[time-nuts] Re: The Collapse of Puerto Rico’s Iconic Telescope [April 5th, 2021 New Yorker]

[Magnus Danielson]

Hi Jim,

On 2021-03-31 01:33, Lux, Jim wrote:
> On 3/30/21 2:56 PM, Wes wrote:
>> You would know better than I, but I was thinking of physical size;
>> 100m v. 70m.
>>
>> Obviously a BIG difference in TX power.
>>
>> Wes
>
>
> It's all about EIRP, baby.
>
> I know they're talking about half a megawatt for GB, but I don't see
> it happening. They've spent so much time making it "radio quiet",
> putting a big honkin transmitter there seems odd.   Just think, a
> return loss from the feed of -30dB (which is pretty good) is good
> fraction of a kilowatt.
Multiple directional couplers to get rid of the energy might help, but
when you are at that level you are pretty well matched anyway.
>
> I think a phased array of some sort is more likely (both for Tx and
> Rx) - the cost of RF parts has come down a lot, and, as we on this
> list know, phasing them all up to a fraction of a gnats eyelash is
> doable. Fiber optics are cheap. And you can form multiple beams
> simultaneously (the LEDA correlator at OVRO-LWA forms hundreds of beams).
>
Yeah, well, there is another thing that bites you, phase stability and
phase control. I've seen the specs of such a baby, and you need to play
a few tricks and have multiple feed back points. It is doable. You gain
some and you loose some. Phased array is for sure the modern approach on
things. Technology have advanced so it's not too hard, but you want to
have a fair amount of self alignment capabilities.
>
> What *is* a challenge (and hasn't really been solved) is how to do
> cryogenic feeds in mass production.  DSN looked at building an array
> of 100 receivers, and nobody would sign up to delivering 100
> cryocoolers that would have sufficient MTBF.   But transmitting -
> that's easy.

In that case the request was not aligned with what industry could
deliver. Sounds like there is room for an advancement program to push
the capability of the industry, so requests like that can be made. Then
that faces challenges to have large enough volume to have multiple
vendor being able to bid on it, and make sure multiple vendors do get bids.

Cheers,
Magnus