General Question About Installation of Remote RD Antennas

MachineLearner

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So, as you may have noticed in my intro, I'm new to the world of CMs, but I am not new to RF in general. I've been a licensed amateur since 2009, and do a lot of tinkering with RF (admittedly, at much lower frequencies).

So, here's a question. In almost every remote RD install, I see the receiver horns/antenna being mounted in the front bumper. In my mind, this immediately creates a problem. In the SHF/EHF bands where X, K, and Ka reside, propagation is line-of-sight and to a lesser degree, reflected energy. In other words, if you can't see the emitter, or a reflected surface of the emitter, you can't receive the signal. That being said, why are remote antennas not mounted on the roof of your vehicles (and not made to be roof mounted)? The lower on the car, the closer the horizon is to the car. The higher you can get the receiving antenna, the farther you can see with that antenna.

Is it purely for the purposes of stealth, or am I missing some propagation phenomenon? Admittedly, I don't usually tinker with frequencies this high. Genuinely curious.
 

NorEaster18

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I don't know intricacies, as I only play with windshield mounts. However, I know there are people here who install remotes in different places, from behind the bumper to the roof. @KASHER1979 is a roof expert
 

RedRocket

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1.Is it purely for the purposes of stealth,
2.or am I missing some propagation phenomenon? Admittedly, I don't usually tinker with frequencies this high. Genuinely curious.
1.Yeah, for some it is.
2.you're not factoring in the "Inverse Square Law" phenomenon. :)
 

MachineLearner

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2.you're not factoring in the "Inverse Square Law" phenomenon. :)
That would only have to do with the power density of the wave at a given distance in free space, but line-of-sight is still required.

If you put a wall in front of a flashlight, it's power density past the wall drops to zero (assuming the wall is made of an opaque material). All light is either reflected or absorbed by the wall, none passes through. As frequency increases, especially above UHF, RF begins to function more and more similarly to light in terms of its interaction with solid objects. As such, a ~34GHz antenna can be thought of as a camera. If there's something in between the camera and the light source, for example, a small hill, the camera will not see the light source. But if you raise the camera up say, 5 feet, it might be just enough to take a picture of the light source on the other side of the hill.

That being said, SHF/EHF frequencies are absorbed to some degree by the atmosphere itself (and the water in the atmosphere), so power density would be lower than predicted by the inverse square law, I suspect this is what you are referring to. Though at the frequencies we are talking about, it's only about ~0.11dB/kM, so that level of attenuation would have very little effect on reception at the antenna... at least not anywhere near enough to even matter for the purposes of an RD. So the benefits of additional radio horizon far outweigh the costs of atmospheric absorption (specific attenuation) and inverse square power density dissipation.

TL;DR: An increase in height of 5 feet increases the theoretical radio horizon by 1.59 miles, in a hypothetical comparison between a bumper height of 1.5 feet to a roof height of 5.5 feet.

Screenshot at Jan 05 21-44-52.png


I don't have the equipment necessary to do so, but I would really like to see a real world test comparison between the same antenna/receiver/system comparing a roof mount to a bumper mount. I'd be willing to bet a roof mount would net far earlier warning with the same equipment.
🤔

(of course, it would also net earlier warning of falses, so....)
 

Jon at Radenso

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There is zero question that mounting an antenna on the roof is ideal. On the flip side, probably less than 1 in 100 consumers are willing to do so when bumper mounting can get still get them a range of several miles. Sensitivity on these receivers is decent; even among non-Theias. It's selectivity that has been mostly lacking.

Everything you are saying is absolutely correct - it just has to do with consumers not being willing to roof mount an antenna.
 

Jon at Radenso

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Yeah, I figured as much. As an amateur radio guy, gaudy antennas on roofs are my wheelhouse. 😁
In college I got REALLY good at pausing outside parking garages and quickly reaching up to unscrew my whips before the people in line behind me got pissed :)
 

KASHER1979

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My detectors perform AMAZING up there , but as @Jon at Radenso already said it won't ever be designed this way simply because it's not going to work for many people, and even those that have roof racks aren't going to want to mount it up there. But IMO it's just crazy good. My old M3s like STIRO and 9500ci, in some cases have been able to see signals much sooner than even my R3s and R7s. It's just crazy. lol

Also my Radenso Remote I have mounted in on the roof as well. It's crazy good!! ALerts before the R3/R7

I had a Stinger.... Put it up there, not so good. Couldn't beat the Redline O I had on my WS..... Not consistently anyway. I never had luck with that unit. But the Radenso, Escorts, Bels, all perform like magic up there. But again we are talking about being outside and ON A ROOF. lol So it's just gonna do better up there than a WS unit in many cases.
 
