<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=Windows-1252">
<style type="text/css" style="display:none;"> P {margin-top:0;margin-bottom:0;} </style>
</head>
<body dir="ltr">
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
As part of the test yesterday, I observed Cygnus A, with the 8-bit samplers, at all high frequency bands from X through to Q. </div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Cygnus A adds appreciable power to the system at X and Ku bands — multiplying the 'cold sky' temperature by 1.4 to 1.6 at X band (higher at the low frequency end), and by 1.2 to 1.4 at Ku bands. The effect at K-band is much reduced (because Cygnus A's radio
lobes are mostly outside the primary beam): a 3 to 10% increase at K-band, and essentially negligible at Ka and Q bands. </div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Early in the EVLA construction period, we found that the apparent gain (as measured by the PDif values) dropped when on very strong sources. This is known to be a false indication — the gain in fact does not drop, although the PDif values would have us believe
it does. Much activity during the EVLA construction and commissioning period failed to find a viable explanation. </div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
The purpose of this note is only to remind everyone that the problem is still with us. Fortunately, the effect is fairly weak:</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<ol start="1" data-editing-info="{"applyListStyleFromLevel":false,"orderedStyleType":10}">
<li style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); list-style-type: "A) ";">
<div class="elementToProof">At X-band, where the Tsys is increased by typically 50% when on Cyg A, the PDif values, for all antennas and IFs, are see to decline. Typical declines are by 1 to 3 %. (This means that, if applied, the flux density of Cygnus A
will be overestimated by about this amount). </div>
</li><li style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); list-style-type: "B) ";">
<div class="elementToProof">At Ku-band, where Tsys is increased by typically 25% when on Cygnus A, PDif values are seen to decline by typically 1%. </div>
</li></ol>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
At the higher bands, no PDif compression is seen on Cygnus A. </div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Rick<br>
<br>
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
</body>
</html>