Questions tagged [transformer]

Impedance matching transformers as related to amateur radio.

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Why do 9:1 ununs use type 2 material for the core?

I do not understand how a 9:1 unun wound on a T200-2 works. I understand the transformer voltage and current ratios. I have wound several toroid chokes and 49:1 ununs and know how they work. What is ...
Dereck's user avatar
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3 votes
3 answers
117 views

Question about Isolating Transformer NZART exam question

I found this question about isolating transformers in the NZART question bank, but I can't figure out the meaning of the answer. Either the answer is misleading or I'm fundamentally misunderstanding ...
spl's user avatar
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3 votes
2 answers
655 views

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.
Andrew's user avatar
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2 votes
1 answer
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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 ...
elgroovy's user avatar
1 vote
1 answer
110 views

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 ...
wbg's user avatar
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2 votes
1 answer
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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 ...
wbg's user avatar
  • 301
7 votes
1 answer
594 views

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 ...
Aleksander Alekseev - R2AUK's user avatar
1 vote
0 answers
93 views

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 ...
rcx935's user avatar
  • 401
6 votes
2 answers
415 views

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 ...
Buck8pe's user avatar
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0 votes
4 answers
311 views

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 ...
kittygirl's user avatar
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4 votes
2 answers
778 views

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?
kittygirl's user avatar
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-2 votes
2 answers
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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) ...
hotpaw2's user avatar
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2 votes
2 answers
636 views

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....
Richard Hum's user avatar
3 votes
2 answers
348 views

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 ...
Erik McKee's user avatar
1 vote
0 answers
102 views

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 ...
Drobot Viktor's user avatar
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 ...
Aleksander Alekseev - R2AUK's user avatar
3 votes
0 answers
1k views

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 ...
OHTO's user avatar
  • 149
-3 votes
1 answer
157 views

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 ...
Ben Madison KO4UXC's user avatar
7 votes
1 answer
3k views

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 ...
Aleksander Alekseev - R2AUK's user avatar
1 vote
2 answers
131 views

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 ...
Buck8pe's user avatar
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5 votes
1 answer
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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 ...
Felix S's user avatar
  • 153
0 votes
2 answers
928 views

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 ...
Karel Capek's user avatar
8 votes
1 answer
6k views

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 ...
Phil Frost - W8II's user avatar
9 votes
1 answer
2k views

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 ...
natevw - AF7TB's user avatar