RoboFocus and interference banding in images.

[strongmanmike]

Hi guys

I have just connected a new Robofocus to my Starfire and I am seeing some
horizontal ligt and dark banding in my images now..? the dark and light bands
are quite narrow, uniform and numerous.

I am testing on a bench with all cables quite seperated

With the RoboFocus system fully connected, the RoboFocus control box plugged
into power and my FLI PL11002 CCD camera on in normal imaging mode I am seeing
this horizontal dark and light banding in each dark frame I take.

The banding problem shows up whether the RoboFocus control box itself is
switched on or not, as long as there is power to the control box the bands
appear, it doesn't help to use a separate mains power point either.

If I physically disconnect the power supply to the Robo Focus control box OR
physically disconnect the cable to the RoboFocus motor then the banding
disappears.

So, the bands only show up in image frames when the Robo Focus system is fully
connected AND connected to power - whether the control box toggle switch is on
or off makes no difference, nor does using a different mains wall socket.

I have not been physically operating the RoboFocus during testing rather just
had it on or off as the case may be.

I haven't been able to see how the banding affects the focus window in software
focus mode but I suspect that best case is that it will still show the lines
(they would be fatter due to a small piece of the full frame being used for
focus) but I may still be able to see the star image and focus with it but I
cannot test this easily. Of course after focusing I would then have to
completely disconnect RoboFocus from power in order to image but then there will
be no power going to the stepper motor either so it may not be able to hold the
focuser in position?

For power to the Robo Focus control box I am using a new 1 amp "Power Tech"
switch mode AC Adapter giving 12vDC Regulated output

Any ideas?

Mike

[DavidU]

Hi Mike, I'm not a huge fan of switchmode supplies in sensitive applications.
1. I would try running the robofocuser with a 12V battery supply to see if the cabling is not giving EMF troubles.
2. Try a standard iron core transformer (regulated) 12v power supply and check for camera banding.
3. Try wrapping the switchmode supply cable in a strip of foil and earth it to ground. (may stop RF radiation).
4 Fit a 10pf to 47pf capacitor across the 12V switchmode + and - cable.
See what happens

[AlexN]

are the power lines for robo-focus running near your data lead for the PL11002? you could try shielding either the Robo-focus power lead or the data lead for the CCD... Do these bands show up in every image? if so, would it not be fair to assume that darks would take care of them? I know that's not really a "Fix" but hey, its somewhere to start...

I would imagine that its electrical noise causing the problem, and I'd assume that shielding the PL11002's USB data lead should make a difference, but for testing purposes, try routing the leads as far apart as possible to see if proximity is causing the issue, or if its actual noise in your electrical setup..

From memory, a DC power line should not interfere with a USB data lead, as both are running DC power, you get your issues come into play when you have an AC lead running next to your USB leads.. (I got noise in my ST10XE images when I had the USB lead running over the 240v lead..)

Things to try i guess...

[AlexN]

Oh, Ps.. Congrats on Robofocus! As if your focus isn't awesome enough anyways :) Do let me know how it goes... It may very well be the next addition to my imaging rig.. Im still tossing up between the FT Digital Focus System and Robo-Focus... If you're willing to say that the Robo-Focus is the goods (once this issue is sorted out) that will be good enough for me!

[rally]

Mike,

Try powering the unit with a 12v battery and see if that removes the problem, if it does then you have isolated the Powersupply as being the cause of the the interference as opposed to the Robofocus itself.

Many power supply supplies are sold with little ferrite cores that go around the power cable to reduce this sort of interference.

Appropriate capacitors to smooth the high frequency ripples might work, but lets work out what is causing it first.

Rally

[strongmanmike]

Having the switch mode power supply plugged in to mains and live but not physically connected to the RoboFocus control box causes no issue (?)...instead it must be physically connected ie plugged in to the RoboFocus Control box AND connected to mains power to see the banding in images, whether or not the RoboFocus control box is on or not.

Mike

[DavidU]

It still could be the supply as it can inject switching transients into the control box.
Looking at their web page the supplied transformer does not look like a switchmode job and the controler case is plastic (ie: not shielded)

[strongmanmike]

How would these switching transients affect the camera images though..? The Robo Focus isn't connected to the camera in any way :shrug: are we talking magnetic fields or something?

