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Why twist the wire in RWTST? What purpose does it serve?
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73
Karl
KI4ZUQ
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You are trying to increase the coupling.
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For the same reason we use coax to feed our antenna, instead of just
running a piece of copper wire from transmitter to antenna.
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A twisted wire pair has a characteristic impedance, similar to coax.
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I'd guess the twisted wire pair used in T501 is higher than the desired impedance of roughly 50 ohms.
Hence the assembly instructions suggests that more tight twists is better.
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From ?
It is generally necessary to control terminating impedances of RF signal paths, especially in
wideband applications where path lengths are not negligible relative to wavelength. Wideband
RF transformers are wound using twisted wires which behave as transmission lines, and the
required coupling occurs along the length of these lines as well as magnetically via the core.
Optimum performance is achieved when primary and secondary windings are connected to
resistive terminating impedances for which the transformer is designed. Transformers having
a turns ratio of 1:1, for example, are typically designed for use in a 50- or 75-ohm system.?
?
?
Jerry, KE7ER
?
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On Tue, Dec 17, 2024 at 05:43 AM, Karl wrote:
Why twist the wire in RWTST? What purpose does it serve?
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It's thoroughly explained in the assembly instructions.
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Al
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It's thoroughly explained in the assembly instructions.
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Yes, I got the part that it works better for more power out in the higher bands. I would have stood on my head whilst winding if the instructions said it would work better! Har, har!
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I then conclude the REASON it works better is better coupling than untwisted. Is that correct?
73
Karl
KI4ZUQ
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This deserves a better answer than I can give.
The twisted pairs are using 1 wire from the input winding and 1 wire from the output winding,
not the more obvious 2 twisted wires on the input winding and two twisted wires on the output winding.
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"Tighter coupling" between two twisted wires (or between inner and outer conductors in coax)
gives a lower characteristic impedance.
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A very tightly twisted pairs of 28 awg wire will have a low characteristic impedance,
approaching that of coax.
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On Tue, Dec 17, 2024 at 06:12 AM, Jerry Gaffke wrote:
For the same reason we use coax to feed our antenna, instead of just
running a piece of copper wire from transmitter to antenna.
?
A twisted wire pair has a characteristic impedance, similar to coax.
?
I'd guess the twisted wire pair used in T501 is higher than the desired impedance of roughly 50 ohms.
Hence the assembly instructions suggests that more tight twists is better.
?
From ?
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On 17/12/2024 14:21, Karl via groups.io wrote: I then conclude the REASON it works better is better coupling than untwisted. Is that correct? Karl, The first paragraph of the Assembly instructions tells of the painstaking development of the transformers. It tells of many experiments, carefully tested, of the final best outcome. As far as I know there has not been an exhaustive truly scientific examination. I think nobody has the equipment required. 73 Alan G4ZFQ .
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RF transformers are well understood.
But not by me.
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In my last post I said:
The twisted pairs are using 1 wire from the input winding and 1 wire from the output winding,
not the more obvious 2 twisted wires on the input winding and two twisted wires on the output winding.
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If the input side was a complete twisted pair (or coax) passing through the core a few times,
the net current through the transformer from the input would be zero, an no energy would be coupled to the output.
That works well as a common mode choke, preventing energy from the antenna system from coming back down
into the shack along the skin of your transmission line coax.? But does allow differential currents to flow unimpeded.
So we often see cores wound with coax.
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A broadband transformer like T501 is a bit more complicated.
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Jerry, KE7ER
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On Tue, Dec 17, 2024 at 06:59 AM, Alan G4ZFQ wrote:
As far as I know there has not been an exhaustive truly scientific examination. I think nobody has the equipment required.
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Here is an article that explains it for me:
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My take is that the twisting of the wires together adds to the magnetic coupling due to the coiling of the wire.?
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73
Evan
AC9TU
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Karl, the instruction page for the output transformer said it helps avoid a very low parasitic resonance on bands from 20 meters and higher.
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73, Dan - W2DLC
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For me, the output increased considerably by winding my 12volt QDX HighBand with RWTST
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T1 Original winding
20m / 2.5Watt / 12.8V / 0.55Amp
15m / 2.1Watt / 12.8V / 0.54Amp
10m / 2.1Watt / 12.8V / 0.53Amp
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T1 RWTST winding
20m / 6.6Watt / 12.8V / 0.89Amp
15m / 6.5Watt / 12.8V / 0.86Amp
10m / 6.0Watt / 12.8V / 0.75Amp
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After rewinding I have reduced the voltage to 11 volts so as not to go much over 5Watt.
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Lasse
?
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I believe the 9v version of the QMX's T501 is a fairly straight transmission line transformer with a 1:1 turns ratio
using twisted wire for a transmission line.
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The 12v version of T501 needs a 3:2 turns ratio which can't all be done as a transmission line transformer,
so that is supplemented by an additional single wire winding which acts more like a normal transformer.
Which is "really weird".
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Still trying to fully understand it, this seems to be the best explanation I've found yet:
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Jerry, KE7ER
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On Tue, Dec 17, 2024 at 05:43 AM, Karl wrote:
Why twist the wire in RWTST? What purpose does it serve?
It serves the purpose of working better than not twisting it.? ? We can spend all week speculating or debating or citing theories as to why but that's not the priority here?
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For some of us, the priority here is operating.
For others, it is learning and understanding how this fascinating radio works.
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Personally, I have never had much interest in operating.
I do most of my communicating via email and web forums.
Occassionally get up out of my chair to talk to the neighbors.
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Jerry, KE7ER
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On Fri, Feb 21, 2025 at 07:32 AM, Bruce Akhurst wrote:
On Tue, Dec 17, 2024 at 05:43 AM, Karl wrote:
Why twist the wire in RWTST? What purpose does it serve?
It serves the purpose of working better than not twisting it.? ? We can spend all week speculating or debating or citing theories as to why but that's not the priority here?
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What does the acronym 'RWTST' mean, or translate into?? Mr Google has not been helpful.
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Really Weird Twisted Sister Transformer.? This is the 12-volt version of the Wierd Twisted Sister Transformer for 9 volts.
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This is in the transformer manual introduction:
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73
Evan
AC9TU
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Karl; There's a longish thread back when the high-band QDX was being built by many, but output power was not as high as many would like. /g/QRPLabs/message/101412Han's adopted the twisted winding method developed by EX0AA et al. vy 72 de Russ, va3rr
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Hi all,
A quick comment about twisting the wires for the transformer: The twisting increases the coupling coefficient , k, between the windings. This reduces the leakage inductance (1-k), thereby improving efficiency of the transformer.
Milt w8nue
toggle quoted message
Show quoted text
On Feb 21, 2025, at 4:16?PM, va3rr via groups.io <va3rr@...> wrote:
?Karl;
There's a longish thread back when the high-band QDX was being built by many, but output power was not as high as many would like.
/g/QRPLabs/message/101412
Han's adopted the twisted winding method developed by EX0AA et al.
vy 72 de Russ, va3rr
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Inquiring mind wanted to know
Thanks
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Karl
Al Scanandoah
Daniel Conklin
Bruce Akhurst
Jason
va3rr