5/8 wave vs. 1/4 wave receiving antennas
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NC1
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prcguy
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A 5/8 wave antenna will have a slightly lower angle of radiation and slightly more gain than a 1/4 wave, considering the ground plane and height above ground are the same for both. With that said, antennas are reciprocal and whatever pattern it has on transmit it will have on receive. Any benefit a 5/8 wave antenna will have on transmit will be exactly the same on receive.
NC1
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A 5/8th antenna element, by itself, actually has no gain. The 5/8th wave depends on radiation from a reflection or radiation from a second source to create gain. Those little radials on a discone are not sufficient to create any gain at all, therefore there will be a net loss due to the coil that makes up the rest of the 5/8 wave which is now off the target frequency.
We are trying to capture pieces of microvolts which are resonant at a certain length, which will pass on the 5/8 without the correct radials and proper ground plane. Transmitting is the same.
prcguy
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What you said here doesn't make any sense to me. It does not conform with any antenna theory I have seen.
There are lots of 5/8 vertical element antennas out there, most with a ground plane and some without. There are 5/8 wave base antennas with ground planes smaller than 1/8 wavelength and some with 1/4 wavelength ground radials. A 5/8 wavelength vertical happens to put more signal near the horizon than a 1/4 under similar conditions. That's where the gain comes from, taking energy that would be wasted in some directions and putting it in a more useful direction.
The absence of a ground plane or very small ground plane will cause the matching circuit for the 5/8 wave to be a little different due to less capacitance between the vertical element and the ground plane, otherwise there is no "reflection or radiation from a second source" to produce gain in a 5/8 wavelength antenna. Please show me where you get this information.
And who is talking about a 5/8 wavelength radiator on a Discone? Not me, but if I was, a 5/8 wavelength vertical radiator could be made with a good match using a VHF/UHF scanner Discone cone as the ground plane and it would have a little more gain than a 1/4 wave whip but probably less than if it had 1/4 wavelength ground radials. The Discone disc would probably aid in matching, becoming a bit of capacitance across the feedpoint for a 39MHz 5/8 whip on top.
There are lots of 5/8 vertical element antennas out there, most with a ground plane and some without. There are 5/8 wave base antennas with ground planes smaller than 1/8 wavelength and some with 1/4 wavelength ground radials. A 5/8 wavelength vertical happens to put more signal near the horizon than a 1/4 under similar conditions. That's where the gain comes from, taking energy that would be wasted in some directions and putting it in a more useful direction.
The absence of a ground plane or very small ground plane will cause the matching circuit for the 5/8 wave to be a little different due to less capacitance between the vertical element and the ground plane, otherwise there is no "reflection or radiation from a second source" to produce gain in a 5/8 wavelength antenna. Please show me where you get this information.
And who is talking about a 5/8 wavelength radiator on a Discone? Not me, but if I was, a 5/8 wavelength vertical radiator could be made with a good match using a VHF/UHF scanner Discone cone as the ground plane and it would have a little more gain than a 1/4 wave whip but probably less than if it had 1/4 wavelength ground radials. The Discone disc would probably aid in matching, becoming a bit of capacitance across the feedpoint for a 39MHz 5/8 whip on top.
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NC1
Member
The topic of the OP is getting lost with this conversation.
I cannot possibly cover the information you are missing in a post or two for you to see your error.
I strongly suggest reading the ARRL Antenna handbook, it dispels popular and incorrect concepts that seem to have transcended time even though the facts have been around for quite a while. It's a good book for your library, or you can start one with it.
Also, you might want to try some antenna modeling software to see where your theory goes south. The software is free for down load, you should check out 4NEC2 Antenna Modeler and Optimizer, and EZNEC Antenna Software by W7EL. Those can teach you infinitely more by having you see it than I could ever do on RR.
For additional resources, check out the ARRL web site - lots of things to learn there as well.
prcguy
Member
I have many ARRL antenna handbooks and the first one I got was around 1973 and I probably have every ARRL antenna publication since the 60s. I've been using EZNEC for about 10yrs and was trained on that by a friend of Roy Lewellen. Many of my antenna mentors were our Senior Staff Scientists and PHDs where I was the range master for our indoor compact antenna/RCS range, so I thank your for your suggestions but I don't see any that would benefit right now.
I would still ask you to point me to some publication that says anything like "The 5/8th wave depends on radiation from a reflection or radiation from a second source to create gain".
I would still ask you to point me to some publication that says anything like "The 5/8th wave depends on radiation from a reflection or radiation from a second source to create gain".
Ubbe
Member
It's the first time in my 40 years of dealing with radio technology that I've seen anyone giving that statement. The only time reflection might be in work with a vertical element are with ground reflections, like the kind of ground in your grass lawn in the backyard and not with ground plane elements, or if you have a reflector 1/4 wave distance behind the vertical antenna. But that is independent of the type of wavelenght antenna used.
