Protecting your instrument

 

 

RF Explorer is a very sensitive device. It can detect signals as low as -120dBm, which is 10E-12mW or 9nA over a 50ohm load.


This extreme sensitivity comes at the price of fragility; your device needs care handling and protection in order to run for many years without problems.


Most RF technicians know the RF instruments have to be protected in order to survive the high Electro Magnetic (EM) fields that may be in the environment. Expensive instruments like $50,000 full sized Spectrum Analyzers and Signal Analyzers comes with a long list of handling procedures the operator must observe in order to limit any chance of damage. Unfortunatelly, the fact that RF Explorer is a cheaper device doesn't mean it can work without protection.


The first and most obvious precaution is to make sure the input RF power is not beyond the acceptable levels of the instrument.


RF Explorer 3G Combo and WSUB3G models are well protected up to +30dBm (1Watt) input power, which is plenty to play safe in pretty much any environment.

However, other RF Explorer models have a maximum safe input power of +5dBm, which is 3mW in the RF SMA port. As an reference, that is the power captured by the RF antenna from a cell phone a distance of 10cm, or from a Microwave oven at about 1 meter distance. Not all the ovens or cell phones work the same, so take this as an indication only.

 

What may not be obvious to all users is this is a limit in any RF frequency band, even if the RF Explorer is powered off.

 

As an example, the RF Explorer WSUB1G -with a frequency range of 240-960MHz- will not detect a microwave oven (2.4GHz) on the screen but can be very well damaged by it. Similarly, a strong 2m HAM or FM high power transmit station won’t be detected by this model, but still induces enough RF power to kill the RF circuitry with ease. And that doesn’t depend on RF Explorer being on or off because the antenna will receive that powerful signal and will inject it into the spectrum analyzer, with serious risk of damage.

 

 

In addition to RF power, you should reduce the likelihood of static discharge over the antenna. In particular, the naked metallic antennas such as the Nagoya telescopic antenna we include in the wideband models. The whip helical plastic antennas included in the narrow band models do not expose the internal contact to the outside world and thus are safer from ESD perspective because don't offer a direct current path to the internal sensitive CMOS component pin, but all metallic antennas needs you to observe good ESD practices, most importantly in very dry winter air: Make sure you have a good hand contact with the metal case of the RF Explorer before touching the antenna and, whenever possible, do not touch the antenna with your hands.

 

For this very same reason, you should never make contact with the antenna to any external energy source. Just imagine what power can be injected inside if you make the antenna contact to AC current or a powerful AC source of any kind!

 

If the RF Explorer RF circuitry is damaged, you will need to send it back for repair, taking time and cost so we strongly suggest using one or several standard procedures used for decades by RF technicians to protect your instrument:

  • The ideal device to protect your RF Explorer against strong RF fields is a RF Power Limiter. There are several options in the market, but we designed a compact, multi-purpose RF Explorer Power Limiter device with a very attractive price and the addition of advanced features such as an embedded 6dB attenuator and a 16V DC block. It will protect your RF Explorer for any power up to 1W (+30dBm) - For more details on this power limiter see this article.

Other options available in the market are for instance this power limiter from Mini Circuits: ZFLM-252-1WL+, available for less than $100, but does not include extra attenuator or DC block functionality, and is significantly larger in size.

An valuable update comes from user Bob Johansen points out this interesting Mini-Circuits application note on power limiters, very useful!

  • If you do not own a power limiter, ideally if you store the RF Explorer in your lab for no use, either enclose it within a metal case to protect it from external RF fields or, if not possible or available, unplug the antenna out of the SMA connector. This will significantly decrease the chances of high RF power get into the RF circuitry. If you know there may be strong RF fields nearby, it is even safer to plug a 50ohm SMA dummy load to the RF connector so the RF circuitry doesn’t receive any external RF field. You can find 50 ohm dummy loads in SeeedStudio for only $8.

  • When operating your instrument in unknown area where strong RF fields may be nearby, never plug the antenna into the SMA connector directly, always use a 30dB SMA attenuator to reduce the potential power received. This will increase the max power you can receive, but will reduce sensitivity as well. Remember this is required even if the instrument is not powered on yet. You can find SMA attenuators in SeeedStudio for convenient 60dB, 30dB and 10dB attenuation values.

