Masters Communications

0.5 - 1500 MHz, 50 ohm Return Loss Bridge - $299.00
Phone: (814) 313-4036

Currently accepting orders.

Email Masters Communications
We generally respond to email the quickest.

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Made in the USA!
Each bridge is hand made in our Warren Pennsylvania shop.

What is it, and what does it do?
A return loss bridge can turn your service monitor or signal generator / signal receiver into an accurate antenna VSWR analyzer. It will provide the same accuracy as antenna analyzers costing thousands more. The RLB1500 is a commercial duty 50 ohm, 0.5 - 1500 MHz return loss bridge (RLB) for antenna/feed line, cavity, and duplexer testing and alignment. Our bridges are individually built and tested and include an actual proof of performance graph. This unit has a 0.5 - 1500 MHz range and minimum 35 dB directivity (40 dB typical). The unit has high quality type N connectors for all ports and is configured with the input and output ports conveniently on the same side. The design will withstand 4 Watts of accidental power input to the DUT port. Use your existing rf generator and receiver/power meter/spectrum analyzer to make accurate measurements. The unit is designed for use in 50 ohm systems.

The basics of a Return Loss Bridge:
In simple terms, the return loss bridge is a device used to measure RF power reflected from a load or device under test (DUT) when power is sourced to the device through the RLB. The return loss bridge has 3 ports. An RF signal generator is applied to the input port. The output port provides an RF signal to go to a measuring device such as a spectrum analyzer, power meter or other device used to measure this signal. The DUT port connects to the device that you are testing (antenna, coax, etc.). A signal is generated into the input port. The RLB applies this signal to the DUT. The DUT will reflect a portion of the signal that it receives (due to impedance mismatch). This RF signal appears at the output port. The closer your DUT impedance is to 50 ohms, the lesser the signal will be at the output port. A perfect 50-ohm DUT will have no reflected power so a perfect RLB will have no output signal at its output port (infinite return loss). If a non-50-ohm load is at the DUT port, there will be an RF signal at the output port. The extreme cases are for the DUT to be a short or an open connection. This will cause maximum reflected power and, therefore, maximum signal at the RLB output port. Return loss is measured from the worse case (short or open) with 100% power reflected. It's the difference amount in dB of the reflected signal of your DUT compared to the worst case reflected signal. The further you go from "worse case" the better. The higher the return loss number, the closer the DUT is to 50 ohms. This is somewhat the opposite when compared to SWR (high SWR means high reflected power or poor match) For example: with an open or short connected to the DUT port and an RF signal source generating into the RLB input port, let's say we measure the RF power at the RLB output port to be -22 dBm. If the open or short were replaced with your load at the DUT port, the amount of power at the RLB's output port would then change. If the output signal is now measured to be -42 dBm, this would be a return loss of 20 dB. The amount of reflected power is 20 dB less than the worst case. This is equal to an SWR of 1.22:1. If this were an antenna, it would be considered an excellent match with about 1% of the power to the antenna reflected. A return loss of 10 dB would correspond to an SWR of 1.91:1 with 10% of your power reflected. This is generally considered a poor match. Most commercial systems want to see a return loss of 18 dB or better.

Directivity is the measure of how well the RLB isolates two opposite traveling (forward and reflected) signals. As the reflected signal becomes smaller and approaches the specified value of the RLB directivity, the measurement uncertainty becomes larger. To get accurate return loss (SWR) measurements, it's important to have a bridge with directivity of 10 to 20 dB higher than what you want to measure. The higher the directivity, the greater the accuracy the RLB can measure small signal levels of reflected power. A perfect 50-ohm load should have infinite return loss, which translates to no output signal from an RLB. If we could build a perfect RLB, the output port would show no signal with a perfect 50-ohm load. In the real world, the highest quality RLB would show a return loss of up to 50 dB. 50 dB would be pushing the physical limits because the N connector itself has a tiny amount of return loss. A higher quality bridge will have higher directivity than needed to provide better accuracy at all levels. The RLB1500 has guaranteed directivity of 35 dB with typical directivity being 40 dB or better over the 0.5 - 1500 MHz range. A 20 dB directivity means that you'll see as little as 1% of reflected power. A directivity of 30 dB is 0.1% and 40 dB is 0.01% ( 1/10000 of worst case reflected power level). The RLB1500 return loss bridge is individually tested and includes a performance evaluation graph.

