape measure. These communal lattice masts are seen in many towns and villages throughout Denmark. Formerly providing a local TV service "pack" by cable for a regular fee. While avoiding the need for aerials or dishes to be installed on every home. Most of these TV services are now provided by a small dish and payment card to go in the receiver. Or TV packs can often be provided on the Internet these days against a subscription.

Signal gain from increasing dish diameter is hard won and still highly dependent on dish quality and accuracy. The cost rises extremely quickly if a brand new, larger dish is purchased. There may even be heavy charges for delivering the over-sized beast. Anything to special order is likely to enjoy a heavy premium. Shopping around is probably wise to minimize the expense.

Trying to save money on cheap, kit-built, segmented dishes is arguably a waste of money. That is, unless great care is taken in assembling and supporting the dish to a very high standard. Any misalignment in the construction of the "petal" segments will result in far inferior performance over a high quality, one-piece dish. The segmented dishes can't be simply assembled and expected to offer upmarket performance for a small fraction of the cost of the best quality dishes. Some dealers will not even stock them for this very reason. Buying, assembling and installing one badly is likely to be a total waste of time and resources. 

Then comes the choice of an offset or prime focus dish. Certain manufacturers, such as Andrews (Previously Channel Master but now called Raven) have produced very high quality offset dishes. These are made in a whole range of sizes from moulded plastic with a reflective mesh hidden under the curved surface. These dishes are easily recognized by the unique rear ribbing. Designed to maintain the accuracy and rigidity of the parabolic dish surface. These dishes are certainly not cheap unless they can be obtained second hand. Their quality is legendary.

Offset dishes have the LNB set low on the nearly upright dish. The satellite signal is reflected downwards at a considerable angle above the dish's apparent axis before it reaches the LNB at the focus. Raven offers a special, offset, C120 feedhorn to match its own offset dishes.

Most other commercial offset dishes use a 40mm LNB specifically designed for offset us. Offset dishes are reputed to have theoretically better performance than prime focus dishes. Though this difference may be the result of the quality differences between various manufacturers. One must compare like with like. Raven provide prime focus dishes as well as offset. It might be instructive to study this manufacturer's technical literature for each type for a more accurate comparison. One must also remember that the Ku-band requires far greater accuracy in dish manufacture than the lower frequency C-band. 

Channel Master (Andrews/Raven) offset dish. Probably a 1.8m [6']in diameter. Note the tiny feedhorn and professional quality LNB.

Prime focus dishes are easily recognized by having equal length, LNB support arms. With the LNB sitting absolutely central to the dish and the dish usually pointing up in the sky directly at the satellite. Prime focus dishes tend to look better in that they are tilted back and thus their more oval appearance looks smaller. They also look more like traditional radio astronomy dishes. The obvious sense of purpose may be more acceptable to some eyes.

After years of using a 120cm Gilbertini offset dish my foray into larger dishes began with a prime focus one. Though there was absolutely no conscious decision involved. Beggars can't be choosers and I found my neglected 6' fibreglass dish quite nearby. A search of the local small ads may save a  lot of money if one is extremely lucky.


Large dishes (over 1.5 meters diameter) have only a very small amateur market in most places. Being of interest only to those seeking very weak TV signals. Which usually means trying to receive TV channels out of their intended geographical range. Perhaps of greatest interest only to immigrants seeking the pleasures of their own domestic TV stations. Which are broadcast in their own, native tongue. Though there are a few hobbyists around who seek weak TV channels as a pastime, of course. These few must represent only a very small proportion of the large dish market. Though there seems to be more interest in the hobby in the USA judging from the number of YouTube videos on the subject.

Depending on your country of abode there may be planning restrictions on satellite dishes. Particularly in built-up areas, on (historical) listed buildings or in their grounds. A neighbour may consider his vast, white,  mobile home (caravan) as something to be immensely proud of. Yet, ironically, the same caravan owner may greatly resent the intrusion of quite a modest sized dish into his view from the terrace.

It doesn't help your cause if your dish is as toothpaste white as their own caravan! Though dishes may be painted with non-metallic paints it must reduce efficiency slightly. A well upholstered, rural garden probably offers a far greater chance of hiding your "carbuncle on the landscape" from view  While a city garden is usually overlooked from a number of angles and is often much smaller. Greatly increasing the sense of scale of the intruder. It's similarity to an upturned UFO may not have been missed by the mischievous neighbour who sees parallels between your dish and your alien status.

