Low Profile VHF Antenna Performance

[PrivatelyJeff]

I think the issue would be that the bike would not provide the mirror image of the other half of the dipole, and thus throw the impedance off.

You can get elevated feed dipoles, but they are just as long as a 1/2 wave….

I meant that the mirror image part would be built to work RF wise, then find some way to make it blend in with the look of the body (sheath the bottom in some tubing or such).

 

[lb2910]

Not sure where you found that, but it's a photo of one type of antenna with a description for a completely separate antenna. I'd not purchase anything from a vendor that wouldn't know the difference between those two antennas.

The Larsen NMO150CK is a kit consisting of an NMO150C antenna and a NMOK mounting kit.
The NMO150C is a 5/8th's wave antenna, which does not have a coil in the whip. It has a 51" tall chrome whip. The "C" indicates the chrome.
The K indicates it comes with the NMO mount with 17' of RG-58 and a PL-259 connector. That connector won't fit your radio without a bunch of adapters that will put a lot of strain on the antenna jack on the radio. That usually leads to a fracture of the solder joint and a non-functioning radio.

The photo you are showing is an NMOU150d.

https://productfinder.pulseelectronics.com/api/open/product-attachments/datasheet/nmou150d

The NMOU150 is a loaded 1/4 wave, and Larsen still shows it at 18" tall. The coil in the whip is to make it look like a cellular antenna for undercover work. Not going to work any better than a regular 1/4 wave antenna.

Mmckenna.. you've officially graduated into the "Guru" status of radiomanship... and yes... I just made up that word. I really hate how sellers will put some random stock antenna picture up and a radio neophyte like myself will order it and get something completely different.... UGH....

I just ordered the Sti-Co from antenna farm for less than $50... I'll cut it to 18" and then mount it with some sort of thin metal underneath to get it to perform better. I do have a piece of thin sheet metal I can cut into a circle for the make-shift ground plate. Any particular diameter it should be?

I'll take a pic and post here when I'm done installing and mounting everything. I can't thank you and the rest of the folks that answered this thread enough. I got just a little smarter today!

 

[PrivatelyJeff]

I meant that the mirror image part would be built to work RF wise, then find some way to make it blend in with the look of the body (sheath the bottom in some tubing or such).

Or you even wire the connectors up so you can use two signal sticks, one pointed down and one pointed up. Just use a small project box with the connectors wired up correctly and a jumper to the radio.

 

[mmckenna]

Mmckenna.. you've officially graduated into the "Guru" status of radiomanship... and yes... I just made up that word.

Well, my employer pays me a ridiculous amount of money to do radio stuff. I do it for free, here.

I really hate how sellers will put some random stock antenna picture up and a radio neophyte like myself will order it and get something completely different.... UGH....

Yeah, e-bay, amazon, many online sellers have no idea what they are selling. To them one antenna is the same as another. It's usually a good indication that the seller has no clue what they are doing and won't provide any useful support after the sale.

I just ordered the Sti-Co from antenna farm for less than $50... I'll cut it to 18" and then mount it with some sort of thin metal underneath to get it to perform better. I do have a piece of thin sheet metal I can cut into a circle for the make-shift ground plate. Any particular diameter it should be?

As big a flat surface as you possibly can. Ideal ground plane for VHF would be 36" or larger.

I'll take a pic and post here when I'm done installing and mounting everything. I can't thank you and the rest of the folks that answered this thread enough. I got just a little smarter today!

That's why we are here.

 

[n0xvz]

Well, my employer pays me a ridiculous amount of money to do radio stuff. I do it for free, here.

And you've been an invaluable resource to many! Myself included!

 

[Giddyuptd]

Yeah, nothing has changed. Those soup can VHF antennas suck just as bad today as they did several years ago. Very narrow useable bandwidth, very disappointing performance. Everyone (and I do mean everyone) that I know who has tried them have replaced them. No one was happy with them.

