Protecting your RF Explorer from strong EM fields

[Ariel Rocholl]

Based on questions from users and realizing not everyone is aware of how to safely protect a sensitive Spectrum Analyzer like RF Explorer from strong RF fields, I wrote down an article with a few suggestions and background info you are suggested to read in order to keep your device safe for years of use.

Please check here.

The most important suggestion is to keep your RF Explorer without antenna when you store it or if you have to go accross strong field areas like RFID points in shops, X-ray scanners in airports, etc.

Any question let me know. We can add more info if required.

Thanks
Ariel

[Ariel Rocholl]

Hi Daniel,

Thanks for your feedback and interest on RF Explorer.

The VLM-33+ is a correct choice if you complement it with a 10dB attenuator, which is part of the Gotham's kit. As you said, it cannot be used directly or you can exceed the maximum +5dBm limit.

The good thing about ZFLM-252-1WL+ is that works fine with no attenuator for RF Explorer. This model wasn't available when Gotham prepared the RF Explorer Accessory Kit. I am working with SeeedStudio to see if it is feasible to offer an accessory kit, but doesn't look like will happen in the short term.

As for your question of what limiters do outside the frequency range is undocumented and, from the manufacturers perspective, you cannot assume anything. In practical terms, what usually happens is the insertion loss increases and thus you incur in higher power losses. So the device remains protected, but the linearity is compromised.

Best regards,
Ariel Rocholl


On Wednesday, July 11, 2012 5:54:33 PM UTC+2, Daniel wrote:

Hello and thank you for your work
I am not an RF-E owner yet, but will order as soon as exp-tech will have the wsub1g available again next week and expand with a wsub3g module later. I'd like you to comment on my following assumptions and possibly correct my wrong understanding since I am not a radio engineer.
You suggest using the ZFLM-252-1WL+ limiter for the 1G base-unit's antenna. Alternatively, Gotham also sells an accessory kit, containing the a bit cheaper VLM-33+. The datasheet quotes some +11.5dBm output power (in limiting range). From my understanding this value translates to "leakage" in the Mini-Circuits application note. As the WSUB1G is "limited" to or sould I say allows a maximum input of +5dBm, the VLM-33+ does not really seem to be a reliable protection.
Regarding the spectrum range of both limiters, what do they do with frequencies out of their specified range? do they attenuate/cut of any power or would they allow power to pass through and therefore do not protect outside their range?

Would it make sense to offer some accessory kit like Gotham yourself via your distributors?

Kind regards


Daniel

[Daniel]

Hi Ariel,

thank you for your reply. During my research, I found this dummy load, that might be neat to add to the units, e.g. for input protection during transport, air-travel, etc. It comes with a little keychain, so it can be attached to the housing or the sma port and does not get lost.

Pic:
http://www.rfparts.com/picts/3016BC.jpg
Datasheet:
http://www.aeroflex.com/ams/INMET/PDFILES/3016B.pdf

Out of curiosity:
Would it be possible to implement some internal input logic that detects if an antenna load is connected and if not switches to some dummy load? Would this raise the price much?


Regards

Daniel

[Mike Westgate]

I think this is just a protective cap not a dummy load or a 50 ohn termination

 

mike

www.mikewestgatesound.co.nz

 

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From: rf-ex...@googlegroups.com [mailto:rf-ex...@googlegroups.com] On Behalf Of Daniel
Sent: Friday, 13 July 2012 1:19 a.m.
To: rf-ex...@googlegroups.com
Subject: Re: Protecting your RF Explorer from strong EM fields

[Ariel Rocholl]

Hi Daniel,

thank you for your reply. During my research, I found this dummy load, that might be neat to add to the units, e.g. for input protection during transport, air-travel, etc. It comes with a little keychain, so it can be attached to the housing or the sma port and does not get lost.

Pic:
http://www.rfparts.com/picts/3016BC.jpg
Datasheet:
http://www.aeroflex.com/ams/INMET/PDFILES/3016B.pdf

Looks like a neat dummy load, easy to carry on and, as you say, does not get lost easily. Thanks for sharing the reference.
 

Out of curiosity:
Would it be possible to implement some internal input logic that detects if an antenna load is connected and if not switches to some dummy load? Would this raise the price much?

Yes, it will increase the price a bit. You need to add a couple of RF switch ICs (to minimize leakage to the load, one switch is not enough), the load itself and then drive some new decoupled and noise free MCU pin to drive the RF switch. Unfortunately there are no MCU free pins available and thus will require a higher pin count MCU, which is really a new design, firmware and certification process, etc.

I think is more cost-effective to consider WSUB3G as the alternative when you think you may be exposed to strong fields and don't want to remove the antenna for transport.

Cheers,
Ariel

[Ariel Rocholl]

From the specs it looks like a 50 ohm dummy load good for up to 1W.

On Friday, July 13, 2012 1:26:06 AM UTC+2, mikewest wrote:

I think this is just a protective cap not a dummy load or a 50 ohn termination

 

mike

www.mikewestgatesound.co.nz

 

Sent: Friday, 13 July 2012 1:19 a.m.

Subject: Re: Protecting your RF Explorer from strong EM fields

[Dave Packham]

what kind of distances are we talking about.  how close can I store it away from an Access Point?

