low profile antenna useage

[WRQW247]

Recently purchased a TRAM 1470 NMO ground plane antenna mount kit, which will be used to locate a GMRS antenna just above the roofline of my Jeep Wrangler.  I'd like to use a low profile GMRS antenna (Laird or similar type).  Will the ground plane mount kit purchased improve the performance of a antenna of this type, or am I better off going with a standard antenna, such as a Nagoya NMO-200C type?  Any shared wisdom is appreciated.

[marcspaz]

 

Just my opinion, while it will work, it is way too much hardware and effort to make the antenna system work.  If you are going to insist on using it, use a Tram 1126B antenna to keep the height down

However, I would ditch the ground plane kit and just buy a half wave antenna, which is about 12 inches tall, or a 5/8 wave antenna and mount it on the hood or swing gate.  The Midland MXTA26, which has 6dB of gain (32" high), is one of the 2 antennas I use.  The other is the Tram 1126B antenna.  Which one I use depends on where I am and what I am doing.  They both work very well.

 

Also, why do you want to install this over the roof line?  An antenna on the hood or swing gate will net you about 4.5 miles of range on level ground, while moving it to top of the Jeep will only extend range another 0.5 miles... maybe.  Again, just my opinion, the cost and level of effort (not to mention appearance) its not worth doing an 'above the roof line' install.

[gortex2]

If you go this route just toss a 1/4 wave on it. 6" vs 3" wont be noticed. I had run one of those on my Motorhome before I switched out to the LAIRD fiberglass stick. Worked fine for my application as I had no ground plane on the motorhome. 

[WRQW247]

Marcspaz, Gortex2

thank you both for the feedback given. For me personally, I do not want to see a radio antenna on the hood of my car. I'd prefer to put in extra thought/effort for a cleaner looking antenna mount, hence my decision to mount the antenna mount (Tram 1470) to my Jeep tailgate, and raise the antenna to be installed above the roof line using a riser/pole/pipe TBD. What are your thoughts regarding the use of the Nagoya NMO-200C antenna, which has the fold-down capability.  I plan to use a Wouxun KG1000G or KG-XS20G radio, depending on the price I have to pay when the time to purchase comes (looking for best deal at that time).

Respectfully,  DG

[KAF6045]

NMO antenna mounts expect to see a flat metal ground-plane (eg: center of a metal roof) to provide the (virtual) lower half of the quarter-wave antenna. Fitting one to the top of a pole on the tailgate may not provide a suitable ground plane, or at best a very weird directional pattern (into the sky diagonally opposite, and into the ground behind it if it sees the vehicle as a ground-plane).

I can't really say how an NMO mount will behave when remote from any real ground-plane -- the closest I ever got to that situation was a Yaesu ATAS-100/120 which attached directly to a clamp-on lip-mount, which meant the base of the antenna was next to the lift-gate metal, using the lift-gate and side panels of the Cherokee as ground-plane, with the whip sticking above the roof-line on 2m/70cm... On 40m the screwdriver lifted the main body about 18 inches to activate the base loading coil (and putting the whip really up high -- but in all cases the /base/ of the antenna was directly next to the ground-plane sheet metal).

 

 

[marcspaz]

5 hours ago, WRQW247 said:

Marcspaz, Gortex2

thank you both for the feedback given. For me personally, I do not want to see a radio antenna on the hood of my car. I'd prefer to put in extra thought/effort for a cleaner looking antenna mount, hence my decision to mount the antenna mount (Tram 1470) to my Jeep tailgate, and raise the antenna to be installed above the roof line using a riser/pole/pipe TBD. What are your thoughts regarding the use of the Nagoya NMO-200C antenna, which has the fold-down capability.  I plan to use a Wouxun KG1000G or KG-XS20G radio, depending on the price I have to pay when the time to purchase comes (looking for best deal at that time).

Respectfully,  DG

 

I personally have zero experience with the Nagoya NMO-200C antenna.  On paper it looks fine.

