Author Topic: Chasing PPMs? Put that cell phone away!  (Read 4160 times)

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Offline dietert1

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Re: Chasing PPMs? Put that cell phone away!
« Reply #25 on: June 07, 2024, 05:33:57 am »
With DIY one could save one GPIB interface using an existing USB to fiber interface on the PC end. This could already serve to separate the measurement setup from the control computer, its displays and whatever is  connected there. At amazon.com i found a USB to fiber ethernet interface "StarTech.com USB to Fiber Optic Converter - 1000Base-SX SC - MM - Windows/Mac/Linux - USB 3.0 Ethernet Adapter - Network Adapter (US1GA30SXSC)" for $233.10.
Remains the fiber ethernet to GPIB controller on the other end. We have a NI GPIB-ENET100 and i could try to use it with a "10/100/1000Mbps Single Mode 1&4 RJ45 Ethernet to Fiber Optic Media Converter j" for $42 at ebay. The DIY could be as little as making quiet supplies for the two adapters on the GPIB end.
A better price and less work than DIY from scratch.

Regards, Dieter

Edit: Even better, the 42 buys a pair of ethernet to fiber adapters, so one would use ethernet on the PC side and save that 233 USB to ethernet adapter.
« Last Edit: June 07, 2024, 06:05:07 am by dietert1 »
 

Offline ftg

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Re: Chasing PPMs? Put that cell phone away!
« Reply #26 on: June 07, 2024, 07:51:31 am »
Cell phones can from time to time send rather powerfull pulses (e.g. to synchronize / reconnect to base)  - enough to be audible with some audio gear.

This was a big issue with GSM, but I haven't noticed audio artifacts with 3G and higher cellular technologies .... although that could be my hearing getting worse with each new generation of cellular technology  :)

You will get artefacts with all pulsed radio systems, i.e. non-CDMA systems. It will audibly be worst with a TDMA system where the pulses are in the audio band, e.g. GSM at 217Hz.

Equipment has been forced to accommodate such pulses, by better shielding and/or electronically filtering out offending pulses (e.g. a 217Hz notch filter).

Obviously older equipment may be more susceptible, since that threat was never envisaged.

In the land mobile radio world there is also TETRA and DMR. Both are timeslotted and the handheld terminals can have output powers between 1W and 5W.
So far worse than what GSM ever had. Thankfully these are rare.
Unless your sensitive equipment needs to exist in a place where there might be users with those close to it.
Say folks from various public safety agencies.

As for cellphones in general.
I was once characterizing the noise performance of some low noise amplifiers and binning op-amps based on their popcorn noise.
Could not have a cellphone or a bluetooth speaker in the same room with me.
Read a decent amount of books while waiting for individual measurements to stabilize.
 
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Offline pdenisowski

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Re: Chasing PPMs? Put that cell phone away!
« Reply #27 on: June 07, 2024, 10:10:41 am »
In the land mobile radio world there is also TETRA and DMR. Both are timeslotted and the handheld terminals can have output powers between 1W and 5W.
So far worse than what GSM ever had. Thankfully these are rare.

Great observation.  Here in the United States we have (of course ...) our own timeslotted version of this: P25/APCO.

I guess the important takeaway here is that shield / screen rooms and boxes are still the way to go if you're making sensitive measurements.

Incidentally, I had a customer once who told me he LOVED working in a screen room because it gave him an excuse not to return anyone's phone calls:  "Sorry, was working in the shield room all day and didn't get your call ..."   :-DD
Test and Measurement Fundamentals video series on the Rohde & Schwarz YouTube channel:  https://www.youtube.com/playlist?list=PLKxVoO5jUTlvsVtDcqrVn0ybqBVlLj2z8
 

Offline dietert1

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Re: Chasing PPMs? Put that cell phone away!
« Reply #28 on: June 11, 2024, 10:38:24 am »
Meanwhile we got 2x tp-link MC100CM fiber to copper adapters and a 20 m multimode cable and it's working with the NI GPIB-ENET/100. Of course these fiber interfaces, their power supplies and the GPIB interface all have switched mode converters inside. A cheap endeavour, yet needs more work.

Regards, Dieter
« Last Edit: June 11, 2024, 10:40:10 am by dietert1 »
 

Offline miro123

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Re: Chasing PPMs? Put that cell phone away!
« Reply #29 on: June 11, 2024, 12:57:42 pm »
Meanwhile we got 2x tp-link MC100CM fiber to copper adapters and a 20 m multimode cable and it's working with the NI GPIB-ENET/100. Of course these fiber interfaces, their power supplies and the GPIB interface all have switched mode converters inside. A cheap endeavour, yet needs more work.

Regards, Dieter
Few years ago I switched my home lab to optical fiber and LIFePO batteries. Later on rearranged the whole heme network. It is 80% fiber now.  I have used those TP- link converters in the past - instead of adapter I used lab PSU set to 9Vdc, later on attached to 3S - Latium battery
 

Offline exe

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Re: Chasing PPMs? Put that cell phone away!
« Reply #30 on: June 11, 2024, 09:05:01 pm »
I switched my home lab to optical fiber and LIFePO batteries

How often do you charge your batteries?
 

Offline miro123

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Re: Chasing PPMs? Put that cell phone away!
« Reply #31 on: June 12, 2024, 07:55:35 pm »
I switched my home lab to optical fiber and LIFePO batteries

How often do you charge your batteries?
Once per few moths. When BMS  reports that. The battery pack is 5S 240Ah LiFePO
 

Offline dietert1

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Re: Chasing PPMs? Put that cell phone away!
« Reply #32 on: June 13, 2024, 02:38:52 pm »
Meanwhile i found that the tp-link media converter is easy to run without it's buck converter if one feeds a 3.3 V about 200 mA linear supply. And it has a metal case.
The NI GPIB-ENET/100 is worse in that respect. It contains two LM2595S switching converters, one for 5V and one for 3.3 V, both with open ferrite inductors. Its enclosure has a metal base with a plastic cover.
Therefore i am studying a STM32H7 based ethernet solution - also avoiding the NI proprietary protocol and their drivers.

Regards, Dieter
« Last Edit: June 13, 2024, 03:02:25 pm by dietert1 »
 


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