Hi Tom, if using an inclinometer on the elevation axis, one can evaluate
the magnitude of the azimuth axis error pretty easily. A method used here is
to set the elevation angle at 45 degrees and leave it there for this test:
starting at az= 60 degrees, record the elevation reading every 30 degrees
to 300 degrees azimuth. Allow several seconds for the system to stabilize at
each reading.
Any tilts in the system will show up as a change in the elevation readings.
Once the az axis tilt errors are identified, one can consider options to co
rrect it or at least partially correct it. In my case, since I could get
into the source code, I added a mathematical based correction to the antenna
position readout. This works great for me but the solution is different
for every station.
This solution also takes care of feed position errors. A user input for the
az and/or el feed tilt for each band is stored for automatic correction by
the software. We use that to correct for both side by side and over/under
multiple feeds. Again, one has to get into the source code to add this
feature.
>From my personal observations the az and el calculations in our software
are quite precise. As you said, the errors are primarily in the az and el
mounts themselves. The degree of software precision is evident by the very
small deviation in the doppler shift calculations we see at 10GHz.
73,
Gerald K5GW
In a message dated 7/27/2016 2:10:31 P.M. Central Daylight Time,
w2drz(a)ramcoinc.com writes:
Hi Gerald,
Thank you for your information, very helpful to better under stand the
problem.
will pass your note to Russ (K2TXB) as he is looking to add the a user
offset correction routine for this type of error problem.
Have also others that responded that have addressed this problem in their
tracking system above 10 GHz .
AS this offset correction need has not been addressed in most tracking
system software ,
the guessing of cause and the correction answers has become more clear to
be related to dish mount errors.
Tom W2DRZ
----- Original Message -----
From: _TexasRF(a)aol.com_ (mailto:TexasRF@aol.com)
To: _w2drz(a)ramcoinc.com_ (mailto:w2drz@ramcoinc.com) ;
_moon-net(a)mailman.pe1itr.com_ (mailto:moon-net@mailman.pe1itr.com)
Sent: Wednesday, July 27, 2016 1:13 PM
Subject: Re: [Moon-Net] 3 cm auto tracking error
Tom, if the azimuth axis is not perfectly vertical (never is perfect) the
actual azimuth direction has a built in error that is related to the amount
and direction of the axis tilt and the elevation angle.
Without getting into the details I will give you an extreme example of the
obscure and not well understood problem:
Assume you live at a latitude that allows the moon to reach an elevation
of 90 degrees. Further assume that there is an azimuth axis tilt of .5
degrees toward the east and the moon is passing through a calculated direction
of 180 degrees.
The calculated azimuth axis would be straight up. The tilt toward the east
changes the axis from a calculated value of 180 degrees to an actual angle
of only 90 degrees. The elevation angle is reduced from 90 degrees to
89.5 degrees.
This is an extreme example but the trend and concept is present for other
latitudes and tilt directions. This is the same problem that is encountered
with multiple side by side feeds in a dish. Working with Al, W5LUA in the
past we have been able to mathematically correct his errors to a large
degree. On my own system, the tower has a slight lean toward the southeast that
requires a correction of about 2 degrees in azimuth as the moon passes
through zenith. The correction varies as the declination and elevation angle
varies.
I hope this is the issue you were asking about. If not, please ignore this.
73,
Gerald K5GW
In a message dated 7/26/2016 4:41:53 P.M. Central Daylight Time,
w2drz(a)ramcoinc.com writes:
Hi,
If on 3 cm auto tracking and must correct moon noise during a QSO?
I am trying to understand why the auto tracking does not do 100% correct
TRACKING,
the cause may be various reasons?.
Those on 3 cm or 5760 and auto tracking,
drop a note on what you find and if have found a cure of the error
problem.
Try to change the W2DRZ controller and AB encoders to hi res (16 bit) on
the
encoders to see if that changes the tracking error.
the USD encoders will then do about 14 bit resolution or "1 tenth a degree"
(0.01) degree.
tom W2DRZ
http://www.w2drz.ramcoinc.com/http://www.w2drz.ramcoinc.com/ProgNotes.htm
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Excellent points Keith! It goes to show that deriving a software correction
solution that works for everyone is going to be a very difficult
undertaking.
I have solutions in place for my own systems but they are not applicable to
other stations as the error sources will be different. I have implemented
a software routine that zeros out the error by pressing a keyboard key.
This is a very elementary solution but does allow good tracking accuracy (with
low winds) for a couple of hours before it needs to be repeated.
Another issue is how long to run motors to keep the antenna on target. One
would think this is a simple d/v calculation but it is far more complex
than that. In my case AC motors are "bumped" every 20 seconds. For various
reasons a given bump time does not always result in the same amount of
rotation. I added a routine that includes a "fudge" factor to increase or decrease
the run time based on the aiming error at the end of each 20 second update
interval. Again, a very elementary solution but it does help.
The elevation motion required in my systems varies depending on the
elevation angle. The geometry of the elevation screws are such that they move
more degrees per revolution at high elevations compared to low elevations.
Fortunately the "fudge" routine also covers that issue.
While this works ok for my needs, the typical user does not have the means
to implement things like this in their tracking software. Hence the
challenge for a universal solution is presented. Who out there is interested in
taking a few hundred hours to meet the challenge?
73,
Gerald K5GW
In a message dated 7/28/2016 12:54:56 A.M. Central Daylight Time,
keith.naylor(a)micronet-uk.com writes:
The issue is really a combination of 2 major issues, one is relatively
easy to solve the other is not.
Alignment of position sensors relative to the rotation axes is
straighforward, maintaining alignment of the axes orthogonal to the
earth is more difficult as the ground below your mount will move over
time meaning sucessive recalibration, we are talking periods of months.
