Introducing the multipurpose RF Explorer Power Limiter + DC block + 6dB attenuator

[Ariel Rocholl]

Introducing the multipurpose RF Explorer power limiter + DC block + 6dB attenuator

The RF Explorer Power Limiter is a custom, 3-in-1 device designed from the ground up to be the perfect protection against strong RF fields.

 

The RF Explorer Power Limiter is assembled in a rugged aluminum case and it is very compact when compared to other market offerings. Not only that, it also includes internal DC block and 6dB attenuator which makes it very versatile yet really small device for all it offers.

 

Why you would need a power limiter? As you can see on this note all RF Explorer models have input signal power ranges beyond which can be damaged. For most models (such as WSUB1G, ISM Combo or 2.4G), the limit is on +5dBm, some others are ok up to +10dBm (such as 433M-915M) but only WSUB3G (3G Combo right SMA connector) is protected up to +30dBm.

The new RF Explorer Power Limiter will allow any RF Explorer model to be protected with external signals up to +30dBm (1 Watt), so you get the same level of protection as in the WSUB3G. Furthermore, the power limiter includes additional functionality inside that will otherwise require external devices increasing cost and size, it is a true 3-in-1 device:

• Power limiter:  protection up to +30dBm, for any frequency range between DC-3000Mhz

• DC block:  You can connect any external source with DC voltage up to 16V with no risk of damaging your RF Explorer or interfering in your measurement.

• Attenuator: Includes an internal 6dB attenuator to help you extend the range of power signal measurements. 6dB attenuation means a ¼ of the input power is received by the unit. To compensate for this extra attenuation you should indicate OffsetDB: +006 in the ATTENUATOR MENU of your RF Explorer.

Feature

• Robust, small and low weight custom aluminum case
• 3-in-1 device with Power Limiter, DC Block and Attenuator
• Easy to connect and disconnect when required
• Wide broadband frequency application
• Directional 1 Watt rating
• Suitable for all RF Explorer models, not required for WSUB3G.

Specification

• Frequency range: DC ~ 3.0 GHz
• DC block: +16V DC
• Input Power rating: 1 Watt (+30dBm)
• Output power max: +4 dBm.
• Attenuation: 6 dB 
• Impedance (Nominal): 50Ω
• V.S.W.R (Max): 1.25 : 1
• Connector type: SMA male – female
• Connector:  Brass / Gold plating
• Body: Aluminum

The RF Explorer Power Limiter is available at SeeedStudio for $45 - that is about five times lower price you would have to pay for features like this in the general market. RF Explorer distributors will have it available soon, contact your local distributor for more details.

As we put significant effort an expense on this design, we will reuse this aluminum cage for additional accessories, including filters for popular R/C, FPV, ISM and HAM frequencies.

[Ariel Rocholl]

The RF Explorer Power Limiter is now available for orders in Europe - from Exp-tech Germany: http://www.exp-tech.de/Hacking---Measurement/Power-Limiter.html

[David Ackrill]

Just ordered one from the supplier in Germany.

Had a very helpful email from them when I had trouble setting up an account, which they did for me, and got through the sales process OK after that.

[Ariel Rocholl]

For anyone interested, Fraser did a full 50KHz - 7.5GHz range test with the RF Explorer Power Limiter and published very useful results: http://www.eevblog.com/forum/testgear/3ghz-rf-limiter-with-dc-block-and-attenuator-for-gbp30-!/

As soon as some higher priorities are out of the road, I will publish a complete datasheet for the device.

Cheers
Ariel

[David Ackrill]

I've just received my Power Limiter - DC Block unit and it's certainly a useful device with the DC to 3GHz bandwidth and nominal 50 ohm impedance.

However, I'm probably missing something but I'll ask the question anyway.

In the specification for the 3 in 1 Power Limiter and DC block unit the specs say

• Input Power rating: 1 Watt (+30dBm)
• Output power max: +4 dBm.
• Attenuation: 6 dB

By my calculation, if I put the full 30dBm or 1W into the 'in' socket and the attenuation is just 6dB, then isn't the output going to be 0.25W (250mW) or +24dBm ?  Or, is there something else inside that is limiting the output to just +4dBm (2.5mW).

Turning the calculation round, to get 4dBm output (2.5mW) with 6dB attenuation suggests that the maximum input is 10mW or +10dBm.  Where does the rest of the power from the 1W (30dBm) signal go?

Also, how hot will the case get with 1W input, if the output is limited to +4dBm, as the rest of the power will need to be dissipated somewhere.  How long will it take the full 1W for?

Thanks

[Ariel Rocholl]

Hi Dave,

Very good questions.

The RF Explorer Power Limiter works as a linear 6dB attenuator as long as the input power doesn't go beyond certain threshold. However, if the input power goes beyond this threshold, the internal PIN diode starts compressing the signal and the device no longer works as a linear device. The internal PIN diode limits the power by reflecting a fraction of the signal back to the source, and another fraction by internal power dissipation - it is actually an anti-parallel, dual high performance PIN diode which can stand with 1W input signals for unlimited time.

If you are interested in more details on how a PIN diode works, the specifics of high performance PIN Limiter diodes and the challenges of a power limiter design for high frequency, I suggest reading the Agilent Application Notes 1050 and 5438 (just google for "Agilent Application Note 1050" and "Avago Application Note 5438") - these are very interesting readings.

As the RF Explorer Power Limiter is apparently getting the attention of RF users beyond RF Explorer, I will be producing full datasheet specification (with frequency response curves including input/output power transfer response) so the device is characterized for any potential use. At the moment I concentrated in minimal documentation and specs required by RF Explorer users who really need to know the device is protected within certain levels.

Ariel Rocholl
http://www.rf-explorer.com

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[David Ackrill]

Thanks for the response Ariel,

I will have a look at those technical sheets as I'm sure that they will help me understand better.

I remember seeing anti-parallel PIN, and other type, diodes in various projects included alternative front ends for radios such as the Yaesu FT290R etc., so it should have struck me that might be what's going on.  I've also used 'ordinary' diodes in anti-parallel on home brew receivers, but not up to these frequencies.

Thanks for the confirmation that it will be able to stand 1W continuously, I've seen test gear in the past rated at various powers but when you read the spec. it's only for a limited time period before the dissipation of energy heats the unit up beyond the limit of whatever the main device/resistor can take.  VHF/UHF dummy loads and some attenuators seem to hide the limitations in the manual whilst printing a large RF handling power on the box...

Cheers - Dave

[David Ackrill]

Having read the Agilent document, I think that I understand where the 6dB attenuator figure comes from as well.

Dave

On Wednesday, 29 May 2013 09:25:09 UTC, Ariel Rocholl wrote:

[Ariel Rocholl]

The design parameters are compatible with 1W sustained RF power, and 100W of pulsed power, for 1uS at 1% duty.

We tested the device with 1.5W continuous and found no problems, but have no device to test the 100W pulsed power so cannot guarantee that.

Regards. Ariel