Ham antennas for the rig

[DaveInDenver]

For this method you'll need to be able to get behind the headliner. You don't have to remove it completely.

Generously cover area with masking tape and mark preferred location.



Do pilot.



Punch hole. This is Greenlee 5003998 3/4" knockout.



Clean hole.



Install NMO base.

I use the Larsen NMO-HF.

LARSEN ANTENNAS NMOHF Larsen Mobile Antenna Mounts | DX Engineering

Free Shipping - Larsen Mobile Antenna Mounts with qualifying orders of $99. Shop Mobile Antenna Mounts at DX Engineering.

www.dxengineering.com

This requires crimping and soldering the coax. They make fully made up NMO bases but I have a crap ton of bulk coax and never need the whole 17 feet they include anyway.

The other benefit to the NMO-HF is it's good to 6 GHz, you know, if I ever need that. It's not that far fetched, these mounts support say a GPS antenna with no loss (e.g. L1/L2/L5 bands between 1.1 and 1.5 GHz). The coax I used would have some loss at those frequencies, though.

The go-to ready to roll is the Larsen NMO-K.

LARSEN ANTENNAS NMOK Larsen Mobile Antenna Mounts | DX Engineering

Free Shipping - Larsen Mobile Antenna Mounts with qualifying orders of $99. Shop Mobile Antenna Mounts at DX Engineering.

www.dxengineering.com

My preference is to spread the load a bit and increase surface to improve ground conductivity from the NMO base to the truck roof. I rough up the oversprayed paint on the underside of the roof, smear a very light coat of dielectric grease* and put a disk of aluminum that coincidentally the O.D. happens to match the largest hole saw blade I have and is 3/4" I.D.

I like a round shape over a square so there's no pointy ends to dimple the roof. Ham's choice here.

*Should note that if I had some I would have used weak bonding silver epoxy instead but didn't have any at the time.

Route cable.



One done.



Repeat if so desired.



Antennas I use are Larsen NMO2/70B dual band applications and Stico Flexiwhip for any single band applications, GMRS, APRS, etc. If done with care you will get VSWR very near 1:1**. I have to run a network analyzer to measure it. My handheld tool isn't sensitive enough to measure it.

**Should note this is only the NMO base with a dummy load. My antennas show a slight reflection, it's darn near impossible not to have some reflection due to less than perfect counterpoise, real world materials, roof rack, etc. Having two antennas this close also is far from ideal, they noticeably interact.

 

[Inukshuk]

I’m just now in the middle of adding a metal plate “shelf” to my Gobi Racks for some new light bars. I took the opportunity to punch a couple of holes to fit that exact style of NMO mount. That’s where I have my 2M HAM antenna. That’s the one that you’re talking about Marco’s being the best, which I agree. Mine does not do so well when it comes to receiving. I regularly hear half of other’s conversations.

I’ve been satisfied with my Midland ghost antenna for my GMRS. I put that on a magnetic mount in the center of my expanded metal roof rack floor or if I have a metal Jerry can laid flat on the rack I slap the antenna on top of that.

I plan to try my 6db GME GMRS antenna on that mag mount, but usually we are all close when using GMRS. HAM is where distance seems to matter more.

 

[Corbet]

I run a Comet SBB-5NMO. 2m/70cm. I can't say why for any particular reason as someone probably just told me to get one back when I was licensed. I've had both folding versions on a hatch mount, fender mount bracket from some guy who makes them under a funny business name. And now on my upper bull bar. I've bent/broken a number of them on tight trails. I know on the roof would be best but I have a RTT. I've thought about building a ground plane above my spare tire and moving it back there. Like a 12" round piece of 1/8" and mount it in the middle. Most of my issues have always been with my coax cable getting damaged.

Anyway here is my antenna, no complaints but never used anything else. You listened to me for a few days in the swell, let me know how it sounded. I had some weird static sound pretty frequently but I assumed that was someone else's bad transmission, or I was picking up another group further away and not receiving them cleanly. I felt like I was able to hear everyone the group. https://www.dxengineering.com/parts...zr-9XBgfJkkGiux1G-M9rf0mG_Wy14BBoCq9sQAvD_BwE

 

[nakman]

Hey @DaveInDenver that backing plate is an interesting idea... I still have time so likely could design those and have a few laser cut, would you want another one? that's like a 4" disk with a 3/4" hole in the center.. .060" thick stainless?

