[evlatests] ea13 birdie @1400 MHz, ad nauseam

[Rick Perley]

Fabulous result!

But what are those 'block' offsets seen at the low frequency end?

Rick

Sent from my iPad

> On Apr 28, 2015, at 6:12 PM, Emmanuel Momjian <emomjian at aoc.nrao.edu> wrote:
> 
> Over the last weekend we got high spectral resolution L-band observations that allowed me to check the "birdie situation" on ea13.
> 
> The results are clearly showing that this antenna no longer has the 1400 MHz birdie and the combs associated with it: the 468.75 kHz comb and the 25 MHz comb. Note that for the latter I checked four of its components (at 1300, 1325, 1400, and 1425 MHz) to establish that they are no longer present.
> 
> Attached are two example spectra showing the situation before and after the work that Dan, Rob and Ricardo did on ea13 about a week ago.
> The file ea13_1400_before.png shows the 1400 MHz birdie and its 468.75 kHz comb as seen in data taken on April 4, 2015.
> The file ea13_1400_after.png shows their disappearance in the new data taken on April 26, 2015.
> 
> Emmanuel
> 
> 
>> On 04/22/2015 01:10 PM, Dan Mertely wrote:
>> Rob Selina, Ricardo Contreras, & I went out to ea13 for an
>> RFI hunting mission and had a lot of success.
>> 
>> One of the main problems was that the LAN switch and media
>> converters up in the vertex room were plugged into an un-
>> switched AC outlet.  They should have been plugged into a
>> switched outlet (LAN devices of all kinds are very noisy!)
>> Rob re-routed the cables and plugged the wall-wart power
>> supplies into the proper switched AC outlets.
>> 
>> >>> I ask that everyone working on antennas be aware of the
>> fact that the LAN switches and media converters are very, very
>> RF noisy.  Please make sure that the Vertex Room switches turn
>> off when the room lights are off, and please also make sure
>> that the LAN switch and media converter down in the Ped Room
>> is unplugged when not in use.  This is important. <<<
>> 
>> In addition, the LOIF and Utility rack RF gasketing "fingers"
>> were greatly damaged due, in part, to a couple of the doors
>> being misaligned.  We fixed the gaskets & re-aligned the doors
>> by adding spacing washers on the hinges.
>> 
>> Now ea13 may be one of the quieter antennas out there in L-band.
>> Please make another check at your convenience.  TNX.
>> -Mert
>> 
>> 
>>> On 4/21/2015 10:42 AM, Rob Selina wrote:
>>> HI Mert,
>>> 
>>> Will you be out at the site tomorrow? I was hoping we might have some time to talk about EA13's 1400MHz birdie and perhaps go do a sweep at the antenna. Assuming you've looked into this one before, is there any pertinent info in /evla/techdocs/rfi ? I did a quick search but didn't see anything.
>>> 
>>> We can talk about it tomorrow (hopefully) so I won't write a book here, but the long and short of it is that Emmanuel, Rick and others have suggested that we focus tracking down some of our self-generated RFI, starting with this birdie on EA13. I wanted to see if this was something we  could perhaps work on together.
>>> 
>>> Cheers,
>>> 
>>> Rob
>>> 
>>> 
>>> -----Original Message-----
>>> From: Emmanuel Momjian [mailto:emomjian at aoc.nrao.edu]
>>> Sent: Wednesday, April 15, 2015 8:59 PM
>>> To: Rob Selina
>>> Cc: Bryan Butler; Rick Perley
>>> Subject: ea13 birdie @1400 MHz
>>> 
>>> Hi Rob,
>>> 
>>> Attached is a spectrum that shows the birdie of antenna ea13 at 1400 MHz. What I don't recall seeing before are the little spikes near the main feature; there are two on the left and two on the right. These weaker ones are also only seen on baselines to ea13. It looks like the birdie has a whole family now!
>>> 
>>> The separation between these features is exactly 30 channels, which is
>>> 468.75 kHz.
>>> 
>>> cc-ing Rick and Bryan to check if they recall seeing the weaker features before.
>>> 
>>> These data were taken on April 4, 2015.
>>> 
>>> I'll look into the 1408 MHz birdie later.
>>> 
>>> Cheers,
>>> Emmanuel
>>> 
>> 
>> On 1/20/2013 11:51 AM, Rick Perley wrote:
>> > The latest 'spectra sweep' shows clear evidence that ea13 is
>> > seriously polluting our spectrum at L-band.  In trolling through the
>> > spectra provided from the data, some baselines common to ea13 show
>> > strong RFI at multiples of 25 MHz, extending from ~1200 MHz through
>> > ~1500 MHz.  There are only a few baselines on which this comb is easily
>> > visible -- these are 13 with 9, 14, 24, 25, and 26.  All of these are
>> > antennas adjacent to 13!
>> >      It's quite clear from this that ea13 is probably the sole source of
>> > the interference.
>> >
>> >
> <ea13_1400_before.png>
> <ea13_1400_after.png>