TEMP-est TEMPerature Equilibration System for Telescopes

Deep Space Products sells these neat looking vent replacement fans for the Celestron CPC series telescopes.  While they have a rather confusing selection of choices depending on whether you have a newer (e.g. EDGE HD) or older model, wedge mounted or separate OTA, etc., most of the difference between the different stock vent configurations are two fans vs. three.  For older scopes without vents there are options to drill your own holes and add theirs, but at that point, why not just add your own fan?  There are a variety of color choices, but even there the ordering process is a bit disturbing, since you’re asked for a backup color in case they’re out of stock on the color you want.  I went for the orange to complement my Celestron gear, and didn’t provide an alternate option.  Luckily I got what I wanted.

The vents look pretty nice, and fit was decent, although not perfect, as far as hole alignment is concerned.  I’m not sure whether to blame that on DSP or Celestron, although the Celestron covers don’t appear to have an interference problem with the screws.  As far as the electrical connections through the back of the OTA, I found that process a bit hokey, with the supplied “Y” jumper cable being too short to route the cable around the clutch pins and focuser shaft, so it sits on the central baffle tube behind the mirror.  That makes me rather nervous about the potential of pinching the wires.


When I plugged the first fan in to my nominal 12V supply (typically 13.8V car battery replacement supply) I was rather disturbed and disappointed at the amount of vibration each fan had.  Even installed, there’s a fair amount of vibration detectable when I rest my hand on the body of the OTA.  Since I bought these to improve my  imaging quality, I’m rather worried at the potential degradation due to the added vibration.  I also don’t want to have to add a circuit to switch this on and off, nor lose the continuous circulation these are supposed to provide.  Just to be sure it wasn’t the power supply, a created a regulated 12V cable specifically for these fans and while I could detect a minor drop in pitch, there was no net improvement in terms of the vibration.

I pulled the fans back out to send back and took a video of the vibration effects. By letting each fan just contact the surface of one of my tables, you can hear the whole assembly bouncing off the table top. Some of them rattle pretty good, and when you get them all going, the vibration at the far end of the table is impressive!

Here’s the greasy jumper wire Y cable that was riding up and down the center tube of the OTA. Now I need to re-grease the tube to put all that back!


Since I was already making the investment, I also sprang for their Fastar cooling fan that goes into the front of the SCT after removing the Fastar objective mirror.  I did so only after contacting DSP to confirm that this would work for my 11″ NexStar  GPS, since I don’t intend to be pulling the objective on the Edge CPC when I’m imaging remotely.  This unit turned out to be even a bigger disappointment.  Unlike other such solutions that come with a storage tray for the objective and are designed to actually ensure circulation through the OTA, this was just a pretty simple block of plastic with a fan attached to one side.  The design assumes that you’re using it on a vented OTA, so it’s really useless for my NexStar GPS unless I open up the eyepiece hole and leave it open for stuff to fly up into.  Without that, the fan would just sit there and cavitate without moving any air into the OTA.



So in all, I’m pretty disappointed in my purchase from Deep Space Products and in the lackluster response from Edward Thomas at DSP once he had my money.  I certainly wouldn’t have bought the Fastar fan had I realized its limitations.  The other components at least saved me the effort of printing my own parts, but I wouldn’t say I got my money’s worth.

As usual, there are more images in the gallery.

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Telescope Collection Menagerie

I have a Celestron 8se that I picked up used and in rather bad shape and after tuning it up I’m planning to resell it to a worthy home.  However, before I let it go I realized I needed to capture a picture of the huge menagerie of OTAs and mounts that I’ve collected in recent years.  Thus, I packed everything up and hauled it all out to the observatory for a photo-op.  I think the results are pretty impressive.  I even have the original culprit telescope framed in the background.  I just should have added all my binoculars and the SkyScout as well!


A trio of Celestron NexStar SCTs:


And a trio of Meade achromatic refractors:


Finally some aerial views:






As usual, there’re more shots in the gallery. Just follow the links.

