Yes, short and simple. Thank you.
By the way, I measured the lenght of my antenna wire for 20m. It is 9,9 m. It is 20cm shorter than formula in hb9sota document for monoband efhw (142,5/f). I think it is because I use it in slope configuration and not vertical.
I also measured resonant frequency in lambda/4 configuration, hoping to get resonance in 40m band. No. Resonance is 7700 kHz
Hi Damir,
You could try adding little coil 5-8 turns on 2-3cm diameter former and 3-4 radials of 5mtr. This is what I use sometimes. Vertical wire is from trapped EFHW for 20/15/10 bands used as vertical, when I want 40 I attach coil and radials. You might need CMC on coax in such situation.
73 Marek
Thank you Marek for your answer.
I know about coil. A friend of mine is using efhw at home and that little coil helps him to get resonance in 7, 14, 21 and 28 without tuner. Without coil resonance goes out of higher bands.
I think, and maybe I am wrong, that aditional inductance with 24 turns instead of 14 turns is doing same job as that coil. Helping to lower resonance on higher harmonics.
But again, maybe, very likely, I am wrong
PS: I reread your answer Marek and I 100% miss the point. You are talking about lowering the frequency of short wire. Yes, you are right. That will help
But, little coil about 2m from 2:14 transformer helps
Hi Damir,
Sorry I wasn’t clear enough. My idea is that instead 49:1 transformer I put little coil and radials. Basically it becomes 1/4GP for 40m band.
The coil you meant is 5-6turns coil on antenna wire about 2mtr from transformer. It is still EFHW.
73 GL Marek
Hello folks,
Following recommendation about toroid winding I did a few experiments (not yet finished).
But a the beginning I want to say thank you for pointing to this ideas.
Here are what I got:
Pic. Separated windings for primary and secondary but with crossing (W1JR). Too much inductance due to fact that this crossing reduced winding capacitance. I want to try 0.4mm wire instead of 0.6mm as on picture. But can be used if you observe to many capacitance (upper graph is reactance with step 10 Ohms ). Measured capacitance for lowest SWR is 88 pF but I soldered 100 pF (don’t have 88 =) )
Pic. Common (not recommended winding) with gathered primary and secondary 3 turns and capacitor 150pF. Unfortunately forget to add reactance graph. Used wire is 0.4mm.
Pic. Separated windings for primary and secondary but WITHOUT crossing. Measured capacitance for the lowest SWR is 70 pF but I soldered 100 pF. Used wire is 0.6mm
It is important to mention that wire diameter impacts on winding capacitance and that is why care about this and don’t solder 150 pF without measurements.
I used variable capacitor 20-250 pF for adjasting for lowest SWR.
Hallo Yuri
Which toroidal material did you use?
73 Armin
Thank you for the insightful comparison.
I would now be interested in how the SWR behaves on a EFHW of 20m in length.
Because I suspect that the antenna wire at the feed point causes additional capacity and the cross-over version might be advantageous on 15m / 10m.
73 Chris
Hello Armin,
Good point, all toroids are FT-82-43 Amidon.
Chris,
I am also very interested in to check this. Hope will find some time and compare with 20 meters DX-WIRE UL.
These are 3 different transformers, not rebuild of single core.
Hi,
to be frank: Heinz @HB9BCB and Owen Duffy have already reported the results of carefully set up experiments and measurements, see above. So while reproducing experiments is usually a good thing, I wonder which novel insights you are looking for 
?
And as far as I can see, you are measuring SWR; that will not be very informative, because you cannot distinguish losses from impedance mismatches. It’s better to either build two identical transformers and connect them back-to back, or use the a series resistor of 50R * N^2 -50R at the output (N is the
turns ratio 1:N), and then measure the insertion loss with the VNA.
In thr case of a back-to-back approach, the actual loss is half of what you measure (because you have 2 devices), in the (better) resistor circuit, you have to deduct the attenuation from the voltage divider formed by the series resistor and the 50r input of the VNA.
All is explained here: Toroid windings for EFHW - #16 by HB9BCB
Please do not take this as offensive; that would be the least I intended with this post.
73 de Martin, DK3IT
PS: The diameter of the wire also influences how tightly the winding will follow the shape of the toroid, which will also affect transmission losses. Tinner wire may exhibit higher resistive losses but a better coupling. See Heinz’ best practice reports.
Hi Martin,
I did this already with different cores.
But testing with this approach requires one import point. The output impedance of transformers should be identical.
