Adapting Invacom ADF-120 feedhorn to Kathrein feed boss.

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Just as a turning exercise in the lathe I made another adaptor to match the Invacom feedhorn to the Kathrein feed boss. Since I had no alloy bar in a suitable diameter I used an old Picador 4" V-pulley for raw materials.

First I fitted the pulley in the lathe with inside jaws fitted to the 3-jaw, Burnerd chuck. Then the boring went smoothly from the 1/2" original to the desired 25mm. I used the Invacom feedhorn as a plug gauge to ensure a close fit when I came close to the correct bore. Then I matched the outside diameter of one pulley flange to the 69.5mm Ø Kathrein original. 

The image shows one side of the adapter. I also ground off the point of the hardened, grub, fixing screw and polished the new, slightly convex, contact face with emery paper. This will save marring the feedhorn throat with the clamping screw. A nylon grub screw would be much better.

The original bowl-shaped feed boss of my own Kathrein 2.2m dish has a matching hole for the original feedhorn.  The critical dimensions are identical to the triangular Kathrein feed boss shown below.

The other 2.2m Kathrein dish has an impressively massive  triangular feed boss. The impression of the skew clamping ring is clearly seen on the upper face of the feed boss. One arm holding screw has been removed for boring out to a larger diameter to take modern coaxial cable.

The skew ring clamps the 69.5mm flange on the original Kathrein feedhorns. Now it can clamp the home made adapter. Allowing the Invacom ADF-120 feedhorn to be used with a modern C-120 LNB and original Kathrein feed boss.

Because of the deeply recessed faces of the Picador cast V-pulley there wasn't enough meat to provide a 60mm seat for the Kathrein skew ring. More by good fortune, than anything else, the three fixing screws of the Kathrein skew, clamping ring will hold the adaptor perfectly central in the boss. The adapter flange is 3mm thick to match the original, Kathrein feedhorns.

While I was using the lathe I bored out the stainless steel, arm fixing screws of the other Kathrein 2.2m dish to match my own. 

This would allow the owner to run modern, high quality coaxial cable neatly inside the hollow, alloy arms. This saves clipping the cable to the outside of the feed support arms with tie-wraps and looks very much neater.

Click on any image for an enlargement.

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Results:

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The erection of the dish on the new pole finally allowed the dish to stay still after adjustment.

Rather amusingly,  Sky News popped up the moment I switched on the system. By sheer coincidence I had aligned the dish perfectly by eye. Getting the UK SB was quite another matter. It needed the dish swinging further East. Then all SB channels immediately became available with reasonable Strength and Quality on the receiver's tuning menu.

Having obtained SQ figures for the IRTE feedhorn I thought I'd better try the new Invacom ADF-120 feedhorn. The problem was a lack of clamping. A search began for suitable raw materials to make a clamping ring. Luckily I found an old Picador 2" V-pulley in cast aluminium.

This I bored out from the original 1/2" to 25mm for a nice sliding fit on the neck of the Invacom feedhorn. Then I turned one side of the pulley to match the IRTE feedhorn's clamping ring. [52mm] Now I could slip the Invacom feedhorn through the newly turned ring and clamp the ring to the IRTE feed boss. The scalar rings were screwed on last. See image alongside.

The change in feedhorns provided an extra 2% on both S&Q. Well worth having! The Invacom feedhorn proved to be rather insensitive to both F/D and focus. I ended up with the feedhorn throat at maximum extension [about 5.5mm] and the scalar rings pressed back against the boss. I then repeated checks for best skew.

I suppose it is possible that the Invacom feedhorn needs a different [more distant] focal point setting compared with the IRTE. Perhaps I should look into this as a potential factor for further gain.

I find it easier to remove the entire feed from the support arms to work on it. This simply involves removing three nuts with a 13mm spanner. A 7mm spanner is very useful when a screwdriver cannot reach the small stainless steel clamping screws for the LNB and feedhorn clamping ring. Swapping feedhorns then becomes a five minute job from start to finish.

It is too soon to say when the UKSB signal will fade. It is only 1.45pm in bright sunshine and clear skies. Many channels were already dropping out by this time when the dish was still hung on the slotted angle stand.