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EdgeHD CPC Elevation/Declination Axis Rebuild

After completing the bearing upgrade on the azimuth/RA axis of my Celestron CPC Deluxe 1100 HD 11″ EdgeHD telescope, I followed up with a rebuild of the elevation/declination axis drive.  This effort was more about addressing issues with the drive mechanism itself rather than just working on the bearings.

The EdgeHD was still on the tripod in the warm room from the azimuth axis rebuild.


I started by removing the clutch knob by loosening the setscrew that captures it and unscrewing, just like the azimuth axis. In fact, several of the clutch parts are identical to the azimuth axis, and the procedure is the same.


Six screws, four short and two longer ones up near the OTA, hold the plastic outer cover from the inside.




Four larger screws hold the metal handle insert to the aluminum frame. All ten screws must be removed to take off the cover. Ideally, these four would be removed first. First two:


Oops, two more!



There’s the inside view of the plastic outer cover and bottom handle.


And a shot inside the drive fork assembly, showing the servo motor, gearbox, and worm gear.



Here’s a close-up of the worm gear and drive unit. The drive looks similar to the azimuth drive, but the main aluminum worm gear is obviously smaller than the brass one in the base.


After slipping the main worm gear off the clutch plate, you can see the rubber sheet on an aluminum assembly that appears identical to the azimuth axis clutch plate. Note the Allen wrench tool being used as a spacer to keep the spring loaded worm from hitting the clutch and getting grease on it.


The declination/elevation axis worm gear is just a simple aluminum part with no additional features. Not a great picture, but I’m not about to take things back apart to get a better one!


The declination/elevation axis has the same two flats and key for attaching the clutch plate.



Close-up of clutch plate showing set screws and center socket head cap screw. Looks a lot like the azimuth axis clutch plate, doesn’t it?


After removing the nut and washer, the same thrust bearing as the azimuth axis is visible.


After laying the scope on its side, declination axis pointing up to minimize stress, the bearing slips out easily.


The removed thrust bearing. Again, this appears to be the same thrust bearing as the azimuth axis.


After cleaning and re-greasing the bearing it’s re-installed.


And finally re-installing the pressure nut and washer on the bearing.


Now comes the fun part, working on the drive assembly itself. I start by loosening the gearbox. Two screws hold the gearbox to its mounting bracket. Removing them allows it to rotate around the worm gear axis.



Here it is tilted up to expose the two socket head cap screws that hold the whole assembly to the frame.


Removing the two socket head cap screws releases the drive assembly.



With the drive detached, we can inspect it from the sides. The “left” side of the drive shows the pivot set screw, worm bearing, encoder, and tension adjustment screw.


From the other side, the cover of the gearbox is held with three screws, and you can see the exposed pivot pin and bushing.


Removing the thee screws to expose the guts of the gearbox reveals five gears total.  There are three floating gears and spacers on pins in the cover and then the motor and output shaft gears.



After removing the set screw and sliding out the pin, the assembly comes apart.  The bushing inserts are both through-hole and nothing holds the pin in other than hydraulic pressure of the grease.  That’s why when I got this scope the DEC axis bounced all over the place.  The pin had slid out of the bushing on the set screw side and was allowing the worm to move back and forth about a centimeter or so.

The shaft coupling appears to be Loctited to the shafts and won’t come loose even with set screws removed.


After cleaning and oiling inaccessible bushings and re-greasing everything, the drive is re-assembled. Keeping the pin in is tricky when installing the set screw, since the grease and any air pressure wants to push the pin out. The set screw must be tightened enough to clamp the axis snugly enough to keep it from sliding back and forth on the axis pin.


Now I can install and align the main drive gear and drive assembly prior to re-greasing.


 


Here’s a side view of the worm gear teeth while they’re nice and clean. This is definitely a much lower-end gear compared to the azimuth axis gear. While it’s obviously not as critical as the RA axis, it’s still more cheaply made, with just a straight cut at an angle, instead of the curved cut on the brass RA axis gear.


Between this and the difference in the drive gearbox, it’s apparent why my RA gearbox has the 1:1 spur gear with no cover, instead of the similar gearbox as the DEC axis as shown in Gary’s guide.  If you go back and look at that guide, you’ll see that the older CPC used the same aluminum worm gear and five gear gearbox on both axes, while on the CPC Deluxe HD, the RA axis uses a bigger brass worm gear with a better overall tooth profile.  That would change the gearing ratio to the servo motor to get the same overall encoder feedback.

