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Author Topic: elevation rotor accuracy  (Read 231 times)

KB8VUL

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elevation rotor accuracy
« on: January 30, 2022, 08:18:32 PM »

Have a question regarding a DIY azimuth rotor project I am about to undertake.
Need to know how accurate I need to be able to track both azimuth and rotation on a satellite tracking setup.

Setup at this point will be a set of 13B2 VHF and a rather large cross polarized UHF beam on a common azimuth mast mounted on top a 20 foot section of Rohn 65G tower.  Not sure what the UHF beam is at this point but I know its over 20 elements and longer than the 13B2 booms.

I have a large worm gear setup that I will be using for the elevation that currently has a 24 volt DC gear reduction motor turning it. I don't know for sure was level of angular control I will have with this.  I know I can drop the voltage to the motor and get it to run rather slow, but I need to make a decision if I need to remove that motor and put a gear reduction stepper or a servo motor on the gear drive to increase the angular control resolution. 

Wanting to NOT skimp on the antenna setup in case I really like chasing birds and move forward with the whole LDMOS transmit amps and preamp setup at the tower and add a small (4 foot) dish to the mount and re-balance the elevation setup after that.  Top plate will be 3/8 or possibly 1/2 plate with the proper thrust bearing and a DIY gear reduction azimuth rotor.  I sort of need the accuracy requirements for that as well.  I am guessing that a HAM M is NOT gonna do it, and would have too much play in it for it to remain repeatable.

I can build to whatever I need.  But I can't see overbuilding it to a great degree.  I have played around with steppers and servo motors doing CNC machining work and converting manual mills and lathes to CNC adding proper ball screws and motors. I have a mill and lathe so creating parts isn't a problem, but if I need to track at an accuracy / repeatability of 1 degree, there is no sense in building this out to have the angular resolution down to 10 minutes or something crazy like that. 

I have seen some of the projects that guys just used linear actuators for their elevation jacks.  And I would be OK with doing that if it's accurate  enough and I can find a jack that I would trust to support the load. 
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N4UFO

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Re: elevation rotor accuracy
« Reply #1 on: January 31, 2022, 02:51:10 AM »

Hi Keith,

Just a casual observation, but are you perhaps looking at older manuals on satellite setups? (Or are you maybe modelling an EME setup?) Have you looked at what people are running these days? I say that because as someone with years of experience at successfully working sats, your antenna plans sound like serious overkill for present day birds. They are all LEOs at the moment and rarely, if ever need as much antenna gain as you are proposing. (Unlike some years ago when they WERE needed for HEO birds.) I managed to work all 488 CONUS grids and never had more than 7 elements on VHF and 11 on UHF. And even that was a bit of overkill. Most guys working the birds are using less than that. (hand held antennas/radios with 3/7 V/U elements) The most popularly recommended set of base antennas these days is the M2 Leopack. https://www.amsat.org/product/m2-leo-pack-antenna-system/ This antenna setup is CP with basically 4 elements on VHF (total of 8, 4 horizontal and 4 vertical) and 8 elements on UHF (total 16, 8/8).

The reason I say all this, is to answer your question... the more gain the antenna has, the more narrow the bandwidth lobe of the antenna has and the more accurate the aiming needs to be. Typically, a Leopack antenna mounted on a Yaesu G5400/5500 rotator setup is the cat's meow. More than that sounds like overkill to me. (What you are proposing is, again, more inline with an EME station.)

And please... I am not sure what 'LDMOS transmit amps' are, but I HIGHLY doubt you need ANY transmit amp AND it would most likely cause serious QRM. The birds today have more of a problem with people running TOO MUCH power and causing swamping of the satellite's AGC circuit, thereby pushing other ops below the threshold of access. Simply put, too much power kicks everyone else off the bird. As a lot of ops are running a mere 5 watts with modest gain antennas.

The issue is more about reception of the bird, not the bird hearing you... low loss feedline and often a UHF preamp located at the antenna is sufficient to overcome that. More than 25 watts is RARELY needed, and again will QRM everyone else on the bird as you capture the AGC and take over the entire passband.

I see you are a licensed radio tech. (I got my license GROL, but never really used it beyond a few 2 way jobs and assisting with some broadcast stuff.)  I hope you take all this in the spirit it is offered. I completely understand the confusion as the 'landscape' of satellites has changed tremendously over the years. I was first on sats back on the late 90s, I only worked RS-12/13, an HF up/down bird, as I didn't have the setup to work anything else. Then when I came back around in 2013 and worked an FM LEO bird for the first time, I was like, 'Whoa! This is completely different!!' So I hope if nothing else, I've re-directed you to an easier and more productive setup.

