Quote from: gil on July 29, 2016, 03:17:47 PM
Thanks Lamewolf, I thought as much after thinking about it a bit more..

Gil

No problem Gil !  But I should add that one would have to make A to B comparisons to be sure just how much better it would work and it may not be all that much better.  But when using QRP power levels like a lot of us do, its best to get as much power into the air as possible - in other words, eliminate as much loss as possible !

Quote from: gil on July 11, 2016, 04:53:00 AM

QuoteWhat frequency range does G8JNJ say it is good for?

Unlike the EARCHI 9:1, the Ruthroff 4:1 has to be used with wires shorter than 1/4 wave.

Gil.

Why would the Ruthroff be limited to wires shorter than 1/4 wave ?  I've never seen that before, but as long as the impedance of the wire is greater than 200 ohms or so that it doesn't drop it too far below 50 ohms on the radio side it would work just fine.  If it drops it to far below 50 ohms, it looks like a short to the radio or tuner making it harder to match and increases the losses.  A wire that is shorter than a quarter wave is going to be below 50 ohms to begin with and will have a lot of capacitive reactance needing canceled to bring it back up near 50 ohms.  Anyway, the Ruthroff 4:1 unun is one of the ones I have experimented with on numerous occasions with various lengths of wire up to and including 125 feet and in fact is what I had on my 88' sloper until I made the 9:1 unun the other day and replaced it.  But it worked just fine with various lengths some of which were over 1/2 wave !

QuoteWhy would the Ruthroff be limited to wires shorter than 1/4 wave?

I don't know... That would be a question for G8JNJ who as far as I know is not a member here.. See reference in previous posts..

Gil.

Quote from: gil on August 02, 2016, 01:56:22 PM

QuoteWhy would the Ruthroff be limited to wires shorter than 1/4 wave?

I don't know... That would be a question for G8JNJ who as far as I know is not a member here.. See reference in previous posts..

Gil.

Been looking for info on that but did not find it.  But the best situation for a 4:1 Ruthroff would be to connect it to a wire that shows around 200 ohms at resonance and the 4:1 ratio transforms this to 50 ohms.  If the wire is 200 ohms at resonance, I guarantee it will be longer than 1/4 wave !  It would probably be more like 3/8 wave.  In fact, I have had good luck with a 4:1 Ruthroff feeding a 100' wire which is about 3/8 wave at 3.5Mhz and about 1.5 wave @ 7mhz.

Interesting.. I would like to know more about end fed wires impedance.. I would guess longer equals more impedance...

Gil

Quote from: gil on August 02, 2016, 05:34:25 PM
Interesting.. I would like to know more about end fed wires impedance.. I would guess longer equals more impedance...

Gil

I'm just giving an educated guess here.
The impedance of an end-fed is mainly determined, not by overall length, but by how close to 1/4 or /12 wave long it is, ignoring multiples of 1/2 wave.  If it's a multiple of 1/2 wave (0.5 or 1.0 or 1.5, etc) it's impedance will be very high (2.5K - 5K Ohms).  At 1/4 wave long, with a ground plane or 1/4 wave counterpoise(a dipole, really) it's around 50 - 70Ohms.  In between those lengths the impedance will vary.  If you could stretch a wire from 1/4 wave to 5 waves long, its impedance would cycle between low and high every 1/2 wavelength of stretch.  Another example is my 63' long EFHW antenna.  It's impedance is ~2.5K at 7MHz, 14MHz and 21MHz even though at 7MHz it's 1/2 wave long and 1.5waves long at 21MHz.

For the 9:1 unun antennas, we keep seeing  these magic tables of wire length.  All of the suggested lengths are NOT some multiple of 1/2 or 1/4 wave at any of the frequencies they say it will operate on.  The lengths must be threading the needle between 1/4 and 1/2 wave for all the frequencies they claim it will work with.

Right. I was thinking of the resistive component increasing with wire length also.. An off-center fed dipole is 200 to 400, a dipole about 73. We are talking about end fed wires though.. Maybe a 1/4 wave end fed is about 200 Ohms...

Gil

Quote from: gil on August 02, 2016, 07:00:58 PM
Right. I was thinking of the resistive component increasing with wire length also.. An off-center fed dipole is 200 to 400, a dipole about 73. We are talking about end fed wires though.. Maybe a 1/4 wave end fed is about 200 Ohms...

Gil

No, a quarter wave at resonance is on the order of about 35-75 ohms.  To reach 200 ohms, you got to look out to about 3/8 wave which is more than a quarter wave.  In a couple of posts back you mentioned that you thought that the longer the wire, the higher the impedance is and that is true to a point.  But take the quarter wave for example which will be around 35 - 75 ohms depending on surroundings, ground losses, height above ground etc and then stretch it out to 1/2 wave and the impedance increase to 2.5K to 5K ohms, but add another quarter wave to that which makes it 3/4 wave (odd multiple of a 1/4 wave) and the impedance drops back to around 35-75 ohms.  Impedance somewhat repeats at odd multiples of 1/8, 1/4, & 1/2 wave !  So just making it longer doesn't mean the impedance is always higher.

kc8aon

A quarter wave with radials yes, but by itself?

Quote from: gil on August 03, 2016, 07:40:09 AM
A quarter wave with radials yes, but by itself?

Still going to be a low impedance if its a quarter wave.  Even if you don't attach a physical counterpoise or ground, you got to take into consideration that a quarter wave is a "current fed" antenna and that current must flow somewhere - be it on the coax shield, equipment cases, or capacitively through you while in contact with the equipment and other nearby structures. But one should never use a quarter wave without some sort of ground return.  This can be a physical earth ground, tuned counterpoise wire or tuned length of feedline, or even a random length counterpoise.  But in the case of a 1/2 wave, the impedance and voltages are higher since it is a "voltage fed" antenna, the importance of the ground is much less and just a simple static ground is sufficient.  The current is still there on a 1/2 wave, its just not at the feed point, its out at the center of the wire just like in a normal center fed half wave dipole.

Definitely. It is easy to picture where voltage and current are just by juxtaposing the wave form on the wire, on paper..
Gil

Quote from: gil on August 03, 2016, 08:29:59 AM
Definitely. It is easy to picture where voltage and current are just by juxtaposing the wave form on the wire, on paper..
Gil

Right !  When using a quarter wave without a ground or counterpoise, you have to picture the other half of the wire as the feed line, equipment, nearby structures, and you and that's where the return current is flowing !

And that is why I never felt pin pricks in my fingers using EFHW antennas, but was bit a few times with random wires..
Gil

Quote from: gil on August 03, 2016, 01:19:39 PM
And that is why I never felt pin pricks in my fingers using EFHW antennas, but was bit a few times with random wires..
Gil

Correct, very little to no current at your end on the EFHW, but lots of current possible with a random wire !
kc8aon