Upgrade of the VLBA C-Band Feed & Receiver Design Review
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Transcript of Upgrade of the VLBA C-Band Feed & Receiver Design Review
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Upgrade of the VLBA C-Band Feed & ReceiverDesign Review
Presented by S durand Designed by Bob Hayward and:Sivasankaran Srikanth (Feed Design)
Hollis Dinwiddie (Mechanical Design)Everett Callan (Master Receiver Builder)
Gordon Coutts & Craig Hennies (OMT Testing)Marian Pospieszalski & the CDL Amplifier Group
Pat Madigan & the VLA Machine ShopMichael Hedrick & the Green Bank Machine Shop
21 April 2011
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• Astronomers were eager to:• Access the Methanol Maser at 6,668 MHz GHz• Access to OH at 6016-6049 MHz• Carry out continuum observations with two IF’s separated
by several GHz to allow the effects of the atmosphere to be subtracted out
Example : IF-AC=4.0-4.5 and ID-BD=7.5-8.0 GHz
• Limitations of the existing C-Band system:• Mediocre sensitivity due to old GAsFET LNA’s• Narrow bandwidth due to:
– Septum Polarizer (4.5-5.2 GHz)– LNA’s (4.5-5.2 GHz)– Warm IF (4.5-5.2 GHz)– T105 Conversion (4.5-5.2 GHz)
Why Upgrade the VLBA C-band ?
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T(Rx) for Old VLBA vs. New EVLA Rx’sAverage of 8 Dual-Channel Receivers
4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.00
5
10
15
20
25
30
35
40
45
50
Receiver Noise Temperature - VLBA vs. EVLA Receivers
VLBA RxEVLA Rx
Frequency (GHz)
Noi
se T
empe
ratu
re (K
)
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Required Specifications
• To modify the VLBA Receiver to give us the RF performance that is as close to that achieved by an EVLA Receiver as possible.
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Sri’s VLBA 4-8 GHz Feed Design
• Profiled Corrugated Horn• Four machined sections • Ring-Loaded Mode Converter• Plugs into old feed location• Total Length = 37.5”• Outer Diameter = 18.5”• Weight = 55 lbs
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Installation of the New Feed at VLBA Pie Town• Done with Feed S/N 01• And Unmodified C-Band Rx• Uses a Transition Plate so an
old Receiver can be attached to a new Feed and thus allow installation of lateral support brackets and turnbuckles.
• Luckily feed is small enough to fit through the hatch (i.e., a crane is not required for hoisting it over the dish).
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Existing VLBA C-Band Receiver
SeptumPol
RCP
LCP
LNA
LNA
PamtechCTB1107
PamtechCTB1107
Omni-Spectra2089-6203-00
T
-30 dB
Narda4014C-30
AtlanticMicrowaveAMC 0935
GAsFET4.5-5.2 GHz
GAsFET4.5-5.2 GHz
TNoiseDiode+20-10 dB
High-Cal( Not implemented on VLBA)
TNoiseDiode-6 dB
Omni-Spectra2020-6617-10
Om
ni-Spectra2020-6616-06
PulseCal
TCal
PA
Reactel6B1-4850-700S12
4.5-5.2 GHz
MiteqAMF-2B-4552
4.5-5.2 GHz
DitomD3I4080-14-8 GHz
DitomD3I4080-14-8 GHz
PA
Reactel6B1-4850-700S12
4.5-5.2 GHz
MiteqAMF-2B-4552
4.5-5.2 GHz
DitomD3I4080-14-8 GHz
DitomD3I4080-14-8 GHz
T
Narda4014C-30
-30 dB
TCal
& PCal
TCal
& PCal
PCal
The Cryogenic Pamtech Isolators were a surprise. There was no mention of them in the VLBA Technical Report #3. There must have been added after the 1st prototype Receiver was built.