Mike

[DavidU]

Well yes, it can create a "noise" that is introduced into the control box(thats is not sheilded for noise)that then may radiate into other sensitive equipment.
This is all similar to various audio problems I get in my job.

[DavidU]

"
The main advantage of switch mode method is greater efficiency because the switching transistor dissipates little power when it is outside of its active region (i.e., when the transistor acts like a switch and either has a negligible voltage drop across it or a negligible current through it). Other advantages include smaller size and lighter weight (from the elimination of low frequency transformers which have a high weight) and lower heat generation due to higher efficiency. Disadvantages include greater complexity, the generation of high-amplitude, high-frequency energy that the low-pass filter must block to avoid electromagnetic interference (http://en.wikipedia.org/wiki/Electromagnetic_interference) (EMI), and a ripple voltage (http://en.wikipedia.org/wiki/Ripple_voltage) at the switching frequency and the harmonic frequencies (http://en.wikipedia.org/wiki/Harmonic_frequency) thereof.
Very low cost SMPS may couple electrical switching noise back onto the mains power line, causing interference with A/V equipment connected to the same phase. Non power-factor-corrected SMPSs also cause harmonic distortion."


extract from wiki


Mike, just try a 12v battery, that will show you.

[marc4darkskies]

Aahhh yes, what David said!! :)

FYI I use a 12V 12A Powertech switchmode supply to my Kendrick dew heater which in turn supplies 12V to my Robo. All of my cables run in a bundle to the pier too (incl a 240 supply to my camera brick on the pier) without any noticable effect. Perhaps filtering electronics or sensitivity to EMI in the camera (SBIG vs FLI) is coming into play too(??).

As others have said, I would firstly separate the cables as far as possible to see if proximity to the camera USB is an issue. Then I'd run from a battery. One of these will almost certainly eliminate the noise.

Congrats on the Robo BTW - it sure improves the whole imaging experience. Try FocusMax too - it's very good and free.

Cheers, Marcus

[strongmanmike]

Thanks everyone :thumbsup:

Well it appears it is the power supply after all.

I purchased a nice cigarette lighter adapter with a nice long cord with the correct centre +ve plug on the end (had a range of connectors) for $20 at Jaycar, connected it to my 33 amphr battery and Hey Presto!... no more lines :cool:

I went to Jaycar and Dick Smiths to look for a non switch mode power supply but no compact ones were available at either outlet, so I got the cigarette lighter adapter instead. I could have wired up the spare plug that came with the RoboFocus but my soldering iron is under the house somewhere :doh:. I also bought those magnets that snap around the power supply wire to supposedly smooth out spikes in the current but they didn't do anything :shrug: ...so I'll take'em back.

Of course this means I will need a battery in the field again :( but at least the wire was 3m long on the cig adapter. The RoboFocus only draws about 0.8 amps so I guess the 33amhr battery should last a while :P

Thanks again, I am sure you can all relate to my frustration today after having bought this bluddy thing from the US for nearly AU$700 then taken the trouble to setup my workshop (on the dinning table see attached:help:) and muck around to get the silly contracption to fit the focuser first, with everything all over the dinning room floor etc only to find the bludy thing had issues once I thought it was a goer :mad2:......buuuut all's well that ends well :thumbsup:
:D
Now to actually listen again to what my wife as been saying all day while I have been cussing and cursing and pretending to listen :help: :D

Thanks again guys

Mike

[DavidU]

Great! Now for some more killa astro photo's:thumbsup:

[strongmanmike]

Actually I run a 10amp 12V power supply at the moment out in the field. This unit currently powers both my Kendrik dew heater controller with two straps plus the FS2 GOTO mount control. The kendrick dew controller plugs into a cigarette adapter which is in turn connected to the power supply terminals while the FS2 connects via push in plugs on the same +ve and -ve terminals on the power supply. Thing is I actually have a double adapter cigarette adapter too, so I am thinking I could plug this into the single cigarette adapter and then run all three things from the same 12V power supply..? That sound reasonable..?