Here’re some views of the worm gear assembly re-greased and ready to go.



For a real hoot, check out this video of the drive in operation, after running it back and forth to run-in the grease. It’s amazing how much wobble the gearbox has on the coupler, which is why it’s mounted on a spring bracket.

While re-assembling the cover, take note. The upper two screws are of different length, with the longer one for the thicker side of the fork pylon. The two screws should extend through the same length.



Now on to the handle-side axis. Remove the aluminum handle first with the two large set screws that attach it to the aluminum frame. The remaining six screws that hold the plastic cover are the same as the other side.


Here’s the handle side cover, inside and out.



And the interior of the handle side fork pylon showing the simple lock nut and the GPS antenna. The antenna is well placed for Alt/Az mode, but not necessarily ideal for wedge mounting.


Here’s a closer view.


After removing the lock nut and washer.


There’s a simple flat roller bearing with another steel washer under the lock nut and several washers.



The roller bearing rides on a large flat washer held on with a thin layer of red Loctite. Mine was not properly centered (obviously slipped before the Loctite hardened) and was rubbing against the top of the shaft.


You can see the Loctite residue on the back side of the large roller bearing washer.


The thrust bearing is under a special lock ring behind the washer. This is where I stopped due to the special tool required for removal. I figure the grease is probably still fine and if I have to get back in it later, I’ll deal with it then!


Here’s what it looks like after centering the larger washer and re-installing the re-greased roller bearing and lock nut.


And finally, putting everything back together in reverse of the way it came apart, the scope is mounted back to the pier.



It’ll be a while before I have time to test everything well and come to any conclusions on the performance of the upgrade/repair/destruction I accomplished here! However, a few comments so far. First, while I was a bit worried that the azimuth bearing felt a bit gravelly when I swung it around manually in AZ mode, once I put it on the wedge, things changed drastically. The ride is extremely smooth under all that offset weight, which puts much more force than the vertical force in AZ mode. I do hear a small clatter every 360 degrees when I roll it around continuously, which almost makes me wonder if I dropped a ball in there. I think it’s just one ball rolling over the small gap in the balls in the outer bearing, but who knows. I can’t imagine how something loose would only clatter in a very narrow region. Beyond that, I do currently have a problem with the DEC axis slipping teeth when I try to pass a certain point. The setup is well balanced horizontally around the pivot, but not top to bottom, as you can see. Previously I had over-tightened the spring tensioner on the DEC axis so it couldn’t slip, but I think I’m going to try putting a piggyback on top again to better balance it and see if that works. I’d rather have the safety of being able to slip a tooth if something binds, but before I was getting quite a bit of hysteresis/backlash from the gear not meshing tightly, so we’ll see if I have to dig back in and adjust that later.

One other thing I’ve noticed is that I may have done too good of a job of cleaning the rubber pads on the clutch plate and the gear pressure plates.  They tend to stick when released and take a bit to break loose when released.

I did run some initial tests with PHD, and while I can’t say much about the RA performance, I did see a very regular sawtooth pattern on the DEC axis performance.  That may be that my polar alignment is off, since I haven’t re-tuned the wedge after remounting, and it does have some play.  From my initial alignment, the NexStar polar alignment indicates I’m off one degree in both axes.  Interestingly, however, after having it lose communication on me and re-aligning, it indicated I was almost dead-on with only seconds of error, so who knows?!!  This was also not a true 1:1 comparison against earlier results as I made one change to the PHD settings, going from the 0.15 pixel default to a 0.5 pixel setting for the minimum error setting.

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EdgeHD CPC Azimuth/RA Axis Rebuild

In a somewhat misguided attempt to improve the tracking on my Celestron CPC Deluxe 1100 HD 11″ EdgeHD telescope, I decided to perform the bearing upgrade described by Gary Bennett on the NexStar Resource Site.

I started by moving the EdgeHD to the tripod in the warm room in order to prepare for the azimuth axis rebuild.