An old, well-weathered 2.2m [7'2"] spun aluminium (?) prime focus dish by Kathrein on a Danish communal TV mast.

The dish must obviously have an absolutely clear view of the sky. Though only in the desired direction of the host satellite and it must be clear over the entire surface area of the dish. No building, trees or bushes must block the delicate signal path from the satellite. Imagine a broad beam of light coming down from the satellite of the same diameter as the dish. No shadow may be thrown anywhere on the dish. Or think of the dish as a huge searchlight. The parallel beam must not shine on anything except the sky.

Larger dishes do not look well attached to a house wall. Nor from a balcony on a block of flats! The scale is all wrong and the supporting wall would need to be very strong! Wind loads on satellite dishes rise extremely rapidly as their area increases!

The bottom line is always: Are you feeling lucky? Enough to invest lots of effort and possibly thousands of pounds (or currency equivalent) in a very large, high quality dish, its mounting and stand in the (perhaps) vain hope of successful reception? A secondhand dish of suitable diameter might be well worth a try. The technology of TV reception via TV packs has changed dramatically. Small dishes and the internet now supply this public demand.

So a large dish may be sitting on an obsolete mast somewhere nearby. Simply because it is far too expensive for the limited funds of the local "TV club" to take it down. Though this is only likely in Denmark it may also be true elsewhere.

I missed a large (1.8m) CM/Andrews dish on a telephone exchange simply because I could not sum up the confidence to ask about it. It disappeared between my weekly visits to the town. As far as I know it was just scrapped. Getting one of the mast-mounted dishes down will probably require a strong cherry picker and formal permission from the owners. Plus a modest sum towards the mast owner's funds. These lattice masts are usually protected at the base from would-be climbers, drunks and over-ambitious children.

Click on any image for an enlargement.

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[P10] All our yesterdays

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Reception with the 6' dish may be partial but it does offer hope of marginally greater success. I have discovered that there is a small range of options for a much better site for the big dish to the north of the house. Invisible from the road the big dish will pass completely unnoticed.

The iron base has to be moved anyway to make better foundations. This also involves moving a load of cast concrete posts. Which were weighing the base down to protect the dish against rocking in the wind. Or blowing away altogether! Despite my original confidence in the stand it now rocks slightly with firm hand pressure on the mounting. Wind drag on so large a surface easily invites rocking. Particularly when rearward lift is caused by side-on winds using the curvature of the dish. No unlike an old fashioned aircraft wing when placed upside down in the wind.

The dish position I have been using for years is badly affected by the wind. Though this site is also the most convenient for a short cable run to the house. A few extra meters of coaxial cable will do no harm with a high output, Inverto Pro LNB fitted. A hedge is slightly infringing on one side of the present dish position. Which may reduce the signal very slightly. The outer edges of the dish having by far the most area compared with anywhere nearer the centre. The new site offers unobstructed skies at the desired satellite's local altitude.

My idea to use a cheap, round, shaving mirror to check feedhorn alignment worked rather well. First I had to dismantle the rather flimsy, metal framed, shaving mirror. Then I taped the bare, flat mirror absolutely centrally onto the big dish's surface. By climbing a builder's stepladder I was then able to easily check feedhorn alignment. Simply by moving my head, with only one eye open, in a circle around the LNB/feedhorn while watching the feedhorn's reflection in the mirror.

Trying to see if the feedhorn is aligned by looking from the side is all but impossible. There are no visual clues to suggest whether it is pointing at the centre of the dish, or not. These cheap, shaving mirror elements are very thin and lightweight. A couple of pieces of sticky tape, one at the top and the other beneath easily held the weight of the glass. The dish helps by naturally leaning backwards to point at the satellite at 25 degrees altitude. A vertical dish would not offer such security against the mirror falling.

Interestingly, the curved, magnifying mirror element had virtually the same calculated focus as my big dish. (Which I confirmed by focusing an image of the sun on my hand) Unfortunately this mirror produced only a very distorted and highly magnified reflection of the feedhorn when fixed to the dish and seen from behind the LNB.

