[evlatests] P band, 4 band and power levels

[Barry Clark]

We are fairly insensitive to the relative power of P and 4 bands.
I should think that fixed attenuators added to the 4 band cable at 
installation time would suffice.  On the spectral plot display, setting 
the peak of the 4 band bump between 0 dB and 3 dB above the P band bump 
sounds OK to me.  But 15 dB sounds too much - it will decrease the headroom 
available to the P band.

> From evlatests-bounces at donar.cv.nrao.edu  Wed Jun 13 16:27:50 2007
> Date: Wed, 13 Jun 2007 16:27:31 -0600
> From: Paul Harden <pharden at nrao.edu>
> 
> 
> 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
> 
> Paul Harden
> 
>