I attempted to measure the force required to rotate the azimuth axis for a before/after test. I didn’t have a force gauge handy, so came up with a pretty simple scheme for using gravity to test for how much weight it took to overcome friction. By determining how much water weight was needed to get the axis to rotate, I could compare after the upgrade. Unfortunately, it turns out most of the friction was from the clutch assembly and not the bearings, so there’s really no way to use this information to determine if I improved anything.


After partially removing the set screw to clear the upper lip of the clutch base, the clutch knob unscrews completely revealing the Teflon pressure plate that lets the knob slip to loosen or tighten the clutch.


The spur gear servo motor drive turns the worm gear on the far side. You can see the black encoder on the back of the servo and the PEC reference sensor on the main worm gear shaft. The spur gears connecting the motor to the output shaft are typically covered with a shroud. Not sure why my unit doesn’t have it. Also not sure why they need a 1:1 gear vs. finding the space to direct drive the worm and eliminate that additional point of play.


The main board cover plate must be removed to get to the third screw on the front side cover panel. Turns out it’s not necessary to remove ALL the screws. The four screws on a rectangular grid hold the controller PCB to the panel, so removing the four screws along the edges allow removal of both the panel and board. See the re-assembly pictures for more info.


After removing the aluminum cover, I can access the third cover screw. I just left the board and cover hanging rather than having to label all the connections before disconnecting.


The main gear just slips off the bottom plate. There’s a bit of grease in the middle to let the brass gear slip when the clutch is disengaged. There’s a textured rubber pad on the plate to actually create the clutch grip.


Here’s a close-up of the clutch plate showing the rubber textured sheet, the grease on the hub, and one of the set-screw holes.


Here’s the brass main worm gear and clutch plate after wiping off most of the grease and contamination.


After removing the two set-screws and center screw, the clutch plate will slide off the center spindle of the AZ/RA axis. There are two flats for the setscrews and a key/keyway to keep the clutch plate solidly attached to the spindle, which is embedded in the non-moving aluminum base of the scope.



The nut came off the center spindle rather easily, although you can see the remnants of red lock-tite.


The tapered shaft bearing slipped out easily, freeing the upper assembly.




Here you can see the upper assembly after lifting off the base. The portion that rides on the outer bearing is just a flat surface with a taper to the middle. A lip around the edge minimizes dust infiltration.


It turns out that the CPC Deluxe HD mount uses a mix of metal and nylon bearings. The balls appeared to be greased in something the consistency of Vaseline. The nylon balls appear to be slightly larger than the metal, but that could be an optical illusion. This mix of metal and nylon appears to work much better than the old approach of using only plastic bearings and after removal of the clutch, the motion was quite smooth and easy. However, by the time I determined that, it made sense to investigate further. By this point, I’m already here so why not try the all-metal approach, saving the existing balls in case I need to put them back.


In the process of removing the bearing balls from the original installation, there were a number of machined metal chips in the bearing and grease that I removed when I cleaned everything up. It’s rather depressing just how dirty the mechanical components were left by Celestron’s manufacturing team.


After cleaning the base of both components to remove all old grease (and any metal bits), you can see the bearing channel and lip.




After removing all the grease with a vigorous dip in solvent (paint thinner) the center capture bearing is nice and clean.


I’m using AeroShell 64 Molybdenum grease, which is a high end aircraft grease with a broad range of operating temperatures and is suitable for high pressure applications. The 1/4″ bearings are stainless steel.


Here’s a picture with all of the 123 stainless steel balls installed with a coating of the moly grease.


Setting the upper body carefully on the base, everything rolls quite nicely, although the all-metal bearings are a bit noisier as the balls rattle against each other. The next step of re-inserting the thrust bearing to capture the unit ended up being the hardest part of the whole process. The tolerance to the center shaft was so tight that the bearing tended to bind with only a mm or so of engagement when not perfectly aligned. This resulted in having to remove the entire assembly multiple times to use the scope to pop of the bound bearing. In the process, the new bearings were upset at least once and had to be re-worked. ARGH! Eventually it went on correctly and I was able to complete assembly. Given the constantly greasy hands, and simple reverse process, it didn’t make a lot of sense to take a bunch of pictures going back.


