[evlatests] ea21 at P-band

[Barry Clark]

The object of the game is to always have the same power coming out of
the T304's for all bands.  For the narrow bandwidth receivers, one can
have a lower power on the T304 input, as a few dB less will be scraped 
off in its filters than is the case for the wide band receivers.

Ken set up the software defaults (just for reasons of being conservative,
I think) to use the table method for setting all four IFs at 90cm and
4m.  The, admittedly very sketchy, tests that I ran a year ago indicated
that the standard setting procedure would work OK for P band, but that
4m might need a resetting of the resampler level in the D351s.

We probably should run a test with standard setup at P band.  The operative
script commands are, if the first band used in the file is Pband:
downc = loif0.getDownconverterAC()
downc.setDownconverterAInputLevelControlMode(2)
downc.setDownconverterCInputLevelControlMode(2)
downc.setDownconverterAOutput1LevelControlMode(2)
downc.setDownconverterCOutput1LevelControlMode(2)

If it works as well as I think it should, we should make it the default.

> From evlatests-bounces at donar.cv.nrao.edu  Tue Apr 10 12:49:00 2007
> Date: Tue, 10 Apr 2007 12:48:30 -0600
> From: Paul Harden <pharden at nrao.edu>
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> Subject: Re: [evlatests] ea21 at P-band
> 
> 
> Walter Brisken wrote:
> > I've reset the attenuators on ant 21, IFs B & D .  Both IFs wanted 12 dB 
> > more attenuation.  
> 
> There has always been a level of uncertainty as just how to deal with 
> the power levels of the narrow-band 74MHz and P-band signals within the 
> otherwise wide EVLA IF.
> 
> I based the design on providing the T302 LSC Converter with about -30dBm 
> power from the 4/P Converter, or, a litle higher than the input power 
> from the L, S and C band receivers.  Granted, these total power levels 
> are based on two greatly different bandwidths.
> 
> There is some latitude in the 4/P Converter in the output IF level.  I 
> would appreciate hearing from anyone involved in P-band testing and 
> observing if they feel the output power from the 4/P Converters needs to 
> be increased or decreased to get some empirical value we can use as a 
> standard.
> 
> For comparison, the output IF power from the 4/P Converters are as follows:
> 
> -34dBm  Ant. 21 (with the increased gain headroom)
> -28dBm  Ant. 17 and 23
> -24dBm  Ant. 14 (old design with the LO leakage problem)
> 
> The Ant. 14 unit power is quite high, in an attempt at the time to get 
> better signal to noise with the LO leakage power.  The new converters 
> have virtually no LO leakage in the IF.
> 
> We are about to begin construction of the 4/P Converters to get caught 
> up and have a converter for all past and present EVLA antennas in the 
> next month or so.  These will be based on -34dBm output power.  Again, 
> if anyone feels this IF power needs to be adjusted, please let me know.
> 
> Paul Harden
> 
> 
> 
> 
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