[evlatests] P band, 4 band and power levels

[Paul Harden]

Ken Sowinski wrote:
> The quick summary is that we need to do a better job of 
 > matching spectral power density between the two bands.

There has always been confusion and disagreement on how to handle these 
narrow band signals.  Theoretically, with the 2-4MHz bandwidth of 4-band 
compared to the 40MHz bandwidth of P-band, 4-band should be attenuated 
in the order of 10-13 dB.  At present, there is no difference in how the 
two bands are handled within the T301 4/P Converter.

Recent power spectral plots confirm 4-band indeed needs about 12dB or 
more of attenuation.  This empirical data lets us know what we need to 
do -- attenuate the 4-band signal prior to upconversion to equalize it 
to P-band's total power.

Attenuators on the 4-band channel can be easily added (there's a place 
for them on the circuit boards).  In the interim, coaxial attenuators 
can be added to "play around" with the attenuation that makes everyone 
happy before modifying the 4/P Converters (a relatively easy mod).

> Except for antenna 18 all the 4 meter bandpasses are about 15 dB above
 > P band bandpasses.  Was the T301 in antenna 18 built differently

The output power and bandwidth from all 4/P Converters are set to 
identical values prior to antenna installation.  The extremely low level 
shown in Ken's chart might suggest a failure in EA18 T301.

 > or is the solar attenuator permanently inserted?

The solar attenuators for 4- and P-band are in the T302 LSC Converters, 
and fully commandable in all M301 antennas.  Separate solar attenuators 
in the 4/P Converter have not been implemented.

Paul Harden