GMRS / CB antenna locations - near A pillar or mid point on hood

[Radio Guy]

Yeah I realize theres not a perfect antenna but I do want to optimize it as much as possible.

Also just to clarify a couple points

• If I used the 102" in my basement, I would put the ball mount on the side of the canopy - not interested in drilling holes in the bed of the truck itself....
  • Most likely though, would be a cowl mounted CB antenna. I do like the 102 on my TJ, but not sure if it is truly beneficial over a mid-load antenna (which is why the question - especially considering the non-SSB radio I am considering)
  • but if a 102 would net a better result overall than a cowl mounted mid-load antenna then that is a route I would consider
• The little puck GMRS antenna, if used, would go on metal (on the canopy not on the fiberglass top). But I am not sure if it really is any 'better' than a standard 1/4 wave antenna
  • that being said, it also probably depends on the radio. If a puck antenna nets better results than a 1/4 wave on cowl, then I see it a possibility
    • this also depends on if there is truly any benefit of the 575 over the 275. if the 275 with a cowl antenna nets the same result as a 575 with the puck antenna then mine as well go with the 275 since its smaller, easier to mount and cheaper

Looking forward to seeing those measurements! Its always been of interest since I use handhelds at work a lot anyway.

Not sure what you mean by the "basement". In my experience (45+yrs of installing this stuff) a 9ft whip on a ball mount on the outside upper bed wall will outperform a shorter 3-4ft antenna on the cowl area. The 9ft whip will be somewhat directional toward the mass of the vehicle as in mounted on the driver side rear it will work better toward the passenger front direction. A cowl mounted antenna will favor the mass of the hood so a driver side cowl mount will work better off the passenger front side.

The extent you go to for a CB install also depends on your type of use. If its just for keeping in contact with others while offroading, that doesn't require the biggest and best antenna on a custom mount with huge ground plane. If CB is a major hobby for you and you like talking all over the world when the skip is in then you will be spending more and the install will be more complex.

I'm a big ham radio geek so all my personal vehicle installs are more elaborate than most plus I test and evaluate a lot of equipment and antennas so my stuff is set up to easily swap radios and antennas. So far I have three NMO mounts and one heavy duty HF/CB mount that will accommodate just about any antenna ever made.

A shortened puck GMRS antenna is a compromise and a simple 6" long wire whip will work a little better.

 

[chorky]

Not sure what you mean by the "basement". In my experience (45+yrs of installing this stuff) a 9ft whip on a ball mount on the outside upper bed wall will outperform a shorter 3-4ft antenna on the cowl area. The 9ft whip will be somewhat directional toward the mass of the vehicle as in mounted on the driver side rear it will work better toward the passenger front direction. A cowl mounted antenna will favor the mass of the hood so a driver side cowl mount will work better off the passenger front side.

I have two 102 whips sitting in the basement of my house un-used. I meant to put them on my old truck but never did. Sold it. But kept the antennas. So if they net a better signal I might consider using them since I already have them.

I dont use CB a ton. But I live in an area where 5-15 miles between parties is a regular occurrence. Also mountainous terrain. But…. Knowing the small CB I will be using I am not sure how big of a difference the 102 will make over a smaller cowl antenna. If that makes sense? This CB does not have SSB capability

I'm a big ham radio geek so all my personal vehicle installs are more elaborate than most plus I test and evaluate a lot of equipment and antennas so my stuff is set up to easily swap radios and antennas. So far I have three NMO mounts and one heavy duty HF/CB mount that will accommodate just about any antenna ever made.

A shortened puck GMRS antenna is a compromise and a simple 6" long wire whip will work a little better.

at one point I thought about getting my license but just dont have the time right now. Good deal about the puck. I sorta figured that would be the case.

 

[Radio Guy]

I have two 102 whips sitting in the basement of my house un-used. I meant to put them on my old truck but never did. Sold it. But kept the antennas. So if they net a better signal I might consider using them since I already have them.

I dont use CB a ton. But I live in an area where 5-15 miles between parties is a regular occurrence. Also mountainous terrain. But…. Knowing the small CB I will be using I am not sure how big of a difference the 102 will make over a smaller cowl antenna. If that makes sense? This CB does not have SSB capability




at one point I thought about getting my license but just dont have the time right now. Good deal about the puck. I sorta figured that would be the case.

A better antenna like a 9ft whip over a shorter Firestick will make any radio talk further, reception will be better but noise and skip will still compete with whoever your trying to receive.

 

[chorky]

A better antenna like a 9ft whip over a shorter Firestick will make any radio talk further, reception will be better but noise and skip will still compete with whoever your trying to receive.

so now what about the GMRS. almost all antennas I see are 3, 5, or 6db gain. To my understanding thats good for flat terrain but hilly areas not so much. I see most antennas under 15" but always thought that the 31.5" was the better option. Suggestions?

