Just purchased the MTMScientific Kit for radio astronomy at 611 Mhz
211 views
Skip to first unread message
Michael
Sep 26, 2009, 7:09:22 PM9/26/09
to Society of Amateur Radio Astronomers
I just realized that I'm part of the list on one of my other emails
(msabi...@yahoo.com). Sorry about that. Geeze! I have so many
emails...
OK, so anyway I am working on a 611 MHz yagi radio telescope from MTM
Scientific (www.mtmscientific.com). I hope to detect Cassiopeia A,
Cygnus A, Taurus A, and Virgo A. The antenna has 13.5 db gain, but the
beamwidth of the antenna is 38 degrees. Looking at radio eyes from
radiosky.com, the seperation of Cygnus A and Cass A seems to be
sufficient that I can detect the difference between them in a drift
scan.
Is this correct?
What can I expect to observe with the MTMScientific kit if in a low
noise environment? are my expectations realistic?
Something else I am interested in detecting are pulsars... I want see
at least one, whether it's some kind of brightness indicator that
searches for the probability of there being pulses with the crab
pulsar's seperation in time, or what. What do you suggest for a
workable set up?
I currently don't have an LNA, can I use a UHF TV LNA for channel 37
radio astronomy?
How do I combine the two parameters (noise figure and gain) of an LNA
to generate a more realistic metric for measuring performance of an
LNA?
What is a good type of alt/azi or ra/dec motor and mount for a yagi
(the cheaper the better)? I want something inexpensive and
weatherproof - mainly to shorten the time required for drift scanning,
and to make cold winter days a little more tolerable.
Can I use a Parallax chip for radio astronomy? For example, to radio
into the house the results of the analog to digital converter from
outside (to prevent having to run cables to the inside of the house).
Thanks,
Michael Sabino.
PS... You can delete the posting by linear_shift aka Kurt
(msabi...@yahoo.com). Sorry about that. Geeze! I have so many
emails...
OK, so anyway I am working on a 611 MHz yagi radio telescope from MTM
Scientific (www.mtmscientific.com). I hope to detect Cassiopeia A,
Cygnus A, Taurus A, and Virgo A. The antenna has 13.5 db gain, but the
beamwidth of the antenna is 38 degrees. Looking at radio eyes from
radiosky.com, the seperation of Cygnus A and Cass A seems to be
sufficient that I can detect the difference between them in a drift
scan.
Is this correct?
What can I expect to observe with the MTMScientific kit if in a low
noise environment? are my expectations realistic?
Something else I am interested in detecting are pulsars... I want see
at least one, whether it's some kind of brightness indicator that
searches for the probability of there being pulses with the crab
pulsar's seperation in time, or what. What do you suggest for a
workable set up?
I currently don't have an LNA, can I use a UHF TV LNA for channel 37
radio astronomy?
How do I combine the two parameters (noise figure and gain) of an LNA
to generate a more realistic metric for measuring performance of an
LNA?
What is a good type of alt/azi or ra/dec motor and mount for a yagi
(the cheaper the better)? I want something inexpensive and
weatherproof - mainly to shorten the time required for drift scanning,
and to make cold winter days a little more tolerable.
Can I use a Parallax chip for radio astronomy? For example, to radio
into the house the results of the analog to digital converter from
outside (to prevent having to run cables to the inside of the house).
Thanks,
Michael Sabino.
PS... You can delete the posting by linear_shift aka Kurt
Randall family
Sep 27, 2009, 2:56:56 PM9/27/09
to sara...@googlegroups.com
Michael,
A couple of comments:
I work at 408MHz which shoud be similar to the 611MHz operation. At 300 to
600MHz the signal levels from the plane of the galaxy are easy to detect.
The sun is very strong at these frequencies also. If the sun is anywher
near my area of interest, it will cover most things up. The sun is an
interesting item of study it it self. During flares its output is very
strong at 408MHz.
I am not familiar with the MTMScientific receiver.
My radio astronomy antenna does not have a motor to move it. I just grab a
couple of wrenches, loosen the mounting bolts, set the antenna at the
desired declination, and tighten the bolts. This is as inexpensive as you
can get. I normally watch one declination for several days, so this is not
a problem. I watch one declination for several days so as to, maybe, get
one scan free of electical interferance. Averaging several scans also can
reduce noise in graph.
