Howdy all,
I was wondering if someone could set me straight on some antenna theory.
Is there substantial gain usually with a 5/8 antenna over 1/4 wave? At the present I have a 1/4 wave uhf 403-430 NMO installed. I use one specific frequency in the 413 MHz range. The repeater is located approx 22km from my normal zone. I am happy with its performance but am always looking for better. The radio is installed in a Windstar with the antenna presently center over the cab. Would it be even worth it to try for a longer antenna?
Thanks.
1/4 wave vs 5/8 wave
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I just added to that forum on RR and my comments may help you.
Chris,
Hamming 31 years
http://www.wa2zdy.com
Wesley Chapel, Pasco County, Florida
Snow? What's that?!
The human race is proof that Darwin was wrong.
Hamming 31 years
http://www.wa2zdy.com
Wesley Chapel, Pasco County, Florida
Snow? What's that?!
The human race is proof that Darwin was wrong.
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RadioSouth
- Batboard $upporter
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chpalmer
- Posts: 105
- Joined: Mon Jun 17, 2002 9:01 pm
- What radios do you own?: Astro Specta, MT1500, HT1550LS
Idea behind the 5/8 wave over coil is to get the current to the center of the antenna, above the coil.
The quarter wave looses more of its signal to ground losses but as stated does do better higher in the vertical plane.
The cars where I work had 5dB antennas on them when I started there. The terrain was very lousy for radio due to the deep valleys and cliffs near the shores of the sound. It was impossible for the guys to get out in many locations due to the very flat vertical plane of these antennas.
I began testing starting with the 1/4 then went to the 5/8 over coil. The 5/8 antennas gave us the best performance in this situation. All bad areas are now more than usable with no other change and talk in doesn't suffer due to the lack of gain on the receive side, that we saw with the 1/.4's. We also use 8x cable kits exclusively for uhf now. The more signal you get to the antenna, the less you have to make up in gain...
What ever you do make sure your cable kit is good quality and the right one for the job.
Good Luck!
The quarter wave looses more of its signal to ground losses but as stated does do better higher in the vertical plane.
The cars where I work had 5dB antennas on them when I started there. The terrain was very lousy for radio due to the deep valleys and cliffs near the shores of the sound. It was impossible for the guys to get out in many locations due to the very flat vertical plane of these antennas.
I began testing starting with the 1/4 then went to the 5/8 over coil. The 5/8 antennas gave us the best performance in this situation. All bad areas are now more than usable with no other change and talk in doesn't suffer due to the lack of gain on the receive side, that we saw with the 1/.4's. We also use 8x cable kits exclusively for uhf now. The more signal you get to the antenna, the less you have to make up in gain...
What ever you do make sure your cable kit is good quality and the right one for the job.
Good Luck!
SWR is not necessarily about signal performance, it's about impedance matching throughout the transmission system.
Case in point- throw a 50 ohm dummy load on your radio- perfect SWR match. Now bend your 5/8 wave antenna a bit to try to slightly degrade the SWR. Any bets on which one will get better range?
The big problem with antenna flex is that the coverage pattern shifts with the antenna, causing it to tilt. Every now and then you will actually run into a situation where that causes problems with being able to complete the signal path, but not that often.
Higher gains will also flatten your radiated pattern, which can be a problem when the other station is high above you, and also offer a narrower operating bandwidth in terms of frequency.
On the other hand, some days that extra horizontal gain can make a difference in a marginal area. It's all about trade-offs and picking the best tool for the job.
Since the OP indicated that a 1/4 seems to be working just fine, my basic response would be "if it ain't broke..."
Case in point- throw a 50 ohm dummy load on your radio- perfect SWR match. Now bend your 5/8 wave antenna a bit to try to slightly degrade the SWR. Any bets on which one will get better range?
The big problem with antenna flex is that the coverage pattern shifts with the antenna, causing it to tilt. Every now and then you will actually run into a situation where that causes problems with being able to complete the signal path, but not that often.
Higher gains will also flatten your radiated pattern, which can be a problem when the other station is high above you, and also offer a narrower operating bandwidth in terms of frequency.
On the other hand, some days that extra horizontal gain can make a difference in a marginal area. It's all about trade-offs and picking the best tool for the job.
Since the OP indicated that a 1/4 seems to be working just fine, my basic response would be "if it ain't broke..."