I have the dummy loads BTW

Dave P

[tre...@gmail.com]

Ariel,
What a wonderful product! I have an HP 8569B, but the RF Explorer uses a fraction of the power, is infinitely easier to set up, and similar performance (albeit with less control) and I use it nearly every day. I can't wait to get hold of the RF generator as well... I have an Si570 kit partly built, but the 6GHz of the RFgen has made me lose interest in finishing it :)

So, back to topic. I bought a 3G Combo device via Amazon, and have used the 15-2700MHz module exclusively. This morning I decided to take a look at the Smart Meters in our neighborhood (at 915MHz span 26), and noted that the lower frequency input, which up until now has had a 50ohm terminator on it, is far less sensitive. In fact, I am not sure it is functioning at all. The 15-2700 is indicating -92dBm peaks, while the other board is stuck at about -115dBm peaks. I checked that the bandwidth was the same in both, 250KHz, even though the LF unit scanned 8/sec rather than 5/sec of the 15-2700.

The box still has the Seeed studio sticker on it, and looks untouched by any previous user. How frequently do you see malfunctioning new RFexplorers?
 

[arocholl]

Hi,

 

Thanks for your feedback. It is great to know you find the product useful, it makes it worth all our work.

 

As for the description you have on the WSUB1G module, that is certainly not expected. Do you get a flat line at -115dB or some activity but erratic and always low? Can you capture data with the Windows application, save it to a .rfe file and send it for review? This looks like a support issue so please send it to rfexp...@arocholl.com

Best Regards,
----
Ariel Rocholl
http://www.rf-explorer.com

 

From: rf-ex...@googlegroups.com [mailto:rf-ex...@googlegroups.com] On Behalf Of tre...@gmail.com
Sent: Monday, October 27, 2014 00:33
To: rf-ex...@googlegroups.com
Subject: Re: Protecting your RF Explorer from strong EM fields

 

Ariel,

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[Mitchell Carter]

Hi! I recently purchased a 6G combo unit which will be used primarily for monitoring the (very congested) wifi networks in my neighborhood.  I did some basic research and determined I would not initially need anything additional prior to using my rf explorer for this purpose.  Having just read your article attached above, I am confused as to your microwave oven reference.  My research determined that while a microwave oven can put out 1000w internally, the signal is confined to the appliance barring damage to the magnetron housing or microwave itself.  My understanding of the science indicates a microwave oven should not be capable of outputting any signal distinguishable from background noise and certainly not sufficient to fry the circuitry on the device  unless it is IN the oven.

If you would please provide input on this topic it would be greatly appreciated.  I tend to use the microwave at least once in a given day, and if I am mistaken I need to know what equipment to use for protection of my equipment.  Especially since the frequency of microwave radiation (2450Mhz) is smack in the middle of my intended scan range.  Thank you!

[Ariel Rocholl]

Hi Mitchell,

Thanks for our feedback.

On your question about owen, the magnetron produce signal that is significantly, but certainly not totally, attenuated by the Faraday cage of the oven. The power level outside a microwave oven is significantly large, not as large as to be dangerous for people, but can break your nearby 2.4GHz communications temporarily.

Unfortunately there is no easy answer as to how much exact power you can expect outside the oven as it depends on the oven itself, where it is located (so signal is focused in one direction only or in multiple directions depending on forniture, design, etc). And it also depends very much of what is inside the oven when it is running, certain food elements absorb RF energy better than others.

You can easily experiment this with your RF Explorer and see how your particular oven works, try with a glass of water, then 3 glasses of water, etc. Please use care when working with an oven of course.

Regarding RF Explorer protection, the good news is your model 6G Combo is really well protected by internal power limiters up to +30dBm (+25dBm in the 5GHz range), so you can safely have it very close to a microwave oven with no risk. The article link is more relevant for WSUB1G and 2.4G baseline models which include no internal protection.

Regards

Ariel

[Mitchell Carter]

Thank you for the prompt response.  My device arrived shortly after my first post and I had done some more research in that time.  Being fairly confident in what I read and having gone back over the specs I decided to test the microwave theory.  I did a standard size coffee mug filled with water and left my device ~10m back while I started the microwave.  I have to say I was rather surprised by the amount of energy escaping.  The frequencies jumped around like crazy and there were no sustained bursts (no surprise given the scttering effect of water).  I eventually made it to within two or so feet from the microwave and was getting signals up to -20dBm which was quite a bit more than what my initial theory.  Needless to say I am shocked at the output, but on the other hand it really showed me the quality of the device.  Great confidence tester for this equipment.  I am impressed!

[Mitchell Carter]

Based on the built in attenuation, it seems as if my 6G combo can also be safely connected to the coax from my cable provider to test incoming signal strength.  I have looked up the conversions (dBmV to dBuV) and the numbers seem to fit within tolerances.  What I am unsure of is whether the load difference (50Ω for the explorer vs 75Ω on cable systems) has any bearing on the calculations.  Do you have any feedback for what (if any) additional attachments I should use in this case?  And more importantly if you can point me to a guide to fill in my knowledge gap.  Thank you in advance!

On Sunday, January 22, 2012 at 4:42:52 AM UTC-8, Ariel Rocholl wrote:

[Ariel Rocholl]

You are correct, a typical CATV distribution cable should be in the range of 0 to +10dBmV (on 75ohm coax), which is lower than -30dBm you can measure without distortion in RF Explorer. If you expect higher level signals, you will need external SMA attenuator not to protect RF Explorer but to avoid distortion in measurement.

A good appnote on this matter: http://www.maximintegrated.com/en/app-notes/index.mvp/id/808 . It explains how the 75ohm impedance impact can be corrected in dB. You may eventually consider using an impedance adapter in the input port, in case you work a lot with 75ohm systems. Impedance adapters (if pure resistive) typically add 6dB loss.