I think I had one of these once...but never used it and not sure where it went.
https://dpdproductions.com/collecti.../products/gmrs-double-5-8-wave-mobile-antenna

 

[Radio Guy]

so now what about the GMRS. almost all antennas I see are 3, 5, or 6db gain. To my understanding thats good for flat terrain but hilly areas not so much. I see most antennas under 15" but always thought that the 31.5" was the better option. Suggestions?

I think I had one of these once...but never used it and not sure where it went.
https://dpdproductions.com/collecti.../products/gmrs-double-5-8-wave-mobile-antenna

Most gain figures on GMRS antennas are not real, they are either dBi or just made up lies. It takes a good 8ft of antenna to reach 6dBd gain and a 2ft tall mobile antenna with a 1/2 wave over a 1/2 wave or 5/8 over 5/8 with a phasing coil in the middle is not quite 3dB gain over a dipole, or about 2.5dBd gain. However it does work noticeably better than a 6in long whip at a distance down the road. Its not so much gain that you will see a huge problem talking down into a deep valley from the top of a mountain compared to a 6in whip. The whip will be a little better in the valley but not drastic.

The problem talking up and down mountains is with a huge 21ft 10dBd gain base antenna on a repeater. That will have lots of dead spots in a deep valley from the top of a mountain, but we don't use those on our jeeps. Ok, I have but not while driving.

This was my last truck set up with a 42ft air powered mast in the bed. My new Gladiator would not handle the load so I had to trade off the mast.

 

[chorky]

Most gain figures on GMRS antennas are not real, they are either dBi or just made up lies. It takes a good 8ft of antenna to reach 6dBd gain and a 2ft tall mobile antenna with a 1/2 wave over a 1/2 wave or 5/8 over 5/8 with a phasing coil in the middle is not quite 3dB gain over a dipole, or about 2.5dBd gain. However it does work noticeably better than a 6in long whip at a distance down the road. Its not so much gain that you will see a huge problem talking down into a deep valley from the top of a mountain compared to a 6in whip. The whip will be a little better in the valley but not drastic.

The problem talking up and down mountains is with a huge 21ft 10dBd gain base antenna on a repeater. That will have lots of dead spots in a deep valley from the top of a mountain, but we don't use those on our jeeps. Ok, I have but not while driving.

This was my last truck set up with a 42ft air powered mast in the bed. My new Gladiator would not handle the load so I had to trade off the mast.

Haha that's awesome. Yeah at work we have some massive repeaters and since the radio folks switched our BK handhelds and everything over to digital we are having major communication problems. so bad its not safe... but thats a different situation.

Ok so it sounds like the 5/8 over 5/8 (which seems to be quite typical) is plenty fine.

So now that that is narrowed down, what about the true difference between the Midland 275 and 575? Is there really a performance difference with cowl mounted antennas or is it not worth the extra cost?

 

[Radio Guy]

Haha that's awesome. Yeah at work we have some massive repeaters and since the radio folks switched our BK handhelds and everything over to digital we are having major communication problems. so bad its not safe... but thats a different situation.

Ok so it sounds like the 5/8 over 5/8 (which seems to be quite typical) is plenty fine.

So now that that is narrowed down, what about the true difference between the Midland 275 and 575? Is there really a performance difference with cowl mounted antennas or is it not worth the extra cost?

The Midland 275 has a 15 watt transmitter and the 575 has a 50 watt transmitter. The difference between 15 watts and 50 watts is 5.23dB and would be noticeable at a distance where signals are getting weak. Midland doesn't provide any info on the receivers to tell if one is better than the other.

 

[Sank]

Echoing radio guy, yeah the 5 dB makes a difference. Keep in mind that a 6 dB increase in the system (antenna gain or power or both) will double your range, so that's quite a bit in practice.

Also I always use dBi, never dBd. But for those of you not radio antenna types, 2.15 dBi equals 0 dBd. In other words, the ideal dipole is 2.15 dB more directional than the theoretical isotropic radiator. In my industry, dBi is how all antennas are rated.

 

[Radio Guy]

Echoing radio guy, yeah the 5 dB makes a difference. Keep in mind that a 6 dB increase in the system (antenna gain or power or both) will double your range, so that's quite a bit in practice.

Also I always use dBi, never dBd. But for those of you not radio antenna types, 2.15 dBi equals 0 dBd. In other words, the ideal dipole is 2.15 dB more directional than the theoretical isotropic radiator. In my industry, dBi is how all antennas are rated.

The 6dB gain vs doubling the distance works on paper and in space but not in the real world here on the ground. For example you can increase antenna gain by 6dB and when you double the distance there could be a mountain in the way that blocks all signals, etc. Then there is ground bounce between the two antennas that can up the signal level if the reflections arrive in phase or they can destroy the path by 20dB or more if the reflections arrive 180deg out of phase.

