Heinz,
What type of Toroid can you recommend that has good efficiency characteristics to replace the FT240-43 and able to handle 100watts power output on SSB?
73’s
Jundy
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Jundy,
You have probably already read that to answer your question you cannot simply apply a simple rule of three calculation to resize a toroidal core for a specific criterion.
As Owen Duffy has repeatedly shown for years, the efficiency of an impedance transformer is determined by 2 main criteria
-
the quotient of the toroid cross-section and the mean field line length and
-
the magnetizing impedance created by the primary winding.
The calculated transformer efficiency for 2 stacked FT-140-43 cores with 3 primary turns is approx. 92%.
For operating modes such as SSB (and CW) 2 stacked FT-140-43 ferrite cores could just about suffice for a transmission power of up to 100 watts, but only if 3 primary turns are used.
Enamelled copper wire of 0.7 or 0.75 mm and a mica capacitor 100 pF/500 volts are recommended, as well as tight winding without gaps and short connecting wires from the transformer and capacitor.
Remarks
Impedance transformers with high coupling ratios in the range of 1:49 to 81 are suitable for use with half wave antennas or multiples thereof. If the wire length is precisely adjusted for a specific antenna geometry, it is possible to use several (harmonic) frequency bands without an antenna tuner.
When operating with random wire lengths, not only an antenna tuner is mandatory, the common mode currents that occur with high SWR could make the use of a common mode choke necessary (e.g. in the coaxial cable about 3m after the impedance transformer).
Many of these serious problems do not interfere with QRP transmit power and can therefore be neglected. If you know what I mean, hi.
73 gl, Heinz
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I don’t think high SWR has anything to do with common mode current.
Hi Jundy,
I agree with the explanations and proposals of @HB9BCB.
If you only want to use one toroid core, Owen Duffy analyzed an alternative one with an interesting geometry: Another small efficient matching transformer for an EFHW – 2643251002 – #1 – design workup – owenduffy.net
In the last article about this core he makes a heat measurement with 50W carrier: Another small efficient matching transformer for an EFHW – 2643251002 – #3 – thermal measurement – owenduffy.net
73 Stephan
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I would like to point out that the losses depend significantly on the frequency.
From my experience, the FT140-43 Amidon with 100W SSB can be used from 10m to 40m without any problems. This only applies to EFHW antennas that are in resonance, e.g. a 20m long wire freely suspended on 40m, 20m, 15m and 10m.
The wire lengths of perhaps 22m or 25m, which are often used without hesitation, require a tuner and can cause the toroidal core to overheat at outputs of over 10W due to the reactive power.
73 Chris
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Yes, that is indeed an oversimplified statement that should not be left as it is.
In the present case of an EFHW transformer, an impedance mismatch is practically unavoidable if the very high-impedance antenna radiator is connected to the feed line impedance via the impedance transformer. This is not only reflected in the SWR value, but also allows a common mode current to flow on the outside of the coaxial screen (which also radiates and thus affects the antenna characteristics).
When connecting antenna radiators of random length or when operating EFHW radiators at random wavelength, this impedance mismatch and thus the influence on both the SWR and the common-mode current increases significantly.
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Hello Heinz,
As i am currently digging for some other ways to improve my EFHW antenna set up for my fixed station, i was surprised to came across with these this new found investigation of Owen Duffy which was explained further by Stephan in his article posted and shared on facebook together with the persistent validation and work of NY4G in this forum and obcourse with the aid of your utmost collaboration.
I am now in my 10years of spending my spare time for this hobby and i am grateful for having this new found information as i am also in a process of having my next homebrew project for portable used.
Thank you much for the reply and guidance and i will be keeping you my update soon.
73’s
Jundy
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Yes Stephan and i will probably sticking with it and gonna have some homebrew these days.
Thanks & 73’s
can you make one for me pls
I have now with me the 2643625002 torroid from digikey arrived last friday for about 7days since i ordered it and as suggested by NY4G. I will be making the transformer per instruction in the link emailed by NY4G, a fellow Filipino living in the US😆. Hoping it will work as suggested in the discussion.
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M6YLY you might just ended with an unfortunate finished product considering that i am a newby.
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Jundy,
In your previous post with the photos of the measurement setup, you didn’t ask a question. Nevertheless, I allow myself a few comments in the hope that these could be useful for you.
First to the wound Fair-Rite 2643625002 ferrite toroidal core: It is wound very tightly and on the inside without any space between the individual windings.
Congratulations on that.
