Dual band antenna for brush country.

[crawler#976]

Since I moved the antenna from the d'side fender to the center of the roof, I've been beating it to death with low hanging branches. In reality, it gets hit less than the fender mount did, but when it does, it really gets whacked.

I already had a Pryme RD-98 SMA antenna for the HT, so all that was needed was adapters to use it for the roof mounted NMO connection. I ordered a Comet UHF to NMO adapter and a SMA female to UHF male adapter. When assembled it is shorter than the Larsen NMO 2/70 coil, and the highly flexible RD-98 will easily bend away form overhead obstacles.

Getting good signal reports - full quieting into the repeater about 16 miles away, and simplex reports of decent audio at a 20 mile range into a full tower setup, both at 5W output.

Only draw back is with the RD-98 I am limited to under 20 watts power. That's OK, since for most trail rides I use 5W anyway.

INFO:

RD-98 antenna http://www.hamradio.com/detail.cfm?pid=H0-001847

Comet UHF-MNO adaptor http://www.hamradio.com/detail.cfm?pid=H0-001411

SMA-UHF adaptor http://www.hamradio.com/detail.cfm?pid=H0-009348

 

[1leglance]

Mark thanks for posting this...
I was just thinking of heading over to Ham Radio Outlet and asking if there is any sort of old school whip setup like the 70's cb's. I figure with my old suburban I can get away with a chrome bar & spring if it will save me on all the bent antennas I have paid for.

It is always funny when I talk to ham guys as so few of them understand WHY I need an antenna that won't get killed by trees/scrub.

 

[crawler#976]

The Larsen NMO 2/70 is back in place, and I found the brush antenna fits fine in the center console.

Lance, I've seen several plain SS whips in the HRO catolog, so I know they are available. However, having tried a setup with a poor ground plain, I'm not sure you would be happy with a bumper or hood mount.

 

[DaveInDenver]

Sti-Co Flexi Whip. No-BS, these are mechanically the ideal antenna for the application.

Downside is they are monoband 1/4-wavelength, so no gain. The flex also means they fade and flop around more than average on the highway.

But forget removing it or folding it over ever. You need about an inch of clearance over your roof, it could conceivably break right at the mount (more like shear off the NMO mount). Not sure I would actually tie it in a knot, but they are flexible.

http://www.sti-co.com/antenna-products/public-safety-antennas/flexi-whip

 

[xtatik]

The best "brush country antenna" is the one you can remove and replace from your truck in the shortest amount of time.
You don't need the longer distance capability of an outboard antenna all of the time. When I get into the thick stuff, I yank the HF/2m antennas off the truck and stow them. The HT takes over in that type of terrain. If I need to contact another party member outside HT range, I stop for minute and put the bigger antennas on...takes seconds...literally.
You may find some antennas can handle a bit more abuse than others, but none of them are engineered for a thrashing and will eventually fail on you....Hopefully, not when you need it most.
Personally, having used them, I find NMO's to be the least desirable and adaptable and they usually entice the user to place the antenna in the most susceptable places on their vehicles. The difference in performance realized by placing antennas **********-dab in the middle of a roof, hood or deck lid is inperceptable in nearly all cases.
I'm a bigger fan of UHF mounts because I can also hook coax directly to where the antenna screws on without adapters. From there I can run the coax out to larger field deployed antennas...whether they be a simple end-fed dipole (Par End-Fedz) or the TW-2010.

 

[DaveInDenver]

You may find some antennas can handle a bit more abuse than others, but none of them are engineered for a thrashing and will eventually fail on you.

Lee (1911) turned me on to the Sti-Co and I began noticing brush fire trucks have them. Mine's been on for most of a year now, can't complain. Twice daily garage door header impacts and typical parking garages, drive-thrus, dead fall and the like. They said if it ever breaks for any reason they'll replace it, so I've taken them up on that. In this case it is actually engineered to be beaten on by public service and military users. OTOH the USFS (and for that matter taxis) just uses Larsen, Maxrad or similar monoband stainless whips and they are clearly beat silly. In that case they probably buy them by the crate and just R&R.

 

[xtatik]

^I've seen them (or similar) on CalFires' brush trucks and crew buggies and I'm sure they'll last longer....But, that's one of my points....they'll only last longer. Eventually, they'll take their last whack and be done. My main point is that the longest lasting antenna will be the one that isn't smacked around. If I succumbed to the idea that I was going to leave my antennas to fend for themselves and eventually found what seemed to be the most durable......I'd buy two, cuz I know I'd eventually need the other.

