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I am again involved an RF design and I am unsure on how to connect up the Balun, minicircuits application note suggests that it is dependant on the polarity/phase of the input signals (which makes sense) but I have seen conflicting implementations of the Balun in evaluation boards from analog devices.

The app note suggests a configuration like such:

{**+** ---- [P* S] --- **Out**}

{**-** ---- [P S*] --- **Gnd**} 

In order to achieve an output which is twice that of the input signal, and this is indeed my aim as I am using a frequency synthesizer with complementary RF outputs.

In the evaluation board I have seen:

{**+** ---- [P   S] --- **Out**}

{**-** ---- [P* S*] --- **Gnd**}

This is also complicated by the fact I am using a config K balun (Tri-Filar) from minicircuits, which also states in the datasheet that the primary port is/should be connected to ground.

So my question is, does the way in which I connect my signals to the Balun matter (either Primary or Primary*)? and should I be concerned about the config K datasheet telling me to connect the primary to ground?

Many thanks

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  • \$\begingroup\$ What RF frequency range are you looking at? \$\endgroup\$
    – Mike H.
    Feb 19, 2017 at 1:53
  • \$\begingroup\$ Three different types of Balun, in my system: 1.8 GHz (TC1-1-13MX+) 5.175 GHz (TCM1-63AX+) * 600 - 700 MHz (ADTL-12) * uses a Tri-Filar configured balun \$\endgroup\$ Feb 19, 2017 at 2:08
  • \$\begingroup\$ The RF frequency range is irrelevant anyway. I just needed to know if connecting them up backwards would render my system useless or not? \$\endgroup\$ Feb 19, 2017 at 12:38
  • \$\begingroup\$ The app note's circuit obviously transform from balanced to unbalanced while the datasheet's statement "Primary is connected to GND" obviously assumes that the primary side is the unbalanced side. Is this your problem? \$\endgroup\$
    – Curd
    Apr 27, 2017 at 9:28

1 Answer 1

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One instance wires the thing as a balun (Common mode choke), the second case is a transformer...

Usually you see the transformer configuration used up to maybe a 150MHz or so, with the balun configuration employed once things get fast, but your best approach is probably to try it both ways and see what the network analyser has to say.

The transformer configuration can be useful when DC isolation is desired, the balun when the non ideal nature of VHF transformers becomes a problem.

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  • \$\begingroup\$ Thanks for the reply unfortunately I do not have the component to hand nor access to a lab over the weekend. I have just seen however that the configuration in the evaluation board is using the transformer in a DC isolated CT configuration (ADTT1-1), whilst the datasheet circuit for the other balun uses a transmission line Tri Filer configuration. (TCM1-63AX+). I am guessing it makes a difference somehow. Ive just done a bit more digging around and how found yet another direct conflict with a suggested datasheet configuration (ETC1-1-13), this is leading me to believe it does not matter. \$\endgroup\$ Feb 17, 2017 at 23:46
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    \$\begingroup\$ Sometimes it does not matter, sometimes it makes a dB or so of difference to something that matters to you (IMD, SNR, Phase noise...). It is situation dependent, and best investigated by experiment. \$\endgroup\$
    – Dan Mills
    Feb 18, 2017 at 13:58
  • \$\begingroup\$ Thanks Dan, I have accounted for a potential loss through some insertable attenuators in my chain. As long as it works I am happy. Yeah as I said I dont have the luxury of testing it as I don't have any of the components in my design. \$\endgroup\$ Feb 18, 2017 at 14:30

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