The wire diameter appears a bit large on the photos (0.8 mm?). This results in a somewhat long winding, which has an unfavorable effect on the winding geometry (increased flux leakage).
BTW, in the secondary winding of an EFHW transformer, only a current that is reduced by the turns ratio compared to the primary winding flows. With a 1:49 transformer, for example, this is only about 80mA at 15 watts.
Now to your measurement setup: The data obtained with it undoubtedly and unfortunately follow the GIGO law (garbage in garbage out).
This is because the calibration reference plane (on the VNA) does not coincide with the measurement reference plane (on the EFHW transformer) - and because it is practically impossible to measure the relevant properties of the “wire loops” in between and to take them into account in the measurements. The characteristic values of these “wire loops” also change greatly, depending on their geometry and position in relation to the immediate environment (e.g. lying on the workbench or floating).
So for the measurement of the transformer characteristic values, its connecting wires should be kept as short as possible, as can be seen, for example, from the measuring arrangement I usually use (photo below).
The second photo below shows the result of a measurement made on a 1:64 EFHW Transformer with this ferrite core. The ferrite core is chosen at random from a number of, for now, about 50 (…), but the measured transformer efficiency of about 88% is not significantly below the value predicted by calculation.
And last but not least, the measurements with a purely resistive nominal load only say something about the selected design of an EFHW transformer. If the transformer is built into a housing and even more so if connected to a real EFHW, the results will differ.
73 gl, Heinz
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Dear Heinz,
tnx again for your very accurate measurement setup. Here my quick and dirty and slightly inaccurate setup.
Unfortunately, the coaxial cable on my 2/15 transformer keeps frequently breaking when the antenna is pulled through the trees.
I fixed it and took the opportunity to measured the attenuation including the 9m RG174 (-1db … -1.4db).
I am satisfied from 80-10m.
73 Chris
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The most important thing is that you’re happy with it, Chris.
Without commenting on this measurement setup and the measured results, I would just like to repeat that the calculated transformer efficiency for an FT-140-43 ferrite core with 2 primary turns is between approx. 59% (80 m) and approx. 71% (10 m ).
The corresponding core losses would thus be between approx. -2.29 dB (80 m) and approx. -1.49 dB (10 m).
Edit
The fact is that in the transformer core, depending on the frequency band, between approx. 41 and 29% of the power supplied is heated up.
These are anything but best values and are therefore no longer up-to-date from an ecological point of view, hi.
Hello Heinz,
you are right, …
… but don’t worry to much. Following the pictures the distance between the SMA-connector and the toroid is about 10 cm. For the highest frequency 14.xxx MHz it’s not more than 0.5 % of the wavelength. The inductance of some cm wire compared to one and more windings around the toroid is also very small. For this measurement the error in the reference plane is neglectable. In my opinion the result shown in the pictures seem to be usable.
73, Ludwig
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That may be true or not, but it means my signal is 0.4 to 0.25 S steps weaker.
Never heard a 8.6 or 8.75 rapport instead of S9 for example.
I don’t care… 73 Chrs
Ludwig,
Yes, of course, you can measure something in different ways and think what you want from the results, hi.
Please note that the sentence you quoted does not already end with the dash, but only with the point.
This means that what I call the “wire loop” also includes the connection of the transformer output to the VNA input (with the inserted resistive nominal load of 2450 ohms, or more precisely, taking into account the VNA input impedance, 2400 ohms).
The capacitive influence that happens to be acting on this (high-impedance) part of the “wire loop” has a particularly “visible” effect on the measurement graphs…this is not just a guess.
73, Heinz
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Am I missing a trick here? I keep reading this but my inverted v EFHW takes me almost as long to erect on a 6m telescoping pole as my inverted v linked dipole, that’s about 8-10 minutes.
[I don’t rush it - especially on a rocky summit or where there’s lots of prickly undergrowth or sheep muck. Both antennas have lasted years of frequent use due to careful handling]
Attaching a 1m coax to the EFHW matching unit is only a bit faster than unwinding 8-10m of RG714 feeder (from its own winder) for the linked dipole. [After years of erecting them on very windy GM summits I have mastered the technique of avoiding getting the dipole’s wires and coax entangled]
It used to be quicker in olden days when I used the EFHW as a sloper but I configure it now as an inverted v because [I read] the mid point radiates the most.
“Easy” is a subjective unit of measurement - and that’s why I think it’s always a bit biased.
Besides, Stephan didn’t say his method was the easiest possible one in the world.
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Yes, whenever I see phases like “the best …”, “Easy to …” [especially in advertisements] I think “compared to what?”.