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Railfan Technology > MFJ glass mount 2 meter antennas (reviews)


Date: 03/16/17 06:18
MFJ glass mount 2 meter antennas (reviews)
Author: austin

Looking into the purchase of one of these for my vehicle. Any one have anything similar glass mounted with good or bad comments? Thanks in advance
JR



Date: 03/16/17 08:39
Re: MFJ glass mount 2 meter antennas (reviews)
Author: TCnR

Used one of those way back in the 80's that worked well for the RR band. There are warnings about using them with modern tinted windows, either damaging the tint layer or simply not working as well compared to simple clear glass. I have seen them recently on the rear window of pick up trucks.

+ should add that I used it for receive only. The antenna was about 18-24 inches which seemed ok for wind and weather. Did not use it for Transmitting and can't imagine it to have any useful bandwidth. The comments below make a lot of sense, would think performance would be better with an old-fashioned antenna on the outside of the vehicle.

++ should also add the next antenna for that car was a 5/8 wave mag mount, which is just about the best possible antenna in my opinion. Almost any antenna outside of the car is a big advantage, but has all sorts of qualifiers.



Edited 2 time(s). Last edit at 03/22/17 17:42 by TCnR.



Date: 03/16/17 09:47
Re: MFJ glass mount 2 meter antennas (reviews)
Author: K3HX

I've had quite a bit of experience with glass-mount mobile antennas.

Don't do it.

Some modern automotive glass has metal incorporated into the mix.  This will
attenuate the signal passing through the glass.  Further losses happen in
the coupling box.

Our shop was tasked to install this type of antenna on a fleet of identical cars
at the insistance of the fleet manager.  Even though the antennas were
mounted in exactly the same place on each car (we had made a template)
they were all different in tuning. Sometimes it took hours to get the tuning
to come out right.  Since the coupling box and the antenna mount were
"permanently" adhered to the window, you could not swap them out. 

In the end, they were all removed and replaced with covered "skate"
antennas which were less awful.

These things are difficult to tune.  A tiny adjustment on the inside coupling
box produces a large change in VSWR. Once adjusted, these things are
difficult to keep tuned.  Heat in the car's interior (sitting in the sun in the
summer) affects the tuning.

Car washes tend to snag on the outside whip and suddenly detach it. This can
be a problem with mag-mount antennas as well  if you fail to remove them
before entering the car washing facility. 

Typically, they are installed on the rear window.  If the rear window has anti-icing
grids, these wires will make it even more difficult to tune and keep tuned. 
If you are determined to use this kind of antenna, PM me and I'll give you a
step-by-step tutorial on how to mount  them.

(Edit: TNcR makes a good point about seeing these on the rear window of
pickup trucks.  The near-vertical orientation of the  rear window is about the
worst place on a pickup to mount these as the proximity of the cab roof near
the bottom of the antenna screws up the pattern.)

RF energy can leak from the feedline and cause all manner of trouble with the
entertainment system, engine control and the host of sensors that tell modern
automobiles what to do and when/how much to do it.
If you install this kind of antenna, please consult with the auto maker to determine
how to route the cable so as to keep interference with the auto's electronics to a
minimum.

These antennas are almost always end-fed, half-wavelength.  There is a current
fad in the amateur radio community attributing all sorts of benefits to this type
of antenna.  The  behavior and quirks of this type of antenna are either not
known to the proponents or intentionally omitted.

Also, if you run high power on 2m, you will let all the smoke out of the coupling
box.  In my experience, 50w out is the limit

For the amateur radio operator - railfan, there is an additional disadvantage
in that when you finally get the thing tuned for 2 meters, it is so narrow-banded
that it will be nearly deaf on the RR frequencies

You will be far better off with a 1/4 wave whip.

Be Well,

Tim Colbert  K3HX


 



Edited 1 time(s). Last edit at 03/16/17 09:57 by K3HX.



Date: 03/16/17 21:26
Re: MFJ glass mount 2 meter antennas (reviews)
Author: mojaveflyer

Excellent explanation, Tim! I hate it when the smoke escapes...

James Nelson
Thornton, CO



Date: 03/17/17 15:38
Re: MFJ glass mount 2 meter antennas (reviews)
Author: austin

Thanks for all your help Tim and everyone else.. I will stick to the solid connections of hard mounts and mag mount.

