9:1 unun ?

Jeg hygger mig lidt med at lave en 9:1 unun. Undervejs undrede jeg mig over at viklingerne skal lægges så pænt ved siden af hinanden.

Så jeg lavede et eksperiment med nogle små ferrit toroider. To med pæne viklinger og to med snoede viklinger. De to 450ohms viklinger blev forbundet. Jeg kunne efterfølgende ikke måle nogen forskel med en NanoVNA.

Er der en fysisk forklaring eller er det bare tradition?

/niels, oz9ny

Svar til #1:
Hej Niels,
den fysiske forklaring er at det du laver er en transmissionslinietransformer, hvis du sørger for at viklingerne har en impedans svarende til den impedans de tilsluttes får du minimum flux i kernen og dermed lavere tab.
(og at den kan håndtere en større effekt som biprodukt )
Dette kan opnås med et vis forhold mellem ledernes diameter og deres afstand og/eller ved at sno dem.
Hvis viklingerne ligger pænt og stramt ved siden af hinanden får du også lavere spredningsselvinduktion.
Du kan f.eks. lave et stykke snoet kabel så vil du opleve at antal snoninger pr. m ændrer impedansen.
Jerry Sewick har lavet en bog der forklarer de nærmere omstændigheder.
Hilsen
Frank

Svar til #1:

Kig på G8JNJ's målinger, anbefalinger og opskrifter - og nej han twister ikke nødvendigvis lederne:

G8JNJ: Baluns and Tuners:
https://web.archive.org/web/20170219191746/http: //www.g8jnj.net/balunsandtuners.htm
Citat: "...
As before I tried constructing many different baluns before I realised that they didn’t work correctly. Most ‘voltage’ baluns or auto-transformer designs don’t work at all well, unless you get the materials or construction exactly right. The simplest and most reliable method I have found is to use two 1:1 current baluns connected in series / parallel. It is important to use type 61 or type K core material if you want to obtain the best results. As other ferrite materials intended for EMC suppression purposes are too lossy and present a noticeable shunt resistance which restricts the maximum impedance transformation ratio that can be obtained.
...
I made a 4:1 Unun consisting of 12 bifilar twisted turns of 18AWG silver plated stranded wire. PTFE insulation, 1.85mm outer dia (CPC part number CB10433) wound on single FT240-61 core.
This gave good performance from 1.8 to 52MHz, with less than 0.1dB loss over most of the range up to 30MHz, and approx 0.5dB at 50MHz. This was measured with a miniVNA by halving the loss of two Ununs connected back to back I could have added more turns without affecting the performance over 1.8 to 30MHz (I started at about 15 turns) but I found could achieve sufficient bandwidth to include 50MHz by sacrificing a bit of additional loss at each end of the operating range.
...
9:1 ‘Voltage’ Unun construction.
Similar to the 4:1 unun, but this was even more difficult to get working. I finally got good performance from 1.8 to 30MHz, with less than 0.5dB loss over most of the range up to 30MHz,
Optimised with 6 trifilar turns of 18AWG silver plated stranded wire. PTFE insulation, 1.85mm outer dia (CPC part number CB10433) wound on FT240-61 core.
..."

og:

Balun construction:
http://web.archive.org/web/20170806130801/http: //www.g8jnj.net/Balun%20construction.pdf
Citat: "...
[Ekstra:]
...
The easiest way to identify most ferrite materials is to wind about four turns of wire through the core and then measure the lowest frequency at which the value of reactive impedance equal resistive impedance i.e. X=R. There will be some variation between different batches and sizes of materials. But if you can plot the results graphically you can easily identify the 'signature' of each material.
Here are my references for some common ferrite materials
FT240-77 0.74MHz
FT240-31 3.5MHz
FT100-33 7MHz
FT240-43 17MHz
FT240-K 22MHz
FT240-52 31MHz
FT240-61 58MHz
Iron powder has a slightly different 'signature' it usually has a very low resistive component, which peaks to a higher value near self resonance. The more lossy the material the broader and lower value of resistive peak is apparent.
T200-52 40MHz Lime Green (& Blue or Red) colour common in PC switch mode power supplies - moderate loss
T200-26 60MHz Yellow & White colour common in PC switch mode power supplies - high loss
T200-2 60MHz Dark Red colour used for HF tuned circuits (& Ruthoff Ununs) - high Q low loss
T200-1 70MHz Blue colour not common - moderate loss
T200-6 100MHz Yellow colour used for VHF tuned circuits - high Q low loss
..."

Svar til #2:
For en transmissionslinje transformer skal impedansen ideelt være den geometriske middelværdi af input og output impedansen dvs.
Zo=SQRT(Zin*Zo). for zin=50 og zout=450 fås Zo=150 ohm.
Ved afvigelser fra denne impedans kan båndbredden reduceres

Svar til #3:

Tak for henvisningerne.

Nedenstående afsnit bekræfter mine simple nanovna målinger:

9:1 ‘Voltage’ Unun construction.
Similar to the 4:1 unun, but this was even more difficult to get working. I finally got good performance from 1.8 to 30MHz, with less than 0.5dB loss over most of the range up to 30MHz,
Optimised with 6 trifilar turns of 18AWG silver plated stranded wire. PTFE insulation, 1.85mm outer dia (CPC part number CB10433) wound on FT240-61 core.
..."

Så jeg laver min 9:1 med tre sammensnoede tråde :-)

/niels, oz9ny
PS Så er der også noget at snakke om :-)

Svar til #1:

Citat: "...
To med pæne viklinger og to med snoede viklinger. De to 450ohms viklinger blev forbundet. Jeg kunne efterfølgende ikke måle nogen forskel med en NanoVNA.
Er der en fysisk forklaring eller er det bare tradition?
..."

Jo mere snoning per meter - jo mere kapacitans per meter - jo lavere karakteristisk impedans.

Kunne du prøve at teste om en snoet ledningspars impedans bliver påvirket af at blive snoet om en ringkerne - i forhold til fri luft?

Balun construction:
http://web.archive.org/web/20170806130801/http: //www.g8jnj.net/Balun%20construction.pdf
Citat: "...
The design of the windings is particularly important for good high frequency performance and low loss. Loss can be minimised by using windings constructed from twisted bifilar, trifilar or coax instead of insulated wire.
The windings must be electrically much shorter than ¼ wavelength (including velocity factor of the cable) at the highest required operating frequency.
...
The characteristic impedance (when measured as a transmission line) of the wire or coax used to wind the transformer do not seem to dramatically influence the performance. However twisted bifilar or trifilar windings or coax provide better coupling between sets of windings and reduce loss.
...
There are four main recommendations:-
...
2. The windings need to be as short as possible, ideally less than 1/4 of a wavelength at the highest operating frequency.

3. Use windings which have as low loss as possible. Twisted bifilar or trifilar wires or coax can be used for this purpose. There is very little difference in performance between Ruthroff transformers built using windings with a characteristic impedance of 50, 75, 95 or 120 ohms.
..."

Svar til #5:
Hej Niels

Præcis som du skriver --- 9:1 med 3 sammensnoede tråde -det virker perfekt her på stn.OZ6AI -i ganske mange år :-))
Vy 73 // Asbjørn