Mike

[DavidU]

Yes!
If the dew system gives no banding problem it should be fine with the Robofocus

[AlexN]

Great to hear you got it all up and running mate..

Just in case you're ever in need of a spare.. I'll gladly swap you my soul for your scope/camera... :D

That thing is a MONSTER! I put my TMB 80/480 + Orion SS Pro next to my laptop and the laptop looks big... You put your AP152 + PL11002M next to your laptop, and all of a sudden, the room the whole shebang is in looks decidedly small :D

I love it... L - O - V - E Love.

[mithrandir]

You might do better to get however many cig adapters you need and wire them in parallel on some 20A or even 50A wire and connect that to the battery. Cig adapters have a limited current capacity.

If you can find panel mount ones you could make it up as a neat box with banana sockets etc. for whatever else you power.

[Bassnut]

The beer bottle on the bench is the problem. Beer bottles radiate all kinds of interference.

[DavidU]

I would need a beer if I have 1/2 million dollars of malfunctioning astro gear on my kitchen table !:whistle::lol:

[mill]

I personally would not use cig adapters :(
The problem with those is that they can slowly separate because of the spring tension on the middle tip.
I had that happen to me i the middle of an imaging session and had to tape them together to prevent them coming loose.
When new they will be nice and tight but after a while they will loosen up and come apart.
Just my 2 cents on cig lighter adapters.

[strongmanmike]

That's what I thought Dave, sounds ok.



She is a beauty that's for sure, actually I just had a kind of argument with my wife last night when we were talking about our wills, I made the suggestion that I'd like some of my good astro gear to be given away to some worthy imagers out there if I die and she nearly hit the roof :eyepop: man I was just trying to give back to a commuity that that I love and she thought that my son should be able to just sell it all to the highest bidder :shrug: ...sorry folks...I'll work on it :thumbsup:

[AlexN]

I would like to think that If i ever have kids and I end up with a setup like yours, that when I died my kid would take an interest in the hobby I enjoyed and try and get some use out of it all... Sure, I'd understand if they were in a financial position in which they required the money.. but in any other circumstance I would like to be able to look down at my family, and see them looking back up at me through the equipment I'd worked so hard to acquire..

[strongmanmike]

Thanks again everyone for your help and suggestions, much appreciated and for you Alex.....look and drool :D

oh and I'm 6ft 1" and 137kg too

he he

Mike

[AlexN]

There is a puddle under my computer desk now.. Cheers...

Mop up on Isle 4!

Im 6'1" too... gives me a good idea of size... ie - DAMN MASSIVE! Your camera/focuser are bigger than my entire setup :P hahaha...

Yes.. Very cool.... **Alex watches the clock and counts down the apporximate seconds until he shall receive a call from Astro-Physics regarding his AP130 Star-Fire.

[strongmanmike]

Everything on that image train and scope is now the highest quality available on the market today....except for the finder = $90 Russian trash ...oh and my thongs = $4.99 from KMart. :D My wife may let me pass those on freely when I die..? :rolleyes:

Once you get that call from Astrophysics and assuming you aren't in an aged care facility by then :rolleyes: you will also need a new mount too :thumbsup: or are you on the AP900 mount list too?

Mike

[AlexN]

on the AP1200 list... :)

haha.. At least you have a finder, even if it is russian trash! :P

From what I understand I have 6 years wait on the AP130, and roughly half that for the AP1200GTO...... by that time I hope to have my new camera.. Just trying to put my finger on exactly what that will be...

[DavidU]

6 years?:eyepop:I get crusified if I can't deliver a custom job in 3 months !
I'm going to print off an AP waiting list for my customers.

[AlexN]

Thems the brakes Dave... From what I remember, Mike waited almost 9 years for his AP152... You must remember, Astro-Physics are actually a very small company, and their production runs are done by model, to order... The finished a run of the AP130 SF EDT's about 2 months ago.. they then move on and do a run of 140mm, 155mm, then they will likely go back to the start do a run of the smaller Traveller scopes, then back to the AP130.. this is, of course, in between doing runs of the AP Mach 1 GTO, AP900 GTO, AP1200GTO and AP3600 GTO mounts... Considering the exceptional quality of every single scope and mount that is sold, their wait times are actually exceptionally low...