From:	Toney Minter 
Sent:	Wed, Oct 13, 2010 at 10:49 AM
subject	update on GBT Ka receiver
	
Andy and Andrew,
 We found that the amplifier in the LO1 tripler had its bias level
way out of adjustment.  This was causing an extremely strong 2nd
harmonic and many other spikes to get into the signal path of the
receiver and into the data.  This should have affected the Zpectrometer.
There were many 1 Jy level, narrow-band spikes in the system.
The 2nd harmonic of LO1 was at a level of 7000 Jy! (29.22 GHz for
the Zpectrometer if I correctly recall that LO1 is set to 14.61 GHz.)
 Also, it is possible that the AutoOOF corrections were not
being applied so that the antenna surface was degrading as the
day went on in your last tests.  (This was not from something that you
did incorrectly.)  We are still looking into this.
 So it seems like we should consider another daytime test along with
the needed night time test of the Zpectrometer.  When would you be
available over the next week or two to perform these checks?  How
much time would you likely need/want for each of the checks?
Cheers,
Toney

*********************************************

From: Ronald J. Maddalena 
Sent: Monday, October 04, 2010 17:43
Subject: Ka-band birdies

All,

Attached is a plot that shows the birdies I'm finding in Ka-band and below
is a table with their rough frequencies, good to 0.5 MHz, and rough
intensities (in Jy).  I'm not aware of any of these existing before in
Ka-band, especially at these intensities and especially the 7000 Jy birdie @
29622 MHz.  This last birdie makes it almost impossible to balance power
levels in the IF Rack for any observations made near 30 GHz.  There are a
few patterns in the frequency of the birdies, especially some of the strong
ones, but the others don't seem to have any patterns to them.

Any ideas where these are coming from?

Thanks!
Ron

Frequency       R1 (Jy) L2 (Jy)
26127.3438      0.002   1.7496
26416.7969      0.0189  0.0916
27875           2.5368  2.2059
28115.625       0.0047  0.6626
28754.6875      0.0092  6.5588
29044.1406      0.0088  0.9409
29192.9688      0.008   8.1611
29333.2031      2.1546  37.8838
29467.1875      0.0035  0.9099
29522.6562      0.0025  4.247
29622.6562      0.154   6934.9375
29722.6562      0.0034  3.9587
29984.375       0.0506  0.2314
30615.625       0.0038  0.4617
32250           0.2116  0.5852
32767.5781      0.0229  0.0672
33474.2188      0.0042  0.1689
34083.2031      0.5363  1.8453
34222.2656      16.3085 2.5751
35517.5781      0.0133  0.0698
36232.4219      0       0.1955
36529.6875      1.1084  0.3326
37252.7344      0.3563  0.3242
38004.6875      2.6693  0.2371
38267.9688      0.0206  0.0563
38751.5625      1.2019  0.4124
39057.0312      0.0006  0.4794
39110.9375      0.0889  0.2398
39400.3906      0.0002  0.7288

 Only R1
 -------
28734.375
33768.75
36844.9219