WRUJ218 Posted October 13, 2022 Report Share Posted October 13, 2022 I'm looking at putting a Nagoya NL-770G (38", 6dBi) or Nagoya UT-72G (20", 3.5dBi) mag mount on top of a round metal roof vent (about 24-30" dia) near the back-side-peak of my roof. The roof is asphalt shingles. Two floors plus attic - guessing the peak is 35-40ft. I haven't measured the roof incline yet. My experience on roofs is minimal so it's hard to estimate, but I find myself on a roof for one reason or other maybe once a year. The incline was uncomfortable and I was ready to be off after my exploratory trip. I have radiant thermal barrier in the attic attached to the rafters, so an attic antenna is unfortunately out. I have a new Wouxun KG-1000G I'd like to use in an upper bedroom. I am interested in using a mobile whip antenna since it should be pretty invisible from the street and neighbors, even if it sticks above the roof peak. I have a few questions if you guys would like to share some wisdom... 1. If I place the mobile antenna on the roof vent, using the vent as a ground plane, what kind of performance hit (not much, or not worth it?) would I take by bending the antenna to vertical at the base of the antenna? I assume the ground plane not being perpendicular to the antenna is where the issue would be? Or would it be better that I just let the whip point out at the same angle with the roof? If I did that, then I suspect that the radiation pattern is far from ideal. Perhaps the lower gain antenna would be better because the lobes are not so directed? 2. I don't mind coax running down the back side of my roof. But I haven't decided whether it would be easier to run the coax into the attic through the vent. In my case, trying to get the coax into the radio bedroom in that little space in the corner of the attic might be impossible, so that might be why I would run it down the roof and then straight in through the exterior wall, with a little careful routing along trim lines. If I do grounding correctly, then I have to run ground wire externally anyway. So I'm leaning towards running coax externally as well. If ya'll would like to share any experience or wisdom about what I'm doing or point me to some useful products, I would much appreciate it! Quote Link to comment Share on other sites More sharing options...
Sshannon Posted October 13, 2022 Report Share Posted October 13, 2022 My rule on metal roofs is to get on them as seldom as possible and to rope off if the pitch is uncomfortable. At that height, and running the cable the way you have to you’re possibly going to lose a lot of signal just in the coax. Be sure to use the best coax you can. Here’s a website that has several charts showing coax losses. Be sure to look at the 450 MHz values: https://www.w4rp.com/ref/coax.html Second, I’m not sure that either of those antennas will get you the performance you might hope. Try putting that mag mount with either Nagoya onto a metal pie plate on a painters pole out in your yard first, or even on the roof of your car. Does it work well enough? If so, then maybe get on the roof. If it doesn’t work then you’ve saved yourself a trip. Quote Link to comment Share on other sites More sharing options...
kidphc Posted October 13, 2022 Report Share Posted October 13, 2022 I have an 8Ft fiberglass antenna in my attic. Fortunately, I have a vent right over my ground location and it was the shortest run. Lately, everyone is trying simplex more. I can hear them but its noisy since the antenna is indoors. i however, plan on installing a mobile antenna on the peak of the eaves of roof side. Which again would be a straight run down to the grounding point. Why is this important? Ground wiring or installations shouldn't have 90 degree bends. Plus it will reduce the cost of the install by using the shortest amount of LMR400 or Heliax, which will end up being a majority of the cost of your install. I plan on using a mobile nmo base mount. They really are for temporary installations. The maintenance is higher, which is a problem. Why not a base vertical? 3 letters HOA. Should hide a tons better then a 1 inch round white fiberglass tube. From the front of the house it is about 54" to the installation point. So really 2 downsides. One N type connector, and maintenance up. The mount i plan on using. https://a.co/d/beQaNDn This is an option as well. Do you even know if the vent pipe is steel or aluminum? If it is aluminum, not going to work. With bends in antennas, it can cause a impedance shift at the bend throwing you out of the band you are trying to use. We often don't want bends in our antennas. You see tractors all the time with their antennas at 45 degrees, since the antenna bends when driving. They do it to keep the Swr swings low. You are going to take a compromise antenna, and make the install a compromise, couple the metal roofs proximity and you are making another compromise. I expect a thread on why you are only getting 1 mile on simplex at 50 watts and can't talk to a repeater without hash when it is 5 miles away. Sshannon 1 Quote Link to comment Share on other sites More sharing options...
