Balum and Unun

Discuss commercial and home made antennas.
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Posts: 12
Joined: Sun Jan 14, 2018 8:10 pm

Balum and Unun

Post by jonesypeter » Mon Jan 13, 2020 8:15 pm


I'm trying to understand Baluns and Ununs. The more I read the more confused I get! I'm only interested in HF.

I understand that a Balun is for linking an unbalanced long wire antenna for instance to receiver input such as the 50 Ohm connector for the RTL-SDR.

I have looked at some of the videos on this site and have seen mention of the Nooelec one:

This one has two input connectors, but another I'm looking at on Bangood only has one - so how would it be earthed (assuming it needs this). ... 13917.html

I notice that Nooelec also do a combined balun and unun: ... bones.html

So my question is when is a balun a balun, and when is a unun a unun. I understand it means unbalanced to unbalanced, but I don't know when I would use it. and how it is different.

Sorry for all the questions, but I'm just getting more and more confused. I'm very confident with computers (its my job), but not with electronics.


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Joined: Sat Oct 05, 2019 10:13 pm

Re: Balun and Unun

Post by VE3EAR » Tue Jan 14, 2020 4:55 pm

A balun (balanced to unbalanced) and an Unun (unbalanced to unbalanced) are two very different devices. A balun is used, for instance, to connect a coax feed line to a half wave dipole. An unun is used to simply transform impedance from one value to another. A good example of this usage is the end-fed wire antenna, which can have quite a high impedance, to a coax of either 50 or 75 ohms.

You say your strength is in computers, but your radio knowledge is limited. Try to get an ARRL Handbook of any recent vintage. You'll find answers to almost any question you may have pertaining to radio in its many pages.

Bruce, VE3EAR

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BALUN and Unun

Post by snn47 » Tue Jan 14, 2020 5:51 pm

Have you read the information provided here? viewtopic.php?f=6&t=4649&p=10992&hilit=BALUN#p10948
antenna and cable can be symetrical e.g. dipole or parallel wire cable and asymetrical e.g groundplane and coax cable.
A Balun adopts symetrical devices to a or unsymetrical ones, e.g. dipole to coax.

However BALUN can not only be used to Balance/Unbalance dipole to a coax cable but also to provide an additional impedance transformation e.g. 4:1 folded dipole ~240 Ohm to match asymetrical 60 Ohm coax cable.
UNUN is a impedance transformation between asymetrical devices.

Both can be made numerous ways e.g. ferrite cores or coax cable.

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Joined: Sun Jan 14, 2018 8:10 pm

Re: Balum and Unun

Post by jonesypeter » Tue Jan 14, 2020 7:01 pm

Thanks for the answers. I found online a copy of the ARRL hardback from a few years back.

So if I use something like the NooElec balun that I linked to above which has the RG174 connector, do I need is it OK to connect that via the '3 meter RG174 extension cable' that comes with the SDR-RTL USB stick, or will that cause issues? Does the included cable count as coax?


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