Trying to move the dish when it is clamped to the pole proved the Kathrein mounting was remarkably rigid. Previously I thought the dish itself was flexing. This proved to be an illusion and only the result of the slotted angle members flexing.

I am running just over 30 metres of new coax to a straight connector on the front wall of the house. If I re-route the cable to enter the house from the back I can save ten yards and have no need for the connector. I will wait until I have solid results over a longer period before I decide to cut the new length of cable.

Despite all my efforts so far the UK SB channels started freezing at 17.45pm. Then they began dropping out just before 18.00. By 18.15 there were literally no UK SB channels left. So, still no evening viewing!

Click on any image for an enlargement.

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The Big Lift 2

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Sunday 22-6-2014. On day four, I lost patience with waiting for the concrete to gain full hardness. Justifying the risk of damage as very low thanks to the depth of the concrete and the excellent balance of the dish relative to the pole. I had also used a strong mix of 3.5:1 of premixed sand and gravel (Dansk: støbemix) to cement.

Now I had to find a safe way to lift the dish to mounting level working alone. My wife had helped me lift the 1.8m fibreglass dish by sliding it up a gently inclined ladder. The 2.2m dish was much larger, even heavier and the necessary lift much higher.

First I lifted the weight of the dish off the slotted angle stand using a [2 x 4 pulley] block and tackle. This was supported by two builder's folding stepladders straightened out and tied together at the top. These ladders have the advantage of strong supporting crossbars for the rubber feet. This makes them very stable even when subjected to side loads. Using normal ladders would have been suicidal!

The first image shows the dish lifted off the stand and lowered safely to rest on the ground. I had to be careful to avoid damaging the LNB but it all went well. It had been blowing a gale all day and it suddenly shifted to the East. Making for a few anxious moments as the dish swung gently between the ladders.

The second image shows the rear view as I dismantled the slotted angle, trapezium stand. This was to make room for the ladders to move backwards to the pole. This involved stepping each ladder backwards in turn with the dish slung between them. Finally I was able to move the rear ladder behind the pole and the waiting alt-az mounting.

I don't have images of the actual lift because I was too busy hanging onto the lifting rope and running up and down the ladders.

A double lift was necessary to get the dish high enough to bolt onto the alt-az mounting. This was just a matter of lifting the dish as high as it would go and then tying it off to the tops of the ladders. The block and tackle could then be released, lowered and retied to the dish on much shorter ropes. Allowing the dish to be raised by another foot or so [30cm] on the second lift.

I was lucky and the top edge of the dish just fitted under the peak of the two ladders when the dish was at its highest.

 

I had planned to use a strong ladder, resting on the stepladders, if necessary to get the extra height. In retrospect, I could have set up the ladders over the pole and rolled the dish between them. As I had to lift the dish off the stand first I decided to walk the ladders instead.

Here the altitude pivot bolts have been screwed through the eyes and into the outer ends of the horizontal mounting channel.

The altitude nut has been adjusted to tilt the dish back to point upwards at 25 degrees for Astra 2 at 28E. The dish angle was checked with a digital clinometer laid against a stiff pipe touching the top and bottom lips of the dish.

The Kathrein alt-az mounting is a simple, but very strong, welded construction. Made from two channel sections of steel then galvanized. The two U-bolts hold the mounting to the pole. While allowing the dish to be rotated on the pole to point to the satellite. The nuts can then be tightened to lock the dish firmly on target.

The dish seems to have shrunk now it is tilted back at 25 degrees and raised on the pole. It looked much larger when nearer the ground.

I promise to tidy up the junk from the previous steps. It doesn't look like it now but this is a 2.2 meter dish. [About 7'4" in diameter]

The bottom of the dish is presently 85cm or 33" above ground level. This will reduce by a couple of inches when the soil is levelled and re-grassed. The garden slopes away from east to west by a couple of feet [60cm] over its 30 yards/metres width.






The 4.3" [110mm] heavy, galvanised pipe has been sunk into a meter depth of concrete. [about 3'3" in old money] The square hole was tapered outwards at the bottom and had a minimum cross section of 40cm x 40cm. [16" x16"]

I tidied up the top of the concrete (above ground level) with a ring of cardboard. This had been lying around looking for a purpose. It will probably disintegrate over time.