Finishing up the re-assembly with a shot of the aluminum cover attached to the controller PCB, you can see the four screws that I shouldn’t have removed that attach the panel to the aluminum standoffs.


Here’s a shot of the re-greased main gear and worm assembly after running everything in.


And finally, all closed up, here’s the finished re-assembly of the AZ/RA axis base.


Next up, I still have to rebuild the DEC axis that’s given me more problems in the past. We’re currently in a full moon phase so there’s no point in remounting it anyway, so I haven’t tested it after the alteration (I hesitate to call it an upgrade at this point). More to follow when I get things tested.

As usual, there are more images in the gallery than I embedded here, so if you follow the link icon, you can browse any details you missed.

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Upgraded to Windows 10

So I finally bit the bullet and upgraded to Windows 10 on my observatory machines.  After the tremendous headaches I had on my main machine when I migrated from the pre-release Windows Insider version to the final released version, I wasn’t anxious to update all my other machines, but needed to do so before the one year “free upgrade” period was over.  The Microsoft tech who finally addressed the licensing and activation problem I was having on my main machine actually recommended I wait for a few months to update anything that I didn’t have to.  I wholeheartedly agreed!

windows-10-logo

Given I was already running Windows 8 that I didn’t care for, and using Classic Shell as a desktop replacement to make in usable (and actually even better UI that Windows 7) there was no reason NOT to do the Windows 10 update, other than the fear of things going wrong.  The biggest concern there was in being able to use some of the unsigned drivers I’m using to control various older pieces of equipment.  I also wanted the option to easily go back if needed, which meant imaging the drives and either setting up for dual boot or just swapping drives, as in the case of my laptop.  That actually ended up being a bigger pain than expected to get dual bootable images, but I eventually got there and performed the update to Windows 10 on one of the images.  As expected, I ended up losing all my drivers as Windows tried to use the latest incompatible versions.  On most I was able to just tell it to downgrade to the older driver, but did have to go through the rigmarole to get one unsigned version of an FTDI driver in place to get my focus motor working again.

At any rate, after re-installing Classic Shell and a few other things, I’m up and running with no real difficulties (other than the one Blue Screen of Death that killed one of my PCs with the roof open, forcing a trip to go reset everything).  Only time will tell if there are any long term issues that I’ll see.

 

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Winter Wide(r) Fields

I’ve spent the last month or so capturing wide field images with my Sigma 70-300 mm on my Celestron Nightscape.  (Ok, so they’re really Fall Wide Fields.)  With the stack of adapters I’m using to get from the Nikon bayonet to the T-ring on the Nightscape, I can only get to focus between 200 and 300 mm.  At 200 mm that’s a wide enough field of view to capture the entire Andromeda galaxy and the full sword of Orion.  The results turned out pretty decent.


 


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We Built a Planetarium!

For a number of years now I’ve been peripherally involved in the effort to bring a planetarium to Central Texas.  The brain child of Torvald Hessel, the effort to create the Austin Planetarium eventually grew into the Texas Museum of Science and Technology, which recently opened its doors in Cedar Park, TX (northern suburb of Austin) about a mile or so from where I work.  A couple of weeks ago I had the privilege to spend some time there and help a little bit with the set up of the new semi-permanent planetarium at the museum.  Scheduling and Customs problems meant that I didn’t get to help out as much as I’d hoped, but I did get to help move the assembled geodesic dome frame into place.  Unfortunately I didn’t have my camera with me then so I missed getting pictures of the frame, but I did get pictures of the covered dome while the field service team from the supplier was working on installing the eight projectors that make up the resulting image.

The dome consists of a metal geodesic framework to create a spherical structure, and then an internal screen and external cover are applied to the framework.  Negative air pressure is used to keep the screen spherical within the framework, while positive pressure keeps the outer cover taught.  Internally, the screen approaches the floor in the front, while going above the door in the back, giving a hemispherical view with a slight tilt.  The exterior is decorated with a combination of lunar landscape, constellations, and steam punk gears.

 




Here’s a shot with the air pressure system in the back. You can also see the vents for air conditioning.