    High Frequency Precision 30dB Attenuator High Frequency Precision 10dB Attenuator High Frequency Precision 60dB Attenuator

  • If the RF power comes from an out-of-band source, but you still want the maximum in-band sensitivity, a SMA attenuator may not be the best option because it reduces sensitivity in all bands. For instance, if you are using the WSUB1G model to monitor a weak 433MHz signal and know there is a strong 1.2GHz source nearby, the attenuator may not be the best option because it will attenuate the 1.2GHz signal but also the 433MHz signal. So in this case a good RF band pass filter may be the best option. There are many different options for filters, not all of them cheap, so look for available options for your band before taking this path. The Mini-Circuits website may be a good place to start.

 

Let us know if you have any question, we take client satisfaction seriously and want to make sure you enjoy your device for years without issues.

If your unit needs repair because the RF circuitry went unresponsive, let us know, we will find the best and most efficient way to offer a cost sensitive repair service.

 

Comments   

# Frank Liuzzi 2012-12-08 03:00
Hello,
I have the RF Explorer 3G Combo and would like to know the maximum DC voltage that each of the instrument's two SMA inputs can safely handle if I directly connect the RF Explorer to a circuit under test that might exhibit a DC offset.

I'm not sure if the RF Explorer 3G Combo is AC coupled or DC coupled.

Thanks
Frank
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# Webmaster 2012-12-08 20:12
Quoting Frank Liuzzi:
Hello,
I have the RF Explorer 3G Combo and would like to know the maximum DC voltage that each of the instrument's two SMA inputs can safely handle if I directly connect the RF Explorer to a circuit under test that might exhibit a DC offset.

I'm not sure if the RF Explorer 3G Combo is AC coupled or DC coupled.

Thanks
Frank


Frank, that is a good question. I've added that detail on the www.rf-explorer.com/models comparison table. The WSUB3G is DC decoupled in both RF connectors up to 16V.

Regards.
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# Renato Galani 2013-03-06 13:33
Hi there!

I was looking the specification of 3G combo and I noticed that left port has a max input of +5dBm and the right has +30dBm. Does it mean that only the right port (WSUB3G) is well protected against strong signals?

Regards,
Renato
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# Webmaster 2013-03-06 15:34
Quoting Renato Galani:
Hi there!

I was looking the specification of 3G combo and I noticed that left port has a max input of +5dBm and the right has +30dBm. Does it mean that only the right port (WSUB3G) is well protected against strong signals?

Regards,
Renato


Renato, that is correct, the connector at the right is +30dBm protected. If you are working in a strong signal EMI environment, use the right connector antenna and keep the left connector with no antenna. Use the left connector when you want extra sensitivity only in low noise environments.
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# EngineerZ 2013-03-09 22:51
Wouldn't an SMA shorting cap offer more protection than a 50-ohm load when the device is not in use? Couln't a strong RF field still induce a voltage across a 50-ohm load, especially if the load wasn't particularly well-shielded?
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# Webmaster 2013-03-11 18:15
A 50ohm termination is the best protection you can get. It not only protects you from external EM fields getting into the internal RF circuit, but also makes a reliable load in case you switch on the internal RF Generator in RF Explorer models that include it.

All recommended SMA termination loads are always shielded, industry standard, if you cannot get one nearby you can order it from SeeedStudio http://www.seeedstudio.com/depot/sma-termination-50ohm-p-1256.html

With a SMA termination in place, you will need kilowatts of external power nearby to get any noticeable power into the RF circuit.

