1/4 vs 1/2 wave groundplane

Status
Not open for further replies.

DY2_TTY

Member
Joined
Mar 1, 2017
Messages
23
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...
 

prcguy

Member
Joined
Jun 30, 2006
Messages
10,536
Location
So Cal - Richardson, TX - Tewksbury, MA
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.
prcguy


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...
 

jonwienke

More Info Coming Soon!
Premium Subscriber
Joined
Jul 18, 2014
Messages
13,023
Location
VA
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.
 

majoco

Member
Joined
Dec 25, 2008
Messages
3,719
Location
New Zealand
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.
 

Ubbe

Member
Joined
Sep 8, 2006
Messages
5,513
Location
Stockholm, Sweden
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
 

prcguy

Member
Joined
Jun 30, 2006
Messages
10,536
Location
So Cal - Richardson, TX - Tewksbury, MA
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.
prcguy



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
 

Ubbe

Member
Joined
Sep 8, 2006
Messages
5,513
Location
Stockholm, Sweden
You are probably correct prcguy, but there is also another aspect that WA6BFH mentioned in another forum:

"A ¼ 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
 

DY2_TTY

Member
Joined
Mar 1, 2017
Messages
23
Thanks for your input guys.... keep them coming, I want to learn everything I could....
 

wa4dou

Member
Premium Subscriber
Joined
Jul 30, 2015
Messages
36
Location
Eastern NC
You are probably correct prcguy, but there is also another aspect that WA6BFH mentioned in another forum:

"A ¼ 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.
 

lmrtek

Active Member
Joined
Feb 11, 2009
Messages
535
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 a moderator:

prcguy

Member
Joined
Jun 30, 2006
Messages
10,536
Location
So Cal - Richardson, TX - Tewksbury, MA
I think those numbers are a little generous and dBi is as viable as dBd when measuring a linear polarity antenna.
prcguy

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
 

wa4dou

Member
Premium Subscriber
Joined
Jul 30, 2015
Messages
36
Location
Eastern NC
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.
 

majoco

Member
Joined
Dec 25, 2008
Messages
3,719
Location
New Zealand
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.
 

wa4dou

Member
Premium Subscriber
Joined
Jul 30, 2015
Messages
36
Location
Eastern NC
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.
 

prcguy

Member
Joined
Jun 30, 2006
Messages
10,536
Location
So Cal - Richardson, TX - Tewksbury, MA
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.
prcguy

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.
 
Status
Not open for further replies.
Top