We are getting only a few short hours of steady pictures and uninterrupted sound around lunchtime. I doubt I can improve much on this rather poor performance with this very old, 6' [180cm] C-band, fibreglass dish. We seem to live under, or very close to, the so-called null line. Which runs north and south right through central Denmark.

To the east of this line there are quite a number of reports of satisfactory reception in the Copenhagen area on quite modest dish sizes. While I know of one, even larger dish than mine, only a few miles east, which gets only slightly longer viewing hours. Morning and evening viewing is still impossible under the null line. There are hardly any reception reports west of us in Jylland/Jutland. When, in theory, it ought to offer far better reception.

Only a much larger dish, or moving home,  offers hope of improved reception over a longer period each day.

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[P9] The simplest answer is often the best.

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I decided to get rid of the arm/boss brackets altogether. However, the boss was a tough piece of aluminium plate which had been hydraulically pressed. The last thing I wanted was to ruin it. So I trapped the centre of the boss very tightly between two disks of MDF in the vice. I could then tap the ears with a plastic headed hammer until they matched the angle of the arms. All without damaging or marking the boss. It took several attempts and I had to check the angles carefully before I was fully satisfied. Had the centre of the plate boss itself been bent the (skew) clamping ring would no longer have fitted. Nor would it have held the feedhorn flat on the boss.

I found that having the wrong angle on the boss ears bent the support arms. This pulled the feedhorn all over the place as I tightened the arm holding screws. Eventually the angles were all correct and the arms now straight and relaxed. By a fortunate coincidence they were also exactly the right length!

Focusing is now very easy just by tightening or loosening the arm fixing screws equally at the dish's rim. The feedhorn can now be easily set in focus to the exact millimeter.

The mounting is now firmly fixed on my massive support pole. Which started life as the base of a professional drawing board. It had a hydraulic lift when purchased cheaply in a flea market. Its massive, flared, cast iron base is further loaded with concrete bars to hold the dish down in high winds. The 'pole' itself is a very thick-walled, steel pipe of 70mm diameter. Sadly it can no longer move up or down after years of exposure to the weather.

The mounting now offers slow motion adjustments in both elevation and azimuth. With the dish being so large (6' in diameter) it has a very small field of view. Trying to turn the whole dish around the pole would be far too coarse a change in angle.

The new, hot galvanized, elevation screw ideally needs spacers so that the nuts can turn more easily without friction. The nuts are also partially enclosed by the pivot support bracket. So spacers would expose them better for the use of a spanner/wrench. Not that this has proved to be a particular problem but I do like to avoid such minor problems where possible. I have replaced some of the rusting mounting screws with stainless steel. As are the new feed supporting, arm fixing screws.

While I can easily get the stronger channels there is still absolutely no sign of the weaker ones. This is a very disappointing result given the time and effort spent on this project so far. I am receiving reception advice from satellite forum members far more expert and experienced than I. Installing satellite dishes for successful reception has never been so difficult as with this one. All due to the weakness of the intended signals.  

Following expert advice on the Astra2 satellite forum I concentrated on a particularly strong channel on the same satellite. By paying careful attention to azimuth, elevation, focus and skew I was able to raise the signal Quality reading to a much higher level than before. The cheap Satfinder meter was not remotely up to the task. Showing increased signal level and audio output just as signal Quality fell on the TV screen.

Once I had achieved the best possible alignment I was able to obtain many of the weaker channels in the UK Spot Beam. Sadly my success was short lived. These same channels became too weak to show smooth video and continuous audio shortly afterwards.

Since the strong channels went on getting stronger and showing even better Quality I think I can safely conclude that the dish has not moved. Either the dish is not large enough for my location. Or it is simply not efficient enough to offer long term viewing at all hours of the day and night. One could say that the journey was rather more interesting than reaching the final goal. I am now suffering from severe project fatigue and considering my options.

Click on any image for an enlargement.

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[P8] A rethink.

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Struggling to overcome the angular difference between the feed boss and support arms blinded me to the obvious. Turn the problem on its side using small pieces of alloy angle to connect the components together. Problem solved. (Tomorrow)

Well, I solved the mismatched angle problem but introduced unwanted rotation. My use of square tubing (for supposedly extra stiffness over angle) offset the arms too much. When, ideally the arms want to be radial to the LNB/feedhorn.