 

I'm not sure how a 1/4 wave antenna and a small mount on the hood or swing gate would look worse/not as clean, compare to whatever you plan on engineering.  You are describing more, larger parts.  Again, just my opinion, but mounting the antenna on the back of the Jeep via a riser/pole with the Tram 1470 will not only not look good, but you will likely not net you any noticeable gain.  Plus you are exposing yourself to additional risk of physical damage to the Jeep and antenna, too.

 

Again... your money, your vehicle... but in my own personal opinion as a life long and current Jeep owner who has tried just about every combination antenna type there is, if I were a gambling man, my money would be on the mobile antenna properly installed on the swing gate without the riser and 1470, actually outperforming the same antenna installed on a riser with the 1470.

 

I hope you prove me wrong... good luck and have fun!

[wayoverthere]

Would something like this no ground plane Laird  be a good option, perhaps just above the spare?

At ~15" it'd probably be a little above the roofline, but not so much to be a height hazard (and the spring for some extra protection).

[WRUF442]

I don't want to hijack the thread, but I have similar questions now that I've received my 25 watt GMRS radio kit from Rugged Radios. The kit has a half wave length 12 1/4" NMO antenna and mag-mount. No ground plane required.

I'm installing on a side-by-side which has an aluminum roof, but no portion of it is truly flat. I'm also somewhat obsessed with symmetry and having a "factory" look. The roll over structure has a center tube right where the antenna should go, so I was planning to use a pair of magnets under the aluminum roof (one on either side of the ROPS tube) to secure the mag-mount. The cable would run to the back edge of the roof, then down into the side-by-side.

Instead of the redneck triple magnet setup, I have a lathe and could make a hollowed-out raised ground plane disk with enough clearance over the roof and center ROPS tube to accommodate the NMO connection. The cable would enter the side-by-side via a hole in the roof under the ground plane/adapter. From my research, the ground plane should be a 6 1/8" radius to work with the 12 1/4" antenna assembly (stick plus base load). I'm guessing this ground plane adapter would wind up being about 5/8" tall, and it would be electrically coupled to the roof and side-by-side frame.

Is the raised ground plane adapter going to work, or am I mixing technologies (ground plane vs. no ground plane required) that shouldn't be mixed?

[KAF6045]

3 hours ago, wayoverthere said:

Would something like this no ground plane Laird  be a good option, perhaps just above the spare?

At ~15" it'd probably be a little above the roofline, but not so much to be a height hazard (and the spring for some extra protection).

"2dBi gain" essentially means it is functioning as a half-wave dipole (reference dipoles are rated 2.15dBi, 0dBd) -- heck, if really just 2dBi, this antenna is a loss compared to a true half-wave dipole. It is base-loaded, which allows for shorter antennas -- but base loaded antennas aren't the most effective; center loaded would be better. Since you are talking a vehicle with no (or little) metal in the covering, mounting low may not matter (unless there is a roll-cage near the mount point) -- it's just your body in the direct beam of RF ; mounting higher could be safer at the power levels of these radios (a base-loaded CB antenna was much longer, so the beam was likely just above the roof line when using a trunk-lip mount, and with a 4W max, less RF exposure than a 5W GMRS HT).

Quote

Evaluation for: Base-loaded halfwave

Input Parameters
Power to Antenna (from Exemption Worksheet)	50.00	Watts
TX Time Ratio (TX / (TX + RX))	0.500
Antenna Gain in dBi (dBd + 2.15)	2.00	dBi
Operating Frequency	465.000	MHz
Ground Reflection Included	True
Distance to Area of Interest	6.00	Feet
Maximum Permissible Exposure (MPE)
Controlled Environment	1.550	mW/cm^2
Uncontrolled Environment	0.310	mW/cm^2

 

---

Operating Mode/Factor: FM/AM/RTTY/PSK-31 (100%)