On the preamp, the noise figure, generally, should be as low as the budget
allows. The gain only neeeds to be enough to cover up the noise of the
following receiver. Too much gain can cause overload and intermodulation
problems. Generally preamp data does not tell about overload levels. I
use the DownEast Microwave 432MHz preamp at 408MHz. They run the GASFET at
50 to 60mA vs. the more normal 10 to 20mA, which degrades the noise figure
slightly. The worse noise figure preamp works better in my system because
it does not get overloaded ! UHF television transmitters are not too far in
frequency from your operation and the preamp will amplify them as well. If
any UHF television transmitter is near you it may be an overload problem.
If a preamp is overloaded, results are usually erratic.
Good luck with your project. Keep the group informed of problems, so we can
offer suggestions.
Bruce Randall SARA director
--------------------------------------------------------------------------------
No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 8.5.409 / Virus Database: 270.13.113/2396 - Release Date: 09/26/09
05:51:00
A couple of comments:
I work at 408MHz which shoud be similar to the 611MHz operation. At 300 to
600MHz the signal levels from the plane of the galaxy are easy to detect.
The sun is very strong at these frequencies also. If the sun is anywher
near my area of interest, it will cover most things up. The sun is an
interesting item of study it it self. During flares its output is very
strong at 408MHz.
I am not familiar with the MTMScientific receiver.
My radio astronomy antenna does not have a motor to move it. I just grab a
couple of wrenches, loosen the mounting bolts, set the antenna at the
desired declination, and tighten the bolts. This is as inexpensive as you
can get. I normally watch one declination for several days, so this is not
a problem. I watch one declination for several days so as to, maybe, get
one scan free of electical interferance. Averaging several scans also can
reduce noise in graph.
On the preamp, the noise figure, generally, should be as low as the budget
allows. The gain only neeeds to be enough to cover up the noise of the
following receiver. Too much gain can cause overload and intermodulation
problems. Generally preamp data does not tell about overload levels. I
use the DownEast Microwave 432MHz preamp at 408MHz. They run the GASFET at
50 to 60mA vs. the more normal 10 to 20mA, which degrades the noise figure
slightly. The worse noise figure preamp works better in my system because
it does not get overloaded ! UHF television transmitters are not too far in
frequency from your operation and the preamp will amplify them as well. If
any UHF television transmitter is near you it may be an overload problem.
If a preamp is overloaded, results are usually erratic.
Good luck with your project. Keep the group informed of problems, so we can
offer suggestions.
Bruce Randall SARA director
No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 8.5.409 / Virus Database: 270.13.113/2396 - Release Date: 09/26/09
05:51:00
Randall family
Sep 27, 2009, 6:32:49 PM9/27/09
to sara...@googlegroups.com
Michael,
I looked at MTMScientific web site. The tuner has a noise figure of 13dB
which is a bit high. The tuner was made for cable TV applications where
signals are strong so 13dB noise figure is good enough for the intended
application. I am going to throw out a little math here. Please put up
with me!
For radio astronomy or space communications use noise temperature is much
more useful than noise figure.
Temperature in Kelvin = T = 290 * ( 10 ^ ( NF / 10 ) - 1) where NF is
noise figure in dB.
For tuner T = 290 * ( 10 ^ ( 13dB / 10 ) - 1 ) = 5496K or call it 5500K
Note that 400 to 700MHz range and a small antenna, sky temperatures will
range from 35K to maybe 200K. These signals will be on top of the 5500k
from the tuner input so they will not be easy to see.
Now lets look at a preamp with 0.7dB noise figure and 17dB Gain. This is
what I got from Down East Microwave for my 408MHz system.
Convert the Noise Figure to temperature as before give
T = 290 * ( 10 ^ ( 0.7dB / 10 ) - 1 ) = about 51K
Convert Gain to a power ratio
GP = 10 ^ ( 17dB / 10 ) = 50 Note that power gain does not have units.
It is the ratio of two powers, so units cancel.
If we put this preamp in front of the tuner, the tuner's noise temperature
will be reduced by the factor of the preamp power gain.
5500K / 50 = 110K contribution from the tuner.
The preamp will also contribute 51K.