By this means the last of the concrete mix was raised above the ground without the risk of a frost heave overhang. Untidy hole edges have a habit of allowing a larger lump of concrete to form than the hole itself. In a hard frost the overhang can actually lever the concrete block out of the ground.

The soil will eventually be levelled around the pole and re-grassed for a neater appearance.

Click on any image for an enlargement.

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That sinking feeling:

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Thursday:  The Invacom ADF-120 has finally turned up in the post! There were no instructions enclosed for tuning to the dish's F/D. Fortunately I had already found these online. So I know were the ballpark lies. 5.5mm throat extension beyond the scalar rings should be about right for the 0.34 Kathrein dish. I will keep an open mind rather than allowing this figure to dictate the results.  I have yet to produce a suitable clamp for the Invacom. Which lacks the IRTE's excellent, built-in collar and skew-clamping ring. It might be possible to use the Invacom's LNB fixing flange with a suitable clamping ring. I have yet to compare the two feedhorns side by side.

The Invacom is a nicely turned bit of kit. With a very high surface finish compared with the much rougher, cast IRTE feedhorn. Though the weather will probably discolour the Invacom quite quickly. Not that it matters in either case.

I took the advice of the satellitesuperstore.uk website [though I didn't buy it from them due to the much higher price and £15 minimum European postage.] They suggested adding some petroleum jelly to the fine adjustment threads to reduce the risk of binding. The clear, light grease is visible in the image alongside. The packaging shows the nominal range of F/D capacity. If they weren't going to enclose tuning instruction why not print a graph on the side of the box?

Now back to the pole hole digging! I seemed to have chosen a particularly warm and sunny time of year to dig. There was a transition around 90cm where I could no longer reach the bottom of the hole with my gloved hand. Not even when lying flat on the grass alongside. Up until that point it was easiest to scoop up the loose soil with my gloved hand. Then I ran out of arm length! The high cost of hole borers and specialist pole hole digging implements was quite ridiculous for making just a single hole. None of our collection of  gardening implements helped much with removing the sticky clay. It either couldn't reach or wouldn't scoop up the soil in the narrow confines of the hole. While the heavily offset, trenching spade simply allowed the clay to roll off the tip each time I tried to pull it back up!

I finally resorted to a salad serving spoon from the cutlery drawer of the local charity shop to lift the loose stuff. Then I hit a stone which lay perfectly across the bottom of the hole in sticky clay. Careful scraping around the stone with my salad server allow me to hook a small crowbar under the stone. I was then able to roll the stone up the side of the hole until I could lift it clear.

After that I began digging with a 6' length of Dexion, slotted angle. It made a handy tool in the deep, narrow hole provided I wore hide working gloves to protect my hands. The clay became steadily damper and stickier until I was able to make quicker progress with the clay sticking well to the angle iron. I passed one meter then 110cm. This was my target and allowed 10cm of large gravel to line the bottom of the hole for nominal drainage. Not that the clay was likely to allow much water movement. First I tamped the bottom of the hole well with a fence post and then worked on the layer of gravel.

Finally I was able to lower the very heavy, 2.67m x 114mm, galvanized pipe into the hole. The bottom flange settled nicely onto the gravel but the heavy pipe was still used as a final tamper for bit more compaction. No point in having the pole slowly sink on me over time. My reckoning suggests that, on the mounting, the bottom of the dish will be slightly less than 60cm or 2' above the ground. Enough to get our rechargeable electric mower under the lip without difficulty.

Tomorrow I shall have to buy some bags of ready-mixed sand and gravel and a bag of  cement. I had deliberately kept the hole neatly rectangular and not much bigger than the welded flange on the bottom of the pipe. So it won't take a huge quantity of concrete.

BUT: Some dish manufacturers suggest a cubic metre of concrete for a dish this size. Given that my dish is very well protected by a very dense 10' high conifer hedge, on the windward side and trees and dense shrubs behind perhaps I shouldn't worry too much? The dish has shown no interest in moving on its lightweight trapezium stand so far despite some gales.

