1/4 wave vs. 5/8 wave

[wa2zdy]

Well IMHO,

I have used a 1/4 wave mobile antenna for 2m for about a year and now am currently using a 5/8 wave mobile.
The 5/8 antenna Receives and Transmits much, much better. By the way the 1/4 was a Diamond, and the current antenna is a cheaper brand.
I can now hear more repeaters AND transmit into them where I couldn't even hear them with the 1/4.

The difference here is that if you're on 2m, you're a ham. Hams use multiple repeaters in non-specific areas. If a 5/8 works better for you, it means you are using repeaters off toward or even over the horizon. In such a case, the flatter radiation pattern will obviously be better.

The original poster appears to be listening to a specific system with a specific coverage area. As an EMT, he only needs to hear his system in a specific area - where he is when he's listening to his system. In that case he must evaluate his specific needs.

If his system transmits from the roof of the firehouse and the coverage area is flat, a 5/8 will almost surely work best for him. (IF he has an adequately sized ground plane under the antenna. If not, the gain of the 5/8 will be lost anyway.) If on the other hand his system is up on top of a skyscraper or mountain and he's never more than a few miles from it, the flatter pattern of the 5/8 will be a disadvantage for him.

As others have said, what will work best for him depends on his situation. Hams will generally find a 5/8 better overall as they drive all over, rather than within a specific coverage area of a land mobile system.

And by the way, the radiation pattern affects reception and transmission equally.

 

[chpalmer]

5/8 over coil puts the current of the antenna about the mid section. The high voltage is in the coil and at the top. The portion of the antenna leaning over in the wind is more apt to be the high voltage and not so much current. If your talking the dual band antenna's, their a bit different.

Ground losses tend to be high with quarter wave antenna's, right?...

The topography I have to cover changes by 600 feet in very short order, with lots of valley's and cliff's. Ive tested 1/4's 3dBd's and 5dBd's on uhf and can say the only bad choice for my area was the 5dBd from any manufacturer for transmit in a test involving techs at the sites watching our spectrum analyzers. The 1/4's did suffer on the receive side of things. Taller, higher gain antenna's just have a better chance to see more of the signal.

Best bet is to get the more of the signal to and from the base of the antenna in the first place. Use a good quality cable kit and have the right ground plane. We use 8x kits exclusively now on uhf. State Patrol here uses 8x or mini 8 on everything they have.

 

[ScanDaBands]

Hey guys while we are on the 1/4 , 5/8ths thing here.....Has anybody ever used a 5/8 "slim duck" antenna on a scanner and if so , did it do ok "overall" ... I'm talking on a wide band scale ok?

 

[chpalmer]

And by the way, the radiation pattern affects reception and transmission equally.

In a perfect lab setting yes... In the field, not so fast.

I can tilt the antenna on a tower in order to cover a specific section of land. However, that same antenna will still pick up a mobile out of the intended coverage area at close to the same signal level as if it where pointed at the mobile transmitting, not so much horizontally but vertically speaking. (And to a point. Eventually, you would be looking down the length of the antenna and logic says that wouldn't pick up well at all....)

This means that a repeater can easily reach that mobile with the high gain antenna down in the valley out a ways with no line of site between them. But because the mobiles antenna is a higher gain model, maybe chosen to make up for the low power radio and high loss numbers of the chosen coax, or just because thats what everyone else runs, the flat signal has no chance of making it out of the valley in the direction of the repeaters antenna.

Go the opposite direction and use no gain and you loose the good reception you had.

 

[joefoss]

Antenna Radiation

I always believed that all 1/4 wave antennas radiate from their tips. Therefore, if your 1/4 wave antenna is longer then a loaded antenna, it will have an advantage. I also believed that the loaded antenna radiates from the coil. Is this assumption I have correct?? Thanks,

 

[joefoss]

Can someone help me?

 

[LtDoc]

It isn't a matter of -where- an antenna radiates from, it all radiates. If you could remove the 'base' of the antenna, or the 'center' of an antenna, then the 'rest' of the antenna isn't going to radiate well at all.
Loading coils don't radiate any more or less than an equivalent straight section of the antenna. Just because there's a lot of wire making up that coil doesn't mean it radiates differently, and that's because of -how- that wire is shaped. A coil in an antenna only has one 'job' and that's to supply a required inductance/reactance. The addition of that inductance/reactance does affect the radiation of the -whole- antenna, but not because -it- radiates 'more'.
There are all kinds of misconceptions about antennas and they are more prevalent than some people would ever believe. Gotta be careful about 'common' knowledge, sometimes it ain't so 'common' or factual.
- 'Doc

 

[prcguy]

An antenna radiates the most where the current is the highest, in the case of a 1/4 wave whip that would be the lower part of the antenna. In a center loaded antenna most of the current is below the coil and the coil does not radiate much. An end fed half wave would radiate more from the center where the current is the max and so on.
prcguy

I always believed that all 1/4 wave antennas radiate from their tips. Therefore, if your 1/4 wave antenna is longer then a loaded antenna, it will have an advantage. I also believed that the loaded antenna radiates from the coil. Is this assumption I have correct?? Thanks,

 

[joefoss]

Antenna

Thanks,
Joe

 

[Anderegg]

I love all this discussion about RADIATING when answering a question about RECEIVING.......

I found in testing on three 800 trunked systems using the RSSI with a 396XT, that a 1/4 wave 800 works better for receive than a 5/8 wave 800........go figure......

Paul

 

[W8RMH]

I love all this discussion about RADIATING when answering a question about RECEIVING.......

I found in testing on three 800 trunked systems using the RSSI with a 396XT, that a 1/4 wave 800 works better for receive than a 5/8 wave 800........go figure......

Paul

Almost as funny as hijacking a six year old thread.

 

[prcguy]

Antennas are reciprocal, whatever the radiation pattern and current is along its length in transmit on a particular frequency is exactly the same in receive.
prcguy

I love all this discussion about RADIATING when answering a question about RECEIVING.......

I found in testing on three 800 trunked systems using the RSSI with a 396XT, that a 1/4 wave 800 works better for receive than a 5/8 wave 800........go figure......

Paul

 

[loumaag]

Topic Closed

Okay. This topic is far from the original point, so it is now closed.