The noise temperature of the combination is 110K + 50K = 160K.
160K temperature is good enough to see many radio astronomy sources with the
antenna gain you are talking about.
Another source of noise temperature is the antenna side lobes. Any yagi
antenna will have some sensitive directions off the side and back. These
minor lobes see the earth, which is around 290K. ( the source of 290 in the
first formula.) I am going to take a guess that the antenna will have
between 50 and 100K due to ground noise. This will add to the 160K of the
receiver. This is still good enough.
Most preamps with good enough noise temperature will have 50 ohm input and
outputs. There will be a small loss going into the 75 ohm tuner input. For
what you are doing this small mismatch loss can be ignored.
Changes in amplification anywhere due to temperature in the system will run
you crazy. Try to protect the preamp and tuner from temperature changes.
Also the diode detector used with the tuner will be light sensitive. Put a
little black paint over the diode. I learned about this the hard way!
Dick Flag, also on the SARA board, is an expert on this sort of thing and
will hopefully throw in some more helpful hints.
Hope this has informed you and not confused you too much.
Bruce Randall
I looked at MTMScientific web site. The tuner has a noise figure of 13dB
which is a bit high. The tuner was made for cable TV applications where
signals are strong so 13dB noise figure is good enough for the intended
application. I am going to throw out a little math here. Please put up
with me!
For radio astronomy or space communications use noise temperature is much
more useful than noise figure.
Temperature in Kelvin = T = 290 * ( 10 ^ ( NF / 10 ) - 1) where NF is
noise figure in dB.
For tuner T = 290 * ( 10 ^ ( 13dB / 10 ) - 1 ) = 5496K or call it 5500K
Note that 400 to 700MHz range and a small antenna, sky temperatures will
range from 35K to maybe 200K. These signals will be on top of the 5500k
from the tuner input so they will not be easy to see.
Now lets look at a preamp with 0.7dB noise figure and 17dB Gain. This is
what I got from Down East Microwave for my 408MHz system.
Convert the Noise Figure to temperature as before give
T = 290 * ( 10 ^ ( 0.7dB / 10 ) - 1 ) = about 51K
Convert Gain to a power ratio
GP = 10 ^ ( 17dB / 10 ) = 50 Note that power gain does not have units.
It is the ratio of two powers, so units cancel.
If we put this preamp in front of the tuner, the tuner's noise temperature
will be reduced by the factor of the preamp power gain.
5500K / 50 = 110K contribution from the tuner.
The preamp will also contribute 51K.
The noise temperature of the combination is 110K + 50K = 160K.
160K temperature is good enough to see many radio astronomy sources with the
antenna gain you are talking about.
Another source of noise temperature is the antenna side lobes. Any yagi
antenna will have some sensitive directions off the side and back. These
minor lobes see the earth, which is around 290K. ( the source of 290 in the
first formula.) I am going to take a guess that the antenna will have
between 50 and 100K due to ground noise. This will add to the 160K of the
receiver. This is still good enough.
Most preamps with good enough noise temperature will have 50 ohm input and
outputs. There will be a small loss going into the 75 ohm tuner input. For
what you are doing this small mismatch loss can be ignored.
Changes in amplification anywhere due to temperature in the system will run
you crazy. Try to protect the preamp and tuner from temperature changes.
Also the diode detector used with the tuner will be light sensitive. Put a
little black paint over the diode. I learned about this the hard way!
Dick Flag, also on the SARA board, is an expert on this sort of thing and
will hopefully throw in some more helpful hints.
Hope this has informed you and not confused you too much.
Bruce Randall
Michael
Sep 28, 2009, 11:50:04 PM9/28/09
to Society of Amateur Radio Astronomers
Bruce,
How does the 5 MHz bandwidth of the tuner from the IF pin (which goes
to the detector and dc amp) factor into the calculations you gave?
Wouldn't bandwidth relate to this as well?
Where did you read that the noise figure of the tuner is 13 dB? I was
only able to find the gain of the antenna (which is 13.5dB). It's
confusing to me how the antenna could have a gain of 13.5 dB (as
stated in the papers that were provided with it), and the receiver has
a gain of 13 dB. Why?
