One more interesting point to make is that the lowest SWR does not always occur at the resonant frequency of the antenna(+feedline). In fact, often times the resonant point (where X=0) does not correspond to where the SWR is the lowest. So, depending on the line loss, you may get better efficiency at the non-resonant, but lowest SWR point.
Very well done Dave!! I wish the write ups in the ARRL antenna handbook were this simple....as a retired computer engineer the math is simple algebra but your explanation makes sense of it........ 73/K6SDW
I'm going to simplify this right now. "Non-Resonant" antennas lose most of their signal strength through feedline losses, both transmit and receive. The more you can minimize feedline loss, the less of a factor "resonant' VS "non-resonant" will be. This is why "open wire" or "ladder line" fed antennas can pretty much ignore feedline loss, while coax fed antennas need to pay attention to feedline loss. 73 de WB4DW
Bingo.. My home antenna is a Random Loop, and it is fed with Ladder line. And the reason why I'm able to function or transmit as well as I do, with a non resonant antenna, is because of the feed Line. Most of the time using a tuner I can get a 1:1 or close to it, but really I don't care to much about SWR because I know it is just going to be reflected back out. Here is the rub, tuners are finicky critters, and can be a PITA at times, so don't be so quick to jump ship to the non resonant antenna because like any compromise, there are drawbacks. However, I love my loop, and less noise as well.
So, if I hook the non resonate antenna directly up to the tuner, I should have no losses Or, is this too simplistic? I am thinking of hooking up a 29 foot wire direct to the so-239 with a counterpoise.
@@maddog222333 That sounds like a classic "random wire" antenna. It should work, if the tuner can match the impedance at the frequency you want to transmit on, however, assuming you are talking about having the tuner inside your shack, there is a good chance this setup will cause RF in the shack, in the form of speaker noise, computer glitches, etc.
Exactly, that’s all that needs to be said. Given an antenna of a particular size wrt the wavelength, all the power you put in except the loss on the feed line and the loss due to antenna inefficiency WILL be radiated. So if you want to use a non resonant antenna, you need a tuner and the multiple reflections on the wire will cause a lot of loss UNLESS you use a low loss feed line.
Hi Dave, thanks for this nice and clear explanation. I am now confident in building my non resonant (too short) doublet antenna, using a 450 ohms feedline. I will adjust the feedline length to tranform the antenna impedance into something reasonable for my homemade antenna tuner. May I suggest a video: could you show us the effect of a manual antenna tuner by connecting an antenna analyser at the output. You could simulate an untuned antenna with a coil, capacitors and resistor. Also showing the effect of some length of feedline, coax or parallel. I think there would be a lot of surprising results. 73 from F1SOC
I would like to hold you to your promise to test the "reflected wave" on the complex conjugate tuned system where your tuner is at the transmitter end of the transmission line. 1. Start with an antenna that is a far piece from 50 +j0. It can be 200 +j0, 50 -j200. Something a ways away from 50 +j0. Like maybe a good 40m dipole on 20m where the SWR is very high. 2. Send a string of 20m pulses from the transmitter side with a pulse generator short enough to see the transmitted and returning pulses on an oscilloscope at the returning end. 3. Insert the tuner and tune for a 1:1 SWR at the transmitter side. You may have to use an amateur rig to have enough power to tune it properly. Use only the external tuner and leave the amateur radio tuner alone and unused. We want only the external tuner at the transmitter side to be making the conjugate match. 4. Using a 20m pulse generator into the tuner, send pulses again to watch for the returned pulses. Compare the pulses as seen with the oscilloscope in both cases. Do not use the oscilloscope when using the high powered transmitter. Preferably use an antenna with a balanced line feeder. Coax cable can work but I'd like to see the returned wave on the scope and I don't want it to be blamed on the coax if we can't see it. Balanced line is easier to probe with a scope. If you need a generator, I can lend you one. I'm assuming you have these pieces of equipment. I'm a retired school bus driver and I have them.