/Ubbe
prcguy
Member
I agree. Ground bounce reflections between antennas can add up to 6dB of gain under ideal conditions when reflected waves all arrive in phase, but reflections can also cause 10-20dB of signal loss when they arrive out of phase. Ground bounce would not be something you would design into an antenna because its unpredictable and relies on terrain between antennas. This is one of the reasons an antenna test range might be between hills with a deep valley in between or a tall tower is used on one side to create a steep angle with no reflection in between.
Does anyone know if the OPs Discone even has a top whip?
Does anyone know if the OPs Discone even has a top whip?
NC1 said:
The 5/8th wave depends on radiation from a reflection or radiation from a second source to create gain.
The 2nd source NC1 talks about is a 5/8th length radial system preferably sloping down at an optimized length and slope angle to achieve best gain at a low takeoff angle as compared to a 1/4 wave with 1/4 optimized radials or a 5/8th wave with the typical non 5/8th wave radials that most ham or commercial design incorrectly reference.
For some good 5/8th wave antenna info read the following about 5/8th wave myths>
5/8th wave mobile antenna vs 1/4 wave
If you have a copy of eznec or the free 4nec antenna analysis programs build a 5/8th antenna model with various length radials, try 1/4 and then 5/8th antennas with radials beginning with 1/4 wave then increasing to 5/8th wave long and observe the takeoff angle over real ground as the radialls length increases towards 5/8th length and as the radialls slope downward.
Try optimizing by sloping the radialls from horizontal to a downward angle from 90(flat) to ~ 30 degrees downward and observe the change in takeoff angle.
The 4nec optimizer is extremely good at arriving at the optimum radial down slope and radial length model.
This all started After experiencing poor results with a commercial 29MHz 5/8th vertical after swapping it out after using a optimized 1/4 wave with 1/4 wave radialls which worked fine, we were able to finally optimize the 5/8 wave antenna by first comparing to the same 5/8th vertical with first 1/4 wave and finally 5/8 wave length downward sloping radials .
The 5/8th antenna with 5/8th down slope radialls being the only design with measurable performance over a 1/4 wave with similar 1/4 radialls or a properly decoupled 1/2 wave sleeve or vertical dipole or even the typical literature 5/8th wave with 1/4 wave radialls as is offered by some 5/8th wave verticals.
I have just recently built a 5/8th wave on 29.6 MHZ using downward sloping physically shortened (~9feet long), inductively center loaded electrically 5/8th wave radialls, with good results.
Our test bed is a 220MHZ TO 29.6 REMOTE BASE system and we have several mobile stations that have been following their same routes in various directions testing various antennas on 29MHZ for 2 weeks at a time per 29MHZ antennas.
Our test started using the 1/4 wave with 1/4 radials then the 5/8th with 1/4 wave radials, which was considerably worse BTW than the basic 1/4 wave with 1/4 wave radials baseline antenna.
prior to changing to a new design we went back to our 1/4 wave vert with down sloping 1/4 wave radialls to get back to our baseline measurements.
We are now testing the full length 5/8 wave radiator with physically shortened, center loaded DOWN SLOPED electrical 5/8 wave radialls with measurable range improvments over the previous two 1/4 and 5/8th wave designs.
The 5/8th wave depends on radiation from a reflection or radiation from a second source to create gain.
The 2nd source NC1 talks about is a 5/8th length radial system preferably sloping down at an optimized length and slope angle to achieve best gain at a low takeoff angle as compared to a 1/4 wave with 1/4 optimized radials or a 5/8th wave with the typical non 5/8th wave radials that most ham or commercial design incorrectly reference.
For some good 5/8th wave antenna info read the following about 5/8th wave myths>
5/8th wave mobile antenna vs 1/4 wave
If you have a copy of eznec or the free 4nec antenna analysis programs build a 5/8th antenna model with various length radials, try 1/4 and then 5/8th antennas with radials beginning with 1/4 wave then increasing to 5/8th wave long and observe the takeoff angle over real ground as the radialls length increases towards 5/8th length and as the radialls slope downward.
Try optimizing by sloping the radialls from horizontal to a downward angle from 90(flat) to ~ 30 degrees downward and observe the change in takeoff angle.
The 4nec optimizer is extremely good at arriving at the optimum radial down slope and radial length model.
This all started After experiencing poor results with a commercial 29MHz 5/8th vertical after swapping it out after using a optimized 1/4 wave with 1/4 wave radialls which worked fine, we were able to finally optimize the 5/8 wave antenna by first comparing to the same 5/8th vertical with first 1/4 wave and finally 5/8 wave length downward sloping radials .
The 5/8th antenna with 5/8th down slope radialls being the only design with measurable performance over a 1/4 wave with similar 1/4 radialls or a properly decoupled 1/2 wave sleeve or vertical dipole or even the typical literature 5/8th wave with 1/4 wave radialls as is offered by some 5/8th wave verticals.
I have just recently built a 5/8th wave on 29.6 MHZ using downward sloping physically shortened (~9feet long), inductively center loaded electrically 5/8th wave radialls, with good results.
Our test bed is a 220MHZ TO 29.6 REMOTE BASE system and we have several mobile stations that have been following their same routes in various directions testing various antennas on 29MHZ for 2 weeks at a time per 29MHZ antennas.