KAF6045 Posted October 13, 2022 Report Share Posted October 13, 2022 10 hours ago, WRUJ218 said: If ya'll would like to share any experience or wisdom about what I'm doing or point me to some useful products, I would much appreciate it! https://www.eznec.com/ Model the roof as a wire grid (spaced for the frequency). Probably start with a vertical half-wave dipole for the antenna (~12.6 inch -- could probably make one out of a wire coat-hanger; tricky part is a non-conductive mast to hold it and small balun) {I don't have enough experience to model what ever internals the Nagoya's have to get those lengths}. Half-wave dipoles don't need ground-plane (but should have a balun, which may be relatively large for the antenna). Quarter-wave (~6.3 inch) does need a ground plane, so may be more difficult to model (you'd need on wire segment connecting to the roof, most likely). Don't bend the antenna... Better to rig a mounting plate that corrects for the slope -- heck, make the plate large enough to be a flat ground-plane for the frequency for use with quarter-wave, while you are at it. Do you have sewer or furnace vent tubes? You should be able to rig a clamp-on mast mount to one of those. Quote Link to comment Share on other sites More sharing options...
WRUS537 Posted October 13, 2022 Report Share Posted October 13, 2022 I have an HOA also, What I did was installed a TV antenna, they can not ban those or cloths lines. Something to do with natural things or something. I then put my gmrs on top of the tv antenna (on the pole) You see the tv antenna but have to be really looking to notice the GMRS antenna. Quote Link to comment Share on other sites More sharing options...
axorlov Posted October 13, 2022 Report Share Posted October 13, 2022 Thin mobile antenna will be nearly invisible on the roof, but I would go with 1/2 wave, to not worry about ground plane. Something like Laird B4502 should do the job. Quote Link to comment Share on other sites More sharing options...
WRUJ218 Posted October 13, 2022 Author Report Share Posted October 13, 2022 Thank you all for the input! Some clarifications from my original post... My roof is asphalt shingles. The round vent near the peak is metal - likely a galvanized steel because another mag mount base I had stuck too it just fine. @axorlovThe Laird B4502 is definitely one I should look at - thanks. It is only 15" with a base coil. I would still use a mag mount base to stick to the metal vent. @kidphcThe vent I'm talking about using is a low-profile flat round passive vent, about 24" diameter, not a pipe. It is just for attic ventilation. @KAF6045Yeah I will probably see what happens without bending the antenna first. I thought about making a platform for a mag mount, but then I have a lot more work to do to make it stealth to my neighbor, if I can even make such a platform stealth. They sell bracketry to lay across your roof peak and weigh it down with blocks, but there's nothing stealth about that. @SshannonGood suggestions. I am getting a Nagoya UT-72G tomorrow for putting on my wife's car, so I will play with it on a baking sheet outside the window for starters, and see how high I can raise it for testing. I was also thinking about the attic thing again. I was wondering how big of an opening in the radiant barrier I'd have to make at the peak of the rafters to get decent signal past it, if I put a ground plane plate up there for a 1/4 wave mag mount. I may have to experiment with that first because that would solve a lot of problems. I realize it's a "everything affects everything", but I might tinker with that, and I can always put the radiant barrier back in place if it doesn't work. Definitely want to keep as much of the radiant barrier intact as possible because that made about a 30F difference in my summer attic temps! @kidphcYes I am interested in seeing if I can get decent simplex comms from my house. I'm not expecting 10 miles or anything with a stealth antenna, but hoping for at least 2-3. That's pretty much our life radius. The repeaters here in San Antonio are awesome and I can get into them from just about anywhere with my HT with OEM antenna. Their network covers the entire city+. But in an emergency situation I'm not expecting to rely on them. I have some experimenting to do this weekend... Sshannon 1 Quote Link to comment Share on other sites More sharing options...
KAF6045 Posted October 14, 2022 Report Share Posted October 14, 2022 2 hours ago, WRUJ218 said: Thank you all for the input! Some clarifications from my original post... My roof is asphalt shingles. The round vent near the peak is metal - likely a galvanized steel because another mag mount base I had stuck too it just fine. Okay... No need to make a wire grid layout for roof modeling 2 hours ago, WRUJ218 said: @kidphcThe vent I'm talking about using is a low-profile flat round passive vent, about 24" diameter, not a pipe. It is just for attic ventilation. @KAF6045Yeah I will probably see what happens without bending the antenna first. I thought about making a platform for a mag mount, but then I have a lot more work to do to make it stealth to my neighbor, if I can even make such a platform stealth. They sell bracketry to lay across your roof peak and weigh it down with blocks, but there's nothing stealth about that. Does the vent have enough of a lip to fit an angle-adjustable clamp-on mount? https://www.hamradio.com/detail.cfm?pid=H0-009011 (May have to flatten part of the vent to allow the clamping surface to fit) You'll have to fit a proper mount/coax system (NMO, double-ended SO-239 bulkhead fitting, etc.) to match an antenna (if trying to use HT style whips, you may need a PL-259<>SMA (of proper gender). Quote Link to comment Share on other sites More sharing options...