Jeff
 



Date: 03/17/17 19:14
Re: MFJ glass mount 2 meter antennas (reviews)
Author: WW

Tim covered it all--they suck.  The simple logic is this:  a poor performing radio with any kind of antenna will be a poor performing radio.  A good radio with a poor performing antenna will also be a poor performing radio.    A radio and its antenna are a system and the system is only as good as its weakest component.   Professionally installed permanent mount antennas generally work best.  The next best choice is usually a mag mount antenna (be sure to keep its cable protected from mechanical damage).  There also can be a considerable difference in reception quality on the railroad band between an antenna tuned for that band and an antenna tuned for the 2M ham band.   The worst of the worst is a rubber ducky portable antenna inside of a vehicle.  That combination has everything going against it for good reception quality.



Date: 03/18/17 04:19
Re: MFJ glass mount 2 meter antennas (reviews)
Author: austin

WW, That I agree with completely. Like I mentioned to Tim on a PM, I was trying to reduce the porcupine appearance of my vehicle. My personal car looks like a porcupine on my rear trunk lid with the array of antennas in it. Might make a State Trooper curious to whats going on within.. But at least I know my antenna connections are 100% mechanically connected and not passing thru a tinted window and "hoping "for a signal to follow thru the glass and tinting as well. It will be Money well saved and less missed photo opportunities in the long run... Since I'm not the youngest Lad out here I will stick with the good "Old School" practices that we all know work very well..... Thanks Guys again for all your feedback...

JR



Date: 03/18/17 08:07
Re: MFJ glass mount 2 meter antennas (reviews)
Author: WW

There are "stealth" antennas available that are pretty well disguised.  Their reception performance varies from considerably worse to about average for antennas.  I don't personally use them, but I know people who do.  As an aside, I have never had one of my vehicles with two-way radio antennas mounted on it tampered with in any way.  I sometimes think that part of the reason is that many potential thieves or vandals think that the vehicle might be an unmarked law enforcement vehicle and simply leave it alone to avoid trouble.



Date: 03/18/17 08:53
Re: MFJ glass mount 2 meter antennas (reviews)
Author: JUTower

Hopefully it isn't too much of a hijack of the thread, since we are discussing automotive antennas... I currently use a 1/4 wave mag mount and it's very good. On my 12-year old car, it hasn't mattered that the mag mount leaves a nasty mark on the roof. (I leave it on all the time, except at the car wash). I will soon be replacing my car with a slightly used car of some sort... what are the pros and cons of going NMO mount? If I was to trade a car in that had had an NMO mount, is there an aftermarket plug so that the next owner doesn't get a hole in the roof?

By the way, Tim K3HX is the antenna guy - he has helped me with a couple antenna projects over the years. 



Date: 03/18/17 09:32
Re: MFJ glass mount 2 meter antennas (reviews)
Author: WW

Yes, there are plastic or metal plugs that will cover an NMO mount hole.  As far as I'm concerned, an NMO mount is about the best vehicle mount.  They are substantial and solid, and nearly every vehicle antenna made comes in an NMO version.  



Date: 03/18/17 12:29
Re: MFJ glass mount 2 meter antennas (reviews)
Author: K3HX

Austin, "flyer," WW, Alex, TCnR et al,

Thanks for your kind words.  Happy to assist.

In no particular order.........

"Stealth antennas."    Our people were tasked with installing a number of these
for a big city police department.  These included a matching network that
tuned the factory AM-FM broadcast outside antenna (pre-Sirius / GPS) and it
worked OK.  The manufacturer also had a model that split off the broadcast
signal and fed it to the automobile radio which stunk.  We installed antennas
that looked like door-mounted rear view mirrors which worked sorta-kinda.
Also installed some rear package shelf antennas made to appear as a rear
package shelf speaker which were a "joy" to mount and tune and didn't work
worth a ****.  They also cost a fortune.

"NMO" mounts.
Cons:
They require a hole in the body.  The best place is in the middle of the roof.
There is a hit in trade-in value if you drill a hole in the roof of a big-dollar ride
like a bimmer or Benz.  If you keep the car for a while, the effect of having a
hole in the roof diminishes. I'd leave the mount in place and not go to the
trouble of removing it.  Covers are available for a few bucks to seal the connector
from the outside and these covers look not unlike a GPS antenna.  You will want
to put a new connector in the new (to you) car.

Good "NMO" connectors (Larsen) are not cheap. 
But....
Youse gets whats youse pays for.

You get one chance to drill the hole in the correct location.  Since Alex is in the
same area as I, he can call me and I'll be able to assist.  I'll send a PM.