It depends on your local geological conditions.
The more significant issue is mechanical displacement of the relative
feed position as AZ and EL changes. All mechanical items will
flex/deflect as the inertia changes wrt to the earth. It is rather
difficult to build a system which is balanced
at all AZ/EL positions, the result is the feed will certainly sag and
the dish itself distort as elevation is increased. This type of error
results in what is generally called collimation errors.
Professional and military tracking systems go to extraordinary lengths
to ensure the inertia of the whole mount and feed is balanced, this
often means bolting heavy weights (such as depleted Uranium) to the dish
and mount subframe.
Even this has diminishing returns and the whole mount sightline needs
calibration offsets added dependent on relative AZ/EL of the mount.
Therefore the whole pointing error is an RSS approximation of all known
errors, most linearity and resolution/accuracy issues can be extracted
and exploited, most mechanical deviation issues require intensive
calibration proceedures against galactic noise sources.
There was an excellent article in DUBUS 4/15 by DF3GJ on this topic
related to the DL0SHF EME station.
73'
Keih G4FUF
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Hello- I am studying what type of filter to place ahead of a tower mounted preamp. I am starting to plan-out my tower mounted preamp set-ups and wish place a low loss bandpass filter ahead of the preamp for 144, 222 and 432 Mhz. These set-ups are for weak signal tropo work. I live close enough to a lot of high power FM/TV transmitters to cause intermod, etc. I like to use a good filter ahead of preamp. I was looking at the DUAL (Antennas- Amplifiers site) bandpass filters. The 144 Mhz filter is rated at 0.21 dB loss. This looks like the type of filter that I would like to use. I have some of the twin cavity tunable filters (F-193/ modified for 144 Mhz) that I am using inside my station as of now. I like these filters as their insertion loss is pretty low, but I hesitate to place one of these in a weatherproof outdoor enclosure due to temperature change / humidity concerns. I am very interested in the DUAL filters and wanted to ask someone who is using any of them to please tell me a few details about the type of filter, construction, etc. I asked DUAL for more information but they will not provide anything beyond what is shown on site. I am interested in knowing the general construction, type of components, etc. The filters are not inexpensive and I thought it was not unreasonable to ask these questions. I am certainly not trying to copy their design etc, I just like to know a little more about what I am buying. I am curious if the 144 bandpass filter at Antennas-Amplifiers is similar to this filter: yu1lm.qrpradio.com/2m%20BP%20FILTER-YU1LM.pdf Thanks anyone for information, Byro W5FH
A reminder that July 30-31st is the 3cm Activity Weekend......for newcomers: The idea of activity weekends is to encourage activity on the higher microwave bands outside contest weekends. There are no restrictions... if you wish then use the logger, telephone, HF....and use any mode. It is not a contest. It enables everyone to make QSOs, test new equipment, feeds, preamps etc. Hopefully some of the big guns get on and provide signals for newcomers to look for.
I shall be in listening mode only I’m afraid with a very restriced window, but with my improved system ( 12dB sun noise) I hope to hear some new ones.
GL, 73 Peter G3LTF
The issue is really a combination of 2 major issues, one is relatively
easy to solve the other is not.
Alignment of position sensors relative to the rotation axes is
straighforward, maintaining alignment of the axes orthogonal to the
earth is more difficult as the ground below your mount will move over
time meaning sucessive recalibration, we are talking periods of months.
It depends on your local geological conditions.
The more significant issue is mechanical displacement of the relative
feed position as AZ and EL changes. All mechanical items will
flex/deflect as the inertia changes wrt to the earth. It is rather
difficult to build a system which is balanced
at all AZ/EL positions, the result is the feed will certainly sag and
the dish itself distort as elevation is increased. This type of error
results in what is generally called collimation errors.
Professional and military tracking systems go to extraordinary lengths
to ensure the inertia of the whole mount and feed is balanced, this
often means bolting heavy weights (such as depleted Uranium) to the dish
and mount subframe.
Even this has diminishing returns and the whole mount sightline needs
calibration offsets added dependent on relative AZ/EL of the mount.
Therefore the whole pointing error is an RSS approximation of all known
errors, most linearity and resolution/accuracy issues can be extracted
and exploited, most mechanical deviation issues require intensive
calibration proceedures against galactic noise sources.
There was an excellent article in DUBUS 4/15 by DF3GJ on this topic
related to the DL0SHF EME station.
73'
Keih G4FUF
Hi folks,
I've recently updated the website to include versions of the DG8 masthead preamp for 4m and 6m bands. Today, I've published some initial information on installing the PAT boards in the FT991, so that you can get a proper waterfall display off this rig.
Remember, orders placed in advance can be collected in Venice at EME2016 - I look forward to seeing you there in a few weeks
Best 73,
Dave
http://hupRF.com
Gerald (and others),
I have been doing some experiments with a Tilt-compensated digital compass in the MABMPU PCB firmware. One nice feature of using an accelerometer in conjunction with Az/El encoders is you can compensate for alignment errors of the mount (tower and/or encoder(s)) across the usable range.
Google Freescale AN4248.pdf for more information on this topic.
Gary, N8CQ
Is there anywhere a REW 14 connector assembly instruction ?
Can't find by google.
73's Erwin/DK5EW
--
Member of the Team of MMMonVHF
http://www.MMMonVHF.de
Homepage: http://www.dk5ew.com
Hello!
I have received some letters asking to check the log JT0 DXpedition.
All questions was forwarded to Dmitry RA9YTX.
They reported that even on the way to the house near the city of Barnaul...
Expedition will answer on questions soon.
73, Alexey RA4SD