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RedRocket

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That would only have to do with the power density of the wave at a given distance in free space, but line-of-sight is still required.

If you put a wall in front of a flashlight, it's power density past the wall drops to zero (assuming the wall is made of an opaque material). All light is either reflected or absorbed by the wall, none passes through. As frequency increases, especially above UHF, RF begins to function more and more similarly to light in terms of its interaction with solid objects. As such, a ~34GHz antenna can be thought of as a camera. If there's something in between the camera and the light source, for example, a small hill, the camera will not see the light source. But if you raise the camera up say, 5 feet, it might be just enough to take a picture of the light source on the other side of the hill.

That being said, SHF/EHF frequencies are absorbed to some degree by the atmosphere itself (and the water in the atmosphere), so power density would be lower than predicted by the inverse square law, I suspect this is what you are referring to. Though at the frequencies we are talking about, it's only about ~0.11dB/kM, so that level of attenuation would have very little effect on reception at the antenna... at least not anywhere near enough to even matter for the purposes of an RD. So the benefits of additional radio horizon far outweigh the costs of atmospheric absorption (specific attenuation) and inverse square power density dissipation.

TL;DR: An increase in height of 5 feet increases the theoretical radio horizon by 1.59 miles, in a hypothetical comparison between a bumper height of 1.5 feet to a roof height of 5.5 feet.

View attachment 137595

I don't have the equipment necessary to do so, but I would really like to see a real world test comparison between the same antenna/receiver/system comparing a roof mount to a bumper mount. I'd be willing to bet a roof mount would net far earlier warning with the same equipment.
🤔

(of course, it would also net earlier warning of falses, so....)
I brought up the Inv. Sq Law b/c even a preferred low mount RD (whether there for stealth or to prevent an expensive theft) can still be an excellent performer via off-axis reflections or propagating under vehicles, as well.
 

Deacon

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TL;DR: An increase in height of 5 feet increases the theoretical radio horizon by 1.59 miles, in a hypothetical comparison between a bumper height of 1.5 feet to a roof height of 5.5 feet.
Well, I’m no mathematician, but that’s an increase in height by 4 feet ;)

I don’t have any remote mount detectors, never have. I definitely set up my windshield mount detectors high and tight against the headliner and recommend others do the same whenever possible. It can only help, especially hardwired in behind a tint strip, both to obscure visibility to others outside the vehicle whether moving or parked and to give the horn(s) the best vantage point for receiving signals.

But for remote mount detectors, it seems like mounting in the grille would be about the best practicable option for most people. Personally I’d rather not have it on the bumper, due less to height considerations than to minimizing the chance of damage during a minor incident with a fender bender, speed bump, or curb. Sometimes stuff happens. They’re called a bumper for a reason ;)

If you have a roof rack on an SUV or minivan or something and don’t mind mounting it up there (at eye level for many vehicles), go for it! That approach will give you the best possible range. About the best possible setup is the kind of MPG-destroying off-road-oriented roof basket type racks you see on top of Jeep Cherokees and Toyota 4Runners and Nissan Pathfinders, etc, often with light bars and such attached (which also helps write off the cabling). But I think too much is made of line-of-sight type considerations for day to day use. The more extreme the sensitivity of the detector in question, the less practical difference it makes.

I do think it would be neat to see a remote enclosure with the cable under the body rather than behind it, or at least have that as an option. Then you could mount it directly to the roof if desired, like an OEM “shark fin” radio antenna or an NMO mount for two-way radio antennas. You could even, in theory, package both horns into a single enclosure like a windshield mount, giving you a single install point in the best possible location. On top of taller trucks and SUVs it would make a ton of sense. But with today’s panoramic sunroofs and heavily curved roofs, I don’t know how broadly applicable it would be, and I doubt many people would want to stick a wart of some sort on top of their high-dollar sports car or sedan. Then there’s the question of how well electronics would hold up over time, baking in the sun. Maybe that’s a dumb question, though.