@Corbet you sounded ok for the most part, maybe a little quiet tbh. But you weren't all that chatty either. but generally on par with the rest of the rigs as far as I could tell.

 

[Corbet]

Hey @DaveInDenver that backing plate is an interesting idea... I still have time so likely could design those and have a few laser cut, would you want another one? that's like a 4" disk with a 3/4" hole in the center.. .060" thick stainless?

@Corbet you sounded ok for the most part, maybe a little quiet tbh. But you weren't all that chatty either. but generally on par with the rest of the rigs as far as I could tell.

Pretty hard to get a word in edgewise with that group. Plus I had the tunes going most of the time.

 

[DaveInDenver]

Hey @DaveInDenver that backing plate is an interesting idea... I still have time so likely could design those and have a few laser cut, would you want another one? that's like a 4" disk with a 3/4" hole in the center.. .060" thick stainless?

Dimensions sound about right. Probably used aluminum sheet that had around, nuttin fancy.

 

[nakman]

Ok well this is going really well, big thanks @rover67 for the assistance (doing most of it)! Things went by so fast I really didn't take many pictures.

the hole...


The headliner...



The master cable puller...



finished install...



I purchased this antenna with NMO mount

STI-CO Flexi-Whip Antenna ROOF-FT-NITI Antenna with NMO kit INCLUDED. Antenna & NMO Mount.

• This Antenna Kit INCLUDES an NMO cable kit. Don't need the NMO kit?• Click here to buy ONLY the ROOF-FT-NITI-M antenna.• Field tunable for VHF or UHF 1/4 Wave Antenna for 136MHz to 1Ghz• Retrofit existing fragile quarter wave antennas with this virtually indestructible VHF / UHF Antenna...

www.arcantenna.com

And watched Marco solder on one of these ends

https://www.amazon.com/dp/B0F47MLJDY?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1&th=1

Next step... @CardinalFJ60 and the big tuna to dial it in! Haven't transmitted yet as the length is still too long for 146mghz.

 

[CardinalFJ60]

Sweeeeeeeeeet! I’ll be there with my antenna analyzer later!!

 

[nakman]

OMG... tuna masters! got me all dialed in, really can't thank you enough guys..




apparently you have to park in the middle of the street for this.

 

[CardinalFJ60]

Got it down to 1.2swr on 460

 

[HoneyBadger]

Has anyone run these before? Would an antenna like this be any good for the desert runs we do?
I like the low profile nature of it. But if it's not really going to be good for anything over a mile, then it's useless.

https://www.amazon.com/dp/B0BRSCK491/ref=sspa_dk_detail_6?psc=1&pd_rd_i=B0BRSCK491&pd_rd_w=630VX&content-id=amzn1.sym.cb5b6664-5cee-4cee-a86e-0e979e3f6231&pf_rd_p=cb5b6664-5cee-4cee-a86e-0e979e3f6231&pf_rd_r=3YESRZX506W44KEJHDK1&pd_rd_wg=y0NjZ&pd_rd_r=c349b6cd-ce3f-4990-bf89-d7fb54bf6b2e&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWw

 

[Pskhaat]

Has anyone run these before? Would an antenna like this be any good for the desert runs we do?
I like the low profile nature of it. But if it's not really going to be good for anything over a mile, then it's useless.

https://www.amazon.com/dp/B0BRSCK491/ref=sspa_dk_detail_6?psc=1&pd_rd_i=B0BRSCK491&pd_rd_w=630VX&content-id=amzn1.sym.cb5b6664-5cee-4cee-a86e-0e979e3f6231&pf_rd_p=cb5b6664-5cee-4cee-a86e-0e979e3f6231&pf_rd_r=3YESRZX506W44KEJHDK1&pd_rd_wg=y0NjZ&pd_rd_r=c349b6cd-ce3f-4990-bf89-d7fb54bf6b2e&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWw

Radio is quantumly funny. My general rule of thumb is that the the antenna in a single orthogonal dimension (up, down, left right, fore, aft) be at least as long as a 1/4 of the frequency's wavelength. There are super edge case exceptions, but this does not meet that criteria on either of the radio bands it tries to accept.

 

[DaveInDenver]

RF is just a subset of general electromagnetic fields, so it very much follows real world physics.

What @HoneyBadger shows is commonly known as the phantom or low profile antenna.

Spoiler: Science Stuff

It doesn't have to be hard, even though I make it so. I talk about black magic but it's not really magic. Any undergrad physics or EE will atest to the reams of homework you do that prove Maxwell and Lorenz didn't break anything Coulomb didn't show in 1780 or Ampere or Faraday later.