Please ask any more questions... and if you need a reading reference, try one of these:

digital:  https://www.amsat.org/product/2020-edition-of-getting-started-with-amateur-satellites-digital-download/
paper: https://www.amsat.org/product/2020-edition-of-getting-started-with-amateur-satellites-print-edition/

You may just see a picture of some guy with the aforementioned handheld radios & antenna operating from Roswell and making reference to a 'UFO' as he talks. ;)  (page Funcube 4-2, picture of me roving in Roswell, NM)

73 & take care!  Kevin N4UFO
« Last Edit: January 31, 2022, 03:05:38 AM by N4UFO »
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KB8VUL

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Re: elevation rotor accuracy
« Reply #2 on: January 31, 2022, 04:11:32 PM »

Hi Keith,

Just a casual observation, but are you perhaps looking at older manuals on satellite setups? (Or are you maybe modelling an EME setup?) Have you looked at what people are running these days? I say that because as someone with years of experience at successfully working sats, your antenna plans sound like serious overkill for present day birds. They are all LEOs at the moment and rarely, if ever need as much antenna gain as you are proposing. (Unlike some years ago when they WERE needed for HEO birds.)

73 & take care!  Kevin N4UFO


OH, WOW.  I guess now I understand the comment my buddy made when I was telling him the full scope of my plans.  His comment was about tracking Voyager.  I didn't understand the comment until now.  I had not mentioned the rest of if here because it was a down the road thing.  But I have a 14 and a 20 foot earth station dish lined up to go get in the spring and was considering and designing the drive mechanism for setting both of them up for independent AZ -EL tracking.  So if a 30 element cross pol UHF and a Cross pol 13B2 is overkill, what does a 30 db gain dish that's 20 foot across fall into?

I had NOT really looked at the current satellite stuff.  I figured that I wanted to try my hand at the HEO stuff and would need 50 and possibly 60dBm of power 100-1000 watt.  That was the LDMOS comment.  That technology will effortlessly produce 60dBm of power with nothing but a still 50 volt power supply.  It's basically just an 'linear amp'.  But it sounds like the 20 watts the radio will product will be sufficient. 
Are there any of the high altitude birds even in operation or has all that stuff died off or been deorbited?

I had been watching some videos of the AZ-EL DIY rotors on ebay and saw a guy that had a GPS, inclination sensor and some other stuff in a box at the cross pipe and figured I needed all that.  Sounds like I would for EME and the power to boot, but the earth station stuff would be overkill for anything short of Earth - MARS - Earth. 

So, it sounds like 20 is plenty and probably too much for most of it.  But a good Gas-FET preamp for both antenna's would be in order and running 7/8 for the VHF and 1-5/8 for the UHF wouldn't be unreasonable.  Just need to skip the 1kw amplifiers for satellite work. 
But it does sound like the accuracy needs to be there for the antenna's due to the beam width.  So the question becomes since I can get stuff pretty tight, is the 'publicly' available data to base the calculations on for the AZ-EL pointing going to be accurate enough if I do build to .5 degrees of repeatability or is it gonna be a waist of time?

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KB8VUL

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Re: elevation rotor accuracy
« Reply #3 on: February 06, 2022, 07:20:42 PM »

I have done more reading and had more time to think on all this. 
I at sort of a crossroads with the original plans due to the new information.  Specifically the current group of birds being LEO and not needing hardly any ERP to work them.  At least the FM birds.  I assume the transponder birds are similar and also will not need high power levels to work them either. 

Still planning on moving forward with the tower mounted yagi's as mentioned before.  BUT, I am now debating the tower height. 
Due to cable length and complexity coupled with the requirement to refile the paperwork with the FCC for the tower height change, I am still against the idea of putting the Rohn tower on top the big tower (Pictures on QRZ under my call).  But I also have the issue of getting older and not wanting to climb very far into the air to work on the rotor and beams.

 I have two 20 foot sections of the Rohn 65 tower that could be stacked and then the array put on top of it and it would allow double duty for both satellite work and terrestrial SSB and FM work as well but 40 feet AGL I am not sure if I am gaining enough to go that extra 20 feet of just put up one section and make servicing stuff easier and do something else with the other section.  AMSL here is 1350 which is 10 feet short of teh highest point in the county at 1360 and it's 500 yards away, so getting over it isn't a problem.  My HAAT is 525 at the top of the tower (240 feet) so even at 20 feet of tower height I am taller than most everything else anywhere close to me. 

Any additional thoughts are welcome. 
Also. as odd as it sounds.  During a typical pass of a satellite, what angular speed is required to maintain contact with the satellite?
Meaning how fast does the beam need to rotate to keep pointing at the satellite?  And for that matter how fast does it need to move in elevation?
Since I am building the rotor system I need to know how fast it needs to track. 
Thanks in advance.