Let's think about this before it is too late. Is the deep, narrow hole (and resulting concrete block) likely to be a real weakness in actual practice? The concrete greatly increases the area of hard material pressing against the relatively weak soil compared with the bare 4" pipe. The larger the block the larger the surface area of the concrete. This considerably lowers the surface pressure per square inch/foot/cm/meter. Since the surface area of the block increases on all four sides. Hole/block depth remains the same in all cases. The lower the surface pressure between soil and concrete block the less the soil can compress.

A larger block of concrete obviously has a very much higher overall weight than a smaller one. Increased weight will greatly resist the block and pole/mounting/dish assembly from tilting. Or even lifting bodily out of the ground in a storm. There will also be a considerable increase in resistance from the surface roughness of the concrete where it is cast closely against the equally rough walls of soil.

So increasing the hole size offers quite a number of obvious advantages at relatively low cost. Except in time required for the excavation itself and a little time more for mixing the concrete. The material itself is fairly low in cost. My own time is free since I am a volunteer working on my own project at home. So there are no travelling costs and meals are normally provided anyway. At least so far. Impatience with the lack of TV might prompt industrial action!

I remember setting a tall 4" steel pole in the lawn on a previous unrelated project. I did not use concrete but tried hard rammed stones and gravel instead. The pole quivered at the slightest touch though it remained upright over time. I even filled the pole with sand to try and stop it shaking. This had no obvious effect.

Am I willing to risk the dish shaking in a wind beyond the tight tolerances for pointing common to such large dishes? Decisions-decisions! Making the hole square in cross section, instead of the present rectangular, would double the width. Thereby greatly increasing the mass and the concrete block's surface area. Unless I hit a large stone the work is not too arduous. Certainly no harder than I've managed so far.

Perhaps the limitations of using a 4" pipe will be the determining factor in the amount of flexure under high wind loads? Filling the pipe with concrete [later] would be much stiffer than sand. While telescoping the lower half of the 4" pipe with a much larger pipe, then filling the intervening space with concrete, would help enormously. Except that I don't have any 8" or larger, steel pipe handy.

I could buy a concrete drainage pipe and slip that over the 4" one while it is down in the hole. Not an easy task given the likely weight of the concrete drainage pipe and the intended height of the 4" pole above the ground! Though this idea would certainly lift the flexure point well above the concrete block/ground surface. To considerably shorten the beam subject to flexure.

The concrete drainage pipe need not reach the bottom of the hole. It's purpose is only to shorten the 4" pipe's unsupported length. So I could half fill the hole. Let the concrete go off just enough to support the drainage pipe. Then continue filling the hole and interstitial space between the two pipes to achieve a uniform mass of concrete. Or, I could support the drainage pipe somehow without pausing the fill. Though I don't think this is really necessary.

Perhaps I am just being too paranoid about pole flexure? It's just that we do get quite a lot of storms with high winds. The Gilbertini 1.2m needed a stack of concrete posts as ballast to hold its massive cast iron stand down. The Kathrein at 2.2m is almost twice the diameter and vastly larger [4x!] in potential, wind-catching area. That is four times the wind loading. I had better star digging again even if I don't add a larger transition pipe. This is all beginning to seem like an awful lot of work for only a few hours of British TV around lunchtime!

One sweaty hour later and the hole has increased to 40cm square by 110cm deep. [Instead of the former 20 x 30 x 110cm deep] I shall undercut the bottom of the hole into a truncated pyramid. The so-called elephants foot foundation block. The pyramidal form resists lifting and toppling due to wind loads and greatly improves resistance to frost heave. The larger base also resists sinking on softer ground. [My damp clay] Much better than a simple cylinder. And, very much better than a typical (amateur dug) conical-shaped excavation with the point at the bottom!

The concrete has been put off for the moment. I am still unsure whether the post hole is big enough.

Well, I have decided to go for a simple pole in a 40cm square hole 100cm deep. I have enough sand and gravel mix to fill a hole that big. Now I just need the cement. I have rammed the hardcore again to be sure.