 

[DaveInDenver]

By that logic, which is true that everything eventually wears out, you should consider that connectors all have limited mate cycle ratings. I was removing my antenna every evening when I got home and putting it back on in the morning, add in a few dozen removals on trails and stuff, it's not difficult to see that you could accumulate several hundred mate/demates annually on a connector (regardless NMO, PL259/SO239 or 3/8") that's not engineered for that. It was wearing out my mounts (both the SO239 for the ATAS and the NMO for my V/U). Threads get loose, center pins wobble or loose springiness, the torque of turning breaks joints.

Point is, yup, eventually your antenna is going to need to be replaced. The NMO mount is mechanically sound as long as you don't disturb it. I agree that it's not ideal for high cycle use, particularly the brass ones, although convenient. The UHF connector handles mates a little better, but is mechanically a problem if you do impact something and they also don't last forever. So I decided that I preferred to just leave the antenna in place and found one that works for my application. I'm not disagreeing, your way works fine. I just didn't want to bother taking the antennas off the roof twice a day.

 

[1911]

Lee (1911) turned me on to the Sti-Co and I began noticing brush fire trucks have them. Mine's been on for most of a year now, can't complain. Twice daily garage door header impacts and typical parking garages, drive-thrus, dead fall and the like. They said if it ever breaks for any reason they'll replace it, so I've taken them up on that. In this case it is actually engineered to be beaten on by public service and military users.

Glad that you like it Dave. I've had mine for several years now and it just stays on all the time now because I can barely tell the difference performance-wise between the Flexi-whip and my much larger 5/8-wave Hustler 2m antenna. If it has suffered at all from years of impacts, I can't tell.

 

[crawler#976]

The difference in performance realized by placing antennas **********-dab in the middle of a roof, hood or deck lid is inperceptable in nearly all cases.

Sorry, but I have to disagree with that part of your post.

I chased performance problems with previously proven components - a Yaesu FT-7900 and Larsen NMO 2/70 antenna. With the antenna on a fender mount the ground plane was so distorted that even at 50W power, transmission was limited to under 10 miles. Reception was also effected. By moving the mount to the center of the roof, the same radio and antenna now work as designed. I used SWR testing equiptment in both locations, and found no differences between them, so the only thing that changed was the position of the antenna.

 

[xtatik]

Sorry, but I have to disagree with that part of your post.

I chased performance problems with previously proven components - a Yaesu FT-7900 and Larsen NMO 2/70 antenna. With the antenna on a fender mount the ground plane was so distorted that even at 50W power, transmission was limited to under 10 miles. Reception was also effected. By moving the mount to the center of the roof, the same radio and antenna now work as designed. I used SWR testing equiptment in both locations, and found no differences between them, so the only thing that changed was the position of the antenna.

That's fine, but by what you've mentioned here, my guess is your performance problems had little to do with placement. Perhaps in moving the antenna you resolved another issue effecting your antenna that you didn't diagnose properly. The SWR is nearly useless in resolving antenna performance issues and the VSWR is the last of my concerns when I build my own or install commercially available antennas. Antenna analyzers and field strength meters are minimally the tools of the trade for these purposes. There are also software packages that can model antenna performance in-place for varied antennas and vehicles such as FEKO and CST, which are used for much, much more sophisticated systems by defense contractors.
http://www.feko.info/

For simple short-shot FM repeater bouncing purposes, it doesn't need to be this complicated.

 

[xtatik]

By that logic, which is true that everything eventually wears out, you should consider that connectors all have limited mate cycle ratings. I was removing my antenna every evening when I got home and putting it back on in the morning, add in a few dozen removals on trails and stuff, it's not difficult to see that you could accumulate several hundred mate/demates annually on a connector (regardless NMO, PL259/SO239 or 3/8") that's not engineered for that. It was wearing out my mounts (both the SO239 for the ATAS and the NMO for my V/U). Threads get loose, center pins wobble or loose springiness, the torque of turning breaks joints.

Point is, yup, eventually your antenna is going to need to be replaced. The NMO mount is mechanically sound as long as you don't disturb it. I agree that it's not ideal for high cycle use, particularly the brass ones, although convenient. The UHF connector handles mates a little better, but is mechanically a problem if you do impact something and they also don't last forever. So I decided that I preferred to just leave the antenna in place and found one that works for my application. I'm not disagreeing, your way works fine. I just didn't want to bother taking the antennas off the roof twice a day.