I think the reason you see so many remote antennas mounted in or around the grille is that’s just plain the best all-around place to mount it for nearly all vehicles.
 
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benzr

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I don't know intricacies, as I only play with windshield mounts. However, I know there are people here who install remotes in different places, from behind the bumper to the roof. @KASHER1979 is a roof expert
X 10 on @KASHER1979 !!

Her is the Roof Mount ADOPTER/MASTER 😎😎👍👍
 

Maz3

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So, as you may have noticed in my intro, I'm new to the world of CMs, but I am not new to RF in general. I've been a licensed amateur since 2009, and do a lot of tinkering with RF (admittedly, at much lower frequencies).

So, here's a question. In almost every remote RD install, I see the receiver horns/antenna being mounted in the front bumper. In my mind, this immediately creates a problem. In the SHF/EHF bands where X, K, and Ka reside, propagation is line-of-sight and to a lesser degree, reflected energy. In other words, if you can't see the emitter, or a reflected surface of the emitter, you can't receive the signal. That being said, why are remote antennas not mounted on the roof of your vehicles (and not made to be roof mounted)? The lower on the car, the closer the horizon is to the car. The higher you can get the receiving antenna, the farther you can see with that antenna.

Is it purely for the purposes of stealth, or am I missing some propagation phenomenon? Admittedly, I don't usually tinker with frequencies this high. Genuinely curious.
Don't confuse "line of sight", meaning straight line RF that must be "visible" to each antenna. There are many examples of radar domes, satellite TV dishes, microwave telephone network installations, WiFi, GPS antennas and the like that have covers over the horns/antennas. Non-metallic covers don't have a meaningful negative impact on RF signals as there is nothing to reflect or absorb the signal. Even at microwave freqs, they'll follow the curve of the earth SLIGHTLY such that telephone microwave installations run each tower on an angle to the last so any "over shoot" doesn't cause interference.

Now antenna height vs. distance is another discussion altogether, but the increased height from the bumper/grill to the car roof is a fairly small measure that wouldn't yield much in the way of increased range, I suspect. As others have mentioned, the theoretical line of sight distance is easily calculated.

Good question, and I hope I've help to clarify the matter :-D
 

MachineLearner

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Don't confuse "line of sight", meaning straight line RF that must be "visible" to each antenna. There are many examples of radar domes, satellite TV dishes, microwave telephone network installations, WiFi, GPS antennas and the like that have covers over the horns/antennas. Non-metallic covers don't have a meaningful negative impact on RF signals as there is nothing to reflect or absorb the signal. Even at microwave freqs, they'll follow the curve of the earth SLIGHTLY such that telephone microwave installations run each tower on an angle to the last so any "over shoot" doesn't cause interference.

Now antenna height vs. distance is another discussion altogether, but the increased height from the bumper/grill to the car roof is a fairly small measure that wouldn't yield much in the way of increased range, I suspect. As others have mentioned, the theoretical line of sight distance is easily calculated.

Good question, and I hope I've help to clarify the matter :-D
Yes, in the case of using the term "line-of-sight" in an RF context, it is generally understood to mean what an RF receiver can see. So for example, if you stand in your kitchen, you probably have a line-of-sight into your yard, even though you are completely surrounded by solid objects, because windows are transparent in the visible spectrum. Same thing is true when discussing RF. A plastic bumper will be mostly transparent.

I was bringing up placement not because of the bumper itself, but solely because of the height. I did the calculations in a follow-up post above, and raising the receiving antenna 4 feet yields a hypothetical increase in radio horizon by 1.59 miles. That's a significant improvement in range, all other things being equal.
 

Maz3

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Yes, in the case of using the term "line-of-sight" in an RF context, it is generally understood to mean what an RF receiver can see. So for example, if you stand in your kitchen, you probably have a line-of-sight into your yard, even though you are completely surrounded by solid objects, because windows are transparent in the visible spectrum. Same thing is true when discussing RF. A plastic bumper will be mostly transparent.

I was bringing up placement not because of the bumper itself, but solely because of the height. I did the calculations in a follow-up post above, and raising the receiving antenna 4 feet yields a hypothetical increase in radio horizon by 1.59 miles. That's a significant improvement in range, all other things being equal.
Agreed. I had read that your concern was having something in front of the detector antenna would "blind" it from receiving the signal, but you've clarified that isn't necessarily the case.