 
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N4UFO

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Re: elevation rotor accuracy
« Reply #4 on: February 06, 2022, 08:42:21 PM »

I had my setup on a ground mounted TV tripod and some EMT pipe... crossboom was about 8' above ground. To me, all you need to do is clear nearby obstructions. Unless you have tall trees, I would think 20' Rohn is enough.

I turned my rotors manually, just bumped them a number of degrees every so often, so wouldn't have a clue as to auto tracking speed, sorry.

73, Kevin N4UFO
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KB8VUL

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Re: elevation rotor accuracy
« Reply #5 on: February 08, 2022, 09:02:46 PM »

Thanks Kevin.  I figure that if I put that much aluminum in the air I should be at least trying to use it for multiple things. 
If you are just manually bumping it every few minutes and that works for the birds then having the ability to move 12 degrees a second on the high speed swing should be more than plenty. That would get me 360 degrees in a minute and not put too much strain on the cross boom. 
And 1 degree repeatability seems reasonable as well. 
I might look at moon bounce and see what those setups require.  Figure that if I can use it for that as well then why not. 
At one point in my life as a ham I had the car with many antenna's and people would ask if I talked to the moon with it. 
Might as well be able to tell them that's at the tower site,,, and I don't talk to moon men I just bounce the signal off it and talk to people here on Earth.

Still debating on the big earth station dishes.  (were at a radio station) but the concrete for those is gonna be rather expensive.  There are 4 kasons that supported the first tower that was erected at the site and was later removed and upgraded.  These are 23 by 23 by 30 so I figure they will hold the big dish if I go that way,,, just not sure what overall condition they are in. 

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WB8PFZ

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Re: elevation rotor accuracy
« Reply #6 on: February 09, 2022, 06:54:03 AM »

Something you may want to look into is a newer product called a S.A.T controller. There are you tube videos. Neat product that makes tracking the bird very simple. Mike
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KB8VUL

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Re: elevation rotor accuracy
« Reply #7 on: February 10, 2022, 09:30:51 PM »

Something you may want to look into is a newer product called a S.A.T controller. There are you tube videos. Neat product that makes tracking the bird very simple. Mike

I looked that up.  Saw that it would work with a G5500 or something to that effect but I couldn't find where it would work with a custom rotor setup.
I am looking at an R-Pi - Arduino setup that is configurable.  The Arduino is very easy to interface to a stepper or servo motor controller, motion sensors and the like and the R-pi... well it's an R-pi. 
The other reason to go that route is if I decide to put up that big earth station dish, that will certainly be a custom drive setup.  The dish is a fixed position setup currently but does have ability to be manually pointed.  Not sure if I am gonna go that route yet, but the cool factor is off the charts and a fence around the whole place with a TRACKING 20 foot dish should get the neighbors REALLY telling stories to each other of whats going on there.  I have already been told the horns on the tower were radioactive.  Been ask to see the underground bunker (don't have one unfortunately).  And that the federal government used the site to monitor peoples cell phone conversations.  So actually having something like big tracking dishes would just add fuel to that fire.  Already looking at doing that with a big 3 phase gear motor with a reluctor wheel for it to give feedback of motion and direction.  Not sure on the elevation system though just yet.  Most likely a big linear actuator with a servo drive. 

For those of you that are going... HUH??
CNC machines all work pretty much this way.  And good ones can move in the thousandth of an inch.  I have equipment currently in my machine shop that can repeatably track to 3 arc seconds. To break that down, if you took a bar 100 yards long and tilted it 3 arc seconds, the far end would move .0625 inches.  Comparatively, one MINUTE of angle at 100 yards is one inch of movement.  Now this is a specialized positioner unit, and none of the machines I have are nearly that accurate.  In fact the expansion of a cutting tool in a mill or lathe due to the heat created during the cut would exceed  push off the cut by a greater amount than this.  But I am thinking that I build a drive setup that will track a couple beams on a bar at 2 or 3 degrees and in truth, the beams and cross bar would flex in the wind a greater amount than that. 


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WA8NVW

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Re: elevation rotor accuracy
« Reply #8 on: February 14, 2022, 08:02:11 PM »

In order to answer KB8VUL's original question, I reply with "What is the 3 dB (power) beamwidth of the antenna array you are building?  You don't need to resolve a higher resolution than 1/2 the beamwidth in either V or H plane.  The signal variation on both transmit and receive will be less than 3 dB by definition.
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KB8VUL

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Re: elevation rotor accuracy
« Reply #9 on: February 16, 2022, 08:35:57 PM »

In order to answer KB8VUL's original question, I reply with "What is the 3 dB (power) beamwidth of the antenna array you are building?  You don't need to resolve a higher resolution than 1/2 the beamwidth in either V or H plane.  The signal variation on both transmit and receive will be less than 3 dB by definition.