Our test started using the 1/4 wave with 1/4 radials then the 5/8th with 1/4 wave radials, which was considerably worse BTW than the basic 1/4 wave with 1/4 wave radials baseline antenna.
prior to changing to a new design we went back to our 1/4 wave vert with down sloping 1/4 wave radialls to get back to our baseline measurements.
We are now testing the full length 5/8 wave radiator with physically shortened, center loaded DOWN SLOPED electrical 5/8 wave radialls with measurable range improvments over the previous two 1/4 and 5/8th wave designs.
Ubbe
Member
prcguy
Member
In 40+ years of using and comparing antennas including lots of A/B testing of 1/4 wave ground planes to 5/8 wave ground planes, I call most of the info in the link BUNK. In every case going from a 1/4 wave groundplane with radials at 90deg or sloping, to a 5/8 ground plane with 1/4 wave ground radials at 90deg like a Hy-Gain Penetrator, the 5/8 wave always shows noticable gain over the ground plane. I've tried this at ground level and on roofs and tall masts, on a hill and in the flat areas of town and the 5/8 ground plane always without fail outperforms a 1/4 wave ground plane.
Same thing doing countless tests between a 1/4 wave whip and various brands of 5/8 whips on the same vehicle and mount, the 5/8 always wins unless your tucked up against a tall hill where the path goes upward at 20deg or more. Been doing these comparisons for maybe 40yrs and way before antenna analyzer programs were available. Countless people have been doing the same for much longer and nobody has ever come up with any results similar to what you are presenting. What we do know is a 5/8 wave radiator needs a ground plane and without it you will not achieve the rated gain of a 5/8.
My Eznec mentor was a good friend of Roy Lewallen, who markets Eznec and one of the first things I learned about Eznec is bad info in, bad info out when using the program. Who is NC1 and what makes him believable?
Same thing doing countless tests between a 1/4 wave whip and various brands of 5/8 whips on the same vehicle and mount, the 5/8 always wins unless your tucked up against a tall hill where the path goes upward at 20deg or more. Been doing these comparisons for maybe 40yrs and way before antenna analyzer programs were available. Countless people have been doing the same for much longer and nobody has ever come up with any results similar to what you are presenting. What we do know is a 5/8 wave radiator needs a ground plane and without it you will not achieve the rated gain of a 5/8.
My Eznec mentor was a good friend of Roy Lewallen, who markets Eznec and one of the first things I learned about Eznec is bad info in, bad info out when using the program. Who is NC1 and what makes him believable?
Ubbe: please point me to a EZNEC file for a quarterwave that shows 8 dbi over real earth?
Even the stock 1/4 models supplied with eznec or those in 4nec typically only produce 1.4 to 1.8 dbi for a quarter wave vertical using models with aluminum or copper wire which have real world losses in the models.
As for a dipoles, eznec as do all nec based programs display ground gain which all horizontal antennas have over real earth, ~ 8 dbi over real earth is well known for a horizontal dipole at its takeoff angle of maximum directivity, the angle which us determined by the horizontal antennas height above ground.
Also I Don't know who NC1 is I just quoted his reply but he is not the individual at the 5/8 wave/1/4 wave myth link, that link is from Tom Rausch, w8ji, respected antenna engineer.
The 5/8 vs 1/4 wave myths link I provided is by Tom Rausch W8ji a respected antenna engineer who also contributes at times to Roy Lewallen of EZNEC FAME and to other antenna model software programmers.
One thing about w8ji is that aside from using antenna software to analyze designs, he has also builds and measures the actual antennas in question to back up or tear apart the models, so how can one claim bunk about w8ji's link when even Roy Lewallen corresponds with w8ji on antenna subjects?
Even Roy Lewallen has been known to be corrected by Tom/w8ji.
http://eznec.com/misc/ibalbrf.txt
Even the stock 1/4 models supplied with eznec or those in 4nec typically only produce 1.4 to 1.8 dbi for a quarter wave vertical using models with aluminum or copper wire which have real world losses in the models.
As for a dipoles, eznec as do all nec based programs display ground gain which all horizontal antennas have over real earth, ~ 8 dbi over real earth is well known for a horizontal dipole at its takeoff angle of maximum directivity, the angle which us determined by the horizontal antennas height above ground.
Also I Don't know who NC1 is I just quoted his reply but he is not the individual at the 5/8 wave/1/4 wave myth link, that link is from Tom Rausch, w8ji, respected antenna engineer.
The 5/8 vs 1/4 wave myths link I provided is by Tom Rausch W8ji a respected antenna engineer who also contributes at times to Roy Lewallen of EZNEC FAME and to other antenna model software programmers.
One thing about w8ji is that aside from using antenna software to analyze designs, he has also builds and measures the actual antennas in question to back up or tear apart the models, so how can one claim bunk about w8ji's link when even Roy Lewallen corresponds with w8ji on antenna subjects?
Even Roy Lewallen has been known to be corrected by Tom/w8ji.
http://eznec.com/misc/ibalbrf.txt
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