Mag mount antennas

Joined
Jan 14, 2019
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13
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MM:0.0 Me/MM:0.0 FL/MM:0.0 CA/MM:0.0 WA
#1
Has anyone who cant use baking pans and pie plates for a counterpoise outside "for fear of getting a hole drilled into his head by the wife" ever attached a mag mount antenna to a vertical L bracket extending 90 degrees downward comparable to the length of the vertical radiator? I could use two 102" whips cut down using an online frequency calculator with one of those dipole type offset brackets used for CB base applications but I already have low band, high band and uhf band base loaded mobile mag mount antennas.
 
Joined
Mar 12, 2014
Messages
1,007
#2
What you're proposing is a dipole. I sometimes use two hamsticks with the mount shown here:

MFJ MFJ-347

It would work with two whips that use 3/8" thread. Although it's hard to see in the photo, the second whip would mount right behind the SO239 connector and would aim 180 degrees from the first whip. I'm not sure how this would work with mag mounts. It seems as it would be more efficient to use two whips instead. What frequency range are you trying to cover? Also, is this for transmitting or is it for receive only?
 
Joined
Jan 14, 2019
Messages
13
Location
MM:0.0 Me/MM:0.0 FL/MM:0.0 CA/MM:0.0 WA
#3
What you're proposing is a dipole. I sometimes use two hamsticks with the mount shown here:

MFJ MFJ-347

It would work with two whips that use 3/8" thread. Although it's hard to see in the photo, the second whip would mount right behind the SO239 connector and would aim 180 degrees from the first whip. I'm not sure how this would work with mag mounts. It seems as it would be more efficient to use two whips instead. What frequency range are you trying to cover? Also, is this for transmitting or is it for receive only?
That's what I was looking for. Thanks.
 
Joined
Mar 12, 2014
Messages
1,007
#4
Great, I hope it works out for you. If you opt to mount the whips vertically, try to keep your coax perpendicular to the whips for at least 1/4 wave (about 9ft for CB) That will reduce the chance of your coax interacting with whips and throwing off your signal.
 

KB4MSZ

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Mar 12, 2018
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Tampa, Florida
#5
A co-linear dipole might be the way to go. It's a true halfwave tall but requires no horizontal ground plane. The coax can exit straight down as well.
 
Joined
Sep 8, 2006
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2,553
Location
Stockholm, Sweden
#7
The picture shows stacked dipoles but colliniar works the same way but the elements are put in a tube and the connection between the elements are not a coax but a coil or a certain wavelenght of wire that are curved up to fit in the tube.

/Ubbe
 
Joined
Jan 1, 2012
Messages
110
Location
South County, Rhode Island
#9
You're right. That photo is of stacked co-linear arrays. Thanks. The MFJ-347 allows me to custom DIY my antennas and still encapsulate them in PVC tubes and have the SO239 connector 90 degrees from center plane.
I've done a lot of antenna work in this area. A few notes that may help. Out of the available options when it comes to insulators, PVC is the least RF friendly. The order goes like this: Teflon tubing, Fiberglass, CPVC than PVC. We had made some custom coaxial dipole antennas for the PEG radio system here in RI and tested these materials for quite a while. The Coaxial dipole is VERY particular when it comes to materials for insulating, the distance between the active and non-active parts of the antenna and can be VERY reactive if the coax is allow to flow around within the tube and skirt of the antenna...all of this had to be meticulously worked out to avoid these issue. BTW what frequency range are you needing this in? Frequency characteristic will dictate if you can get away with your idea. We are developing an antenna for a PEG TAC repeater allowing low power duplex operation using two separate antennas (and no duplexer) within a fiberglass tube. Again this is in the PEG VHF low band (40-50Mhz). I've tried the dual mag mount with one antenna directly in line with one another but the dense was much too high. This problem improves when a ground plan of about 2sq foot is added but of course this is unpractical. Using a drooping radial ground plan as the TX antenna at the top of the fiberglass pole while having the RX antenna about 5ft below inside the pole seems to work so far.
Is this antenna that you need for transmitting or just receiving? Also what band is it for? you had mentioned CB but is that what band you need this antenna for?
 
Joined
Jun 30, 2006
Messages
7,195
Location
So Cal - Richardson, TX - Tewksbury, MA
#10
The photo is a phased dipole array. A co-linear array would be stacked elements where they are mechanically connected together, usually with a 1/4 wavelength phase reversing element in between.

You're right. That photo is of stacked co-linear arrays. Thanks. The MFJ-347 allows me to custom DIY my antennas and still encapsulate them in PVC tubes and have the SO239 connector 90 degrees from center plane.
 
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