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Mobile 102 Inch Whip w/spring

GLM927

Member
Oct 25, 2020
3
0
11
Ontario Canada
Hey Folks

Question for y'all... I own a 102 with spring but have a triple magnet mount for it, but will this be alright to push power through.? Approximately 700 watts on the AM band and SSB.

I do not want to drill into my vehicle.!

Any idea's.?
 

Alexis Mercado

Well-Known Member
May 17, 2016
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I wouldn't put 700 watts through a mag mount...(I know some have and gotten away with it) I definitely wouldn't run a 1/4 wave whip on a mag mount unless stationary.

My .02

Your mileage may vary.
Why not put many watts through a mag mount ?

Why you use it if stationary ?

I am asking because I plan to go to a key down competition and I was thinking to use a full size 1/4 wave whip, just for the competition. Would it be more efficient than a center load coil antenna ?
 

Dopple

Member
Apr 9, 2022
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Breedlove mounts are what you seek. I'm probably going to get one of those for my Tarheel antenna.
 

The DB

Sr. Member
Aug 14, 2011
1,996
1,490
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St. Louis, MO
Why not put many watts through a mag mount ?

For one, magnet mounts use capacitive coupling, which means there is a space between the magnet and the metal it is "attached" to, effectively creating a capacitor, which means when there is enough power, just like a capacitor, there will be arcs through the dielectric (i.e. your car's paint). This will change the "dielectric constant" of the capacitor, which will affect things like the antenna's SWR, in some cases drastically. This can lead to blown final stage transistors, which in an amp can be a very expensive fix. Said capacitive coupling also tends to cause CMC problems on a coax. Have you seen or heard of anyone using coax length to "tune" an antenna? When this happens you are not tuning the antenna, your just using one problem (that many apparently don't realize is an actual problem) to hide another. This type of problem is especially common when using magnet mounts, and will be amplified by running a lot of power i.e. more than 100 watts) through said antenna system.

Why you use it if stationary ?

I'm not sure why he wouldn't. You do need a triple or quad magnet mount, a single five or six inch diameter magnet will definitely not be enough to hold that long of an antenna on a moving vehicle.

I am asking because I plan to go to a key down competition and I was thinking to use a full size 1/4 wave whip, just for the competition. Would it be more efficient than a center load coil antenna ?

A full length whip, through a magnet mount will be "more efficient" (hey look, those words again) than a center loaded whip, also through a magnet mount, and mounted in the same location.

The thing is, a proper permanent mount (like the Breedlove mount mentioned above) will me "more efficient" (hey look, now you've got me using those words...) than any magnet mount, and sometimes noticeably so. The reason is, again, the capacitive coupling in a magnet mount that I mentioned above, all of the RF energy that travels between the antenna and ground plane has to travel through a capacitor, which has its own impedance, and by the very nature of capacitors, will add loss.


The DB
 

M0GVZ

Sr. Member
Oct 18, 2011
1,758
1,518
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I am asking because I plan to go to a key down competition and I was thinking to use a full size 1/4 wave whip, just for the competition. Would it be more efficient than a center load coil antenna ?

People don't use magmounts in keydown competitions because other than the reasons mentioned that they're not rated for the power a fixed mount provides a much better connection to the RF ground. The more efficient the RF ground the more current can flow in your antenna and the stronger signal you radiate.

Also if you're using a 102" whip then why are you using a spring if it's stainless steel? There's no need to if you use a fixed body mount or a lip mount, it'll just bend over and spring right back.
 

Alexis Mercado

Well-Known Member
May 17, 2016
266
146
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People don't use magmounts in keydown competitions because other than the reasons mentioned that they're not rated for the power a fixed mount provides a much better connection to the RF ground. The more efficient the RF ground the more current can flow in your antenna and the stronger signal you radiate.

Also if you're using a 102" whip then why are you using a spring if it's stainless steel? There's no need to if you use a fixed body mount or a lip mount, it'll just bend over and spring right back.
I am using a spring because a 102 whip is too short. It should be around 108” long for 11 meters. The spring will add the length required.
 
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w9cll

W9WDX Amateur Radio Club Member
Jan 19, 2013
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Hard mount if you want to run that kind of power. When you run that kind of power mobile you will be dealing with all kinds of issues with the electronics in the that will trump any issues with the mount.
 

w9cll

W9WDX Amateur Radio Club Member
Jan 19, 2013
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Chicago, IL
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Breedlove mounts are what you seek. I'm probably going to get one of those for my Tarheel antenna.
You will not be sorry, I used one with a High Serria side kick on my car. I have quit doing HF mobile these days because I work from home permanently now so I am hardly in the car anymore.
 
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Holydvr

Well-Known Member
Nov 2, 2018
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I once used a quad magnet with a steel whip and spring on a ‘77 Power Wagon. Only ran around 3-400 watts through it though peak. Never had an issue at 70mph as far as stability on the vehicle.
 

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