Weds 18/6/14: Concrete completed in windless, hot sunshine and 70F. I mixed the concrete in a wheelbarrow using a rake and 3.5:1 støbemix to cement. Total expenditure 200DKK [about £20] and I still have one and a half bags of cement and some sand/gravel mix left. I have enclosed the casting and lower pole in polythene to retain the moisture while the concrete goes off. Though, after today, the temperature is due to drop and become more cloudy.

I have been monitoring the temperature of the spun alloy, Kathrein dish to see if the thinned surface paint (from cleaning) affects solar temperature gain. Quite unexpectedly, it remains quite cool. There is also no sense of warmth, at all, at the focus while placing my hand over the feedhorn with the sun full on the dish. A good result.Though the risk of frying the LNB is much lower on a prime focus dish compared with an offset one. The latter usually have a plastic cap over the concealed feedhorn where heat might be concentrated. The prime focus dish has a naked, metal feedhorn with little or nothing to absorb heat.

At day four since I poured the concrete I am still waiting for it to gather more strength before fitting the heavy dish on the steel pole. Despite the polythene skirt being constantly covered in droplets internally the concrete surface is always dry when I lift the plastic to check. I have been adding water each time and shading the base from the summer sunshine to keep the concrete cool.

Click on any image for an enlargement.

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Backward Progress?

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Realigning the dish brought back Astra 28E UKSB for the usual short reception period around lunchtime. The feedhorn extension ring seemed to help.

Now I have to decide whether it is really worth all the effort to dig a deep hole and fix a mounting pole in concrete. I have had the galvanised pipe for weeks but still have the dish hanging temporarily on an angle iron trapezium.

Will a firm pole and the original mounting provide any extra signal? It would certainly ensure the dish didn't move. The large dish is extremely sensitive to pointing. The problem with poles is that they are fixed. You don't get a second chance to position it perfectly. There is a bank falling away behind the dish position with mature shrubs beyond. Which rather limits where the pole could go.

Access is still required behind the dish for adjustment. Though pushing the dish back as far as possible would be beneficial for other reasons: It takes up slightly less space in the parking area and looks slightly smaller with increased distance from the house.

Height is another important consideration. Cars can be parked closer to the dish since it will see over them better on a taller pole. While a taller pole exposes the dish to slightly stronger winds and provides less shelter from shrubs and hedges. Reaching the feed is more difficult but not unduly so from a stepladder. However, a taller pole increases the leverage the dish loads put on the pole in high winds. Better not to let the dish be exposed to high winds!

Tuesday: My new Invacom feedhorn has now been with DHL Germany for five whole days without moving! [According to their own Track and Trace web page] I paid extra for premium airmail too! Thank you DHL for falling over yourselves to get the item to me! You can look forwards to my negative comments on Trust Pilot.

Wednesday: DHL finally updates its T&T to say the package arrived in Denmark on Sunday, 3 days ago. Though it took them four days to update this information. Still no word whether it is out for delivery.

Now it seems the package might have been handled by Deutsche Post for delivery via Post Danmark but who knows? DHL's T&T web page can't even carry the tracking number over from German to English! A new search has to be made in the new language every time I hit the English button. Which means copying the tracking number to paste it into the new language search box! It is 2014 isn't it? Don't you believe it! No post, at all, again! 

I tried digging a pole hole in the ideal spot and found 50% hardcore and 50% half bricks. Two feet (60cm) further forward and I found just hard, compacted soil. I have reached about 24" so far but it is far too hot and humid to continue today. I shall start digging again tomorrow when it is cooler. There seems to be a layer of hard clay down there now. As long as I don't hit any rocks, cables or pipes it should go quite quickly. The hole still needs to be enlarged to take the welded pole flange. I didn't want to dig a large hole straight off in case I hit more hardcore.

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Matching the feedhorn to a faster dish III [Director's cut]

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So much for the plans of mice and men. It was late afternoon before I was able to work on the feed again. By which time, of course, there were no SB channels available.

The IRTE complicates the issue (considerably) by having a concave curve to the forward edges of the scalar rings. The Invacom which I was trying to emulate is flat across the face of the scalar rings. There is obviously more to feedhorn deign than throwing a few rings around the waveguide throat. The original Kathrein feedhorn has only one scalar ring and is supposed to be matched to the dish. Yet the (supposedly mismatched) IRTE bettered my brass copy [with the missing C120 LNB fixing added] by 2% points of Q.