In my case, then I checked losses of two identical transformers (connected in series), I noticed that SWR of S11 shows about 1.5
This means that some transformer e.g. the first has 3050 Ohms and second has 3350. Checking SWR with 3200 Ohms shows the same almost SWR for both transformers. But in case of serial connection we need variable capacitors for both cores for tuning to 1.0 SWR.
Im my cases with and without capacitors the difference was about 0.2-0.3dB.
And my point in this that losses due to output impedance mismatch and measurements losses are bigger that lossos with different winding patterns.
I think the more important is inter-turn capacity of winding.
In case of producing tight winding the inter-turn capacity will be bigger than increased inductance =)
BTW, thank you for interesting discussion =)
I read this full thread and just want to check result by myself =) but with different core material not Feir Rite or Amidon, but with has similar specs.
These checks were part of project for building QRP EFHW koppler by [HB9BCB].
Here are videos, but only RUS lang for now ( not Eng subt).
But it is enough for getting familiar to scroll and see pictures.
This is most likely due to the large variance in A_L of the cores. Did you measure the inductances of the primary and secondary windings?
No, din’t measure. Will do next time.
This is a good point!
Thank you.
Yuri,
The transformation ratio of a real broadband transformer (with a ferrite core) will never correspond exactly to the nominal transformation ratio.
Deviations of up to 3-5% are not exceptional for transformation ratios of 1:9 and greater.
Even if the real transformation ratio were exactly the same as the nominal one or if 2 real broadband transformers had exactly the same transformation ratio, what would you have gained with a view to the very different impedances of real EFHW antennas (depending on frequency, height above ground and antenna conductor properties)?
I hope you can understand what I mean by that.
73 gl, Heinz
That’s why I always build the transformer first and then cut the cable to length… the length is always a bit different… also because of the shortening factors…
73 Armin
Thanks you, Heinz
There is no doubt that despite the winding pattern, core size, wire diameter there are plenty of factors which influenced antenna and transformer output impedance.
In some cases radiation might have more capacitive reactance and you need longer wire, in some cases shorter wire.
The original discussion was that I need to check loses by connecting two transformers in series. But this performed already tons of times.
I only showed SWR with different winding patterns, which is more crucial for me when I want to have real working e.g. 40-20-15-10m bands SWR < 1.5/1.7 with fixed counterpoise or coax cable about 1 or 2 meters length.
Talking about monoband EFHW or at least two bands (you plan to work or adjust for single band) it is very easy.
Even with SWR on dummy load 3300 Ohms SWR > 3. You can compensate this reactance by wire length.
In case of real multi-band EFHW you need take case about broadband transformation with possible lowest SWR to have acceptable SWR on all bands. Partial reactance is appreciated due to fact that harmonics (20, 10m) for 40m band EFHW have slightly different impedance, but requres experiments what I am doing =)
Yury,
If an analyzer with a graphical display is available for these experiments, it might even be fun, hi.
You will then also realize that with a multi-band antenna, the unwanted SWR differences generally occur on the harmonic frequency bands,
- because, with an identical antenna radiator, the velocity factor for the harmonic frequency bands differs from that of the fundamental band, i.e. the resonance lengths of the harmonic frequency bands do not exactly correspond to the calculated multiple
- the decisive factor for the velocity factor is the quotient of the half wavelength and the wire diameter, which is why the resonance length of the fundamental frequency band for the harmonic bands is a bit too short. With a 40/20/10m EFHW antenna, this difference can be approx. 22cm at 20m and approx. 33cm at 10m, depending on the wire diameter.
If no ATU is used, the antenna length at the feed point of the antenna can be adjusted to the desired resonant frequency of the harmonic band using pieces of wire (example below).
With angled antennas (e.g. inv-V, inv-L) there is an even greater influence on the resonance length of dipole antennas due to the greater capacitive coupling between the antenna legs and against the ground. As a result, the resonance length decreases continuously up to an apex angle of 90° by up to approx. 5% and the impedance drops.
If I remember correctly, I used the following wire extensions for the antennas on a 10m mast (apex approx. 8.30m, ends up approx. 2m) to compensate for the above-mentioned effects:
- EFHW 40/20/15/10, extension for 20m band: 0.5m
- EFHW 80m, extension for 40m band: 2m
As mentioned above, with a suitable antenna analyzer, the effects of these influencing factors can be visualized, which greatly simplifies the whole work.