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Cell Phone Booster Review

Introduction

With the remote location of the observatory, I’m pretty limited on my choices for internet, especially since I’m more interested in uplink data rates rather than downlink, in order to facilitate remote control of the observatory.  Of course being able to stream videos while I’m out there is nice too!  At any rate, the uplink limitations and latency pretty much knock  out satellite service, and point-to-point wireless services are very limited in my area.  That really only leaves cellular service.

I originally bought a zBoost 3G cell booster which has performed quite well.  At the time I was resigned to living with the 500 kBps or so I could get from 1xEV-DO on the Sprint network.   I initially purchased a 3G phone from Virgin Mobile (an MVNO on Sprint’s network) but before I got around to activating it, Sprint activated their 4G LTE network along the highway about 5-6 miles from the observatory.  I was surprised and excited to discover that the zBoost booster worked for their 4G signal, but never really investigated what Sprint had done at the time.  So, back to Virgin Mobile for an LTE phone to take advantage of the additional bandwidth, although that came with a 2.5 GB LTE cap before it throttled down to 3G (and later 2G!) speeds.  I also added a Wilson Electronics wide band directional antenna (a small log periodic dipole array in a radome) and was able to regularly obtain 5 Mbps uplink and downlink speeds.


In February of this year I obtained a pair of signal boosters (Home 4G and Connect 4G) from weBoost (formerly the same Wilson Electronics who makes the antenna above) through the Amazon Vine program.  Both units have essentially the same amplifier module in them, and despite the claim that they worked for all US carriers, I wasn’t able to get them to work properly for the Sprint network.  After quite a bit of diagnostics on the land and in the lab, weBoost agreed that they really weren’t suitable for my application due to the fact that the channel Sprint is using for LTE is at the edge of the band over which they’re designed to work.  Rather than going into all the details here, you can see the review on Amazon for more information.

During the discussions with weBoost, they suggested that their more expensive (i.e. over twice the price) Connect 4G-X would likely work better for the Sprint network.  I told them I’d be glad to test it for them, and after a bit of pressure from some readers of my review, they took me up on it and sent me a unit to test.

Initial Impressions

First off, right out of the box (or even in the box) it’s apparent that this kit is a major step up from the Home and standard Connect models.  The packaging is about three times the size, owing to the larger cables and booster amplifier module.  The booster itself is in a heavy cast metal case (providing a better heat sink) compared to the small plastic case for the boosters in the Home/Connect 4G.  The 4G-X booster is about 7 x 9″ compared to a little over 4 x 6″ for the 4Gs.  The kit also comes with a pair of Wilson low loss cables (75′ and 60′ I believe) for the interconnections between the antennas and the booster, as well as a 700-2700 MHz LPDA directional antenna for the outdoor connection and patch panel antenna for internal distribution.  These are the equivalent antennas to those provided with the Connect 4G, but unlike the 4G, which uses cheaper 75 Ohm cable typically used for cable TV, these are all 50 Ohm cables and connectors.  The superior performance of the low loss N-type cables does come at the cost of some flexibility (both literally and figuratively), and will require a bit more professional level of installation than your typical cable TV installation.  Unlike the F connectors used on the 75 Ohm RG-6 cables, N connectors cannot be easily installed in the field and require special tools and expertise.  Thus, you’re generally relegated to using the supplied cables or order specific lengths as needed.  Also, the much larger connector size will require a sizable hole for penetration into the building.  Overall, this is much more of a professional grade solution and will need that additional care in the installation.

I started my analysis by simply swapping the new 4G-X amp for my zBoost amp in my existing system.  My first impression from that test was extremely positive.  The apparent performance is significantly improved over the Home and Connect models, with 7-10 Mbps data rates (10+ burst, ~7 sustained) on uplink and downlink.  That also exceeds the ~5 Mbps from the zBoost unit I’ve been using.  The only problem I found was a side effect of just how much gain this amp has, in that it was difficult to get  enough isolation between the network antenna and the interior one, even though the physical separation is on the order of what is recommended (probably 40 feet horizontally and 20 in elevation, with the antennas facing in opposite directions).  Even after completing the permanent installation and taking steps to mitigate the feedback loop (see discussion at the end of the testing segment below) I still couldn’t completely eliminate a partial overload from other signals from other carriers/towers in the same band I’m interested in.  This is simply another indicator of just how powerful this amplifier unit is.  If you’re just trying to bridge the connection between a strong external signal into a shielded interior (e.g. metal building) this amplifier may actually be overkill.