On the other hand, a shunt capacitor will not offer a predictable protection because the impedance will vary with frequency. For instance a capacitor will not protect you at low frequencies, usual in some RFID congested areas. In contrast, a SMA termination has a predictable, stable response from DC to 3GHz, usually much more.
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# hubert 2014-06-21 14:23
Hello,

I have a RF explorer 3G combo. I put a RF Explorer Power Limiter on the left SMA. If I want to measure next to a talkie walkie that emits 4W (UHF GP340 for example), how I should proceed to not to bend my RF explore and have a proper measure ?

cordially
hubert
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# Webmaster 2014-06-22 23:27
Quoting hubert:
Hello,

I have a RF explorer 3G combo. I put a RF Explorer Power Limiter on the left SMA. If I want to measure next to a talkie walkie that emits 4W (UHF GP340 for example), how I should proceed to not to bend my RF explore and have a proper measure ?

cordially
hubert


The power limiter will certainly protect your RF Explorer even if it is very close to the 4W RF source. However for the measurement to not overload the analyzer, start by a 10mts distance and get closer till you are measuring no more than -30dBm.
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# Tony 2014-09-26 07:38
Quoting Webmaster:
Quoting hubert:
Hello,

I have a RF explorer 3G combo. I put a RF Explorer Power Limiter on the left SMA. If I want to measure next to a talkie walkie that emits 4W (UHF GP340 for example), how I should proceed to not to bend my RF explore and have a proper measure ?

cordially
hubert


The power limiter will certainly protect your RF Explorer even if it is very close to the 4W RF source. However for the measurement to not overload the analyzer, start by a 10mts distance and get closer till you are measuring no more than -30dBm.


But how do I understand the RF-Level present in the measuring zone. For instance let say I am transmitting at 100watt in ham band and there is a rf leakage which i am not aware of it - WHAT HAPPENS IN this scenario to RF EXPLORER
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# Webmaster 2014-09-26 11:07
Quoting Tony:

But how do I understand the RF-Level present in the measuring zone. For instance let say I am transmitting at 100watt in ham band and there is a rf leakage which i am not aware of it - WHAT HAPPENS IN this scenario to RF EXPLORER


There is no perfect answer to this, all sensitive RF devices including your cell phone are in danger if a strong RF source is very close. If you need 100% safety, use a narrowband pass filter so all frequencies are attenuated except the one you are trying to measure. This is standard industry practice with spectrum analyzers of all sizes and prices if they have to work in a risky environment.
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# JW 2015-01-01 11:14
Is it safe to connect my 3G Combo directly to my TV antenna? We aren't particularly close to the transmitter, but the signal is strong (according to my receiver).

Also, how about connecting it to the 'RF out' of my VCR?
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# Webmaster 2015-01-07 12:16
It is safe if your TV antenna is not DC feed with more than 16VDC. In addition to that, you need 30 or 40dB attenuation for the signal to fit in the linear range of the device.
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# Alain 2015-04-15 20:04
What happens to the RF limiter after a strong signal over its limit is applied; is it blown like a fuse or it short the excess and lets true the signal at the instruments' limit or it opens and resets after a while?

Thank you
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# Webmaster 2015-04-15 20:13
Thanks for your question.
The power limiter will correctly limit input power up to 1Watt sustained input power. Beyond that limit, the PIN diode manufacturer offer no guarantees, and therefore you may expect the power limiter to be permanently damaged and need replacement.
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# Adrian 2015-10-12 03:35
Can I hook up the WSUB1G scanner to a Shure or sennheizer paddle antenna? will it over load the scanner?
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# Webmaster 2015-10-21 00:09
That should be ok and not overload the unit.
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# cristian 2016-02-11 05:52
I can connect directly 3g combo to 50 db with bird43 sampler to measure FM signal with a 100w power?
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# Webmaster 2016-02-11 12:27
It depends if the bird43 has a coupled port you can connect the RF Explorer to. For correct linear reading you need RF Explorer input to be -30dBm or less. A 50dB attenuator will increase that up to +20dBm, so if the bird43 delivers that power range from a coupled port you are ok, otherwise you will need a separated coupler.
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# Ray 2016-10-11 15:20
I need to carry the RF Explorer with me while traveling as 'checked' luggage. Is the x-ray or other imaging/scanning harmful to the device? If so, what do you recommend? Thanks.
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# Webmaster 2016-10-11 15:50
We suggest connecting a 50ohm dummy load on each SMA port, this should be enough to guarantee normal x-ray levels won't harm the device.
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