RE: L-Band at Ceduna
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From: <David.Jauncey_at_email.protected>
Date: Thu, 21 Jun 2007 00:05:13 +1000
Dear John,
Many thanks; it certainly looks better than before and suggests that the
bad baseline deflections were possibly due to interference rather than
side-lobes. However, it's still worthwhile mapping the beam if and when
they get a chance.
Cheers,
Dave
-----Original Message-----
From: John Dickey [mailto:John.Dickey_at_utas.<!--nospam-->edu.au]
Sent: Thursday, 21 June 2007 12:02 AM
To: Jauncey, David (ATNF, ANUTECH - Acton)
Cc: Brett.Reid_at_utas.<!--nospam-->edu.au; vlbiobs_at_atnf.<!--nospam-->csiro.au
Subject: RE: L-Band at Ceduna
Dear Dave,
Since their first emails, Brett and Aidan have found a better centre
frequency that avoids some interference and greatly stabilizes the
baseline. Here's an improved scan on 3C161. They find Tsys ~ 1200 Jy,
maybe somewhat better depending on the frequency. They are both eager
to try running V211b tomorrow night - our first L band VLBI from
Ceduna...
cheers,
jd
On Wed, 20 Jun 2007, David.Jauncey_at_csiro.<!--nospam-->au wrote:
>Dear Brett and Aidan,
>
>Bloody well done; this is an excellent start!
>
>However, a couple of comments: firstly, I am concerned about the high
>level of "side-lobes" apparent in both scans. In the top scan the
start
>and end of the scan shows up to ~40% displacement from the baseline
>level on both sides. In the second scan, this drops to almost 20% and
>appears where you might expect to see the first side-lobes.
>
>These displacements don't appear to be due to bad baselines, i.e. 1/f
>noise, as the edges of the second scan repeat very closely at the
>beginning and end. So it would appear that the displacements are most
>likely real.
>
>I suggest that, as part of your tests that you try mapping the L-Band
>beam in Az and El in single dish mode. Perhaps making the scans longer
>to begin with and then similar long scans half of the HPBW off from
the
>centre on either side of the main peak, and so on so as to get long
>scans, of at least 12 or so HPBWs, so as to cover the main beam out to
>half a dozen HPBWs either side in both co-ordinates.
>
>If these are side-lobes, then two second side-lobes of ~50% would
>account for your high apparent Tsys in Jy. So if you get the geometry
>right, i.e. focus and alignment, and a bigger tertiary dish then you
>should be in excellent shape. Jim's suggestion would then give you
every
>reason to quit the Naysmith focus and go for the tertiary focus for
most
>frequencies. However, I do suggest that, if this proves to be the
case,
>then please make sure that the receivers and noise diodes are properly
>thermally stabilised so as to avoid the current "difficulties".
>
>Cheers and again, great stuff,
>
>Dave
>
>
>
>-----Original Message-----
>From: owner-vlbiobs_at_atnf.<!--nospam-->csiro.au [mailto:owner-vlbiobs_at_atnf.<!--nospam-->csiro.au]
>On Behalf Of Brett Reid
>Sent: Monday, 18 June 2007 3:33 AM
>To: vlbiobs_at_atnf.<!--nospam-->csiro.au
>Subject: L-Band at Ceduna
>
>Hi,
>Aidan and I have installed a test reflector (1.5m offset satellite
dish)
>
>at the vertex of the 30m dish and an L band receiver from Hobart. We
>aligned the dish optically so that the ray from the center of the feed
>goes to the center of the offset dish and on to the center of the
>subreflector. We checked the alignment at 12 GHz using the Optus D1
>satellite and the small K band feed used for satellite TV. We were
>pleased with a beam width and alignment demonstrated with this test.We
>then changed over to the L-band feed. The first scans were pleasing
with
>
>a system temperature obtained of around 1000 Jy. No further alignment
>has been done. We know that a larger dish will collect more of the
>signal. The vertex tube is 2m internal diameter and our experimental
>1.5m reflector does not fill this.
>
>The 2 channel plot that Aidan performed is attached. The 2 channels
are
>linears. The frequency is 1400 MHz, The bandwidth is 64MHz. We intend
to
>
>try linear to circular conversion through the quadrature hybrid in the
>morning once we have wound a test helix.
>
>Both the L-band feed and extra reflector should be easily removed for
>other frequency use.
>
>Pictures are to come.