Frankly my only negative comment would be that I actually had to go online to find the  real  manual that described the status lights, etc.  The kit just came with a single page quick install sheet and directed you online for the manual.  That seemed a rather insignificant savings not to include a printed manual with that information, and more importantly, if a user were out trying to install this where they didn’t have internet access (which is essentially what I was doing), then expecting them to go online to figure out why it s not working is probably NOT the best idea!

Here are a few pictures of the antenna installation and setup. First is the new weBoost antenna mounted horizontally and lower in elevation and pointed towards a different tower. You’ll see in the antenna analysis later why that’s still not quite enough isolation.

 


Here’s the large penetration through the wall after sealing it back up.


Here’s the booster sitting on top of the warm room ceiling. The flat panel patch antenna (not shown) points down through the ceiling to the room below.


Laboratory Testing

The remainder of this review is going to get rather technical and provide results obtained in my wireless lab using equipment most people would never have access to.  My first step was to perform a gain comparison between the 4G-X and the (in this case) Home 4G amplifier, which is identical to the Connect 4G amp down to part number, but has a different connector for the indoor antenna.  The results below show that the 4G-X is superior in gain, bandwidth, and flatness.  With up to 70 dB of gain (granted only at a couple of frequencies) the performance is pretty impressive! Given that for a free-space line-of-sight condition, every 6 dB corresponds to roughly 2X in range (probably more like 1.5x in typical environments), the improvement in downlink range is obvious. Add to that, every 3 dB corresponds to twice the power output, so the difference in cost for the better amplifier is not surprising either.  Note to be fair that the difference between the 50 Ohm system used to measure both amps and the 75 Ohm system of the 4G amps may have some impact on the performance, but that is generally expected to be small given the way these were tested.


Zooming in on the peaks in each band shows a 6-10 dB improvement of the 4G-X over the 4G.


The difference in the roll-off and smoothness of the filter in Band 25 at 1995 MHz where the Sprint LTE channel resides is apparent.  Note however, that some of the ripple in the 4G results may be due to the 50/75 Ohm mismatch.


The uplink results aren’t as markedly different between amps in the high bands, although differences in the filters are still visible, and the low band gain is better on the 4G-X.




Next I developed a test to specifically evaluate Band 25 LTE performance of a cell phone.  Here I tested receiver sensitivity of the phone on the low, middle, and high (Sprint LTE) channel of Band 25 with and without the amplifier in place at different data rates.  This gives a true measure of realized gain, taking into account the degradation introduced by the amplifier itself.  The results showed that the 4G-X is still maintaining 50-55 dB of gain across modulations over the no-amp case.  I tried repeating this test with the Home 4G but unfortunately couldn’t even get a stable connection.

 


Finally I hauled a spectrum analyzer out to the observatory to see what was happening on my land.  The bottom curve is the measured signal directly out of the cable attached to the LPDA directional antenna with no amplification, and the upper curves are for the three different amplifiers.  For the most part, all three show about 60 dB of gain over the un-amplified signal.  However, this data clearly shows the problem with the (in this case) Connect 4G in Sprint’s G-block spectrum (right side of the curve), where the signal is rolling off over 10 dB across the channel.  In this case, the 4G-X outperforms even my zBoost amp by about 6 dB or so.  Again, not bad!  However, to be fair, one should note that cell signals are not constant in level, so these curves are representative samples of signals that varied up and down quite a bit over time.


