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  #1 (permalink)  
Old 03-22-2017, 11:05 AM
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Default 1/4 vs 1/2 wave groundplane

Hi I made a 1/4 groundplane antenna for use with my Baofeng GMRS-V1. It is mounted just 8 feet high inside the house. I am able to reach about 2.5 miles with it.
If I replace it with a 1/2 wave, granted the SWR is the same as the 1/4 wave, will it give me a little more reach, lets say 3 miles instead of the 2.5 I get with the quarter wave?

Sorry if this is a stupid question, thanks for your answer...
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Old 03-22-2017, 11:22 AM
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Its hard to estimate increased range due to your local terrain. But what you expect is slightly better performance that you can hear. If you are very weak at 2.5mi then it might be a little less noisy with the better antenna. If there is no signal at all at 2.5mi then the better antenna may not make it, or you could now have a very weak signal where there was none before but its not going to be night and day.
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Originally Posted by DY2_TTY View Post
Hi I made a 1/4 groundplane antenna for use with my Baofeng GMRS-V1. It is mounted just 8 feet high inside the house. I am able to reach about 2.5 miles with it.
If I replace it with a 1/2 wave, granted the SWR is the same as the 1/4 wave, will it give me a little more reach, lets say 3 miles instead of the 2.5 I get with the quarter wave?

Sorry if this is a stupid question, thanks for your answer...
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Old 03-22-2017, 1:09 PM
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A vertical dipole (which is what you want) has to be fed by a horizontal feed line, or the feed line will interfere with the antenna. It probably wouldn't be the best option for you.

What will make a HUGE difference is getting the antenna outside, and above the roof line of your house. Any antenna inside the house is going to perform poorly.
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Old 03-22-2017, 4:29 PM
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What will inprove your range with both antennas would be getting them as high in the air as you can ........

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Old 03-22-2017, 6:19 PM
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A half-wave ground plane? Sorry, doesn't work - a quarter wave has a very high impedance (all volts and no current) at the far end and a very low impedance at the bottom (all current and no voltage). If you bend the radials down a bit the impedance at the bottom rises a bit and is a good match for 50 or 75 ohm coax and so into your receiver. A half wave still has a high impedance at the far end, but a half-wavelength away at the bottom it is back to high impedance. If you want to match this to your low impedance cable you need a transformer - hams have made EFHW transformers for the HF bands.....

EFHW matching unit | VK3IL Blog

......but goodness know how they would work at VHF.

Stick to the quarter wave ground plane and get it outside - it'll do the job.
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Old 03-22-2017, 7:25 PM
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The 2.5 miles to 3 miles increase is 20% which means you have to increase the radiated power 40%.
An ideal 1/2 dipole antenna will have a 2.14dB increase of radiated power compared to a 1/4 GP. That is a bit more than a 50% increase.

To make a real dipole, that is a balanced antenna, properly connect to the coax, that is unbalanced, you must use a balun. Otherwise the dipole will work as a bad 1/4 with a lousy ground pin that is worse than your current 1/4 GP. The balun should be a 1:1 type for 50 or 75 ohm. The missmatch loss between 50 and 75 ohm is something like 0.2dB and the balun itself will probably also give a loss of 0.1-0.2dB but you will still have your needed 40% increase in power.

/Ubbe
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Old 03-22-2017, 8:38 PM
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An ideal 1/2 wave dipole will have 2.14dB gain over a theoretical isotropic radiator but not a 1/4 wave ground plane. The difference between a 1/4 wave ground plane and 1/2 wave dipole is on the order of a 1dB or so.
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Originally Posted by Ubbe View Post
The 2.5 miles to 3 miles increase is 20% which means you have to increase the radiated power 40%.
An ideal 1/2 dipole antenna will have a 2.14dB increase of radiated power compared to a 1/4 GP. That is a bit more than a 50% increase.

To make a real dipole, that is a balanced antenna, properly connect to the coax, that is unbalanced, you must use a balun. Otherwise the dipole will work as a bad 1/4 with a lousy ground pin that is worse than your current 1/4 GP. The balun should be a 1:1 type for 50 or 75 ohm. The missmatch loss between 50 and 75 ohm is something like 0.2dB and the balun itself will probably also give a loss of 0.1-0.2dB but you will still have your needed 40% increase in power.

/Ubbe
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Old 03-23-2017, 9:31 AM
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You are probably correct prcguy, but there is also another aspect that WA6BFH mentioned in another forum:

"A wavelength Ground Plane (or Mono-pole) is half of a dipole. Its major currents flow in the mono-pole radiator, and virtually none in the counterpoise. Its angle of radiation is very high, whereas, the (vertical) dipole has a radiation pattern near the horizon. Consequently, and practically speaking, the Ground Plane has half the gain of the half-wavelength dipole."