Tough to argue your logic here Dave. It's true that everything will eventually wear out. In my case, the mounts are easily the least expensive component in my array (both on the truck and at home). So, replacing them occasionally makes more sense to me. When I'm out in the desert areas I never worry about my antennas and leave them in place. The occasional Joshua Tree can be easily avoided and the pucker-bushes give enough. In the mountains and our chapparral blanketed foothills, I yank em' and store em' ....no wear and tear, and no worries. The HT works fine in these cases both for truck to truck and into repeaters up 20 miles out with a simple Diamond whip on the HT from inside the cab. Hearing people tell of problems getting a signal out to ten miles with any external antenna boggles the mind. There has to be something else going on in these cases.

 

[DaveInDenver]

LOL. Different solutions to different problem. These Sti-Co whips aren't terribly expensive, about $30 for the whip. That's about twice what a generic 1/4 whip would cost, say about $18 for a Larsen NMOQ as comparison. So the flex comes with some premium. OTOH, an NMO-K is about $20 and talk about a PITA to replace, fish through the headliner, down behind the interior panels... I prefer to let the antenna take the punishment, lots easier to R&R.

One other reason I wanted to stop removing the antenna daily is that at 6AM without the first cup o' joe you know there's a major chance of cross threading something...

What I think mounting the antenna in the center of flat sheet does primarily is equalize the pattern, no odd azimuthal lobes. The fringe performance with gain is really only noticeable when stationary. Moving it's hard to tell much difference.

PS: You working with the EMSS tools? It's been cool as we've slowly moved into the bus side of things, G&N, avionics, C&DH, downlinks, modems rather than just payloads. Getting to do waveguides and antenna sims and 3D board EMC sims. Plus, I now know how bad my back-of-the-napkin ISS helix made with PVC and coax really was. ;-)

 

[xtatik]

One other reason I wanted to stop removing the antenna daily is that at 6AM without the first cup o' joe you know there's a major chance of cross threading something...

Ahaa! See.....This is not an antenna performance problem.....LOL.

What I think mounting the antenna in the center of flat sheet does primarily is equalize the pattern, no odd azimuthal lobes. The fringe performance with gain is really only noticeable when stationary. Moving it's hard to tell much difference.

You nailed it here. No doubt you can skew patterns with different placements. But, while mobile it's hardly perceptible if all other antenna installation concerns are met, especially for a group like us. Their are way bigger concerns for getting a signal to an intended target. Bigger concerns as in how big is that mountain range between me and the repeater? Or, how deep in this slot/box canyon can I be? But, even having said that.....how effective is the "ground plane" on my HT? Which BTW, can easily hit every repeater in a 20 mile radius and a couple that are close to 80 miles away with only 5 watts.
There are too many variables to inventory for every situation and geographic location while mobile. I say...just throw the stick up there and fire away.
This forum has countless threads covering antenna choices that are all borne of the same questions. Seems people fear getting it wrong and my message is to RELAX. Just get that thing mounted so it won't fall off and run with it. Save the experimentation and yearning for perfection for the antennas that require it. FM mobile antennas are usually like Pop-Tarts. If you can open the package, you're half way there.

 

[xtatik]

PS: You working with the EMSS tools? It's been cool as we've slowly moved into the bus side of things, G&N, avionics, C&DH, downlinks, modems rather than just payloads. Getting to do waveguides and antenna sims and 3D board EMC sims. Plus, I now know how bad my back-of-the-napkin ISS helix made with PVC and coax really was. ;-)

Heck no. It's all play to me, and I just run with basic (maybe a bit more) antenna theory and physics. Every once in a while I get to show my mad McGyver skills by getting a lawn chair or a piece of barbed wire to "load up" on 10m. I used to model with EZNEC when you could get it as a free download, but lost it to a grenaded hard drive. Haven't missed it. But, I have lunch once a month with my Dad and his SCDX group. A few of the guys that attend are in the business and build all types of antennas for all manner of super secret destructive devices, LOL. It's funny cuz they pull up with antennas duct taped to their vehicles and talk of how they "sell" their products. They're all excited/worried about some big antenna show/convention down in San Diego that's coming up. I guess the Navy has some type of in-house engineering firm down there that reviews vendors and products at this event.