K40 VS ?

[aocfm]

Hello from a newbie, I've got a cobra 75wxst that I use on a Cat D6 dozer for directing trucks around jobsites. I'm using a K40 with a magnet mount but have never been able to get an swr lower than 4. The specs for the 75 recommend a top load antenna and the K40 is a baseload. Would this be where my problem lies?
Does anyone have a suggestion for an alternate antenna? I need one thats rugged enough to take some bouncing around on a daily basis, preferably magnet mount or some other quick mount type.
I like the 75wxst because it is so easy to setup and haven't ever had a bad comment from anyone about transmitting or reception noise. I listen to it through a pair of Peltor AM/FM headphones as I have an open ROPS.

 

[Switch Kit]

for what you are aimming at ,it sounds like your K40 is working for you but SWR is bad .....IM guessing a grounding problem here ? Do you have the magmount stuck on the meatest part of the tractor where it would more then likely have the most ground plane for the antenna itself ? You might try moving the antenna around and try and take different readings on your meter . Another Antenna would be the Wilson 1000/5000 magmount ....I personally believe it's a better antenna then the K40 even though the K40 should work for you just fine in your situation. Good Luck to you.

 

[aocfm]

K40

Hi Switchkit,
The antenna is on top of the ROPS which is about a 5'x7' sheet of 3/8" steel but now that I think about it the ROPS is isolated somewhat from the rest of the ground plain by 1" thick rubber grommets for vibration and noise reduction, so maybe thats part of the problem, eh!

 

[Switch Kit]

hmm ? 5 by 7 is a pretty good size ....What kind of meter are you using to check it with ? .....a 4 huh ? .....would that be in the red zone after you calobrated the meter then checked the SWR ? You can adjust the stinger (antenna) on those i believe ? sliding it up or down should change the SWR in either direction there's usually a little set screw that holds the stinger in place. You did say that your hearing folks pretty well and they are hearing you as well ? That's a good thing !! If your not running power and you could at least get that match down to under a 2 I think you will be just fine for what your doing .The lower the better of course.

 

[nvcowboy25]

hum

check the coax and get ya a bolt or to and a pice of ground strap frof roof to rops bars and if the coax is bad look at the end were it goes in to the coil it is probally shock losse i had a k-30 that i uswed on my four wheel that happend to the probolic shaft in the coail part of the ant broke fro hiting tress and bounching aroud they are not very sturdey in my opion bet that is your problem just run ya a fiber glass shorty ant of the rops you are talking probally less the 5 miles any way right . not a tech just my 2 cents

 

[snoope]

aocfm,

Our operators use both the K-40 magnets and the Wilsons (both the 1000 and the 5000 )..The D-5 op.
has his mounted in front of his windshields (no problems with tree branches down there )...And the excavator guys mount them anywhere away from their booms :shock: ..

The best signal is from the Wilson 5000 but thats the most $$$..and they all run smaller radios :roll: :roll: ..

Open ROPS, you got to be the man 8) ,our guys would go home if they did not have full cabs ..

Good luck in finding a solution to your swr's.....and getting a machine with a cab .


Snoope back quiet

 

[351_bear]

antenna swr

id go with a little wil magnet mount there cheaper than the 1000 or the 5000 or run a standard magnet mount with a half breed on it

 

[Cheech]

What about a fixed antenna with a quick disconect at the bottom? Would work better than a magnet mount if tuned right.

 

[Master Chief]

The K40 has a small capacitor inside the base unit. If this is a used (and abused) K40, it is possible that this capacitor is blown. Try installing the antenna on a car and see if there is any change. If the SWR is still real bad, it could be the capacitor.

You have enough metal under the antenna, even if it is isolated from the frame. None of the equipment I've seen does this as the whole purpose of the ROPS is to provide Roll Over Protection. Soft mounts would tear away! It IS possible that the operator position or the cab is isolated though.

The Wilson Lil' Wil was a great suggestion. Same goes for the Wilson 1000. No need to spend extra $$$ on the 5000.

 

[351_bear]

antenna swr

might as well eliminate the whole firestick idea francis fiberglass idea it sounds like your in a brushy area with low lying branches on our shovels we use maxrad antennas or a magnet mount with a half breed on it works great we deal with a lot of brush around here so thats what sorts of antennas we use some people use francis or titans but a month or 2 later there snapped in half all the big dxers live down town so they run what ever