/Ubbe
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Old 03-23-2017, 10:57 AM
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Thanks for your input guys.... keep them coming, I want to learn everything I could....
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Old 02-03-2018, 2:26 PM
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Quote:
Originally Posted by Ubbe View Post
You are probably correct prcguy, but there is also another aspect that WA6BFH mentioned in another forum:

"A wavelength Ground Plane (or



Mono-pole) is half of a dipole. Its major currents flow in the mono-pole radiator, and virtually none in the counterpoise. Its angle of radiation is very high, whereas, the (vertical) dipole has a radiation pattern near the horizon. Consequently, and practically speaking, the Ground Plane has half the gain of the half-wavelength dipole."

/Ubbe
You're right in that a 1/4 wave has half the gain of a halfwave. The 1/4 wave has 1.21 dbi gain and the halfwave has 2.14. Half of human observers can't even sense a change in a signal of 1 db, therefore the best bang for the buck is to get an antenna outside and in the clear, with low loss cable so that antenna height gain isn't nulified by feedline loss.
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Old 02-03-2018, 2:30 PM
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Pay particular attention to prcguy and ZL2MC in this thread.
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Old 02-11-2018, 7:56 PM
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Yes, a 1\2 wave ground plane will have 2 db gain over a 1\4 wave gp
and a 5\8 wave will have 3 db gain over a 1\4 wave gp

DBI is a non existent reference which is meaningless when comparing gain over a ground plane

Last edited by MOTEX; 02-11-2018 at 8:05 PM..
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Old 02-11-2018, 8:32 PM
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I think those numbers are a little generous and dBi is as viable as dBd when measuring a linear polarity antenna.
prcguy

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Originally Posted by MOTEX View Post
Yes, a 1\2 wave ground plane will have 2 db gain over a 1\4 wave gp
and a 5\8 wave will have 3 db gain over a 1\4 wave gp

DBI is a non existent reference which is meaningless when comparing gain over a ground plane
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Old 02-11-2018, 9:07 PM
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Quote:
Originally Posted by MOTEX View Post
Yes, a 1\2 wave ground plane will have 2 db gain over a 1\4 wave gp
and a 5\8 wave will have 3 db gain over a 1\4 wave gp

DBI is a non existent reference which is meaningless when comparing gain over a ground plane
Actually a reference to dbi is quite valid, establishing a reference point from which all antenna gains are derived. A 1/4 wave antenna exibits about 1.2 dbi gain, while a halfwave exibits 2.14 dbi, or an increase of .94 db.
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Old 02-13-2018, 12:58 PM
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All this talk about gain is based on a theoretical antenna out in free space that is not connected to anything. As soon as you start bringing it in to the real world you never notice the difference between a 1/4 wave and a 1/2 wave. The 1/4 wave needs no matching devices to 50 or 75 ohm coax, whereas the 1/2 wave needs a matching transformer or strange impedance coax stub tuner - both of which introduce slight losses.
An increase of 0.94dB over a theoretical 1/4 wave? Phooey - you'll never hear the difference.
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Old 02-13-2018, 1:18 PM
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Quote:
Originally Posted by majoco View Post
All this talk about gain is based on a theoretical antenna out in free space that is not connected to anything. As soon as you start bringing it in to the real world you never notice the difference between a 1/4 wave and a 1/2 wave. The 1/4 wave needs no matching devices to 50 or 75 ohm coax, whereas the 1/2 wave needs a matching transformer or strange impedance coax stub tuner - both of which introduce slight losses.
An increase of 0.94dB over a theoretical 1/4 wave? Phooey - you'll never hear the difference.
Martin, I can certainly respect your opinion, because it's true for many folks. Those in pursuit of every fraction of a db advantage might disagree. You may not pursue the weakest of signals but some do. In some applications, in land mobile radio, 1/2 wave antennas have been historically preferred where no ground plane was available. I personally prefer the 5/8th wave most often.
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Old 02-13-2018, 5:08 PM
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Many people will never notice or care if they lose 0.94dB of signal, its small and almost insignificant in the police scanner world. On the other hand, if a multi million $$ satellite antenna project I'm working on misses the gain spec by 0.94dB, then someone may not get paid. Even a half dB missing on a 60+dB gain antenna will cause grief.
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Quote:
Originally Posted by majoco View Post
All this talk about gain is based on a theoretical antenna out in free space that is not connected to anything. As soon as you start bringing it in to the real world you never notice the difference between a 1/4 wave and a 1/2 wave. The 1/4 wave needs no matching devices to 50 or 75 ohm coax, whereas the 1/2 wave needs a matching transformer or strange impedance coax stub tuner - both of which introduce slight losses.
An increase of 0.94dB over a theoretical 1/4 wave? Phooey - you'll never hear the difference.
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