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Dual band NGP antenna for off-road use

Joined
Dec 19, 2002
Messages
903
#21
Are you basing the "it doesn't work as well" on just SWR? Dummy loads have low SWR but don't radiate.

Also keep in mind the Tram is only a 1/4 wave on VHF and so has no gain compared to the Larsen. That can be good or bad depending on your circumstances.
 
Joined
Oct 31, 2018
Messages
16
#22
Are you basing the "it doesn't work as well" on just SWR? Dummy loads have low SWR but don't radiate.

Also keep in mind the Tram is only a 1/4 wave on VHF and so has no gain compared to the Larsen. That can be good or bad depending on your circumstances.
Yes, I was basing it on SWR only. I was TX'ing out in the open and checking it with a digital SWR meter. I tried several frequencies (per my previous message) in both the VHF and UHF bands, including GMRS and even MURS.

I read somewhere that cutting off the ball at the top of the antenna could improve frequency response on GMRS, but it might make lower end UHF (closer to 440) worse. Thoughts?
 
Joined
Jul 27, 2005
Messages
10,052
Location
Point Nemo.
#23
I read somewhere that cutting off the ball at the top of the antenna could improve frequency response on GMRS, but it might make lower end UHF (closer to 440) worse. Thoughts?
Someone is pulling your leg. Cutting the ball off the end of the antenna does nothing other than shorten the antenna, making it resonate at a higher frequency, and create an "eye-poke" hazard. The ball is basically there as a safety device. On some antennas, the ball is plastic and plays no part in the RF function of the antenna.

As for the SWR issues….
SWR isn't the be-all end-all measurement for a good antenna, it just tells you how much energy is being reflected back down the cable.
Reflected power can be caused by a number of issues. Where is your antenna mounted? How is it mounted? Are there any other antennas mounted nearby?
It could need some adjustment. The entire whip radiates on VHF and UHF, but on the UHF side, it's co-linear. On VHF, it's half wave, and should be pretty broad banded. In other words, you may have it a bit too short to work well on UHF, but it's "close enough" on VHF.
Try lengthening the antenna a bit from the base. Loosen the set screw and pull it up a bit and try again. The UHF side is more narrow in useable bandwidth than on the VHF side.
 
Joined
Oct 31, 2018
Messages
16
#24
I tested the Larsen in a real-world situation today. I drove my rig to work and listened to the traffic across about 150 programmed repeaters (most out of the local area, but about 50 within range). I got traffic on lots more than I was getting with the Tram.

Tram = lower SWR's, not as good of real-world performance
Larsen = higher SWR's, better real-world performance
 
Joined
Jun 13, 2018
Messages
356
Location
Colorado, New Mexico- and now in Washington DC
#25
Hey U- Op :)

I just read your question (a tad late) - by now you have no doubt mounted something on your Jeep ?

If not, here is my two cents- if you have done so...?... Oh well--

I have a Jeep Wrangler Unlimited with the fiberglass roof. That roof, right there, presents a challenge to any antenna- and I am making the assumption you have a similar situation;
ie: a Wrangler with the hard fiberglass top


Ah ! what was a girl to do ?


I will get to that in a moment, but first, let me deviate this discussion a few degrees.

You received some good information (excepting that weird advice about cutting off the ball on a whip-- No, don't do that -- "Kid, you'll just put your eye out" *. )

I am going to address the practical side of this antenna issue- at least from my perspective.
I don't know where you off-road, but where I do it can vary between open the Upper Sonoran Desert to the Alpine Tundra. In between is a lot of Limber, Lodgepole pine lined goat tracks that pass for roads (the Central Rockies of Colorado) - those trees alone- they love to snatch away any antennas.

Long, long ago the mountains taught this Cowgirl that except for Motorola low band whips, with their awesomely serious stainless steel springs/ball mounts- nothing was going to survive in my "hills"-- excepting the humble 18" NMO mount'd vertical (also a Motorola design.)

Okay, enuff background colour-
On my Wrangler I drilled a 3/4" hole thru the the fiberglass roof (Horror!.. but, heck- its MY jeep)- and I mounted a NMO connector. Yes, it needs a ground plane- and in my case I used a sheet of copper PC board cemented to the underside of the roof- the NMO connector passes thru it- the coax is soldered to both the connector and to the board (~ 7 by 20 ? ").

How well does it work?.... Its approximately a quarterwave between 140 to 160-something MHz's, with an SWR of <2:1. Its 3/4 wave (and resonant) on ~420-470, with a likewise SWR. Nothing's perfect, but it has survived many a Jeep trail that a flatlander's antenna would have been destroyed. SWR and radiation patterns start to become minor deals.

Have I been concerned that this is not the ultimate antenna, radiation pattern, SWR etc. wise ?...
........simple answer--- No. This antenna is still on my vehicle when many others would have long ago been in some ditch.)

U-Op, you are and off road'er- you know sturdy beats cutesy every time.

Lauri :sneaky:

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* Sorry, and with an apology to one of my TV favorite Christmas movies- "A Christmas Story"
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Last edited:
Joined
Jul 27, 2005
Messages
10,052
Location
Point Nemo.
#26
Good advice. I used 1/4 wave VHF whips for dual band amateur (2 meter/70 centimeter) use for years. And it works well. Hard to destroy a 1/4 wave whip (I've tried, low parking garages, tall truck).

