5/8 vs 1/4 wave

[libslayer]

Could someone tell me difference between the two. Also perhaps the pros and cons. This is for my work truck. The end run will be my 29LX with a 300 Texas Star linear. Thanks in advance fer your help. Also. I haven't yet purchase the linear but it's what's available for about $50 from a friend if mine. If a different one is recommended I think y'all are the ones who would know. ;D



#DeepInTheHeartOfTexas- LibSlayer

[spitfire441]

Sept 28, 2013 17:06:23 GMT -5 libslayer said:

Could someone tell me difference between the two. Also perhaps the pros and cons. This is for my work truck. The end run will be my 29LX with a 300 Texas Star linear. Thanks in advance fer your help. Also. I haven't yet purchase the linear but it's what's available for about $50 from a friend if mine. If a different one is recommended I think y'all are the ones who would know. ;D



#DeepInTheHeartOfTexas- LibSlayer

Ok, I need to make a few CB myths clear as well as a bit of antenna theory.
On 27 MHz, where the CB band is a 1/4 wave antenna is approximately 8 1/2 feet or 17 feet for a 1/2 wave or just over 21 feet for a 5/8 wave. The formula for a 1/2 wave antenna is 468 divided by the frequency in MHz equals the 1/2 wave length for the frequency.
Now the reason you need to understand the previous is these are full size antennas for the band.
1/4 wave ground plane and a 1/2 wave dipole are for our pourposes here are the same antenna. A 1/2 wave dipole has a 1/4 wave radiator and a 1/4 wave RF ground, a 1/4 wave ground plane has the other half of the antenna as either 1/4 wave radials or the body of your car/truck as the other half of the antenna or ground plane.
Got that?
OK, a 5/8 wave antenna is 21 feet long "end fed " antenna, not being "naturally reasonant" as a 1/4 or 1/2 wave, these antennas require a matching network to make them work with your radio.

Now that you have digested that:
A 1/4 wave and half wave antennas have a sort of roundish ballon type radiation pattern with slight gain over a isotropic radiator (a scientific standard by which antenna gains are compared)
Now a 5/8 wave antenna has a squished pattern or imagine if you could, squishing a ballon in the center, it is smaller in hight but spreads out around the "horizon", that is gain, changing your radiated pattern from where its not needed (strait up) to where it is needed ( to the horizon).
Now moving on:
If you look at all available mobile antennas, the "king daddy" for mobile gain is the 1/4 wave or 108" whip. That is the biggest antenna you can practically mount on a mobile.
All other mobile antennas, I don't care what their claim for gain in CB fantasy land is but, they are shortened various amounts and designs claiming this and that. All the antennas are LESS gain than a 1/4 wave, because they are shortend, but are still 1/4 wave electrically (to the RF).
The longest antenna you can mount practically is the one you want, that one will be closest to a real size 1/4 wave gain but still less gain.
No such thing as a shortend 5/8 wave antenna, it is a loaded 1/4 wave in one form or other.

Spitfire 441

[libslayer]

WOW, that was a great explanation that I actually understood. It also explains why I was having such a hard time tuning the Wilson 1000. I replaced it after a week of frustration with my old K-40 2' top loaded whip. I've heard great things about the steel at dimensions you've described. Thank you so much for your help and explanation. I'm very excited to have found this forum.

[spitfire441]

Sept 29, 2013 19:58:04 GMT -5 libslayer said:

WOW, that was a great explanation that I actually understood. It also explains why I was having such a hard time tuning the Wilson 1000. I replaced it after a week of frustration with my old K-40 2' top loaded whip. I've heard great things about the steel at dimensions you've described. Thank you so much for your help and explanation. I'm very excited to have found this forum.

I'm glad I could help you with a bit of antenna theory, it will help keep the "snake oil salesmen" at bay.
Top loaded antennas are a very good type. The more metal before the load is better for radiation efficiency vs. a same length bottom loaded antenna.

[Sandbagger]

Sept 28, 2013 17:06:23 GMT -5 libslayer said:

Could someone tell me difference between the two. Also perhaps the pros and cons. This is for my work truck. The end run will be my 29LX with a 300 Texas Star linear. Thanks in advance fer your help. Also. I haven't yet purchase the linear but it's what's available for about $50 from a friend if mine. If a different one is recommended I think y'all are the ones who would know. ;D



#DeepInTheHeartOfTexas- LibSlayer

There really is no such thing as a true 5/8th wave CB mobile antenna. A 5/8th wave antenna is approaching 22' long, and to shorten that to a practical length would negate any gain that you would get from having a full 5/8th wave. The only full length mobile antenna is the 102" whip antenna . It is (with the addition of the 6" spring) a full 1/4 wave, which will have a gain of 1 (unity). Anything shorter than that is what is known as a "loaded" antenna. Loaded antennas have the advantage of being more convenient to mount on most cars and trucks without hitting overhead objects. But there is a price to pay. While a loaded antenna can be electrically equal to a full length antenna, the lack of radiating surface means that less of your signal is being radiated, while a percentage of that signal is being consumed as heat in the coil. There is a LOT of brain swelling theory that explains how this all works, and which types of loaded antennas are better than others, but a general rule of thumb is that the longer the antenna (up to the full 9' 1/4 wave) the better it will radiate.