Easily overcome by the use of metal angle instead of box section. Ensuring the arm clips overlie the boss fixing bolts will reduce offset to the absolute minimum.

Note that the feed boss is still reversed. When I tried it the correct way I'd need much longer arms to push the feedhorn out to the focal distance. I don't want to change the arm unnecessarily at this point. At least not until I settle on a practical way of holding the feed head perfectly still.

I still like the arm clips but need to reduce their ability to rotate around the arms. Any offset from radial greatly increases the torque on the clips due to imbalances.

I'm not sure the rubber boot on the LNB works. There is a bump on the LNB casting which might encourage rainwater entry. Self amalgamating tape is probably a better option but not until the design and tuning are complete.

Well, I've had to give up on the clips. They rotate on the arms too easily. I made some angle brackets, again using the clips, to make the arms radial. The head still flopped about.

Now I've flattened the brackets to the correct angle to match the arms to the boss. I'm using more expansion sleeves on the inner ends of the arms and bolting the boss direct to the brackets. It's a fiddle to get the focal distance to the feedhorn correct but I'm getting there. Finding enough screws and nuts is always a problem.  When it is finalized (famous last words) I'll use stainless steel fasteners.The image shows the latest iteration. Provided all the nuts are tightened with the head aligned it stays absolutely still. Focusing can take place by adjusting the nuts.

I have now removed one nut from each of the screws holding the boss. This achieved a better focus. The strong channel is back with the Satfinder shrieking right down to almost no gain on the control knob. This equated to 5 bars out of 8 for Signal and Quality on the satellite receiver.  

Click on any image for an enlargement.

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[P7] It's all in the detail.

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A fresh search of the shed found a pot of assorted plastic pipe clips. I really ought to add more storage space for glass jars. Just to avoid having so many things sitting invisible and forgotten in stacked boxes on racking.

There were several unused 12mm clips so I immediately replaced the strip metal clamps on the dish. The angles of the arms in the clips were still just a little awry. So I drilled out some small rubber tap washers and placed these over the screws between the clips and the boss. This allowed the clips to settle firmly onto the pipes with the rubber taking up any variation on angle  between the feed boss and the clips. Ideally I need some wedge shaped washers. The sort of thing found on some bicycle brakes might do. Once I decide what I intend to do in the long term I will replace the present, overlong screws with shorter stainless steel ones. 

Now I was able to remove the short studs at the rim, arm support brackets. Since I no longer needed any adjustment there. I was now able to use the short stainless steel, hex head screws and expansion sleeves as originally planned. Though I will need new Fischer expansion sleeves if I intended to add smarter arms.

All focus adjustment now takes place at the pipe clips. They really do hold incredibly tightly! Requiring considerable finger strength to slide them along the feed support arms. The head assembly is now much tidier and solidly secure against random movement. Once I find the optimum focal distance for the feedhorn I could drill through the arms and secure the clips permanently.

A standard rubber boot slid nicely over the base of the Inverto LNB to keep moisture away from the coax F-plug. I also taped the cable to the lower support arm to keep things neat.

Jobs still to do include longer pole clamping screws. To enable a solid purchase on the smaller 70mm pipe. Except that I don't have any handy in that size. Particularly in hot galvanized or stainless steel. Another trip to a DIY superstore will provide these. Then I can fix the dish accurately on that recalcitrant satellite. A suitable packing piece will give the rest of the screws something solid to work against. Where one of the four welded on nuts has stripped its thread. Much easier than finding a welder to add a new nut to the galvanized mounting sleeve. With all the attendant problems of disfiguring rust and toxic fumes.

I also want to clearly mark the centre of the dish to speed up alignment. A piece of electrical tape will do for the moment. It is far too cold and windy to spray paint.

A flange on my focus checking spacer pipe would be handy to ensure the feedhorn is pointing at the centre of the dish. The flange will sit true on the dish surface during alignment checking rather than wobbling about on its 2" diameter. Though it will need a perfectly straight spacer tube to work as intended. A tube to sit in the outer scalar ring with a long pointer for feedhorn alignment on the centre of the dish makes even better sense!