Michael Sabino
> >> (msabino...@yahoo.com). Sorry about that. Geeze! I have so many
> > --------------------------------------------------------------------------------
>
> - Show quoted text -
How does the 5 MHz bandwidth of the tuner from the IF pin (which goes
to the detector and dc amp) factor into the calculations you gave?
Wouldn't bandwidth relate to this as well?
Where did you read that the noise figure of the tuner is 13 dB? I was
only able to find the gain of the antenna (which is 13.5dB). It's
confusing to me how the antenna could have a gain of 13.5 dB (as
stated in the papers that were provided with it), and the receiver has
a gain of 13 dB. Why?
Michael Sabino
>
> > No virus found in this incoming message.
> > Checked by AVG -www.avg.com
> > Version: 8.5.409 / Virus Database: 270.13.113/2396 - Release Date:
> > 09/26/09
> > 05:51:00
>
> --------------------------------------------------------------------------------
> > No virus found in this incoming message.
> > Checked by AVG -www.avg.com
> > Version: 8.5.409 / Virus Database: 270.13.113/2396 - Release Date:
> > 09/26/09
> > 05:51:00
>
>
> No virus found in this incoming message.
> Checked by AVG -www.avg.com
> Version: 8.5.409 / Virus Database: 270.13.113/2396 - Release Date: 09/26/09
> 05:51:00- Hide quoted text -
> No virus found in this incoming message.
> Checked by AVG -www.avg.com
> Version: 8.5.409 / Virus Database: 270.13.113/2396 - Release Date: 09/26/09
>
> - Show quoted text -
Randall family
Sep 29, 2009, 7:58:20 AM9/29/09
to sara...@googlegroups.com
Michael,
There is a reference area on their web site that has the manufacturers specs
on the tuner. 10 to 13dB noise figure is typical for CATV tuners because
that is what is needed for good quality picture. These things are made by
the thousands, so saving a few pennies on each unit adds up... they won't
add in any performance that the TV viewer will not see.
5 MHz bandwidth is good and bad. Both the radio astronomy (RA) signals and
receiver noise are random processes. More bandwidth sees more of both
signals. The amount of change in the receiver output due to the RA signal
is only related to the noise power ratio. More bandwidth is also a bigger
target for interference to hit! Interference has always been my limitng
factor.
There is another important bandwidth effect... the readings are smoother
because there more is random stuff addded together. This is proportinal to
the square root of bandwidth. If you use 4 times the bandwidth, you get a
2:1 improvement in random wiggles in your output graph. These smoother
readings allow you to see smaller changes. The other thing that interferes
with seeing small changes is gain changes in the receiver due to room
temperature changes. Usually the limit of useful bandwidth in amateur
setups is gain drift.
Bruce
--------------------------------------------------------------------------------
There is a reference area on their web site that has the manufacturers specs
on the tuner. 10 to 13dB noise figure is typical for CATV tuners because
that is what is needed for good quality picture. These things are made by
the thousands, so saving a few pennies on each unit adds up... they won't
add in any performance that the TV viewer will not see.
5 MHz bandwidth is good and bad. Both the radio astronomy (RA) signals and
receiver noise are random processes. More bandwidth sees more of both
signals. The amount of change in the receiver output due to the RA signal
is only related to the noise power ratio. More bandwidth is also a bigger
target for interference to hit! Interference has always been my limitng
factor.
There is another important bandwidth effect... the readings are smoother
because there more is random stuff addded together. This is proportinal to
the square root of bandwidth. If you use 4 times the bandwidth, you get a
2:1 improvement in random wiggles in your output graph. These smoother
readings allow you to see smaller changes. The other thing that interferes
with seeing small changes is gain changes in the receiver due to room
temperature changes. Usually the limit of useful bandwidth in amateur
setups is gain drift.
Bruce
G. Warren Coleman
Sep 29, 2009, 10:00:38 AM9/29/09
to sara...@googlegroups.com
Michael Sabino
Antenna gain and amplifier gain are separate and independent of
each other. It is only coincidence that they are 13.5 and 13 dB respectively.
Best wishes,
Warren Coleman
Antenna gain and amplifier gain are separate and independent of
each other. It is only coincidence that they are 13.5 and 13 dB respectively.
Best wishes,
Warren Coleman
Reply all
Reply to author
Forward
0 new messages