[Pafgbt] Purple Plague

[Steven White]

Yes, we can make these measurements with a power meter.  We also have other
options for down conversion and detection using the absorber and cold sky.

→  Steve  →


→-----Original Message-----
→From: pafgbt-bounces at nrao.edu [mailto:pafgbt-bounces at nrao.edu] On
→Behalf Of Rick Fisher
→Sent: Wednesday, April 10, 2013 3:25 PM
→To: pafgbt at nrao.edu
→Subject: Re: [Pafgbt] Purple Plague
→
→Thanks, Matt.  That's good to know.
→
→Looks like the immediate task is to verify the noise and gain performance
of
→the amplifiers currently in the Dewar.  Bob, Steve, is there an easy way
to do
→this without the PAF back-end and fiber link?
→
→Rick
→
→On Wed, 10 Apr 2013, Matt Morgan wrote:
→
→> Hi Rick,
→>
→> No, the ones with packaged transistors shouldn't have this problem,
→> unless they are bonded incorrectly inside the package, which as David
→> said is highly unlikely considering it is a commercial part.
→>
→> So perhaps in this instance the Purple Plague was actually a Red
Herring.
→>
→> Unfortunately, then, It still begs the question to me why so many of
→> the amps appear to have failed at this time.
→>
→> Matt
→>
→>
→>
→> On 4/10/2013 2:21 PM, Rick Fisher wrote:
→>>  Matt, I cannot recalled whether you said that Sandy's packaged
→>> amplifiers,  like the ones in the PAF, are subject to purple plague.
→>>
→>>  Rick
→>>
→>>  On Wed, 10 Apr 2013, Steven White wrote:
→>>
→>> >  Figure 2 is the same as the amplifier designated as the spare.
→>> > When  Mitch  tested this amplifier, he encounter oscillations in
→>> > both and could only  test  one amplifier at a bias of 1.2 V.  This
→>> > may explain the high noise  temperature measured ~ 13-14K versus
→>> > Figure 3 & 4 measurements.
→>> >  Yesterday,
→>> >  the amplifier was tested in GB and did not oscillate, but the gain
→>> > was  closer to 33 dB than 39 dB of S21 measurement of the document.
→>> > *IF* all  the  amplifiers in the dewar are the packaged design, the
→>> > situation may not  be as  dire as if the chip version was used.  We
→>> > are planning to test the spare  amplifier cold next week for noise
→>> > and S parameters.
→>> >
→>> >  Also, a swap of IF paths at the output of the dewar is suggested
→>> > to  verify  the problem, a good channel with a low gain LNA
→>> > channel.
→>> >
→>> >  Steve
→>> >  ?
→>> >  ?But we definitely need to take some steps to resolve this.
→>> > Mainly  because  it is  ?urgent to let Toney Minter know if we can
→>> > meet the 2nd week of June  ?schedule, or need to fall back.  ?He
→>> > has been alerted to the fact that  we  have  ?this issue.
→>> >  ?
→>> >  ?Anish said he was confident that the high noise temp channels
→>> > were "in  the  ?dewar" and not in the backend.  But it would be
→>> > good to do something to  ?prove that irrefutably.  Steve, you
→>> > suggested a cable swap test.  Or,  is  there  ?any bias monitoring
→>> > on the amplifiers themselves?
→>> >  ?
→>> >  ?Beyond this further diagnostic, we should decide whether there is
→>> > any  more  ?software/hardware to test (it may be useful to resolve
→>> > the  ?attenuation/sensitivity issue), while the receiver is in OTF
→>> > and cold,  or  ?whether to bring the receiver back to the lab.
→>> >  ?
→>> >
→>> >
→>
→>
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