It's odd how much smaller the dish looks in profile and even from behind compared with the view from the front. The boundary hedge is winter bare at the moment. So the dish will disappear more once the hedge is in full leaf. If the dish proves itself on the target satellite I might even consider a lower stand. Just moving it back, or resiting it completely, would reduce its visual impact. The high output LNB would allow a longer cable. Rather than its present situation as close as possible to the house.

Click on any image for an enlargement.

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[P6] Feed boss angle problem!

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The angles on the new boss are obviously designed for through-the-dish support arms. See the image where the new arms are fixed at the rim brackets. (Just like the originals) I used handy wall plugs just to prop the inner ends of the arms in place.

The difference in the angle where the arms meet the new boss is so large that I cannot just make the holes larger and crank down on the nuts. I need to keep the boss perfectly flat so that the skew ring and feedhorn lie perfectly flat and true to the dish. So trying to bend the boss will guarantee it all ends in tears.

I think the only simple way around the problem is to make small brackets. These will match the angles at the cost of greater complexity and some cosmetic untidiness.

Though I could bend the arms the aerial tubing is seam welded and not particularly tough material. Bending the arms would be a finicky job trying ensure the boss ended up at exactly the correct height and perfectly square to the dish. Nor do I presently own a pipe bender and the cheapest tend to distort the tube.

Or I could drill holes in the dish and make shorter arms held by dish-penetrating screws, load spreading washers and expansion plugs.

Problem solved! I just found a 12mm plastic pipe clamp which will hold the arms very firmly. While still allowing sliding motion for focusing. It just required the feed boss to be inverted. The feedhorn and clamping [skew] ring fit just as well as before. There was no room for the arms to go under the ears but they easily fit on top instead. I just need to obtain two more clips from somewhere. I can no longer remember where this clip came from.  

My first attempt to use the white plastic clips with inverted boss proved to lack clearance for the feedhorn. The clip has to go on top of the boss.

Then I found some simple metal clamps to fix the feed temporarily to the arms but ran into all sorts of other problems.

The mounting was intended for 80mm pipe and my existing pole was only 70mm. So I turned a brass cap for the pole to locate the top within the 80mm  socket and to stop it moving. Then I discovered one of the threads on a welded-on pole clamping nuts was stripped. So I couldn't clamp the mounting firmly to the pole even with the pinch bolts fully screwed in.

Getting the dish up on top of the existing pole was a real struggle. In the end my wife had to help me walk the dish and mounting up a ladder until it could be dropped over the pole. The pole was far too tall for the prime focus dish and the dish itself looks absolutely vast from the end of the drive.

I quickly obtained one strong channel on the satellite but could not get anything from the weaker ones. The strip metal arm clips I used were far too flexible and the feedhorn was too far from the dish. So I brought my checking spacer tube into play to reset the feedhorn to the correct focal distance. I shall just have to find more of the strong plastic clips to ensure stability of the head once adjusted.

Then the top security nut on the elevation screw proved to jam on the bracket to dish fixing screw heads. So I had to dismantle the entire elevation screw and turn the nut to half the thickness in the lathe and then dome it to ensure clearance at all angles of elevation.

After all these issue were resolved I had moved the dish well off target and could not get the strong channel back despite the Satfinder meter screaming its head off.  I have a tiny 4" B&W CRT TV which I used as a monitor for the satellite receiver alongside in the garden. A larger, colour monitor would be a vast improvement for reading signal quality bars but I have nothing suitable for outdoor use.

I was convinced I had the correct satellite but it wasn't. I checked Satpointer again on the computer and found a distant building to align on. As soon as I turned the dish that way the strong channel was back. Still nothing from the weaker channels. A long, tiring and frustrating day with little real progress to show for it. Though I did get the dish mounted and a signal from it.

I learned today that the Satfinder meter doesn't care which channel is selected on the receiver. It will scream on every satellite it finds. It also makes a different tone on each transponder.

I also learned that I should take nothing for granted until proven correct. I wasted at least an hour searching for a signal on the wrong satellite. With the mounting flopping about on the pole I was constantly losing my elevation setting as well as azimuth. Today was still, overcast and spitting with rain. Tomorrow gales are forecast. I just hope the dish stays on the pole! I shall have to lash it down before going in search of more white, plastic clips.

Click on any image for an enlargement.

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