The Stico antenna may be a good option, but do understand that if you want to run a 1/4 wave VHF whip, you do need to consider the ground plane under the antenna. Getting good performance and proper radiation from the antenna will require a ground plane 1/4 wavelength in all directions under the antenna. Not a reality on a motorcycle. You can cheat a bit and run a smaller ground plane, but don't expect outstanding performance. Most motorcycles would benefit from a 1/2 wave antenna that does not require a ground plane. But those will be a bit over 3 feet long.

Best shot is to either remove the antenna each night, or use the Stico whip.

He would be better off with a quarter wave then a laird can. In a decent center coverage the can was ok but beyond of that forget it.

 

[krokus]

@lb2910 How are you planning to interface with the radio, while it is in the pouch/holster? Are you using a BT speaker mic?

 

[lb2910]

@lb2910 How are you planning to interface with the radio, while it is in the pouch/holster? Are you using a BT speaker mic?

Yeah.. I have a BT system that syncs everything together....

 

[mmckenna]

Yeah.. I have a BT system that syncs everything together....

OK, just plan out your antenna connection carefully. Putting strain on the antenna jack on the radio is a bad idea. Use no adapters, and be careful with the coax.

 

[lb2910]

OK, just plan out your antenna connection carefully. Putting strain on the antenna jack on the radio is a bad idea. Use no adapters, and be careful with the coax.

My connection plan will be the mount the Sti-Co antenna via NMO mount on top of the box with some thin sheet metal to act as a ground plate on the underside of the lid. As you said, as much metal as I can use given the confines of the top of the box. I'll run my RG58 coax cable down the lid via the lid connection hinge, through an existing hole in the bottom of the box, through a heat/weather resistant sheath down to the side of the bike where the radio will be in the pouch where I'll put a relief/strain loop. With the help of a very knowledgeable tech from Antenna Farm, I will actually crimp a connection that will thread directly into the antenna port. This will negate me having to use a BNC adapter which would make a more bulky and longer connection into the antenna port. All connections will be heat shrink wrapped to make water proof. I'll have the rain cap on the NMO mount when the antenna isn't needed and I have a small rubber cap that will fit nicely over the coax connection to protect that when not in use.

And thats my plan..... am I missing anything

 

[mmckenna]

And thats my plan..... am I missing anything

Nope, sounds like a good plan.

Try to measure out the length of cable you'll need and have them cut it before putting the connector on. No need to coil up a bunch of unused coax in the box.

 

[AK9R]

Mmckenna.. you've officially graduated into the "Guru" status of radiomanship...

Oh, he's much more than that. I think he now teaches the gurus.

Well, my employer pays me a ridiculous amount of money to do radio stuff. I do it for free, here.

And, we are very fortunate to have you here as a regular contributor. Thank you.

 

[lb2910]

OK, just plan out your antenna connection carefully. Putting strain on the antenna jack on the radio is a bad idea. Use no adapters, and be careful with the coax.

For that reason, they are sending me the connector and I'll crimp it myself. I have the tools to do a solid crimp. This way I can run the coax, measure exactly what I need and cut/crimp to fit.

I did want to ask you if there is a neat and tidy way to secure the cable to the box itself. I was going to use some sort of adhesive but that seems like it would be messy. And the box gets a lot of heat sitting in the sun and adhesive doesn't like heat. Any ideas?

 

[mmckenna]

I did want to ask you if there is a neat and tidy way to secure the cable to the box itself. I was going to use some sort of adhesive but that seems like it would be messy. And the box gets a lot of heat sitting in the sun and adhesive doesn't like heat. Any ideas?

The normal wire routing clips with double sided tape are usually useless in most applications. I rarely use them. When I do, it's important to prep the surface. I usually clean the area with alcohol to remove and grease/oil first. But heat would kill the adhesive.

If it's a fiberglass or similar box, I'd probably look for a suitable epoxy. Use the wire clips, but take the double sided tape off the back and use the epoxy to attach them. If it's bare fiberglass, you may be able to get a fiberglass repair kit and use the resin/hardener from that.
Usually the stuff I do at work is a 'performance first, looks second' thing, so running a stainless steel machine screw through the box would not be out of the question. But if this is your personal bike, that's probably not what you want to do.

As for the wire clips/zip ties, use the black UV resistant ones. If any of this is exposed to the sun, the cheap white/natural colored ones will fail after some time in the sun.

