RF bridge for antenna measurements

I got a comment that recommended this RF BRIDGE 0.1 – 3000 MHz from http://www.transverters-store.com/rf_bridge/rf_bridge.html. It looked really interesting as I was planning to build something similar myself. The price was very reasonable ($10) so I had to test out it. Did the ordering, and quite quickly I received a letter from Ukraine that contained this:

Here is the device:

Here is circuit diagram from the product page:

Here is test setup for testing a 450 MHz antenna with RF noise generator and RTL-SDR:

Here are two pictures: First is output terminated to 50 ohms and second with 450 MHz antenna connected to RF bridge output

 

Those measurements show that this RF bridge can be used successfully for antenna measurements. It gives quite similar performance than my previous measurements with directional coupler. The advantage of this bridge is that this can be used to measure matching other impedance than just 50 ohms – just use a suitable reference against which you want to compare matching (it can be 75 ohms resistor or something mote complicated). Based on this tests the RF BRIDGE 0.1 – 3000 MHz from http://www.transverters-store.com/rf_bridge/rf_bridge.html seems to deliver what it promises.

Here are some measurements on RF bridge with Rigol spectrum analyzer tracking generator up to 1.5 GHz. Those small grey adapters on the SMA connectors you see on the pictures are 10dB and 20dB 50 ohms attenuators that I use as close to 50 ohm terminator in this quick measurement…

 

7 Comments

  1. Tomi Engdahl says:

    $15 Ebay Return Loss Bridge
    https://www.youtube.com/watch?v=ct_ZUYTRkOA

    I evaluate a $15 RF Return Loss Bridge I purchased on Ebay and compare its performance against the $85 Directional Coupler I have previously been using for Return Loss tests.

    Dan Nelson
    4 kuukautta sitten
    Hi James, I think you might want to review your DUT setup procedure, I’ve swept the ZFDC-20-5+ and a ZFDC-20-5 on my Agilent VNA and found them to be exceptionally flat, nothing like what you are showing here.

    Reply
  2. Tomi Engdahl says:

    Boxed RF BRIDGE Compared
    https://www.youtube.com/watch?v=lqd_6s8ZfqM

    Evaluation of Ebay Boxed 500kHz-2500 MHz RF Return Loss Bridge with comparisons to the Mini-Circuits ZFDC-20-5 Direction Coupler used as a Return Loss Bridge, a $45 Boxed RLB and the $15 046 PCB bridge that I recently purchased on Ebay. Please note that the performance shown may not fully represent the capability of these RLB’s since I am not using 40dB Precision Reference loads or attenuators in this video since I do not have any available. I am using surplus Mil Spec loads however. These should provide better than 20dB return loss with most providing 25-30dB over the 0-1500 MHz frequency range of the DSA815-TG. I would recommend either of these RLBs for use below 500 MHz or so with the Boxed unit being the best performer from 500-1500 MHz. The boxed unit is available at: http://www.ebay.com/itm/121863951721 The PCB 046 unit can be found at: http://www.ebay.com/itm/332052527822

    Reply
  3. Tomi Engdahl says:

    3MHz-1200MHz RF Reflection Bridge Directional VSWR SWR Bridge/Antenna Analyzer
    https://www.banggood.com/3MHz-1200MHz-RF-Reflection-Bridge-Directional-VSWR-SWR-BridgeAntenna-Analyzer-p-1386844.html?p=27131452996820140438

    Widely used in the antenna measurement debug, debug and test RF matching circuits. Device swept return loss measurements.
    Microstrip circuit design, to meet the requirements of high frequency RF operating frequency range: 3MHz — 1200MHz.
    High directivity. Typical directional 30dB and 500MHz, 27dB and 1GHz, 26dBa and 1.2GHz.

    Specification:

    Working frequency range: 1MHz – 1200MHz
    High directivity: 1-30MHz 28dB
    30-1000MHz 33dB
    1000-1200MHz 27dB
    Insertion loss: 13dB
    Radio Frequency Interface: All three ports are SMA buses, and the general SMA buses with external threads and internal holes.

    Reply
  4. Tomi Engdahl says:

    #158: Directional Coupler Basics & how to sweep SWR of an antenna | Return Loss | VSWR
    https://www.youtube.com/watch?v=iBK9ZIx9YaY

    This video describes the basic properties and specifications for directional couplers, and shows their basic operation on an oscilloscope. Typical applications are discussed, along with a practical example showing how to sweep the VSWR, or Return Loss, of an antenna using a directional coupler and a spectrum analyzer with a tracking generator.

    Reply
  5. D J Long says:

    I bought one of these – it was useless Because:-
    The pairs of 100R resistors where not connected together; The wring of the cables through the ferrite was wrong.

    Reply
  6. Tomi Engdahl says:

    The I received worked and seemed to be built so that it matches the circuit diagram pretty closely.
    The major difference is that that on OUT there is no attenuation resistors, just one 0 ohm resistor.

    The 100 ohms resistors were wired as in circuit diagram.
    The wiring through ferrites match the circuit diagram?

    Do you mean your product was baddly build? (they need better quality control)
    Or do you think that the original design as shown in the circuit diagram is flawed?

    Reply

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