You can substitute the wire part of an antenna with a coil substantially or completely. It's leveraging the magnetic part of electromagnetic to create the EM field using an inductor. The E-field and B-field are inseparably related, so you're not picking a side in the Bohr-Einstein arguments or anything. If you make your EM-field using magnetics someone using a wire antenna that relies completely on electrical can still receive it.

In this case by using the magnetic field you legitimately can shrink the dimensions and it'll still work. The total energy remains the same. How well that energy travels isn't the same necessarily either. That's getting into the weeds of near vs far fields. But just realize that those wireless chargers are basically two totally magnetic field radios.

The E-field is oriented 90° orthogonal to the B-field and there are conditions at interfaces (e.g. when you use a wire to couple the field into a circuit). None of this breaks the EM reciprocity that describes how a magnetic field and electric field are related. You have one, you get the other whether you want it or not.

But here's the rub. If you're using the E-field at one end you have to rotate an other antennas primary orientation 90° to best use the related B-field. You have an inefficient coupling if an E-field antenna is oriented in the same plane as the B-field.

That is something that is not typically done with phantom antennas, so you have a significant performance roadblock. When the antenna is short and omnidirectional the field shape geometry doesn't as strongly favor one over the other but comparing antennas with gain, specifically one that is designed to maximize E-field performance, the orientation mismatch will become more obvious.

It's a matter of efficiency and expectation.

For UHF a 4" tall phantom antenna is likely going to perform practically the same as a 1/4λ whip, which for 70cm ham and GMRS is roughly 6.5" tall. This is to say if the form factor works for you then you aren't giving up much. In fact what's inside a phantom can is probably pretty much what you'd see using a short wire and small loading coil, just on a printed circuit board or built in a more robust way, which might be an advantage even.

Now that said you also may have the same downsides as a 1/4λ whip in terms of impedance matching, ground plane dependence and such. Read the specs closely. Being a physical science RF can't do quantum (some say actual black) magic. If a phantom antenna claims it's got 6 dB of gain and will reach 100 miles that's marketing bullshit, plain and simple.

Now, on VHF these phantom antennas generally suck, even as a single band. There's no short cuts. A 1/4λ wire on 2m is ~19" and relying on magnetic instead of electrical is a significant real world compromise trying to shrink it. It can be done but it's usually for a specific reason, like you need the toughness and can live with it because you only have one frequency of interest (e.g. narrow bandwidth, the geek speak) and the antenna is firmly mounted on a roof pointed at the other station that also never moves.

The one Travis shows at Amazon I'm willing to say is probably a poor choice for dual band. There's no way to really build a dual band VHF/UHF general purpose mobile phantom antenna that is going to work. For 2m caravan distance it might but don't count on anything more. It's what hams would call a dummy load that happens to leak some RF. You could get the same VHF performance from a old school light bulb filament. And to be honest, if your primary use is urban and repeaters this may be completely acceptable trade-off. For simplex or needing distance to hit a repeater it probably shouldn't be your first choice. That actual antenna may be fine on UHF, although that's more of a quality question and it's some unpronounceable, unknown brand on Amazon. I'd leave it to the student to draw conclusions.

Generally there's no reason not to keep a single band phantom antenna on the list for 70cm or GMRS if you want the low profile and rigid nature of them. Again, keeping mind it won't have gain and you will probably want to mount it in the middle of a ground plane, so the lip mount style isn't going to be your first choice.

Next time you're cuffed in the back of a patrol car look at what they use, which are very often low profile antennas like this because they're hard to snap off, so the rugged nature of them isn't a bad thing. Scott's Aussie style antennas leverage this construction, but that brings additional problem in how robust the mount has to be since they're trying to hit good efficiency, ground plane indifference and higher gain targets, too.

 

[AimCOTaco]

Travis,

Where do you want to mount the antenna? -that can be a determining factor in what to use.

If you need to use one of those clamp style mounts I'd start with the good stuff; for me thats usually Comet or Diamond. You're more likley to end up with sealed cables of appropriate construction with the better brands, there are lots of ways to cut costs here. Moisture in the dielectric insulation between the center and outer conductors will kill your performance over time so be picky. NMO is a good base system and allows you to swap through lots of different antennas as needed. You can have a fancy performance antenna for open spaces and a beater whip for convoying around on tight trails.