Average Power at the Antenna	25.000	Watts
Estimated Power Density at AoI Distance	0.24134	mW/cm^2

 

	Compliance Distance	AoI in Compliance
Controlled Environment	2.37 feet	True
Uncontrolled Environment	5.29 feet	True

---

I assumed a talk ratio of 50% (for example two minutes transmit, two minutes receive, repeat). Controlled environment is "you", knowing the radio is in operation; Uncontrolled is random people passing by who do not know there is a transmitter in the area. I chose 6 feet as the distance from the antenna to personnel. That report is from a Python port of an Amateur radio RF Safety calculator.

[KAF6045]

13 minutes ago, WRUF442 said:

I don't want to hijack the thread, but I have similar questions now that I've received my 25 watt GMRS radio kit from Rugged Radios. The kit has a half wave length 12 1/4" NMO antenna and mag-mount. No ground plane required.

Technically, if using a mag-mount, you have a ground-plane -- the metal that the magnet sticks to is capacitively or directly coupled to the shield side of the coax. (It's my Larson dual-band window glass mount that has me perplexed -- the whip screws to the outside part and is just what would be the central conductor of the coax, which capacitively couples through the glass to the inside part where the shield side is terminated. Best I can make out is it uses the outside of the coax back to the radio as the ground-plane).

If you are planning to cut a hole in the roof, discard the mag-mount and use a through-hole NMO base&coax. The aluminum roof would be the ground-plane. https://www.hamradio.com/detail.cfm?pid=H0-014933

Edited August 24, 2022 by KAF6045
Added last paragraph

[wayoverthere]

1 hour ago, KAF6045 said:

"2dBi gain" essentially means it is functioning as a half-wave dipole (reference dipoles are rated 2.15dBi, 0dBd) -- heck, if really just 2dBi, this antenna is a loss compared to a true half-wave dipole. It is base-loaded, which allows for shorter antennas -- but base loaded antennas aren't the most effective; center loaded would be better. Since you are talking a vehicle with no (or little) metal in the covering, mounting low may not matter (unless there is a roll-cage near the mount point) -- it's just your body in the direct beam of RF ; mounting higher could be safer at the power levels of these radios (a base-loaded CB antenna was much longer, so the beam was likely just above the roof line when using a trunk-lip mount, and with a 4W max, less RF exposure than a 5W GMRS HT).

I assumed a talk ratio of 50% (for example two minutes transmit, two minutes receive, repeat). Controlled environment is "you", knowing the radio is in operation; Uncontrolled is random people passing by who do not know there is a transmitter in the area. I chose 6 feet as the distance from the antenna to personnel. That report is from a Python port of an Amateur radio RF Safety calculator.

Yeah, from Marc's experience, it sounds like the height gain isn't good for as much of an improvement, range wise, as I'd have guessed, compared to just mounting to the gate or taillight. The main advantage i was looking at is not needing a ground plane (or the ground plane kit mentioned above) compared to something like a 1/4 wave. 

Getting a little less rf exposure isn't exactly a bad thing either, though.

[marcspaz]

@WRUF442 the antenna height you mentioned indicates that it is a half wave antenna and should not need a ground plane.  Also, if you are good with cutting a hole in the roof, just put the mount directly in the roof.  If you switch to an antenna that needs a ground plane, that aluminum roof panel will do just fine.

 

@wayoverthere and @KAF6045, you don't need 6 feet... the safe power density at 50w FM 100% duty cycle for 5 minutes is 1.55 mw per cm squared.  That is only about 3 feet.  But I don't know anyone getting a full 50w out of a no gain antenna and I don't know anyone who is keying full power for 5 minutes either. 

 

Most people with 50w radios and a no gain antenna see about 32-35 watts.  If you calculate for that, plus 2 minutes of exposure and a 50% duty cycle (2 min on, 2 min off is more realistic), now your safe distance is about 1.5 feet.

