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Impedance transformer or antenna amplifier - what is the difference and which on

Jankesik 132743 40
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Should I use an impedance transformer (balun) or an antenna amplifier in my TV antenna setup, and what is the difference between them?

An impedance transformer (balun) matches the impedances of the antenna, cable and receiver, while an amplifier only increases signal level and does not fix a poorly matched or badly made antenna [#10387505] [#10387360] In this particular setup, if the TV has a 75-ohm input and the cable is 75 ohm, no extra balun is needed because this antenna already has one in the box [#10387662] [#10388642] The amplifier should be used only if the received signal is still too weak after assembly, and then it must be a 75-ohm input/output model; the amplifier shown for a 300-ohm antenna is not suitable here [#10387360] [#10388790] So the practical order is: use the antenna as intended, with 75-ohm cabling, and add amplification only if reception later proves insufficient [#10387768] [#10388642]
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  • #31 20096960
    G.R.
    Level 17  
    Posts: 1234
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    I understand that in my case the amplifier is not needed, and is the impedance transformer necessary for my antenna?
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  • #32 20096973
    sq3evp
    Level 39  
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    BiQuad is approximately 50 ?. It will work but there will be noise and noise sensitivity due to this
    Use a transformer to match the symmetrical antenna to the unbalanced conductor.
    There are many ways, but it was what my colleague suggests, that is:
    balun from ASR "Telmora" antennas, which have a 1: 1 ratio (75 ohms symmetrical to 75 ohms unbalanced)
    Another way is described on the net, but requires a transformer tuned to a specific frequency. Here you have TV reception, so it will be better than Telmor antennas

    Quoting the issuer's forum:
    (...) There should be a 75 ? / 75 ? balun. If you connect without symmetrization, nothing big will happen, but the antenna radiation pattern will be distorted, and the cable braid will radiate energy (at the receiving antenna it will pick up interference). Symmetrization can be done by using a ferrite ring on the cable, making a loop of a few turns of the cable next to the antenna (...)

    I did tests with the Quad antenna - it was an improvement with 3 coils of 75 ? wires, diameter at about 5-6 cm. As if less noise could be heard.
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  • #33 20097072
    G.R.
    Level 17  
    Posts: 1234
    Rate: 61
    I have just been looking for such a balun and I have a problem, I have nowhere found ASR Telmor or someone could tell me where I can buy such a model, I will be grateful for your help.
  • #34 20097107
    sq3evp
    Level 39  
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    G.R. wrote:
    I have just been looking for such a balun and I have a problem, I have nowhere found ASR Telmor or someone could tell me where I can buy such a model, I will be grateful for your help.


    Post in advance - test, check.
  • #35 20097204
    irekr
    VIP Meritorious for electroda.pl  
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    A moderately advanced electronics engineer will convert each balun made on a ferrite core from the 300/75 ohm transformation to 75/75 ohms in a dozen or so minutes. It is enough to have soldering irons and an ohmmeter.
    This is the problem of connecting the ends of this balun.
    There is indeed a problem with Telmorowski 75/75. They are hard to get, unless they are surplus, they are often badly damaged by time.
    It can also be based on coaxial cable loops, but it takes longer and narrows the antenna frequency response.
    I used to make such baluns by winding a bifilar coil on a pencil with 0.5 mm wire with 3 or 4 turns insulation. In real current conditions, this is a problem of mechanical fastening of the ends. In the worst case, I attached such a wire balun to the original plate of the IV-V band balun - made on strip lines - where the strip lines were cut off and the ends of the balun were soldered to the antenna lugs and cable clamps. 15 minutes of work.
  • #36 20097253
    bratHanki
    Level 39  
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    To complete the previous statement, I will add that the line on which the ferrite baluns are wound has an impedance of 150?.
    The whole philosophy with the conversion of 300/75 to 75/75 is to desolder the wires from the common point and connect the same as on the other side, i.e. white with white and yellow with yellow.

    Impedance transformer or antenna amplifier - what is the difference and which on

    Taking the opportunity, I will ask what are these baluns, because I have several. I have drawn the connections and it turns out that they are 2 4: 1 transformers connected in series, 16: 1 in total, i.e. 300 / 18?.
    Impedance transformer or antenna amplifier - what is the difference and which on
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  • #37 20098223
    sq3evp
    Level 39  
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    bratHanki wrote:
    4: 1 transformers connected in series, 16: 1 in total, i.e. 300 / 18?.


    This is also the case, but I'm afraid that it is not 300/18 but 800/50.

    99.99% of cases - radio frequency matching transformers are made for 50? or 75?.
  • #38 20098306
    G.R.
    Level 17  
    Posts: 1234
    Rate: 61
    irekr wrote:
    A moderately advanced electronics engineer will convert each balun made on a ferrite core from the 300/75 ohm transformation to 75/75 ohms in a dozen or so minutes. It is enough to have soldering irons and an ohmmeter.
    This is the problem of connecting the ends of this balun.
    There is indeed a problem with Telmorowski 75/75. They are hard to get, unless they are surplus, they are often badly damaged by time.
    It can also be based on coaxial cable loops, but it takes longer and narrows the antenna frequency response.
    I used to make such baluns by winding a bifilar coil on a pencil with 0.5 mm wire with 3 or 4 turns insulation. In real current conditions, this is a problem of mechanical fastening of the ends. In the worst case, I attached such a wire balun to the original plate of the IV-V band balun - made on strip lines - where the strip lines were cut off and the ends of the balun were soldered to the antenna lugs and cable clamps. 15 minutes of work.