[libslayer]

So I'm gonna go out on a limb here and guess that if I unwound the wire on my loaded antenna it would be about 108" long? Would that be fairly accurate?

#DeepInTheHeartOfTexas- LibSlayer

[Sandbagger]

Sept 30, 2013 21:17:55 GMT -5 libslayer said:

So I'm gonna go out on a limb here and guess that if I unwound the wire on my loaded antenna it would be about 108" long? Would that be fairly accurate?

#DeepInTheHeartOfTexas- LibSlayer

That all depends on the design. In some cases the answer would be yes, or at least you would be close. In the cases of base loaded whips, probably not. There are only a few windings on the core to provide the proper impedance match.

[mark4]

Sept 29, 2013 16:39:31 GMT -5 spitfire441 said:

Sept 28, 2013 17:06:23 GMT -5 libslayer said:

Could someone tell me difference between the two. Also perhaps the pros and cons. This is for my work truck. The end run will be my 29LX with a 300 Texas Star linear. Thanks in advance fer your help. Also. I haven't yet purchase the linear but it's what's available for about $50 from a friend if mine. If a different one is recommended I think y'all are the ones who would know. ;D



#DeepInTheHeartOfTexas- LibSlayer

Ok, I need to make a few CB myths clear as well as a bit of antenna theory.
On 27 MHz, where the CB band is a 1/4 wave antenna is approximately 8 1/2 feet or 17 feet for a 1/2 wave or just over 21 feet for a 5/8 wave. The formula for a 1/2 wave antenna is 468 divided by the frequency in MHz equals the 1/2 wave length for the frequency.
Now the reason you need to understand the previous is these are full size antennas for the band.
1/4 wave ground plane and a 1/2 wave dipole are for our pourposes here are the same antenna. A 1/2 wave dipole has a 1/4 wave radiator and a 1/4 wave RF ground, a 1/4 wave ground plane has the other half of the antenna as either 1/4 wave radials or the body of your car/truck as the other half of the antenna or ground plane.
Got that?
OK, a 5/8 wave antenna is 21 feet long "end fed " antenna, not being "naturally reasonant" as a 1/4 or 1/2 wave, these antennas require a matching network to make them work with your radio.

Now that you have digested that:
A 1/4 wave and half wave antennas have a sort of roundish ballon type radiation pattern with slight gain over a isotropic radiator (a scientific standard by which antenna gains are compared)
Now a 5/8 wave antenna has a squished pattern or imagine if you could, squishing a ballon in the center, it is smaller in hight but spreads out around the "horizon", that is gain, changing your radiated pattern from where its not needed (strait up) to where it is needed ( to the horizon).
Now moving on:
If you look at all available mobile antennas, the "king daddy" for mobile gain is the 1/4 wave or 108" whip. That is the biggest antenna you can practically mount on a mobile.
All other mobile antennas, I don't care what their claim for gain in CB fantasy land is but, they are shortened various amounts and designs claiming this and that. All the antennas are LESS gain than a 1/4 wave, because they are shortend, but are still 1/4 wave electrically (to the RF).
The longest antenna you can mount practically is the one you want, that one will be closest to a real size 1/4 wave gain but still less gain.
No such thing as a shortend 5/8 wave antenna, it is a loaded 1/4 wave in one form or other.

Spitfire 441

[mark4]

Yeah, like a Astroplane that claims to be a folded 5/8 wave?

[homerbb]

So as not to confuse the topic by introducing a base antenna into the explanation of mobile antennas, regarding the Astroplane, I own one and will comment. It is, I believe, a center loaded 1/2 wave antenna with a capacitance hat on the top shortening the upper half and moving the current maximum upward with a unique bottom half.
It is the odd bottom half that generates the most debate.

[bluebird]

Sept 29, 2013 19:58:04 GMT -5 libslayer said:

WOW, that was a great explanation that I actually understood. It also explains why I was having such a hard time tuning the Wilson 1000. I replaced it after a week of frustration with my old K-40 2' top loaded whip. I've heard great things about the steel at dimensions you've described. Thank you so much for your help and explanation. I'm very excited to have found this forum.

i have tried many mobile ants. but none can compare to the 6 coil alum fat boy ants.

[hotrod]

Oct 1, 2013 6:07:11 GMT -5 Sandbagger said:

Sept 30, 2013 21:17:55 GMT -5 libslayer said:

So I'm gonna go out on a limb here and guess that if I unwound the wire on my loaded antenna it would be about 108" long? Would that be fairly accurate?

#DeepInTheHeartOfTexas- LibSlayer

That all depends on the design. In some cases the answer would be yes, or at least you would be close. In the cases of base loaded whips, probably not. There are only a few windings on the core to provide the proper impedance match.

IF you had a 7 foot top load antenna it would probaly be close to the performance of a 102 whip.the skipshooter is a great top load antenna.
a 2foot top load isnt even in the ballpark. id start with at least a 5foot top load . but thats just me.the center loaded metal coils perform
good too but i find there more for if your running alot of power