Ever listen to your FM car radio when you come to a slow stop and the station fades in and out rapidly about every 6ft? That is multipath distortion or signals from the station bouncing off stuff and arriving out of phase with signals direct from the tower. The main signal is plenty strong but the out of phase reflections can destroy reception when they arrive 180deg out of phase.

 

[chorky]

The 6dB gain vs doubling the distance works on paper and in space but not in the real world here on the ground. For example you can increase antenna gain by 6dB and when you double the distance there could be a mountain in the way that blocks all signals, etc. Then there is ground bounce between the two antennas that can up the signal level if the reflections arrive in phase or they can destroy the path by 20dB or more if the reflections arrive 180deg out of phase.

Ever listen to your FM car radio when you come to a slow stop and the station fades in and out rapidly about every 6ft? That is multipath distortion or signals from the station bouncing off stuff and arriving out of phase with signals direct from the tower. The main signal is plenty strong but the out of phase reflections can destroy reception when they arrive 180deg out of phase.

thats why I wanted to go with a 0db gain antenna. So to my understanding in laymans terms a 0db antenna is better for hilly terrain as it makes a well rounded signal path (imagine a bubble around the vehicle) whereas a high db gain is more flat and straight of a signal for distance. So sorta like the difference between a flood light and spot light. Right? Or am I off?

that being said I also thought that a longer antenna, being mounted near the hood, would be better than a short antenna for signal to extend to the rear. And further figured that a top load or mid load antenna would provide better rear signal length than a bottom load antenna. But the only 0 or 3db gain antennas I ever see are less than 18”. Only the 5/8 over 5/8 high gain antennas seem to be tall enough to poke over the roof by a few inches. But maybe that doesnt even matter.

 

[Sank]

The 6dB gain vs doubling the distance works on paper and in space but not in the real world here on the ground.

We're saying the same thing. The antenna directivity has to be aimed at your intended direction for that to help. But 5 dB gain in radio power has no directivity, so that's what the takeaway should have been to readers.

 

[Sank]

So sorta like the difference between a flood light and spot light. Right? Or am I off?

Yep you got it; 0 dB of directivity is more flood like, and 6 dB is more more spot like...more directive.

We're ignoring antenna efficiency in this conversation (the difference between gain and directivity), which would confuse more than necessary. So let's just keep it simple.

 

[chorky]

Yep you got it; 0 dB of directivity is more flood like, and 6 dB is more more spot like...more directive.

We're ignoring antenna efficiency in this conversation (the difference between gain and directivity), which would confuse more than necessary. So let's just keep it simple.

Efficiency is also important though... But I am still surprised that all the 0 gain, or even 3 db gain antennas are quite short... I would think that would inhibit good operation.

That being said....I can't seem to find hardly any antennas with a low db gain. So, what kind of performance loss in the mountains would one really notice with a 5/8 over 5/8? since its a high gain antenna (spot beam). And is there any way to quantify this type of performance visually to give us non-HAM's a better depiction of what actually happens? I have found photos of sketches online in regards to antenna and wattage performance but it always relates to general HAM frequencies like the 2m/70cm band - haven't found anything of the like for GMRS, or CB for that matter

I did just a quick google search - and the 467.x frequency band is 65cm in length which translates to 25.5 inches.

So, if my theory and math is right here, a 5/8 over 5/8 at 31.5" long is two 5/8 antennas (15.25' rounded from 15.9375") stacked on top (not sure how this actually affects signal though). But a 'standard' off the shelf antenna I found is 18" long which translates to essentially a 5.6/8 (not sure what other fraction that might be - 0.7 of the original wavelength).

So this is where it gets confusing to me. Because the CB band, I think is also called the 11m band (433 inch), is a 27.4 MHz range with a 36' (432 inch) wavelength. So this makes sense that the 102" whip with the 'standard' 6" spring is 108" which is 1/4 wavelength (the 'perfect' antenna).

So by the math, a 1/4 wave 0db gain antenna for GMRS is 6.375 inches tall - however, I never see any of these unless I'm looking in the wrong place. A half wavelength would be 12.75" tall. And a full wavelength is 25.5" (again never see these....). But, a 5/8 wavelength would be 15.9x inches long

So how does the 18" GMRS antenna factor into this? It seems to be a sub-fractional length of the original signal wavelength - not sure how this affects signal, but it bothers me when it doesn't make sense. Wouldn't just a standard 25.5" antenna be better performance? Its confusing to me how these various lengths are calculated and how they affect performance.

 

[chorky]

To add.. this antenna https://www.rightchannelradios.com/products/stryker-center-load-antenna-1 is effectively a 1/8 wave of the CB 11m band.

So the confusion is the antennas I have seen for CB break down into even fractions/numbers. Whereas the GMRS antennas do not.... So there must be more to it than just the length of antenna in relation to the frequency length.

 

[sarguy1941]

Any UHF 1/4 wave will work on GMRS. They are on just about every form of sales locations so not sure why you cant find them. Its in the middle of the LMR band.

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