Note too that at this point, the 4G-X was flashing orange on a couple of bands, indicating it was throttling the gain.  Thus, there’s potentially more gain to be had there, but really no way to get away from all the other clutter in the band.  I ended up installing the antennas/cables that came with the 4G-X and changing the orientation to maximize the Sprint channel while minimizing everything else.  I had to switch cell towers to a more obstructed line of sight, lowered the height of the antenna, and changed to horizontal polarization to get the best G-block signal.  However, that still never got me to a point that the Band 2/25 light quit flashing orange (although it did clear the warning on Band 5).  As you’ll see in the next section, the antenna directivity isn’t doing enough to isolate me from picking up signals from other towers, even when they’re 90 degrees away.  Thus, I’d expect this to be a significant problem for users even closer to the cell tower.  weBoost’s suggestion for this is to either try to point away from the interferers (and thereby reduce your direct signal too) or add metal baffles to try to increase the isolation from the side lobes.  Neither are ideal solutions, but there are limits to what you can do in this sort of situation.

Antenna Patterns

Finally, I managed to get some time in the wireless chamber to measure the radiation patterns of the two antennas provided with the Connect 4G/4G-X.  The internal panel antenna is also used as the external antenna for the Home 4G.  I tested the 75 Ohm versions, but would expect the 50 Ohm 4G-X units to be the same.  I didn’t try to determine gain, since that wouldn’t have been valid due to the 50/75 Ohm mismatch, but the directivity numbers will give you an idea of the antenna performance, excluding mismatch and losses.

First up is the directional LPDA used for the external link.  The pattern is well behaved across the specified band and about what I’d expect from this antenna design.  It’s not as narrow as could be obtained by the use of a narrow band Yagi antenna, but the 8-9 dB of directivity across the entire band makes for a decent performing antenna.  However, with over 100 degrees of beamwidth in the H-plane at the low band frequencies, and still 70+ degrees in the high bands, it’s easy to see why when vertically polarized as shown in the first picture, you’ll still get a decent amount of signal from the sides, with only a 5-10 dB reduction at 90 degrees from boresight.  On the other hand, it also means you don’t have to be pointing perfectly towards the cell tower to get the full benefit of the antenna.  Things are considerably better once you place the antenna horizontal, as evidenced by the E-plane results, which are down 15 dB or more at 90 degrees.  So as long as the horizontal component from the desired tower doesn’t drop by more than a few dB, the improvement can be substantial in terms of isolation.




 


The flat panel antenna is not quite as well behaved, which again isn’t all that surprising.  The design is obviously a dual patch antenna with two major resonant frequencies in the PCS and Cell bands.  It’s pretty well behaved in the low bands, but has some oddities in the high band patterns, and breaks up completely in between.  So, unlike the LPDA, this antenna really won’t be useful for anything outside the cellular bands that it’s designed for.  The directivitiy is generally lower and the beamwidths wider than the LPDA (although as the pattern breaks up at higher frequencies that changes), which is what you want from something designed to cover a large area in a house or building.





So in all, the antennas are well designed for their target applications.  It would be nice if weBoost published the antenna pattern specs as an aid for users who are trying to mitigate interference problems and adjust their systems.  While the average consumer might not know how to use this information, the installers of this professional grade system should.

Conclusions

I still have plans to try to tweak my setup and see if I can get out of the overload condition and get a little more performance from the 4G-X booster, but I’d say the 4G-X kit as a whole is a superior product for its intended application.  I’m quite pleased with the performance improvement I’ve seen so far.

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I Backed LightSail!

The Planetary Society with Bill Nye (the Science Guy) had a Kickstarter campaign to develop a light sail CubeSat using public funds.  I just received my notice that they’ve completed the campaign and are ready to send me my goodie bag for supporting the project.  I came across the backer graphics and thought I’d post one here.  I might try to find a spot for it on the main page and direct that here.  For more information click on the image below or go to www.planetary.org.

i-backed-LightSail-patchblack-504x504

I’ll see about posting pictures of all the swag once it arrives, but the level I bought includes a centimeter of sail (I don’t get that, it has to go to space!  I just get a certificate.), the ability to send my name (and my family’s names) to space (digitally), and some mission patches, pins, and T-shirt.

 

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Links of Interest Page Added

I’ve added a Links of Interest page with a lot of detail providing a handful of links to places I regularly visit or would like to regularly visit.  I also included information on some of my favorite telescope equipment vendors.  I hope you find it useful.  I’ll be adding a menu link to it from the main page when I get a chance.

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