 

[lb2910]

The normal wire routing clips with double sided tape are usually useless in most applications. I rarely use them. When I do, it's important to prep the surface. I usually clean the area with alcohol to remove and grease/oil first. But heat would kill the adhesive.

If it's a fiberglass or similar box, I'd probably look for a suitable epoxy. Use the wire clips, but take the double sided tape off the back and use the epoxy to attach them. If it's bare fiberglass, you may be able to get a fiberglass repair kit and use the resin/hardener from that.
Usually the stuff I do at work is a 'performance first, looks second' thing, so running a stainless steel machine screw through the box would not be out of the question. But if this is your personal bike, that's probably not what you want to do.

As for the wire clips/zip ties, use the black UV resistant ones. If any of this is exposed to the sun, the cheap white/natural colored ones will fail after some time in the sun.

I ordered some UV clips with the adhesive backing last night. I'll replace the backing with a dab of good epoxy to hold the cable clips in place. I shouldn't need more than a few given the size of the box. Thanks again for all the great advice. I'll post pics of the final result next week.

 

[lb2910]

The normal wire routing clips with double sided tape are usually useless in most applications. I rarely use them. When I do, it's important to prep the surface. I usually clean the area with alcohol to remove and grease/oil first. But heat would kill the adhesive.

If it's a fiberglass or similar box, I'd probably look for a suitable epoxy. Use the wire clips, but take the double sided tape off the back and use the epoxy to attach them. If it's bare fiberglass, you may be able to get a fiberglass repair kit and use the resin/hardener from that.
Usually the stuff I do at work is a 'performance first, looks second' thing, so running a stainless steel machine screw through the box would not be out of the question. But if this is your personal bike, that's probably not what you want to do.

As for the wire clips/zip ties, use the black UV resistant ones. If any of this is exposed to the sun, the cheap white/natural colored ones will fail after some time in the sun.

For the ground plate.. is there a minimum or recommended thickness to use? You said foil previously.. so would aluminum foil work? Or better to use something with a bit more thickness???

 

[mmckenna]

For the ground plate.. is there a minimum or recommended thickness to use? You said foil previously.. so would aluminum foil work? Or better to use something with a bit more thickness???

Thickness doesn't matter. Aluminum foil would work fine. If you can apply and adhesive and glue it in place, that would work.

I used to have a plastic roof on my UTV. I put down some adhesive backed foil tape in an "X" pattern on the underside of the roof with the NMO in the middle through the plastic roof and the foil. Worked just fine.

https://www.amazon.com/Nashua-Multi-Purpose-Length-Width-Aluminum/dp/B002EX855S/ref=sr_1_3?dchild=1&keywords=foil+tape&qid=1625376036&sr=8-3

 

[lb2910]

Thickness doesn't matter. Aluminum foil would work fine. If you can apply and adhesive and glue it in place, that would work.

I used to have a plastic roof on my UTV. I put down some adhesive backed foil tape in an "X" pattern on the underside of the roof with the NMO in the middle through the plastic roof and the foil. Worked just fine.

https://www.amazon.com/Nashua-Multi-Purpose-Length-Width-Aluminum/dp/B002EX855S/ref=sr_1_3?dchild=1&keywords=foil+tape&qid=1625376036&sr=8-3

That is a novel idea... I attached a pic of the tour pak the antenna will be mounted on. I can get that foil tape at my local Home Depot. I'll center the antenna and do the "X" pattern underneath the lid as you said. Would this be better, worse or the same (performance wise) than if I attached a full sized foil square underneath?

 

[mmckenna]

Probably no noticeable difference.

 

[krokus]

That is a novel idea... I attached a pic of the tour pak the antenna will be mounted on. I can get that foil tape at my local Home Depot. I'll center the antenna and do the "X" pattern underneath the lid as you said. Would this be better, worse or the same (performance wise) than if I attached a full sized foil square underneath?

Since that is the LE tourpack, it will be interesting to see if you get any RFI from the circuitry. It would make sense that HD has that managed, since they know radio equipment will be used on/with the bike.