Don't focus on the gain figures. Many will try to convince you that increasing the ERP via antenna gain is always a win/win situation. It's not. Lower gain antennas with round/fat radiation patterns can often out perform higher gain antennas in some situations. I've fixed repeater coverage issues by switching to lower gain antennas many times.
 
Joined
Jun 16, 2013
Messages
3,228
Location
Texas
#27
Lauri that reminds me, of my Cherokee (of the Four_Oh generation). I have a Larsen NMO27 on the hood channel that I have yet to throw bouncing around some similar goat trails in areas between Wolf Creek Pass and Leadville. Been going strong for 5 years now. Can't say the same about the now worn out tie rods that have been working overtime the last decade to keep those 32's where I point them...currently it's just a case of herding between the lines (time for tie rod upgrades). I keep a 1/4 wave of choice on the the roof for VHF (nice thing about Cherokees is they are tin tops).
 
Joined
Jun 13, 2018
Messages
356
Location
Colorado, New Mexico- and now in Washington DC
#28
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".... I've fixed repeater coverage issues by switching to lower gain antennas many times........"


An important consideration.... especially in mountainous terrain. A high gain, low angle of radiation can be inferior to the simple pattern of a quarter wave antenna. Often the station you wish to talk to is at a considerable elevation difference, not to mention that the signals may be coursing off strange reflective mountainsides, or thru tight narrow passes. In these situations, a noisy signal is better than no signal- which is often the case with a low angle, high gain irradiating into some low hillside.

A Real Life scenario-
For temporary field work we often used 400 MHz radios, with a repeater placed on the highest hill, mountain top etc. available. My guys would use simple quarter wave's mounted on the side of short portable towers, but they would mount the antennas inverted. To the practiced eye this looks a bit strange, but the science is also simple- a high gain antenna will 'shoot' the RF out in a flat plane to the base of the antenna---- there is a minimal dipping down ward to cover the valleys, canyons etc. beneath a site.
That would be great for talking to the next mountain peak, but not so good for things in the valleys below. The unassuming little quarter
wave, up-side-down, fills in those valleys.
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Unless one is a perfectionist, it doesn't matter (to me anyway) if the signal is a perfect "full quieting" or a bit scratchy when it comes to this mobile stuff. That perfectionist may find they have lost all signals when that tree branch 'lost' their antenna.

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Lauri :sneaky:
 
Joined
Jun 16, 2013
Messages
3,228
Location
Texas
#29
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".... I've fixed repeater coverage issues by switching to lower gain antennas many times........"


An important consideration.... especially in mountainous terrain. A high gain, low angle of radiation can be inferior to the simple pattern of a quarter wave antenna. Often the station you wish to talk to is at a considerable elevation difference, not to mention that the signals may be coursing off strange reflective mountainsides, or thru tight narrow passes. In these situations, a noisy signal is better than no signal- which is often the case with a low angle, high gain irradiating into some low hillside.

A Real Life scenario-
For temporary field work we often used 400 MHz radios, with a repeater placed on the highest hill, mountain top etc. available. My guys would use simple quarter wave's mounted on the side of short portable towers, but they would mount the antennas inverted. To the practiced eye this looks a bit strange, but the science is also simple- a high gain antenna will 'shoot' the RF out in a flat plane to the base of the antenna---- there is a minimal dipping down ward to cover the valleys, canyons etc. beneath a site.
That would be great for talking to the next mountain peak, but not so good for things in the valleys below. The unassuming little quarter
wave, up-side-down, fills in those valleys.
.
Unless one is a perfectionist, it doesn't matter (to me anyway) if the signal is a perfect "full quieting" or a bit scratchy when it comes to this mobile stuff. That perfectionist may find they have lost all signals when that tree branch 'lost' their antenna.

.
Lauri :sneaky:
Another real life scenario.

Most of my work these days (though I still dabble in wide-area coverage systems here an there) is warehouses and schools. We've found that most of the time a simple ANT450D covers a building (that the antenna is mounted on) better than something like a DB404B. We selected ANT450D's to provide the ability to stack multiple antennas on a single mast and since majority of our customers are utilizing portable radios anyway, it really doesn't make a ton of sense to throw more than 10W ERP out to begin with.

Once or twice I've even gone with antennas with electrical downtilt in VHF and UHF.
 
Joined
Jul 27, 2005
Messages
10,052
Location
Point Nemo.
#30
Yep. I've got a UHF repeater system (3 linked repeaters) on a couple of ridge tops. All users are on 4-5 watt portables. The repeater is set for 10 watts output. No reason to get lopsided on the coverage.

The ANT450D's are great antennas. I put one of those up at this site:


There's about 4000 feet of vertical drop in 1/4 mile of horizontal distance. Some well meaning person tried putting a 6db vertical up there. The system had mediocre coverage out towards the horizon, but due to the terrain, the accessible "horizon" was pretty small. The users were complaining of almost no coverage under the repeater. It was pretty much useless.
I put the single bay ANT450D up there and mounted it with about 15º mechanical down tilt. That brought the coverage down to where it could be used. There's still a few minor dead spots, but that's due to too much dirt being in the way, and no amount of antenna is going to fix that. Will eventually look at the other two repeaters and probably replace the antennas.
 
Joined
Feb 28, 2019
Messages
63
#31
All antennas are a two polarity/contact thingy. That other contact has to be somewhere and with a mobile its the vehicle's metal body. That "no groundplane" idea is hog wash. If it isnt the vehicle's body, then its the feed line (most usually).
 
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