WRUC860 Posted October 16, 2022 Report Share Posted October 16, 2022 Quote Just a suggestion, but run some LMR-400 coax since you will have a long run. Much less loss than RG58. You don't mention what radio you are using, but especially with a HT, you only have a few watts to begin with, don't let them escape your coax. Quote Link to comment Share on other sites More sharing options...
wayoverthere Posted October 16, 2022 Report Share Posted October 16, 2022 It's hard to beat a 1/4 wave "hatpin" for stealth. Even with the whip (all 6" of it) above the roofline, it'd be hard to notice, especially sitting by the vent. Alternately, for stealth, I might go with one of laird's "phantom" (about the only brand I'd give that type a chance) antennas, since they have some no ground plane needed options. A black one mounted at the top of a vent pipe (on a bracket painted black to match the pipe) add a tee and a 90 degree bend up inside the attic to bring the cable out, but keep water out, and go. https://theantennafarm.com/shop-by-categories/shop-all/mobile-antennas/300-512-mhz-uhf/no-ground-plane-antennas/11431-laird-connectivity-trab4500n-detail (I'd paint/sharpie/peel the logos off too, to help it blend with the pipe) Quote Link to comment Share on other sites More sharing options...
jec6613 Posted October 16, 2022 Report Share Posted October 16, 2022 On 10/13/2022 at 6:43 PM, WRUJ218 said: I'm not expecting 10 miles or anything with a stealth antenna, but hoping for at least 2-3. That's pretty much our life radius. The repeaters here in San Antonio are awesome and I can get into them from just about anywhere with my HT with OEM antenna. Their network covers the entire city+. But in an emergency situation I'm not expecting to rely on them. Getting an antenna on the roof, 10 miles with 5 watts is quite reasonable even with the dinky little ones that come with Midland's "Micromobile". Actually, in a pinch, throwing one of those on the lid of your gas grill does pretty good as well - just getting it outside of the home will help a lot. As a rule of thumb, in GMRS in most situations, the extra height of getting it to the top of the roof will help range more than a lower-down higher performing antenna. However, topography around you will impact that more than anything - for instance, anything bolted on to the backside of my home does as well as something on the roof because of my local topography - I can reach about 1 mile in one direction, and 50+ in the other so long as I have at least 10 watts. Quote 1. If I place the mobile antenna on the roof vent, using the vent as a ground plane, what kind of performance hit (not much, or not worth it?) would I take by bending the antenna to vertical at the base of the antenna? I assume the ground plane not being perpendicular to the antenna is where the issue would be? Or would it be better that I just let the whip point out at the same angle with the roof? If I did that, then I suspect that the radiation pattern is far from ideal. Perhaps the lower gain antenna would be better because the lobes are not so directed? Honestly, so long as you're within about 30-ish degrees of vertical, not worth it to bend the antenna. Anything under 3dbi gain is going to be effectively an omnidirectional antenna anyway, and you're close enough to vertically polarized that you can talk to all of the other vertically polarized GMRS users no problem. At most normal antenna sizes, the polarization will matter about as much as pure antenna gain. Quote I don't mind coax running down the back side of my roof. But I haven't decided whether it would be easier to run the coax into the attic through the vent. In my case, trying to get the coax into the radio bedroom in that little space in the corner of the attic might be impossible, so that might be why I would run it down the roof and then straight in through the exterior wall, with a little careful routing along trim lines. If I do grounding correctly, then I have to run ground wire externally anyway. So I'm leaning towards running coax externally as well. Whatever you do, ground it correctly and get a good lightning arrestor - I use TMS personally. Lightning strikes are no joke! IMHO: If you have a gable, I'd run it discretely along or behind the facia board, and just drop an NMO mount into the center of the vent (maybe after making a flat area with a hammer) at the top of the roof, at about the same distance from the end as it is wide, seal it thoroughly to the roof, and then slather the connector with dielectric grease and put one of the little 2.1 db gain antennas. I wouldn't even bother with a Laird Phantom, Midland Ghost, or similar, they're really great on vehicles, but on a structure, they don't perform much if any better than the 1/4 wave verticals that everybody gives you for basically free. If I didn't have a gable, then I'd punch it down through the barrier into the attic, then seal it all up afterwards. Sshannon 1 Quote Link to comment Share on other sites More sharing options...
wynterspop Posted October 16, 2022 Report Share Posted October 16, 2022 I bought one of these. Inexpensive, small, and works great. You could easily attach it to the vent pipe. https://www.jpole-antenna.com/shop/462-mhz-land-mobile-gmrs-j-pole-antenna/ Quote Link to comment Share on other sites More sharing options...
Borage257 Posted October 17, 2022 Report Share Posted October 17, 2022 The N9tax jpoles are pretty good for discrete mounting too. If the roof and insulation allow (ie not metallic) a small yagi in the attic might work too. Quote Link to comment Share on other sites More sharing options...
BearFamily Posted October 24, 2022 Report Share Posted October 24, 2022 You can always try something like a Melowave Shadow antenna. They're pretty small and wouldn't be readily visible across the peak of the roof. Quote Link to comment Share on other sites More sharing options...
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