[evlatests] [Fwd: P-band gain loss when 4-band dipoles are UP]

[Rick Perley]

    Ravi sent this to a select audience -- I think it deserves wider 
distribution.

    I'll add that I've never tried to measure the effect of the 4-band 
dipoles on P-band observations.  The measurements I made were at L, S, 
and C bands. 
    There is no surprise that the effect is there, nor in that it's 
larger at P-band than at L-band. 

    Rick

-------- Original Message --------
Subject: 	P-band gain loss when 4-band dipoles are UP
Date: 	Fri, 17 Aug 2012 11:39:42 -0600
From: 	Ravi Subrahmanyan <subrahmanyan.ravi at gmail.com>
To: 	Namir E. Kassim <namir.kassim at nrl.navy.mil>, Frazer Owen 
<fowen at aoc.nrao.edu>, Rick Perley <rperley at aoc.nrao.edu>, 
brian.hicks at nrl.navy.mil, Charles Kutz <ckutz at nrao.edu>, Steve Durand 
<sdurand at aoc.nrao.edu>, Paul Harden <pharden at aoc.nrao.edu>



Greetings!

I did a comparison of P-band sensitivity with and without the 4-band feeds.
I looked at Psum when the antennas were pointed on Cygnus-A and on GOODS field.
And I took the ratio of Psum(Cyg-A) / Psum(GOODS).

On July 19 we had P-band observations without the 4-band dipoles.
On Aug 09 we had P-band observations with 4-band dipoles UP.
The numbers in the table below are the Psum ratios:

                 July19                      Aug09
Aug09/July19
            PolA       PolB         PolA      PolB           PolA        PolB
ea15     2.9289     2.8953     2.7030    2.6697        0.9229     0.9221
ea18     3.2775     3.2365     3.1565    2.9994        0.9631     0.9267
ea25     3.1205     2.8069     2.9276    2.6001        0.9382     0.9263

ea15 does have -12dB reduced gain on the 4-band channel, so at least
this antenna
ought to be less influenced by the high power that gets added when the 4-band
dipoles are connected.

The average loss in antenna gain at P-band is 7% when the 4-band dipoles are UP.

cheers
Ravi