MOST EXCELLENT explanation Dave! Optimizing antenna SYSTEMS for specific situations requires the knowledge you share with our Amateur Radio community. 73 UT1ZT ND5CH Chuck
Thanks for the explanations, Dave, but I think some of the maths is not right, e.g. the efficiency equation ( as pointed out below). Also, at resonance, I don't think Xc, nor Xl, each equal zero; Xc+Xl=0. Would you agree?
Great video, but one thing I still don't understand. Let's say we use a military style radio, that has a few meters vertical antenna attached directly to a really good internal tuner that can match it 1:1 on all HF bands. We use it on 40m and only for CW so we don't care about bandwidth. Would it be as efficient as a half wavelength dipole? To rephrase the question, would it be able to reach as far (same power out, compensated for radiation pattern)?
Thanks.. More on this general topic would be helpful. Some time model a dipole antenna 140 ft in length [40 ft in above ground] feed with 50 ft of 450 ohm ladder line. Model it from 80 - 10 meters. Assume a good antenna tuner like SA2060 is used. Model resistance/reactance/angleofradiation/lobes etc. Thanks..
When did a horizonal dipole change from 75 ohms to 50 ohm as you mentioned in this video? Tilting the ends of the wires downwards the ohmage will lower near 50 ohms inverted dipole.
@@jerrykr7kz it is a demonstrable effect, do you doubt it? the impedance reaches about 100 ohms at a quarter wave above ground and drops to about 50 ohms at a half wavelength up.
@@jerrykr7kz Some of the radiated power is absorbed in the ground over which the antenna is placed. I think this has the effect of making it seem as if there is a resistor across the feedpoint of the dipole, thus lowering its input resistance.
Hi Dave, I believe I was recently a victim of snow static and fried out some components on my transceiver's tuner board just before the so-239 connector. Other's have theorized that because it was a heavy snow storm in the north east at the start of winter field day, that I had built up static at some point which may have cause the destruction. The antenna I was currently using was my 80m OCFD (guanella balun), has a DC short between shield and center conductor, and my shield is grounded when it enters my house. I have watched your videos on lightning protection, but how up for a video for winter static protection? Thanks for all you do. 73!
Efficiency % = Rr / Rr + R ohm x 100...........eg Rr 50 / Rr50 + 2ohm x 100 = 96.15%. Electrically short antenna ? (note this efficiency calc is for Radiation resistance NOT feedpoint impedance.) Take a 20m long dipole in free space. freq =3.55Mhz no loss element. Rr = 11.74 Then add say 2 Ohm for element. we got 11.74 / 11.74 + 2 x 100 = 85.44% Amazing efficiency for an antenna half as long as resonant. but not so fast. We then need to put the thing over ground. Thats a whole nother calculation. And best left for modelling software. Ground loss will make up a larger % of the lower radiation Resistance.
Thanks Dave. I assume that the radiation pattern will be affected by resonance? If so, is it possible to "mismatch" a non-resonant antenna in order to change the radiation pattern to "point" at a particular direction (that it would not normally be strong at) and compensate by using extra power? e.g. if my antenna is weak to the west, say by 6db, if I increase my output by 6db I will compensate for that "loss" (although receive will not be similarly enhanced). If I can alter the radiation pattern by mismatching or by altering the height of my wire antenna and compensating by extra power can I affect and enhance my antenna's capability?
The feedline match or mismatch has no effect on directive pattern, however making a dipole longer than a halfwave will definitely change the pattern. In the halfwave dipole, all radiation directly broadside will be in phase and thus add up in that direction. Soon as you go longer than 1/2 wave, all radiation broadside to the dipole is no longer in phase. So there will be some reduction in radiation broadside and some increase is radiation a bit off broadside. As the length of the dipole approaches a full wave the radiation directly broadside becomes a null. However the radiation peaks in 4 directions halfway between broadside and the end of the wire. Most all antenna books will have plots of antenna patterns for “long wire” antennas showing how the pattern changes with length in wavelengths. A shorter than halfwave dipole still has all its radiation directly broadside in phase.
Nice try, but I'm afraid you lost 90% of today's hams. Before understanding this, they need the foundation of ohms law and complex numbers. Next, you can blow them away with the Smith chart! Good topic though - I have met broadcast engineers who believe "resonant" (zero j) are always more efficient.
