On 03/12/2015 02:43 PM, George Herold wrote:
> On Thursday, March 12, 2015 at 2:11:52 PM UTC-4, Phil Hobbs wrote:
>> On 03/12/2015 01:34 PM, George Herold wrote:
>>> On Thursday, March 12, 2015 at 12:35:55 PM UTC-4, John Larkin wrote:
>>>> On Thu, 12 Mar 2015 09:00:01 -0700 (PDT), dagmargoodboat@yahoo.com
>>>> wrote:
>>>>
>>>>> On Thursday, March 12, 2015 at 11:51:22 AM UTC-4, John Larkin wrote:
>>>>>> On Tue, 10 Mar 2015 17:22:27 +0100, Gerhard Hoffmann wrote:
>>>>>>
>>>>>>> Am 10.03.2015 um 15:57 schrieb John Larkin:
>>>>>>>> On Tue, 10 Mar 2015 08:44:40 -0500, John S <Sophi.2@invalid.org>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> On 3/9/2015 10:36 PM, John Larkin wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Has anybody used this one?
>>>>>>>>>>
>>>>>>>>>> http://www.ti.com/product/lme49990
>>>>>>>>>>
>>>>>>>>>> Sounds too good to be true.
>>>>>>>>>
>>>>>>>>> Note that the GBW is 110MHz on page 1 of the specs :)
>>>>>>>>
>>>>>>>> Yup. The ADI low-noise amps, still relatively noisy, are slow. The
>>>>>>>> LT1028 is below 1 nv/rthz but has issues.
>>>>>>>
>>>>>>> The AD797 is not significantly noisier or slower, if at all.
>>>>>>> I really like the ADA4898-2.
>>>>>>>
>>>>>>> Depending on how it's measured, a little bit lower ft than the LME, but
>>>>>>> more than twice the slew rate, no 300 KHz noise mole hill like LT1028,
>>>>>>> and with 2 amplifiers/SO-8 quite a good price, especially if you average
>>>>>>> 20 devices for _really_ low voltage noise from low impedance sources.
>>>>>>>
>>>>>>> < http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf >
>>>>>>>
>>>>>>> and, related:
>>>>>>>
>>>>>>> <
>>>>>>> http://www.hoffmann-hochfrequenz.de/downloads/NoiseMeasurementsOnChemicalBatteries.pdf
>>>>>>>>
>>>>>>>
>>>>>>> <
>>>>>>> http://www.hoffmann-hochfrequenz.de/downloads/Noise_Measurements_On_Some_Laboratory_Power_Supplies.pdf
>>>>>>>>
>>>>>>>
>>>>>>> regards, Gerhard
>>>>>>>
>>>>>>
>>>>>> All the batteries have similar curves, especially at low frequencies..
>>>>>>
>>>>>> Is there any chance that the presence of DC increased the preamp
>>>>>> noise? It wouldn't take much leakage in the input coupling cap to
>>>>>> upset the preamp. I assume the preamp is a bunch of paralleled jfets..
>>>>>>
>>>>>> Some simple tests could discount that possibility. It looks like the
>>>>>> Tadiran is the lowest voltage and has the least noise below 1 Hz.
>>>>>>
>>>>>>
>>>>>
>>>>> The preamp was massively paralleled ADI op amps (in the previous reference).
>>>>>
>>>>> Cheers,
>>>>> James Arthur
>>>>
>>>> OK, but there must be a biggish DC blocking cap. [1]
>>>>
>>>> One easy test: connect 4 batteries in series adding, nom 6 volts,
>>>> measure noise. Then connect them series opposing, nom 0 volts, repeat.
>>>>
>>>> That assumes the noise is uncorrelated between cells. That's not true
>>>> for thermal effects, and batteries have relatively huge TCs. So
>>>> mummify them in bubble wrap an see if that changes anything.
>>>>
>>>> [1] leakage in capacitors is non-metallic, so the electron ordering
>>>> effect of metallic conductors is not present. So maybe capacitor
>>>> leakage has shot noise.
>>>
>>>
>>> I was interested in the coupling caps. In his first paper (about the preamp
>>> ) He first used 16 10uF X7R ceramics (50V 1206), (160 uF and 10k ohm), he then switched to mylar.. but too big so went back to the ceramics.
>>>
>>> I've got noise problems of my own at the moment. I was testing some new mirrors in a Fabry-perot cavity and discovered that our diode laser is noisy. Grumble... I think it's current noise.. at least there is all this "new" interference peaks on the spectrum.
>>>
>>> Here's a slow scan through the F-P transmission.
>>> https://www.dropbox.com/sh/1dzk4zwo44cw0m0/AACwTtJik_847xD42xYclsKVa?dl=0
>>>
>>> The first two are the noisy laser controller, (TEK00, TEK01) the last two the old demo version. The width is only a few MHz, so just building shake gives me a bit of jitter on the spectrum.
>>>
>>> George H.
>>
>> What's the span?
>>
>> Looks like mode hopping to me--you wouldn't have those sharp jaggies if
>> it were FM noise--the sidebands would have at least the same width as
>> the carrier. Small differences in the temperature and bias current can
>> change that.
>
> Hi Phil, I don't think it's mode hopping... it would be much worse.
> I can get feedback from the F-P cavity, but I monitor the transmission through an Rb cell and that spectrum stays clean.
>
> It's a confocal F-P cavity, FSR = 385 MHz, (20 cm radius), with a finesse of 100 - 150 or so.. depending on how well I set the mirror position.
>
> So the width of the transmission peak is 3-4 MHz.
>
> It looks to be current noise..interference from somewhere.
> (Well I see current noise from the noisy unit and not the other.)
> Though I want to make sure of that before I start drilling down.
> I also wonder about noise on piezo drive signal...
> Grumble, one good way to ruin my day.
> My bigger concern is that there are other "bad" units out there that
> we'll have to recall... but I'm getting ahead of myself.
>
> George H.
Hmm. Yes, ordinary mode hopping would make it a lot wider than 3 MHz,
that's for sure, but those spiky things can't be ordinary noise
sidebands, because genuine sidebands couldn't be narrower than the main
line.
I suppose it could be acquiring and then losing self-lock on the cavity,
which can happen pretty fast. What does the AM noise look like? Does
the shape change when you change scan speed?
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net