Pros:
The "NMO" connector is the de facto industry standard so you can put on anything
from a 1/4 wavelength whip  to a colinear 2m on it.
It works better than a mag-mount.
It won't be swept away by a low hanging  branch or the low roof of the drive-in
window at "Fetid Burger."
No danger of pinching the lead-in.
Harder to steal / vandalize.

A note for the more technical types.  Recently purchased an ICOM marine radio of some
vintage from an estate of a ham.  Really cheap.  To my amazement ,it worked.  Investigating
the circuitry I noted it had a stagger-tuned set of helical resonators in the receiver chain.
(a very selective filter that keeps out much of the garbage)  The frequency range of the marine
band helical resonator set covers the RR band.    Just something to consider at the next hamfest.

Be Well,

Tim Colbert  K3HX


 



Date: 03/18/17 17:12
Re: MFJ glass mount 2 meter antennas (reviews)
Author: WW

Placement of the antenna is very important.  It is the roof, trunk lid, etc. that creates the ground plane for the antenna.  Poor ground plane = poor reception.  The car's roof is ideal because the roof provides a good ground plane and it is the highest point on the vehicle.  The disadvantage is that the antenna may be tall enough to drag and even get caught on garage doors, overhead parking structures, etc.  This is particularly a problem on SUV's and 4WD pickups.  On a sedan, a trunk mount compromises a bit in reception, but still does OK, and is generally out the way of getting caught by low-hanging doors, overhead structures, etc.  Some people will mount the antenna on the driver's side of the vehicle in front of the windshield frame, essentially opposite of the vehicle's regular radio antenna.  The hood will act as a good ground plane if the radio signal is coming from in front of or from the right of the vehicle, but will be considerably poorer if the signal is coming from the left or from the rear of the vehilce.   Still, if one is driving a tall SUV or 4WD that has to be parked in a low roof clearance location, it may be the only option.  

One of the huge drawbacks of a glass mount antenna is that it has a terrible to non-existent ground plane.



Edited 1 time(s). Last edit at 03/18/17 17:13 by WW.



Date: 03/19/17 06:37
Re: MFJ glass mount 2 meter antennas (reviews)
Author: austin

WW and Tim, No need to apologize for any Hijacking of the thread. This was intended for a informational and learning thread from my prospective. I currently have a older (17yrs) 4 door sedan and I have both my Maxrad 5800 antennas mounted to the trunk lip NMO mounts along the back lip closest to the rear window along with my K40 lip mount CB antenna as well (haven't used the CB radios in ages but its still mounted) and all the antennas have a ground strip mounted below the set screws and is wired and mechanically fastened to the trunk lid sub-frame to make a good ground connection. Have never had many issues with receiving at all. Sitting at Milbury,oh on the water level routs I can easily pick up radio transmissions 30 miles to the east on good weather days. And for my truck location I had the antenna NMO mount installed on the drivers side front fender (special mount and bracket) mechanically fastened to the body panel. Recently moved it over to the passenger side fender since all my in and out of the truck and bumping it became a nuisance to me. Truck are by far the worst for mounting options and keeping your good ground plane in check also. Best spot for a mag mount I fount on the truck was the center of the roof with a 5/8 wave whip on the coil and base. 1/4 wave is OK for close local action but when out and about on a road trip like Sand patch or the west slope you need all the reception you can get. 

Jeff
 



Date: 03/19/17 14:46
Re: MFJ glass mount 2 meter antennas (reviews)
Author: WW

austin,

It sounds like you've got a good setup.  I wouldn't mess with it if it is working well for you.  I've also used the trunk lip mounts with pretty good success.  Not as good as a full roof mount, but pretty good.  On the receive side, I've found no antenna that works better than a Larsen NMO-150 tuned to the railroad band.  On vehilcles where that is too tall, I generally use a shorter unity gain Comtelco antenna, again with the length tuned to the railroad band.  That is slightly weaker in marginal reception areas than the Larsen, but still pretty darn good.

My distance record for consistent, good railroad band reception (pre-2013 narrow-banding), that was using a trunk or roof mount NMO-150 and a Kenwood TM-271 amateur mobile radio, was being able to easily hear the Union Pacific Cheyenne Mountain repeater west-southwest of Colorado Springs, Colorado from Cheyenne, Wyoming--170 air miles distant.  From Cheyenne I could also hear repeaters located on Laramie Peak near Douglas, Wyoming, roughly 110 miles to the north-northwest.  That was one of the best radio/antenna combinations that I ever used.  The 271's replacement radio, the TM-281 is, from what I've seen, just as good and will tune the splinter analog channels.  



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