- To: Charles T Stelzried
-
From: Robert C Clauss
-
Subject: BWG Antenna "Vacuum
Top" Determination
-
Cc: Samuel.M.Petty,
Stephen.D.Slobin,
-
James.S.Shell
-
Date: Sun, 22 Nov 1998 09:40:47
-
- Summary:
-
- The "Vacuum Top" at
DSS-13 with the KaBLE I maser was 17 K. This
-
value seems to be in good agreement
with measured and calculated
-
values for DSS-25
prepared by Slobin on 10/15/98.
-
The DSN can do better than the 24.5
K "Vacuum Top" at 32 GHz used
- in the Preliminary Definition
and Cost Review (PDCR) on October 19,
- 1998. A 15.6 K "vacuum Top"
is realistic.
-
- DSS-13 Top measurement and
"Vacuum Top" estimate:
- The KaBLE-I maser was used to
measure the system operating noise
-
temperature (Top) at DSS-13 in
December 1992. The dichroic plate,
-
which was not well-matched at 33.68
Ghz, was removed to enable Top
-
measurements that would characterize
the performance of future DSN
-
Ka-band systems. The maser was tuned
from 33.68 GHz down to 33.06
-
GHz, the lowest frequency the maser
could achieve at the time.
-
The Top at 33.06 GHz measured 24.5
K; Jim Shell recorded the data
-
in his notebook.
-
- The December 1992 measurements
were made during clear, cold, dry
-
conditions and the atmospheric
contribution at the zenith was
-
estimated to be between 7 K and 8 K.
A summary of the Dec. 1992
-
33.06 GHz noise contributions is
compared with the values used
-
by Slobin in "kastelz1.xls"
at 30 degrees elevation angle.
-
- Noise Source
DSS-13 1992 DSS-25 1998
-
Maser
HEMT, kastelz1.xls
-
- Cosmic Background 1.9
1.8
-
- Antenna 8.0 9.28
- BWG Mirrors 2.0
2.17
-
- Dichroic Plates
none 3.40
- LNA Te 5.0
20.00
-
- Vacuum Top 17.0
34.50
- Atmosphere 7.5 (one,
24.77 (two,
-
dry winter) moist summer)
-
------------------------------------------------------------
-
Top Measured at Zenith 24.5
59.27
-
- The major differences seem to be
the LNA effective noise
-
temperatures (HEMT - maser = 15 K)
and the estimated dichroic plate
-
contributions at DSS-25 (3.4 K).
Subtracting 15 K from 34.5 K gives
-
a vacuum Top of 19.5 K for DSS-25
with a Kable-I like maser and two
-
dichroic plates. Removing the two
dichroic plates would reduce the
-
predicted vacuum Top to 16.1 K.
-
- Stelzried's 1998 road-map used a
multiple-cavity-maser with a Te of
-
4 K, which would reduce the DSS-25
"vacuum Top" prediction to 15.1 K.