 

Of course, the further away it is, the safer you are.  Just wanted to point out numbers based off of more realistic usage.

[KAF6045]

Normally I tend to use a 3 min on, 3 min off as it fits both the FCC controlled environment 6-minute window, and the uncontrolled environment 30-minute window (both basically come out as 50% transmit ratio), and the timings would probably be a worst case for me on the Amateur gear (though since I made Extra I have yet to /speak/ on HF -- PSK31 and FT8 were my last modes, and running at half power if not less). And assuming a "rag-chew" session. A lot of my Amateur radios are configured with 3 minute time-out-timer.

I just grabbed the 6ft distance as a possible range for a rear corner mounted antenna to driver's seat, and for people that might be walking by (though I believe they are considered transient and fall into the controlled environment distance, not the uncontrolled -- permanent neighbors for example)

I tend to use a worst case situation for the required evaluation of the Amateur stations (need to model the recently installed dual-band ground-plane antenna -- maybe sometime after I replace the weathered OCFD that is now showing a best SWR around 5-6:1 on non-amateur frequencies. The 40m/20m/10m/6m bands are so bad the antenna tuner goes through fits every time I tried keying up. Not helpful for FT8 when the tuner is clicking away during the entire transmit window.

I've not gone to the effort to model the mobile antennas -- even with EZNEC 7 now free, I'm not ready to build of a mesh representation of a 2008 Jeep Liberty nor a Larsen dual-band glass mount (I did do a mesh of my house's metal roof for the OCFD, just to ensure a worst case gain pattern WRT the neighbor's bedrooms (they have a two-story vs my single layer, and the masts are only about 10ft above my roof -- about 25ft total height... Terrible but anything taller runs the liability of a storm dropping a mast on the neighbor's house. I could do the mag-mounts as a small flat mesh would do for ground plane, but with 15W max on the GMRS, and I'm sitting near the null in the pattern I'm not overly concerned (I have to find someone to speak to first )

 

[WRUF442]

Hole in the roof: I guess I didn't describe this adequately. The roof lies on a center tube of the roll cage, so a direct mount antenna would have to be offset to one side or the other. Aesthetically, that is a non-starter. The raised ground plane/adapter provides clearance over that tube so the antenna could be centered.

Using the roof as a ground plane: my research indicated the ground plane needs to be perfectly flat. As I mentioned, no portion of my roof is flat, though the back half is close. 

 

[marcspaz]

OK, I'm tracking you on how the bar sits. What you're talking about doing with a riser plate so you can center it should be fine. 

 

 The roof definitely does not need to be perfectly flat. Whoever told you that definitely does not know what they're talking about. The only time I could think of an issue where you would want the roof to be flat or level as for esthetics to make the antenna straight-up-and-down. But even that is not a requirement.. Vertical antennas is going to work just fine even at a slight angle in one direction or another another. They just don't look as nice.

[WRQW247]

On 8/24/2022 at 3:03 PM, marcspaz said:

 

I personally have zero experience with the Nagoya NMO-200C antenna.  On paper it looks fine.

 

I'm not sure how a 1/4 wave antenna and a small mount on the hood or swing gate would look worse/not as clean, compare to whatever you plan on engineering.  You are describing more, larger parts.  Again, just my opinion, but mounting the antenna on the back of the Jeep via a riser/pole with the Tram 1470 will not only not look good, but you will likely not net you any noticeable gain.  Plus you are exposing yourself to additional risk of physical damage to the Jeep and antenna, too.

 

Again... your money, your vehicle... but in my own personal opinion as a life long and current Jeep owner who has tried just about every combination antenna type there is, if I were a gambling man, my money would be on the mobile antenna properly installed on the swing gate without the riser and 1470, actually outperforming the same antenna installed on a riser with the 1470.

 

I hope you prove me wrong... good luck and have fun!

To all who have replied, I'm going to go out on a ledge and risk looking like a fool... 

