Hi,

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Most Distribution Amplifiers have one Input and several Outputs. When connected to multiple devices, you want good isolation both filtering and galvanic. It is very easy to run into a Ground Loop between instruments OR Other Items attached to the equipment set up (like an EUT) or even a chamber wall. Here are a few ideas for preventing that problem…

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HP5087A - Distribution Amplifier

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A good older inexpensive Distribution Amplifier is the HP5087A with the 10MHz Input and 12 Isolated 10MHz Outputs. They were configurable when they were ordered.

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It has 3 separate Inputs Options.

Option 31 has a 5MHz, 1MHz, and 100kHz Inputs. They split out to 4 each 5MHz Outputs, 4 each 1MHz Outputs, and 4 each 100kHz Outputs.

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Option 32 has one 5 MHz Input and 12 each 5MHz Outputs.

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Option 33 has one 10MHz input and 12 each 10MHz Outputs.

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Option 34 has one 5MHz Input that splits out to 4 each 5MHz Outputs, and includes a divider chain to provide 4 each 1MHz Outputs and 4 each 100kHz Outputs.

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If you see one for sale, make sure it has the Frequencies that you want.

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Each of the 12 Output Amplifier Modules include Filtering for High Isolation and purity. They also include independent Power Filtering, Phase-matched Push-Pull Output Amplifiers with Tuned-Output Transformer Coupling capable of at least 5V P-P Signal Levels into 50 Ohm Loads. Each Output is independently adjustable from 0 to 3V RMS. A Switchable Panel Meter shows the selected level of each output.

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Each Output is independently adjustable from 0 to 3V RMS into 50 Ohms. Other specifications include Load Isolation of 50dB minimum, SSB Phase Noise is down 145dB , Channel-to-Channel Crosstalk is down 60dB and Non-Harmonic content is down 80dB.

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One thing to be aware of is that this device and the Fluke device listed below do not galvanically isolate the outputs. Some of that is to control EMI, some to establish the Distribution Amplifier as the Master Ground. You may run into a Ground Loop situation. If that occurs, refer to the information on the Mini-Circuits Isolation Transformer listed below. I have used the Mini-Circuits solution effectively many times to solve a Reference Distribution Ground Loop Issue.

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Fluke 203A - Distribution Amplifier

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HP also made a rebranded Fluke 203A. It has the same options and specifications.

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Argo Systems AS-211

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Another good option is an Argo Systems AS-211. This is my 10MHz House Reference and Distribution Amplifier. It includes an Efratom FRK Rubidium Source, Independent Filtered Power, Filtered and Isolated Output Channels. It works very well and the FRK can be GPS Disciplined. I like it a lot.

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It can also be configured (Modified), to have an external reference (like a GPS Disciplined OCXO input), to be an input instead of the FRK and Output to the Distribution Amplifier.

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Video Distribution Amplifiers

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Lots of other less expensive Distribution Amplifiers out there. I tried the Video Box thing and wasn’t satisfied. Some of these I have heard work well.

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10 Base-T Ethernet Transformers

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By the way, the Old Ethernet 10 Base-T Output Transformers on Ethernet PC Cards can work to Isolate each Output from others.

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Ground Loop Isolation Transformer

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Mini-Circuits also makes a really good Isolation Transformer FTB-1-1+ that provides very high isolation.

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These can be used to solve individual Equipment and System-wide Ground Loops. It is a 200kHz to 500MHz Full Isolation Transformer. It breaks the galvanic return path of the equipment or Reference Distribution System. It forces the offending equipment to stay on its own Ground Return or Earth Return.

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You can isolate one equipment or a string of equipment. It can also help break the Return Path for Equipment Under Test (EUT) situations.

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It is BNC FM In and BNC FM Out. They also make a Male/Female version too. You just patch it in place.

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My opinions only. Good luck.

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Ross

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