Keep
New
N/A
Toss
Key:Cryo
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Upgraded VLBA C-Band ReceiverO
MT
T
-30 dB
RCP
LCP
TCal
TCal
& PCal
PCal
LNA
LNA
Hyb
rid
Dorado3ICC60-1
Dorado3ICC60-1
Mac
tech
CA
7205
U
In HEMT4-8 GHz
InP HEMT4-8 GHz
-30 dB
T
Narda4014C-30
Narda4014C-30
Omni-Spectra2089-6203-00
T
NoiseDiode
-10 dB
Noise/ComNC3205-G
10 dB
Omni-Spectra2020-6617-10
PulseCal
TCal
& PCal
RCP4-8 GHz
Out
PA
TTEK5221-4/8G
4-8 GHz
CiaoCA48-281G=26dB
DitomD3I4080-14-8 GHz
DitomD3I4080-14-8 GHz
PA
TTEK5221-4/8G
4-8 GHz
CiaoCA48-281G=26dB
LCP4-8 GHz
Out
DitomD3I4080-14-8 GHz
DitomD3I4080-14-8 GHz
Note that we leave out the High-Cal feature, which has never been used on the VLBA
Keep
New
N/A
Toss
Key:Cryo
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Modifications & Problems• Making the modifications to the RF path of the receiver were
relatively straight forward.• However, cooling the beast was a problem.
– The old VLBA receiver had its Septum Polarizer tied to the 50°K Stage. – We wanted the new OMT to be tied to the 15°K Stage since it has more
resistive losses. • Hollis spent quite a while fighting to minimize the final
temperature that the 15°K Stage reached.– It was hard to get it much below 30°K and the temperature was very
dependent on how many other receivers were on the same Helium line.– Required reducing the weight of the OMT as well as adding Space
Blankets around the 50°K Radiation Shield.• It was also decided that the Thermal Gap assembly used in the
EVLA design would need to be improved.
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EVLA-StyleOMT &
Thermal Gap
Includes:
“Old” Thermal Gap+
Heavy Blocks+
Absorber Strip
AN72 Absorber wrapped around
Thermal Gapto prevent
Cavity Resonances.
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VLBA-StyleOMT &
Thermal GapIncludes:
New Circular Thermal Gapwith Choke Ring and long standoffs
+“Swiss Cheese” Blocks
to reduce thermal mass+
Mount for Hybridmakes for an integrated
Circular Polarizer
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Recent Cool-down Results• Thanks to Hollis’ new Thermal Gap Assembly, the
Model 22 is now cooling the RF Tree in the Prototype Receiver down to acceptable temperature levels.
• The 15°K Cold Stage temperature is also less susceptible to variations from other fridges being connected to the Helium lines:– ~12-14°K when alone– ~14-16°K with one Model 350 on the loop– ~16-18°K with two Model 350 on the loop
• The 2 x Model 350 scenario is what occurs on a VLBA Antenna.
• VLBA C-Bands typically 15-25°K
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VLBA C-Band Prototype (VC#11)
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4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.00
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Receiver Noise Temperature on VLBA C-Band #11-RCPUnmod (Circ) & Modified (Linear) Rx vs. EVLA Rx C#16 (Circ)
(RHH : 13 April 2011)
VLBA C#11, Unmodified, CircularEVLA C#16, Old T-Gap, CircularVLBA C#11, New T-Gap, Linear
Frequency (GHz)
Rec
eive
r T
empe
ratu
re (K
)Early RF Sensitivity Tests on VC#11Old EVLA vs. New VLBA Thermal Gap
Using the new T-Gap assembly with its proper Choke Ring yields a vast improvement over that
achieved on the EVLA with the old T-Gap design.
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VLBA C-Band ReceiverOld vs. Interim vs. New Configuration
C
RCP
LCP
RCP
LCP
Old T1054.5-5.2 GHzConverter
Module
4.5-5.2GHz
L104 #2
IF OutputA & C
500-1000 MHz4.5-5.2 GHz
C
RCP
LCP
RCP
LCP
New T4054 - 8 GHzConverter
Module
4.0-8.0GHz
IF OutputA, B, C & D
500-1000 MHz
4.0-8.0 GHz
L104 #2
L104 #3
Old C-Band Rx with Old T105
Modified C-Band Rx with New T405
C
RCP
LCP
RCP
LCP
Old T1054.5-5.2 GHzConverter
Module
4.5-5.2 GHz
4.0-8.0GHz
IF OutputA & C
500-1000 MHz4.0-8.0 GHz
(From old Rx) L104 #2
4.5-5.2GHz
Modified C-Band Rx with Old T105 SMA
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Downconverter Design3900-5900 and 5600-7900MHz
Front Panel
Front Panel
Front Panel
Front Panel
3400 to 8600 MHz
512 to 1024 MHz3900 to 5900
5600 to 7900
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Conclusions• Thanks to the new Thermal Gap design, the
upgraded VLBA C-Band is now superior to the EVLA receiver.
• Expect T(Rx) < 10°K from 4.2-8.0 GHz• It is now probably the most sensitive
wideband system in the world at this frequency.
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Questions ?