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DC block and Tee adapter configuration for phantom supply?

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neazoi

neazoi

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Hello I am building this
**broken link removed**
and I would like to have a phantom supply for the LNA (supply voltage through the same rf coaxial cable).

Is my configuration of the DC blocks and the Tee adapters correct?

I am wondering about the Tee adapters losses as well as the DC blocks power handling capability.

Tee adapters I am using: **broken link removed**

DC blocks I would like to use: Mini Circuits, P/N BLK-18-S+ 0.01 to 18 GHz/Low Loss
 

The device you need is a "bias T". These are basically diplexers and will have 3 ports: "DC in", "RF+DC" and "RF". They will have a dc blocking cap on the "RF" path. Mini-Circuits (and others) sell integrated bias Ts that may work for you.

**broken link removed**

I see two Ts in your diagram, but there's no path in your sketch for current to get to the LNA?
 

pstuckey said:
The device you need is a "bias T". These are basically diplexers and will have 3 ports: "DC in", "RF+DC" and "RF". They will have a dc blocking cap on the "RF" path. Mini-Circuits (and others) sell integrated bias Ts that may work for you.

**broken link removed**

I see two Ts in your diagram, but there's no path in your sketch for current to get to the LNA?
Click to expand...
hello,
I have separated the T and the dc-block, instead of buying a bias-t. the t adapter I use is just connect the dc to coaxial without using any internal coil like a bias-t would do. can I use just a bias-t on the lna side and then just a dc block and a T adapter on the receiver side, or do I need two bias-T?
 
Last edited:

That SMA tee is going to have a very poor flatness on the thru RF path. At some frequencies, the port going to the DC supply will will act like a **broken link removed** going resonant. That will cause a deep notch in the insertion loss and loss at the adjacent frequencies.

You want a true bias-tee device, such that the AC block (inductor) is located directly on the RF line (electrically, very short).
https://en.wikipedia.org/wiki/Bias_tee
 

enjunear said:
That SMA tee is going to have a very poor flatness on the thru RF path. At some frequencies, the port going to the DC supply will will act like a **broken link removed** going resonant. That will cause a deep notch in the insertion loss and loss at the adjacent frequencies.

You want a true bias-tee device, such that the AC block (inductor) is located directly on the RF line (electrically, very short).
https://en.wikipedia.org/wiki/Bias_tee
Click to expand...

can I use just a bias-t on the lna side and then just a dc block and a T adapter on the receiver side, or do I need two bias-T?
 

neazoi said:
can I use just a bias-t on the lna side and then just a dc block and a T adapter on the receiver side, or do I need two bias-T?
Click to expand...

That depends on the DC biasing requirements of the LNA. Look at the spec sheet, it should tell you if you need to supply DC to both the input and output of the LNA. What LNA device are you using? (make/model #)
 

enjunear said:
That depends on the DC biasing requirements of the LNA. Look at the spec sheet, it should tell you if you need to supply DC to both the input and output of the LNA. What LNA device are you using? (make/model #)
Click to expand...
please see this url. **broken link removed** I have updated it with photos from the lna head, which is composed of different parts. the relays require 24v whrereas the amplifiers require 15v, which will be supplied by an on-board regulator.
 

Please post the part number or datasheet of your LNA.

Typically, dc power is fed into the amplifier on the "RF out" pin of the amplifier. In this case you would just need one bias tee, where "RF+DC" of the bias T would be connected to the "RF out" of the amplifier.
 

pstuckey said:
Please post the part number or datasheet of your LNA.

Typically, dc power is fed into the amplifier on the "RF out" pin of the amplifier. In this case you would just need one bias tee, where "RF+DC" of the bias T would be connected to the "RF out" of the amplifier.
Click to expand...
this is the amplifier **broken link removed** but since the head has other components on it (relays and second preamplifier) I think I need two bias-T.
have yo got any specs for the Agilent 33150A bias-T? basically the max current.
 

Your LNA has a discrete pin for Vcc. So you can't feed the power directly through the coax into the LNA. You can still run the DC power up the coax and then wire it over to the pin. In this case you still use a bias T but attached differently.

Connect the "RF" port of the bias T to the "RF out" port of the LNA. "RF+DC" will be facing away from the LNA. Then jumper two wires from the "DC" port of the bias T to the Vcc and ground pins of the LNA.
 

pstuckey said:
Your LNA has a discrete pin for Vcc. So you can't feed the power directly through the coax into the LNA. You can still run the DC power up the coax and then wire it over to the pin. In this case you still use a bias T but attached differently.

Connect the "RF" port of the bias T to the "RF out" port of the LNA. "RF+DC" will be facing away from the LNA. Then jumper two wires from the "DC" port of the bias T to the Vcc and ground pins of the LNA.
Click to expand...

Yes, I am going to use exactly this configuration. I will correct the transceiver diagram. bias-T are not so inexpensive as I thought though and I am going to need 2 of them, one for the lna and one on the other end...
 

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