RLB1500 Return Loss Bridge

Using your RLB
Many service monitors have "swept return loss or SWR programs" built in. When used with a return loss bridge, these programs provide a frequency vs. return loss graph on your screen. You need two cables. One is from your service monitor output port (RF Source) to the RLB input port, the other is from the RLB output to your service monitor's antenna port (RF Measurement). Your service monitor will poll you to "begin test" with an open or short connected to the DUT port. It will then have you connect your DUT (antenna or coax) to the DUT port. It will then give you a graph of your DUT performance. There are many ways to capture and save this graph for later viewing or comparison. Try not to move your cables or RLB from the time you start the cal with the open or short until after the sweep of your DUT. At higher frequencies, this may cause errors in the results. If your service monitor does not have a Swept Return Loss Program, you can still use the bridge in a manual method. Similar to above, you need to connect a signal source to the RLB input, and some device to the RLB output port to measure the RLB output. This can be a spectrum analyzer or power meter. Generate a 0-dBm signal with your source. Set your signal source to the desired frequency and measure the RLB output with an open or short connected to the DUT port. The RLB output is viewed with your spectrum analyzer or power meter. You can check one frequency, several, or sweep up and down and note the signal level(s). Now connect your DUT to the DUT port. Observe your power reading on your spectrum or power meter. Subtract your original reading from this reading (or vice versa with negative numbers) and this is your return loss. To test your RLB, it's necessary to have a precision 50 ohm termination. This will allow you to sweep your RLB from 0.5 - 1500 MHz to make sure its working properly. If your service monitor has a RLB program, you should see return loss vs. frequency similar to the graph on the left below. We offer the Narda 370 BNM, 50 ohm N male termination for testing this RLB. Off-Site link - Using your RLB with HP's RF Tools Software

Typical Performance:


Here is a typical return loss graph printed from an HP E6380A Service Monitor. The left graph shows the typical response when sweeping the Narda 50 ohm precision load. Sweeping to 1500 MHz shows this return loss bridge is working properly with a better than 35 dB directivity over this range. The graph on the right is a sweep of a 10-meter yagi antenna. At the top, the maximum return loss was 15 dB at 28.6 MHz. Generally, you want to sweep just 1-2 MHz to get the resolution needed to see the best impedance match, as well as the usable frequency range. The RLB1500 is a valuable tool for duplexer tuning, as the frequency which exhibits the lowest insertion loss and the frequency which exhibits the best impedance match may not coincide.

See this off-site link: Duplexer Tuning with a similar return loss bridge for details.

The RLB1500 was compared to several higher priced units and provided similar results for return losses below 40 dB.

VSWR Return
1.01 46.1 0.0 100.0
1.02 40.1 0.0 100.0
1.06 30.7 0.1 99.9
1.10 26.7 0.2 99.8
1.20 20.8 0.8 99.2
1.22 20.0 1.0 99.0
1.30 17.7 1.7 98.3
1.50 14.0 4.0 96.0
1.91 10.0 10.0 90.0
2.00 9.5 11.1 88.9
3.00 6.0 25.0 75.0
4.00 4.4 36.0 64.0
5.00 3.5 44.4 55.6

Pricing and Ordering Instructions

To place an order, call (814) 313-4036 or, preferably, email Masters Communications We generally respond to email the quickest.

RLB1500 0.5 - 1500 MHz RLB (includes performance chart) Specifications $299.00
Narda N male 50 ohm 35 dB precision test load with chart (these are hand-selected, used / tested) $40.00
MCL N male 50 ohm 40 dB+ precision test load with chart (these are hand-selected, used / tested - limited quantity) $75.00
QTY=2 - 24 inch N male to BNC male RG400 (made from new cable w/ H&S connectors) test cable set (2 cables - for input and output connections) $40.00
QTY=2 - 24 inch N male to N male RG400 (made from new cable w/ H&S connectors) test cable set (2 cables - for input and output connections) $40.00
6 dB BNC to BNC fixed attenuators (QTY=2) for cable end to your equipment $35.00
6 dB N male to N female fixed attenuators (QTY=2) for cable end to your equipment $49.00
Huber Suhner 4901.17.A 50 ohm power divider (used for distance to fault measurements - New) $250.00
RLB1500 Kit with Narda load, carry case, and test cable set (choice of N or BNC) $439.00
RLB1500 Kit with Narda load, carry case, (2) 6 dB BNC to BNC attenuators, and BNC cable set $459.00
RLB1500 Kit with Narda load, carry case, (2) 6 dB N to N attenuators, and N cable set $473.00
For HP8920 and 8921 owners:
RLB1500 Kit with Narda load, carry case, (1) 6 dB BNC to BNC attenuator, (1) 6 dB N to N attenuator, (1) N to N cable and (1) N to BNC cable
RLB1500 Super Kit:
Includes carry case, Narda load, test cable set (your choice N or BNC), (2) attenuators (your choice N or BNC), and the Huber Suhner Power Divider
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Payment Methods:
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We will invoice you through PayPal for convenience in payment and shipping.
We will accept your company check. Must clear before your order is processed for shipment.

This web page, this web site, the information presented in and on its pages is © Copyrighted 1995 and (date of last update) by Kevin Custer and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.

Updated as of date below - Kevin Custer