In re-reviewing the posts shortly after I posted, I realized it was in fact you that had done the math, but I was unable to edit my post as five minutes had passed and mine had locked down - I hope I didn't offend in not acknowledging your calculations.

It would be interesting to know the practical one-way distance the radar would cover to better evaluate any real world benefit in the increased line of sight, keeping in mind that both the radar and detector are using directional antennas so they have to be pointed toward each other regardless. Mountain top to mountain top range would be spectacular though ;-)
 
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MachineLearner

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Agreed. I had read that your concern was having something in front of the detector antenna would "blind" it from receiving the signal, but you've clarified that isn't necessarily the case.

In re-reviewing the posts shortly after I posted, I realized it was in fact you that had done the math, but I was unable to edit my post as five minutes had passed and mine had locked down - I hope I didn't offend in not acknowledging your calculations.

It would be interesting to know the practical one-way distance the radar would cover to better evaluate any real world benefit in the increased line of sight, keeping in mind that both the radar and detector are using directional antennas so they have to be pointed toward each other regardless. Mountain top to mountain top range would be spectacular though ;-)
Not at all, I probably should've been more clear in my original post about why mounting within the bumper was concerning to me. But speaking generally, the higher the antenna is off the ground, the better performance will be, in almost every circumstance.

Radar detectors (at least for the moment), are a somewhat different animal than RF in general, because there are aesthetic considerations, and raising the antenna will also cause falses more frequently. Hopefully Theia will solve the latter problem. The former will always be a concern for most people.

X, K and Ka band are in the SHF/EHF bands, as such, their propagation is actually slightly less than inverse square, given that both the water in the atmosphere, and the atmosphere itself absorb energy at those frequencies. But without doing the calculations, I'm betting an R3 (for example) could detect a signal at 10 miles pretty easily, if given line-of-sight to the emitter. The limiting factors are terrain, buildings and foliage, and height of the receiver. It could be a really interesting experiment to take a radar gun up on a tall building, and shoot it at a detector say 10 miles away, where there is nothing between the transmitter and the receiver.
 

Godowsky17

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Not at all, I probably should've been more clear in my original post about why mounting within the bumper was concerning to me. But speaking generally, the higher the antenna is off the ground, the better performance will be, in almost every circumstance.

Radar detectors (at least for the moment), are a somewhat different animal than RF in general, because there are aesthetic considerations, and raising the antenna will also cause falses more frequently. Hopefully Theia will solve the latter problem. The former will always be a concern for most people.

X, K and Ka band are in the SHF/EHF bands, as such, their propagation is actually slightly less than inverse square, given that both the water in the atmosphere, and the atmosphere itself absorb energy at those frequencies. But without doing the calculations, I'm betting an R3 (for example) could detect a signal at 10 miles pretty easily, if given line-of-sight to the emitter. The limiting factors are terrain, buildings and foliage, and height of the receiver. It could be a really interesting experiment to take a radar gun up on a tall building, and shoot it at a detector say 10 miles away, where there is nothing between the transmitter and the receiver.
No doubt the RF would be detected at 10 miles in such a circumstance, as the R3 has detected LEOs at close to that distance even in real-world scenarios. 15 or 20 miles might be more of a challenge.
 

Phantom Z3

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@nicholat has a roof mount. I believe it's a NR DSP. Looks goofy but it works on his van!

Tbh I have an R3 and my car is really low and roof mounting is definitely not an option (you know, because water) so very little use for a remote mount.
 

Brainstorm69

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X, K and Ka band are in the SHF/EHF bands, as such, their propagation is actually slightly less than inverse square, given that both the water in the atmosphere, and the atmosphere itself absorb energy at those frequencies. But without doing the calculations, I'm betting an R3 (for example) could detect a signal at 10 miles pretty easily, if given line-of-sight to the emitter. The limiting factors are terrain, buildings and foliage, and height of the receiver. It could be a really interesting experiment to take a radar gun up on a tall building, and shoot it at a detector say 10 miles away, where there is nothing between the transmitter and the receiver.
Even a $40 detector did 12 miles against Ka 34.7 here:

 
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