The targeted vehicle is a Jeep Wrangler JKU with removable fiberglas top. As such, in my opinion, the fiberglas rooftop would not provide any sort of ground plane effect. The antenna proposed (Nagoya NMO-20C) based upon what I could learn/find, is a 1/2 wave, center loaded antenna.  With this understanding:

Q1)  could I create the necessary ground plane for the proposed antenna? 

If yes, would a small circular disc be suitable?   

What diameter?

Q2)  If the proposed antenna is a 1/2 wave antenna, is a ground plane required?

As you can determine, I'm against the hood mount/ fender mount approach.  If there is a lip mount that can be attached to the rear swing gate of a Jeep Wrangler, plse advise.

[axorlov]

15 minutes ago, WRQW247 said:

If the proposed antenna is a 1/2 wave antenna, is a ground plane required?

Nagoya NMO-200C on GMRS frequency is a colinear array of two 5/8-wave elements (according to what I see on baofengtech and amazon). I hazard to guess it will work acceptable without ground plane. There are plenty of examples on this forum of 5/8 antennas on all kind of Jeeps installed without ground plane on lip mounts, tailgates, spare carrier, etc. Ground plane will help, but not required, imo.

[marcspaz]

1 hour ago, WRQW247 said:

To all who have replied, I'm going to go out on a ledge and risk looking like a fool...

 

No one here was born knowing anything.  We had to learn everything.  We are here to help... so there are no foolish questions.  Fire away.

  

1 hour ago, WRQW247 said:

The targeted vehicle is a Jeep Wrangler JKU with removable fiberglas top. As such, in my opinion, the fiberglas rooftop would not provide any sort of ground plane effect. The antenna proposed (Nagoya NMO-20C) based upon what I could learn/find, is a 1/2 wave, center loaded antenna.  With this understanding:

Q1)  could I create the necessary ground plane for the proposed antenna? 

If yes, would a small circular disc be suitable?   

What diameter?

 

As mentioned above, the Nagoya NMO-200C (I assume that is what you meant) is not a half wave.  It does require a ground plane.

 

You can definitely add a piece of metal to create the ground plain.  For best performance, you would want it to be round and at least 1/2 wave in diameter, about 12".  14" would be better.  It needs to have a ground wire for best performance, sharing the same ground as the radio and antenna.  However it's not 100% required.  It will work better, though.

 

Also, the top is an isolator, so the plate needs to be outside with the antenna.  I would use a mix of 60 lbs double-sided Gorilla Tape (for instant hold) and RTV (for extended hold) if you don't want to use nuts and bolts to hold it down.  I know I wouldn't cut into my top. 

 

It's critical to keep in mind that if you put a ground plan on the roof and put a fixed or mag mount antenna, regardless of the way you attach the ground plan, it is not going to hold a very heavy antenna.  Highway speeds will eventually rip it off or the top may fail, if you have a heavy antenna or something with high wind drag.

  

1 hour ago, WRQW247 said:

Q2)  If the proposed antenna is a 1/2 wave antenna, is a ground plane required?

As you can determine, I'm against the hood mount/ fender mount approach.  If there is a lip mount that can be attached to the rear swing gate of a Jeep Wrangler, plse advise.

 

If you had a 1/2 wave antenna, a ground plane would not be required.

 

As far as a lip mount that can attach to the swing gate, I have have several JK's... 07, 08, 10, 3 2013's, 14, 15 and 16... every one of them had either a Diamond or Comet lip mount.  I prefer either the Comet RS-730 or the Diamond K400 with the appropriate antenna connection (based on your antenna choice and mounting type). 

 

Be sure to install the mount on one of the top corners of the swing gate, so the antenna is an appropriate distance from the spare tire and carrier.  I used to put mine all the way on the passenger's side (about 2"-3" away from the edge) adjusting it so it clears the glass when you open the back window.  This kept it away from the window wiper motor and the spare tire and carrier.