[evlatests] P-Band sensitivity

[Paul Harden]

On 12/5/2013 9:02 AM, Vivek Dhawan wrote:
>Does Paul's Tsys include the galactic emission?

For P-band, Trx runs in the 50-60K region, measured mid-band at 350 MHz. 
  For Tsys, I add 40K for Tsky, the value provided me some time ago by 
NRL and Ravi based on the Cane model.  I do not know what additional 
temperatures may be added by the dipoles, ground temperature, etc.  The 
coaxial feed from the P-band dipoles to the LNA inputs inside the 
receiver is only about 18-20 inches.  I have measured this total loss at 
around 0.1-0.15 dB max., though still about 7-10K.  (74 MHz is a far 
different story!).

LN2 hot/cold load tests are used to measure receiver temperatures.  It 
is measured at 350 MHz through a 30 MHz wide bandpass filter to band 
limit the power.  For consistency, the same filter has been used on all 
receiver tests.  I just scrounged the lab and finally found some filters 
for 250 and 400 MHz.  I will try to measure Trx on one of the receivers 
this afternoon or Friday at 250, 350 and 400 MHz to get some values over 
the P-band bandwidth.  I have never done this before to see how much 
slope or differences there may be.  I also have a filter for 327 MHz if 
anybody thinks pulling Trx at that frequency would serve any value. 
Also, is there any value to measuring Trx at any frequency outside of 
the 230-470 MHz bandwidth?

I will report the results.  I will be glad to adjust any of my numbers 
if felt necessary.  I'm mostly using values given to me when the LBR 
project first started, and we know the values given me for desired 
output power and Tcal were way too high.

Paul