First I switched the Fortec Star Passion HD receiver to Sky News on Astra 28E and checked the bare feedhorn S/Q @ 78/75% for a baseline. I refitted the ring and I instantly had 79/82% !! 7% points increase in Q is certainly worth having! What went so wrong yesterday?

Then began the task of turning the ring down to make it shorter to see what would happen. I started with a 5.5mm extension and reduced it to 4mm. 79/85%!! That's more like it! Then I reduced the extension to 3mm. S/Q dropped to 79/82%. Whoops! A bit too much!

I tried pulling the ring out a little to compensate but S/Q would not budge from 79/82%. Mind the gap!?!

So I was forced to turn another ring with more extension. This went very quickly this time because I had the old ring to measure. The throat dimensions were again matched to the IRTE feedhorn.

I made the extension too long expecting a much worse result: With a measured 5mm extension beyond the plastic cap I now had S/Q of 79/84%. Good enough! That's 9% points of Q over the bare feedhorn! I removed the new extension ring again to check. The bare feedhorn was still showing 78/75%. The new (5mm extension) ring is shown fitted to the IRTE feeedhorn above. The darker ring is just a reflection of the extension ring in the clear plastic cap.

I seem to have come full circle. Allowing for the thickness of the plastic cap the extension now matches the Invacom tuning literature at 5.5mm for 0.34 F/D. Should I shorten the ring slightly to try and get that 1% Q back again? I am now haunted by the thought that the plastic cap is insulating the extension ring when it ought to be earthed to the body of the feedhorn to form the entire waveguide from one lump of metal. I could always add the plastic cap to the extension ring if I knew what adhesive to use.

I tried other channels but still no UK Spot Beam on 28E at this time. [19.00pm CET] 

Will the considerable "improvement" in Q on Sky News spread itself across the UK SB when there is a signal tomorrow? Who knows until I try? Why were my results so poor yesterday after I fitted the extension ring? I have absolutely no idea at the moment! Was I using a different frequency yesterday? Is the ring altering the feed [LNB/feedhorn] frequency response? Read tomorrow's exciting episode! When it (probably) all goes horribly wrong again! ;)

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Tomorrow was cancelled. At least it was for the UK Spot Beam. Not one single channel showed a signal! I removed the ring thinking this was the cause but this had no effect. The Pan Euro beam was fine but with strange ups and downs in signal Quality. All depending on whether the extension ring was in place, or not. The presumption must be that the extension ring spoils the (supposedly flat) frequency response of the IRTE feedhorn. I have now ordered an Invacom ADF-120 feedhorn to see if it helps to get a better F/D match.I shall have to devise a clamp for the feedhorn neck to adapt it to the central feed boss.

Realigning the dish brought back Astra 28E UKSB for the usual short reception period around lunchtime. The feedhorn extension ring helped.

Now I have to decide whether it is worth the effort to dig a deep hole and fix a pole in concrete. I have the pole but I have the dish hanging temporarily on an angle iron trapezium. Will a firm pole and the original mounting provide any extra signal? It would certainly ensure the dish didn't move. The large dish is extremely sensitive to pointing. The problem with poles is that they are fixed. Access is still required behind the dish for adjustment. Though pushing the dish back as far as possible would be beneficial for other reasons: It takes up slightly less space in the parking area and looks slightly smaller with distance. Height is another important consideration.

Tuesday: My new Invacom feedhorn has now been with DHL Germany for five whole days without moving! [According to their own Track and Trace web page] I paid extra for premium airmail too! Thank you DHL for falling over yourselves to get the item to me! You can look forwards to my negative comments on Trust Pilot. Wednesday: DHL updates to its T&T say the package arrived in Denmark 3 days ago. Though it took them three days to update this information. Still no word whether it is out for delivery today

Wednesday: It seems the package might have been handled by Deutsche Post for delivery via Post Danmark but who knows? DHL's T&T  web page can't even carry the tracking number over from German to English! A new search has to be made in the new language every time I hit the English button. Which means saving the tracking number to paste it into the new box. It's 2014? Don't you believe it!

Click on any image for an enlargement.

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