I’ve used 2 wire 300 ohm ribbon to make 3 band elements. Once I had measured the Vf it was just cut and use; no interaction in terms of lengths for best SWR. I did not get 1.0:1 VSWR without a tumer.
The multi core wire works best if the last m or so for each band is spread from the rest. Again don’t expect a perfect match. Vf will be ???
You might also consider a link vertical.
The biggest detuning effect is the support mast. Taping the wire/s to a squid pole will tune it to another frequency compared to the one it is resonant at when hanging free.
BTW Kirchhoff’s law works fine on any frequency. The impedance of a dipole is about 4,000 ohms (+/_) at the end. Needs a few volts to get power into it but the current flowing into the end point is equal to the current flowing out. You just have to look at a tiny piece of the end and not compare currents say a metre apart.
Hi Steve, this company builds “Fuchskreis=EFWH” Tuner to use with a halfwave wire.
Easy setup with a fishing pole. but on 20m you need a 10m pole :-),or fold it around a smaler pole. site is only in german. i orderes one tuner from them 1 week ago and when it arrives i go for a test with vertical from 40m-10m. the only company i know who builds this tuners for QRO. So before anyone order, i will write a report after a first test. with a 40m long wire you can tune all bands from 80-10m without any counterpoise.
In reply to 2E0YYY:
No magic, just a keen and committed operator with an antenna up high.
Hi Andy,
i agree, on my last sota´s i had used only simple linked dipole as inv.V. or endfeeded halfwave wires ( j-poles with 450ohm match ). with this simple inv.V. dipoles on highs at around 20m or higher its no problem to work dx. its fun to work with high antennas also on 40m and lower. now i´m qrv for 90% with linked dipoles without tuner. the first years i only used dipoles with ladder line and symetric tuners. but the resonant dipoles with links from anderson poles works pretty good and swr is good on different heights.
BTW Kirchhoff’s law works fine on any frequency. The impedance of a
dipole is about 4,000 ohms (+/_) at the end. Needs a few volts to get
power into it but the current flowing into the end point is equal to
the current flowing out. You just have to look at a tiny piece of the
end and not compare currents say a metre apart.
I must disagree. If Kirchoff’s first law is valid, then it can be applied at any and every point along the conductor. This implies that the current is the same everywhere along the conductor, including the open end. This is plainly absurd - we know that the current at the open end must be zero. There must be at least one point at which the current going in is not equal to the current going out; in fact there is a small difference at all points except the nodes and antinodes.
The concept of “displacement current” was invented in an attempt to make the “law” apply to time-varying circuits, but this is just a mathematical trick. It is far more straightforward to accept that Kirchoff’s Laws as stated are applicable to circuits with unvarying electric and magnetic fields.
You’re right, of course, that the “law” can happen to apply at the feed point.
Transmission Line theory is more applicable to understand what is happening. KL is mainly used in power systems and DC analysis type problems in such instances where traveling waves are not an issue per say.
Transmission Line theory is more applicable to understand what is
happening. KL is mainly used in power systems and DC analysis type
problems in such instances where traveling waves are not an issue per
say.
In reply to G3CWI:
Now come on gents, we’re comparing unlikes.
KL works at all frequencies under steady state. It is a powerful piece of logic for solving network problems. Transmission line theory is useful for dealing with lengths of, er, transmission lines.
Murphy’s law is useful in explaining away our lack of care or forethought. There’s a law for just about everything. Some are easier to use in specific situations. Misapply any one and you get garbage. KL is fine at rf but you do need to understand that if you move from point A to point B and B is a finite distance in terms of the phase of the signal then you have to allow for that. You also have to do that at 50 Hz with long lines. An open circuit 50 Hz line hundreds of km long has a higher voltage at the far end than at the sending end. Upsetting for some. KL still applies.
Of course I would not use KL to solve my transmission line matching problems. It’s not the sharpest tool for that. A Smith chart perhaps.
KL is good to use to show that all dipole antenna feed points are balanced. Which is what we were talking about. Someone introduced the feed lines as a diversion.
The feed lines are usually unbalanced and that’s where the old wives tales start.
But I can see it’s going to take a full 60 minute lecture with blackboard and chalk to make progress.
I just want to make the point that Kirchoff’s law is really just a nice piece of logic. If a point is to remain at the same potential in a steady state circuit, the quantity of charge entering is equal to the quantity of charge leaving. Otherwise it is not a steady state condition. Think RMS for ac SS.
Yes but you are not considering standing waves there, The standard wave equations are derived from KL but it is essential you do not confuse the two or confuse other people who could be reading this !
“An open circuit 50 Hz line hundreds of km long has a higher voltage at the far end than at the sending end”
Not true, reflected waves from a non matched load termination will reflect almost all of the power back to the source but it crucially depends on wave length. The maximum end potential of any line in an open termination can only equal the source voltage on a balanced or unbalanced line - not greater !
Standing waves and complex impedance is a far better way of understanding antennas and thus to consider power transfer. KL is the reference theory for many AC analysis problems, but it should not be used to model complex impedance based problems. Power systems engineering tend to use KL directly, however it can make the maths very laborious having to deal with complex quantity division etc as well as considering different power quantities. Standing wave theory is very simple and it gives you a far better feel for what is happening for any antenna system that you wish to employ or understand.
It doesnt matter if you are considering the feeder or the radiating element(s) of a dipole w/e, the same applies. KL will give only the termination conditions which may appear balanced when not considering SW’s !
Just a constructive input from an electronic engineering student nothing else meant.
If a point is to remain at the same potential in
a steady state circuit, the quantity of charge entering is equal to
the quantity of charge leaving. Otherwise it is not a steady state
condition.
Yup! And if the frequency is non-zero, it’s not steady state!
Think RMS for ac SS.
This is where we differ, but we’re probably going to have to agree to disagree.
KL1 works for RMS AC if and only if, following Maxwell, you introduce the concept of displacement current to balance the equation.
http://www.allaboutcircuits.com/vol_2/chpt_14/7.html I said it was equal to no greater then the source Voltage which is true for exact wavelengths. We are considering SS not pre SS though ! Which ok momentarily you could have higher voltages before SS that is correct.
Well obviously, but that’s a very special case which you hadn’t previously specified, and which certainly didn’t apply in the assertion you were attempting to refute.
As others have said, this is a thread hi-jack and it is probably not sensible to continue here. Email me at the address on qrz.com if you want to discuss further. I didn’t think the point I introduced was at all contentious!
Its fine, I am not interested in who is right or wrong here. I am not refuting anything I am clarifying what I said before, regarding the original statement was considered in open circuit config which my theory supports. As regarding to what is rubbish on the internet Andy I think you will find AllAboutCircuits is a noteworthy page, last time I checked I didn’t sound like a Yorkshire man either despite it being an interesting accent. On that bombshell I wont comment any further, thread hi-jacking or not, I read from the bottom, its reflector not a forum.
