[evlatests] 451.5 MHz RFI blip

[Dan Mertely]

When I first looked at our monitoring data after WNMT Co
announced the change, it looked like they had changed their
period from the original every 4 minutes, as advertised.
It turns out however that that may not (yet) be the case.

They did reduce the length of the transmission burst, and
they did reduce the power substantially (/6?), but closer
checks with our monitor seem to suggest that they have not
yet increased the transmission repetition interval.

(Since we were originally sweeping from 200-500 MHz with a
10 KHz RBW, our sweep time was too slow to catch every (now
480 mS) transmission--especially now that the power is reduced.
For the past 2 days we've narrowed our sweep to only 450-470
MHz, and now the original 4 minute TX repetition interval is
still seen.)

I have made them aware of this fact and they've said that they
are still working on increasing the time between transmissions.
So far, so good.  The transmission is weaker, and the duty cycle
has been reduced from around 0.8% to 0.2%.  If they can keep
their promise of lengthening their off time between transmissions
from 4 to to 10 minutes, the duty cycle will be only 0.08%.

More improvement coming.  Stay-tuned...

Thanks Ken, Vivek, & Huib for checking on this.
-Mert

On 2/26/2015 7:10 PM, Vivek Dhawan wrote:
> Ken & I studied this a day or 2 ago (after Mert's message).
>
> We found the 4-min pulse to be much weaker than before.
> These data were taken without the solar attenuator. It used
> to saturate even with the 20dB solar attenuator in place.
>
> It is still quite apparent in the 'psum' data, i.e. total power
> in the IF band covering 448-576MHz (IF 4 in the plot attached).
>
> The period is very clear, but not every pulse is the same
> strength (we were tracking a source, the sidelobes were
> moving).  It is about 20dB above noise in a 128MHz subband.
>
> Working backwards, assuming I did this correctly, it seems to
> be consistent with a few 10's of watts transmitted by a low-gain
> anenna from ~40km away, 1MHz BW, into our isotropic sidelobes.
>
>
> On 02/26/2015 05:07 PM, Huib Intema (NRAO) wrote:
>> Hi all,
>>
>> In today's P-band test data I have *not* (clearly) seen the 4-minute RFI
>> blip at 451.5 MHz. Since the test consists of three 5-minute scans with
>> gaps of a few minutes, I may have missed it since the new blip-rate is
>> reported to be once every 10 minutes. It may also be that, since the
>> blip power was lowered, it is now difficult to separate from other RFI
>> sources. I'll keep monitoring this.
>>
>> -- Huib
>>
>>
>>
>>
>>
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>
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