Thank You...
As of right now I don't have those figures in front of me.
The VHF antenna will be two 13B2's on a single boom offset 90 degrees and 1/4 wave like is suggested in most everything I have read.
The UHF antenna is an off the shelf item but I can't tell you what it is right now.  I do know it's a cross polarized 90 degree offset antenna manufactured by some company due to the build quality.  Probably a Cushcraft But I am not sure and I haven't dug into it very much yet. 

So I guess the question is can I use the 3db beam width numbers off a single 13B2 as reference?  Actually I will most likely want to use the UHF beam as it's 30 ish elements and I would assume tighter. 

I have considered doing something at 1.2 and possibly 2.4 Ghz, but that stuff would be a DIY project and probably not as tight as the UHF monster. 

The other thing I am looking at is a set (VHF and UHF) egg beaters. I will be building those as well.  I can't justify the price that M2 wants for theirs for a specific application that I may or may not like.  These would be mounted elsewhere so they were out of the way of the beams.


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N4UFO

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Re: elevation rotor accuracy
« Reply #10 on: February 16, 2022, 09:13:53 PM »

The other thing I am looking at is a set (VHF and UHF) egg beaters. I will be building those as well.  I can't justify the price that M2 wants for theirs for a specific application that I may or may not like.  These would be mounted elsewhere so they were out of the way of the beams.

To paraphrase the thinking of a whole lot of sat ops out there... No, just please, no. They don't hear well and in practice end up making an eager ham cause QRM to everyone on the bird because they can't properly hear the bandpass. That said... to experiment and learn, fine. Just lower your expectations and keep wary of the potential of QRMing ongoing QSOs that you cannot hear. Either by 'walking' over them or by jacking up your transmit so high in order to hear yourself that you cause the AGC to kick up overly high and push weaker stations below the hearing threshold. I was once on the continental divide in NM trying to give out a rare grid with my 5 watt portable station and could not be heard because of an overpowered station talking away in the upper end of the passband. And if you don't understand the AGC threshold, etc. I recommend doing some reading... AMSAT satellite guide comes to mind; I believe it's covered in there.

73, Kevin N4UFO
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KB8VUL

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Re: elevation rotor accuracy
« Reply #11 on: February 18, 2022, 09:26:09 AM »

The other thing I am looking at is a set (VHF and UHF) egg beaters. I will be building those as well.  I can't justify the price that M2 wants for theirs for a specific application that I may or may not like.  These would be mounted elsewhere so they were out of the way of the beams.

To paraphrase the thinking of a whole lot of sat ops out there... No, just please, no. They don't hear well and in practice end up making an eager ham cause QRM to everyone on the bird because they can't properly hear the bandpass. That said... to experiment and learn, fine. Just lower your expectations and keep wary of the potential of QRMing ongoing QSOs that you cannot hear. Either by 'walking' over them or by jacking up your transmit so high in order to hear yourself that you cause the AGC to kick up overly high and push weaker stations below the hearing threshold. I was once on the continental divide in NM trying to give out a rare grid with my 5 watt portable station and could not be heard because of an overpowered station talking away in the upper end of the passband. And if you don't understand the AGC threshold, etc. I recommend doing some reading... AMSAT satellite guide comes to mind; I believe it's covered in there.

73, Kevin N4UFO

Sounds like the eggbeaters are NOT such a viable option for antenna's and I should look at other options..
Possibly a smaller array sitting on a couple sticks of Rohn 25 or similar and an smaller rotor possibly? 
Will need to evaluate available feed line for that... would most liely need to be 7/8 for both UHF and VHF if I went that path. 

Maybe that system gets the '3D printed' rotor assembly and repurpose a couple 3 element VHF yagi's I have for control station radios (radios used for access to specific repeaters from radio console).   Have some significantly smaller UHF yagi's for that as well.

As far as the AGC and cutting others out.  If I am reading what has been said here and elsewhere correctly.  The signal level received at the bird is directly related to the amount of signal coming from the bird and there is both AGC and a limited gain level available for ALL downlink returns with passband birds as opposed to the FM birds that have all the signal for the downlink dedicated to a specific downlink frequency.  Oddly enough this is anso how the DAS / BDA system I design and install for in building public safety radio coverage work and also suffer from a similar shortcoming.  They have a total output level of +33dBm for all passed frequencies.  If they hear ONE frequency it can be amplified to as much as 33dBm.  If there are 2 signals each can have a maximum of 16dBm out and it continues to 'divide' accordingly.  And of course there is also an AGC circuit in case someone near the install site happens to transmit on a frequency in the downlink bandpass that would swamp the downlink 'receiver'.  Of course I am doing a straight frequency pass through, unlike the birds that I assume down convert the RX frequency to an IF frequency and pass it into a mixed on the transmit side for either a straight or inverse conversion to the down link transmit frequency and it's broadcast from there.  same thing happens on my uplink frequency going out to the RF site I have the donor antenna pointed at. 

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