>
>Regards,
>Brett and Aidan
>
>
Received on 2007-06-21 00:05:31
Date: Thu, 21 Jun 2007 00:05:13 +1000
Dear John,
Many thanks; it certainly looks better than before and suggests that the
bad baseline deflections were possibly due to interference rather than
side-lobes. However, it's still worthwhile mapping the beam if and when
they get a chance.
Cheers,
Dave
-----Original Message-----
From: John Dickey [mailto:John.Dickey_at_utas.<!--nospam-->edu.au]
Sent: Thursday, 21 June 2007 12:02 AM
To: Jauncey, David (ATNF, ANUTECH - Acton)
Cc: Brett.Reid_at_utas.<!--nospam-->edu.au; vlbiobs_at_atnf.<!--nospam-->csiro.au
Subject: RE: L-Band at Ceduna
Dear Dave,
Since their first emails, Brett and Aidan have found a better centre
frequency that avoids some interference and greatly stabilizes the
baseline. Here's an improved scan on 3C161. They find Tsys ~ 1200 Jy,
maybe somewhat better depending on the frequency. They are both eager
to try running V211b tomorrow night - our first L band VLBI from
Ceduna...
cheers,
jd
On Wed, 20 Jun 2007, David.Jauncey_at_csiro.<!--nospam-->au wrote:
>Dear Brett and Aidan,
>
>Bloody well done; this is an excellent start!
>
>However, a couple of comments: firstly, I am concerned about the high
>level of "side-lobes" apparent in both scans. In the top scan the
start
>and end of the scan shows up to ~40% displacement from the baseline
>level on both sides. In the second scan, this drops to almost 20% and
>appears where you might expect to see the first side-lobes.
>
>These displacements don't appear to be due to bad baselines, i.e. 1/f
>noise, as the edges of the second scan repeat very closely at the
>beginning and end. So it would appear that the displacements are most
>likely real.
>
>I suggest that, as part of your tests that you try mapping the L-Band
>beam in Az and El in single dish mode. Perhaps making the scans longer
>to begin with and then similar long scans half of the HPBW off from
the
>centre on either side of the main peak, and so on so as to get long
>scans, of at least 12 or so HPBWs, so as to cover the main beam out to
>half a dozen HPBWs either side in both co-ordinates.
>
>If these are side-lobes, then two second side-lobes of ~50% would
>account for your high apparent Tsys in Jy. So if you get the geometry
>right, i.e. focus and alignment, and a bigger tertiary dish then you
>should be in excellent shape. Jim's suggestion would then give you
every
>reason to quit the Naysmith focus and go for the tertiary focus for
most
>frequencies. However, I do suggest that, if this proves to be the
case,
>then please make sure that the receivers and noise diodes are properly
>thermally stabilised so as to avoid the current "difficulties".
>
>Cheers and again, great stuff,
>
>Dave
>
>
>
>-----Original Message-----
>From: owner-vlbiobs_at_atnf.<!--nospam-->csiro.au [mailto:owner-vlbiobs_at_atnf.<!--nospam-->csiro.au]
>On Behalf Of Brett Reid
>Sent: Monday, 18 June 2007 3:33 AM
>To: vlbiobs_at_atnf.<!--nospam-->csiro.au
>Subject: L-Band at Ceduna
>
>Hi,
>Aidan and I have installed a test reflector (1.5m offset satellite
dish)
>
>at the vertex of the 30m dish and an L band receiver from Hobart. We
>aligned the dish optically so that the ray from the center of the feed
>goes to the center of the offset dish and on to the center of the
>subreflector. We checked the alignment at 12 GHz using the Optus D1
>satellite and the small K band feed used for satellite TV. We were
>pleased with a beam width and alignment demonstrated with this test.We
>then changed over to the L-band feed. The first scans were pleasing
with
>
>a system temperature obtained of around 1000 Jy. No further alignment
>has been done. We know that a larger dish will collect more of the
>signal. The vertex tube is 2m internal diameter and our experimental
>1.5m reflector does not fill this.
>
>The 2 channel plot that Aidan performed is attached. The 2 channels
are
>linears. The frequency is 1400 MHz, The bandwidth is 64MHz. We intend
to
>
>try linear to circular conversion through the quadrature hybrid in the
>morning once we have wound a test helix.
>
>Both the L-band feed and extra reflector should be easily removed for
>other frequency use.
>
>Pictures are to come.
>
>Regards,
>Brett and Aidan
>
>
Received on 2007-06-21 00:05:31