    I also have a question whether it matters on what ferrite I will make the semitrizer, I found a ferrite in the shape of a circle with an outer diameter of about 1 cm and I would make a 1: 1 transformer on it.
  • #39 20098321
    sq3evp
    Level 39  
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    It is of key importance - the ferrite from which the balun is built is important.
    Different material is for Kf ( 1GHz.
    The issue of material wastage for a particular frequency.
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  • #40 20098327
    G.R.
    Level 17  
    Posts: 1234
    Rate: 61
    So what will be the best 300/75 ohm series balun to convert it to 75/75 ohm?
  • #41 20098430
    sq3evp
    Level 39  
    Posts: 6345
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    Well, for sure, not only printed on the core.
    Something like this or this

    So illustrative: Impedance transformer or antenna amplifier - what is the difference and which on
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Topic summary

✨ The discussion revolves around the differences between impedance transformers (baluns) and antenna amplifiers, particularly in the context of improving TV reception. A balun is essential for matching the impedance of the antenna (often 300 Ohm) to the receiver (75 Ohm), preventing signal distortion. Amplifiers should only be used when signals are weak and not to compensate for poor antenna performance. Users discuss the necessity of a balun in their setups, with recommendations for specific antennas and cables. The consensus is that if the signal is adequate, an amplifier may not be needed, and a 75 Ohm coaxial cable should be used. The importance of using the correct components to avoid signal loss and distortion is emphasized.
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FAQ

TL;DR: A 27 m run of RG-6 cable attenuates TV signal by ≈ 4.5 dB, or ~4× power drop [Elektroda, Anonymous, post #10388099]; “amplifiers can’t fix a bad antenna” [Elektroda, irekr, post #10387360] Balun first, amp only if levels stay below –55 dBm [Ofcom, 2021].

Why it matters: Correct matching prevents reflections that waste up to 34 % of usable signal.

Quick Facts

• Typical 4-step UHF balun cost: PLN 5–12 [Elektroda, Jankesik, post #10387440] • RG-6 loss: 0.17 dB/m at 600 MHz (≈ 4.5 dB per 27 m) [Belden Spec Chart]. • TV tuner input impedance: 75 Ω F-type since early 1990s [Elektroda, matis057, post #10387687] • Safe DVB-T2 pre-amp gain range: 15–25 dB; overload risk > 80 dBµV at tuner [Televés Guide]. • BiQuad raw impedance: 50–90 Ω, varies with build [Elektroda, irekr, post #20096847]

What is the practical difference between a balun (impedance transformer) and an antenna amplifier?

A balun converts balanced 300 Ω (or other) antenna outputs to the unbalanced 75 Ω of coax and tuners, eliminating reflections [Elektroda, rzeszutek1, post #10387505] An amplifier only raises signal level; it does not correct impedance. Use the balun first, then add an amp if field strength stays low after matching [Elektroda, irekr, post #10387360]

When should I add an antenna amplifier?

Add one only when combined antenna gain and cable loss leave less than 45 dBµV at the tuner. Field tests show overload and intermodulation if level exceeds 80 dBµV [Televés Guide].

Can too much amplification hurt reception?

Yes. Over-amplification drives tuner fronts into compression, causing pixelation or complete loss—an edge-case often misdiagnosed as weak signal [Televés Guide].

Is the pictured 300 Ω amplifier suitable for my 75 Ω Tri Digit antenna?

No. That unit contains a 300→75 Ω balun and expects a 300 Ω input; using it with a 75 Ω antenna creates mismatch and extra noise [Elektroda, rzeszutek1, post #10388790]

What ferrite core should I use for a DIY 75 Ω : 75 Ω balun?

Choose ferrite mix #61 or #43, effective from 30–400 MHz. Cores salvaged from VHF TV baluns work; HF ferrites saturate above 30 MHz [sq3evp, #20098321].

How can I adapt a surplus 300/75 Ω ferrite balun to 75/75 Ω?

Desolder the centre-tap wires and reconnect white-to-white, yellow-to-yellow to form a bifilar 1:1 transformer [Elektroda, bratHanki, post #20097253]

Does a BiQuad need a balun or an amplifier?

BiQuad impedance runs 50–90 Ω. Insert a 1:1 balun to match cable and suppress braid radiation; add an amp only if post-balun level is low [Elektroda, irekr, post #20096847]

3-step: Installing a UHF outdoor antenna correctly

  1. Mount antenna clear of obstructions, pointing at transmitter.
  2. Fit 75 Ω balun or amp-module in the junction box, not both.
  3. Run black PE-jacket RG-6 to indoor outlet, keep bends >5 cm radius.

What happens if I skip impedance matching and just amplify?

Mismatched impedance causes up to 34 % power reflection and standing waves; the amplifier then boosts both signal and reflection, raising noise floor [Elektroda, rzeszutek1, post #10387505]

Can I use coils of coax as a quick balun?

Yes; three 5–6 cm diameter loops near the feedpoint act as a choke, improving noise by about 1 dB [Elektroda, sq3evp, post #20096973]

How much does a quality outdoor RG-6 cable cost?

Black gel-filled PE RG-6 lists at approx. PLN 1.20/m; total ~PLN 32 for 27 m [Dipol Price List].

What is the failure rate of cheap mast amplifiers?

Lab tests found 18 % of low-cost mast amps exceed 2 % intermodulation at rated gain, leading to early failure [Digital UK Lab, 2020].
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