[evlatests] [Vlite-external] EA14 polarization and VLITE

[Bryan Butler]

it was my understanding that the inputs from the 4 dipoles were combined 
to still make true "X" and "Y" (or "H" and "V") polarizations.  is that 
not true?  maybe we should ask steve?




Rick Perley wrote, On 6/27/14 15:14 :
>       ... in case this is not yet sufficiently confusing, remember that
> the new MJP design dipoles are rotated 45 degrees w.r.t. the antenna's
> principle axes.  So 'H' and 'V' will have no physical meaning any more
> ...  (fortunately, P-band remains o.k.)
>       We'll need an easy-to-remember way of identifying which pair of MJP
> feeds correspond to which IF channel ...
>
>
> On 06/26/2014 05:53 PM, Paul Harden wrote:
>> We swapped the polarization Thursday on VLITE antenna 14 and should now
>> be correct.
>>
>> Here's the problem.  Nomenclature for the low band linear polarization
>> has been standardized such that:
>> Horizontal antenna = RCP
>> Vertical antenna = LCP
>>
>> The input connectors on the VLITE module are labled "Ch. 1" and "Ch. 2."
>>     There is no indication what polarization is assigned to what channel.
>>     The 50/50 choice used was obviously wrong.
>>
>> What polarization is assigned to Ch.1 and Ch.2?
>>
>> When installed, RCP was connected to Ch. 1 and LCP to Ch. 2, which
>> caused the reported swapped polarization.
>>
>> LCP now goes to Ch. 1
>> RCP now goes to Ch. 2
>>
>> This channel assignment needs to be standardized, and perhaps some "LCP"
>> and "RCP" labels made to eliminate the channel references.
>>
>> Also, there are two 30dB coaxial amplifiers on the Ch.1 and Ch.2 inputs
>> on the VLITE module, amplifying the low band receiver output by 30dB.
>> Typical LBR receiver output is about -75 dBm/MHz on the cold sky,
>> meaning about -45 dBm/MHz input to VLITE.  I don't know how much
>> internal amplification there, the ADC range, or the compression points,
>> but seems this much amplification would seriously limit the dynamic
>> range and gain headroom of the VLITE module.
>>
>> Paul
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>
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