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Touching coax cable connection
- Thread starter Limeybastard
- Start date
So it looks like i was on a sort of wild goose chase. I was out in the open earlier trying to fault find or should i say locate source of this issue.
As you may know I'm running a Wilson 1000 magmount, no this unit has a so called screw down cap for when you remove the whip and coil, I assumed it protects it against water intrusion. I noticed when I remove the cap the threaded ground part of the base of the magmount is wet, so i dried it . Lord knows if water also gets into the center pin area. Once i dried the threaded part of the magmount coax , no more ground issue.
But I did run into another probable issue, swr. I cant seem to get Chanel 1 swr down low enough , swr meter was all over the place even before i switched the slider to ref from frwd. Power on 2970n4 was lowest setting. Swr was fine when I had set it up a few weeks ago .
I dont think the wilson is supposed to let in water or is just that a dust cap?lol
As you may know I'm running a Wilson 1000 magmount, no this unit has a so called screw down cap for when you remove the whip and coil, I assumed it protects it against water intrusion. I noticed when I remove the cap the threaded ground part of the base of the magmount is wet, so i dried it . Lord knows if water also gets into the center pin area. Once i dried the threaded part of the magmount coax , no more ground issue.
But I did run into another probable issue, swr. I cant seem to get Chanel 1 swr down low enough , swr meter was all over the place even before i switched the slider to ref from frwd. Power on 2970n4 was lowest setting. Swr was fine when I had set it up a few weeks ago .
I dont think the wilson is supposed to let in water or is just that a dust cap?lol
Road Squawker - to quote Peanut, I don't care who you are - that was funny as Hell.
Limey - just try it. No more info is needed. Simple fixes are always the best. If your SWR goes up or your TX declines then either fix the coax or replace the antenna. Otherwise, enjoy your radio.
Limey - just try it. No more info is needed. Simple fixes are always the best. If your SWR goes up or your TX declines then either fix the coax or replace the antenna. Otherwise, enjoy your radio.
If a good SWR was all that was required to have something working properly it'd make life so much simpler but sadly it isn't.
If it changes AT ALL then you've a grounding issue and your coax is forming part of the antenna. I will tell you this though. If you get a CB antenna, put it on your vehicle and it is either low SWR out of the box or can be done within the range of adjustment then you've not got a good RF ground and have losses somewhere. Mobile CB manufacturers choose lengths which account for the lowest common denominator, a magmount. When you start using fixed mounts and especially when you do bonding which massively improves RF ground efficiency on a vehicle, the antenna length needs shortening and 99/100 times that involves having to cut the antenna because you find you need to cut off multiples of inches. In my case it is typically 3-4" off a Sirio Performer 5000.
It isn't. The coupling to ground with a magmount is capacitive anyway and doesn't rely on physical contact. That pad would only start to be an issue as you turn up the wick on the TX power but at legal limits it isn't.
Cheers M0GVZ, when I original fitted the Wilson 1000 magmount my swr levels were on chan 1 needle wouldn't move on chan 40 1.4 or there abouts or less.
I only connected the swr meter to it yesterday to check with the new radio and the number were much higher , radio tx was turned to min. The needle of the swr meter was jumping when I was adjusting the dial on the swr meter fwd and while testing the swr. Best I got was 1.5 on ch40 and 2.5 on ch1. I had already maximized the lenght of the wilson 1000 , anymore and it fall out lol. I think perhaps the moisture on the magmount coax threaded area was giving me issues.
I just found an interesting post by a member called Shockwave on this thread, sounds similar to what I was experiencing when trying tune antenna.
http://www.worldwidedx.com/threads/2970n2-strange-problem.151183/page-5
http://www.worldwidedx.com/threads/2970n2-strange-problem.151183/page-5
The Wilson 1000 needs the 66 inch stinger to tune properly at least mine did... and that was a roof mount.
Shockwave hasn't posted in years, unfortunately. Was a good guy.
What they were talking about in that thread and what you guys are talking about here are two different animals completely. That thread is a problem with the final output signal not being all within frequency, or even close. As power with those signals goes up the problem seems to get worse. Ultimately, the problem is caused by the radio or the amplifier (or the radio putting to much power into the amplifier). It should be noted that with this problem, touching and moving the coax will not change the SWR results or tune.
In your case, the problem is caused by an inadequate ground connection caused by the magnet mount, which causes part of the signal that should transfer through the mount onto the chassis to not make the jump to said chassis, and forces it to find another route. Unfortunately the other route is through the outside of the coax, and this is what causes the problem you are seeing.
Apples and oranges.
The DB
Oh I see. I was talking about after my initial issue of the RFI, when I was attempting to check SWR levels. Basically my swr meter would jump similar to what was being discussed on on that thread. Whereas when I check SWR on another older radio it wouldn't jump and behave erratic.
I need to run further tests or better still probably disable onboard amplifier to set reliable swr. Also, my Wilson 1000 magmount was wet on the threaded coax threaded part.
Good point as mine keeps telling me to make mine longer ! When doing swr. But on other radios it's almost flat reading.
That makes perfect sense. The more power you put through the poorer the RF ground performs and the poorer the RF ground the longer the radiating element needs to be. So other radios you are putting out less power so the RF ground, even though it is a poor one is more able to cope and gives a different reading.
Maybe this'll explain. Basically it is all about the flow of electrons. In an antenna system there needs to be a source to drain from and also return or "sink" to in order for a current to flow in the antenna. The RF ground provides that source and sink. When there are insufficient electrons to draw from and not enough capacity to return them to what you're using as the RF ground then it'll try to to use any other source or sink which is why your coax then comes into play.
Very simplistically (for those that know the theory please don't bite my head off as its purely illustrative):
So when you transmit with 4W you'll be moving about say 100X electrons. Lets assume your RF grounding system is capable of supplying and sinking 80X electrons. So 100X isn't much more than 80X so there's not that much of a problem, it'll just try to find the extra 20X from other sources aka the coax. Now lets up the transmit power to 100W. You're now trying to move 2500X electrons. Your RF ground system is still only capable of moving about 80X electrons leaving you 2420X electrons short and that is going to create all kinds of problems.
So looking at the above and how it affects what signal you radiate. Lets say that the entirety of all sources that the antenna system can find only comes to 1250x electrons. No matter how much your amp tries there simply aren't enough electrons available to shift to put the full current through the antenna that a 100W amp is capable of so it bangs through what it can, 1250X electrons, meaning your radiated signal is only as strong as a 50W amp attached to an antenna system with a decent RF ground. The remaining 1250X electrons the amp can't do anything with are lost as their energy is turned to heat in the antenna system
Cheers, so in essence the antenna subsytem of the rig when using powers over 100W for example ( as the stryker 955 was fine ) need to be near perfect, else any short coming will surface.
Yeah or in my case migrate to home base
I couldn't emulate that touching the coax issue again after that time, so many variables.
Fixed mounting and bonding, yeah definitely. Hinges on trunks and hoods are OK for DC conductivity but poor for RF so bonding straps across those to bond the hood/trunk to the main body make a significant difference. Try it yourself even if you're using a magmount. Get your SWR meter out. Check what channel it starts to rise and hits a certain point, say 1.3:1, note that down then go the other way and do the same. Do some bonding, just even one strap across the hinge of the hood to the body. Do the test again and you should find that the SWR point you were measuring now occurs on lower channels. That's because the resonant frequency of the antenna is dropping as the RF ground improves. If you were to use a 102" quarter wave whip without any matching coils and an antenna analyser you'd see the frequency of the resonant point where x=0 had dropped and also that the value of R comes nearer to the perfect 36.8 Ohms.