Questions tagged [transformer]

Impedance matching transformers as related to amateur radio.

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How to make a 1:2 UnUn

Does anyone have a drawing or instructions on how to make a 1:2 unun like the one in the picture below ? I searched this question on this site and on the internet with no luck.
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2 votes
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Resonant RF transformer using a piece of wire (no capacitors)

I previously posted this in electronics StackExchange here, but I believe Ham is more proper place for it as it closely relates to antennas. I'm curious if it is possible to build a spark-gap Tesla ...
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Current Transformers in Series versus a Single Voltage Transformer

I've read that the commonly used 49:1 (7t:2t) auto transformer for Multi-band End-fed Half-wave (EFHW) antennas has criticisms as not being very efficient. I haven't found any other designs that ...
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Is there value in grounding the virtual null in an auto transformer?

I've been learning how to make 49:1 auto transformers to run end fed half wave antennas. As I understand it, the twisted lead forms a zero voltage point which acts like a ground. Assume I'm using ...
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Why ferrite-core transformers are wideband while air-core are not?

While experimenting with end-fed antennas I've made two 1:49 transformers. The first one has an air core, as shown in the article by John, M0UKD. This transformer doesn't even work as a transformer ...
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Why does transformer in mcHF kit use coax?

I'm building my first kit, it's the mcHF SDR radio. Two of the transformers, which relate to the Power/SWR circuit (no further explanation given) use coax on one of the coils (and only one turn at ...
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6 votes
2 answers
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Purpose and sizing of capacitors placed across RF push-pull power amplifier transformer windings

I keep finding RF push-pull power amplifier designs specified with a small(-ish) capacitor across the primary (or secondary) windings of the coupling transformers. Here's an example: This is one ...
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What cause `multiply` has difference result between `float` and `complex` signal?

Construct 2 similar flow graph in Gnuradio,just different with data type. complex type data has a correct result.But ...
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Why does a sine wave show two peaks in the frequency domain on GNUradio?

I constructed the flow graph in GNUradio 3.7 as below: I know a sine wave has only one frequency, so what causes the frequency sink to show two peaks?
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Can an end-fed be fed with an Isolation transformer? [closed]

Typical half-wave end-fed antenna kits include either a 9:1 or 49:1 toroidal balun or unun, which is a transformer for impedance matching, but with one primary winding endpoint (for the coax shield) ...
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Can I wind my 9:1 unun with two wires instead of three?

All the 9:1 unun tutorials out there are using three wires to wind, but I was wondering if it is possible to wind it using two wires similar to how this 49:1 is built (https://elginradio.files....
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1:4 Guanella unun current balun

I am having trouble understanding the 1:4 Guanella current balun here. So at DC, or low frequencies, I think the current path would be a short to ground. At higher frequencies, I am getting confused ...
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1 vote
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How to cut phasing/transformer coax in a right way?

I'm building RHCP crossed dipole for 137 MHz satellites reception (I'm using 137.5 as a central frequency). My calcs are: frequency is 137.5 MHz λ is 2.18 m one dipole leg length equals to the λ/4 so ...
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10 votes
3 answers
2k views

Can a 1:1 transformer be used as a protection from static electricity?

It's well-known that under certain conditions verticals and dipoles can gather static charge, which is a common reason of transceiver damage. There are several ways to solve this issue. Some hams ...
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9:1 unun material and power loss

I need to build another 9:1 unun and I start searching for my toroids... (I have build 2-3 something like 4 years ago)... In parallel I checked on Google about the correct toroid etc so I found 2-3 ...
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Carrier telephone system adaptation

In amature radio, users can use what is called a phone patch to enable them to use a phone to establish connection to another party or user. Phones are usually two wire and dont lend themselves to ...
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1 answer
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How to measuring ferrite core efficiency vs frequency

There is an unknown ferrite toroid. I would like to figure out whether it can be used in an audio transformer, or maybe in a 1:4 transformer on given HF frequency. The experiment I came up with is ...
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2 answers
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Toroid Coupling Issue in Common-base Amplifier

I'm working on an old school VFO for the 15 meter band based on a JFET Hartley oscillator. The plan is to follow the oscillator section with a JFET buffer, then a CB amplifier (for increased reverse ...
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How to build a balun transformer for 2m RX with low insertion loss

I'm looking into ways to match a 137MHz RX dipole antenna to an unbalanced coax + amplifier. I know there are several types of baluns which can be categorized under magnetic baluns (where there are ...
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2 answers
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Broken IF Transformer (tiny and 455 KHz)

I broke so called 'IF transformer' on my radio. I was just slightly trying to regulate it to follow an instructions that is found on Wikihow page. My aim was to listen to the conversations of pilots ...
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7 votes
1 answer
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How can a quarter-wave transmission line transformer be implemented with lumped elements?

Sometimes designs call for quarter-wave sections of transmission lines. There are some situations when using actual transmission lines would not be practical: The necessary characteristic impedance ...
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9 votes
1 answer
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What's this "crossover" toroid winding called and what is its purpose?

I am winding an EFHW matchbox and many of the designs I've found (including the diagram provided with the kit I bought) include a sort of "twist" when winding them: (Image taken from this post and ...
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