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SWR problems
- Thread starter BIG clean GREEN
- Start date
BIG clean GREEN
Well-Known Member
If that is the case with regard to earthing then how are mag mounts earthed, when they (or mine) sits in a rubber protection cup 
How the bl**dy hell should I know? I've a cupboard full of hammers. What d'ya want?
Blimey. I can't tell you everything you know. You'll never learn if I just give you all the technical stuff in an answer.
Cough.
Blimey. I can't tell you everything you know. You'll never learn if I just give you all the technical stuff in an answer.
Cough.
mag mounts work by having a capacitive coupling to the body. The outer braid of the coax is already connected to earth at the radio end, or should be. Putting a strap from the antenna mount to a bit of metal on the gutter or roof or a handy hinge bolt somewhere is mostly about stopping RF current going back down the coax outer into the car and causing mischief and also can help prevent receive noise problems. I don't think that's your problem, you've already tried it with your mag mount? Get another meter on it so you can rule out or blame the meter and if you rule out the meter get another antenna on it so you can blame or rule out the antenna 
If it's neither of those then it's a cable or connector fault 
If it's neither of those then it's a cable or connector fault BIG clean GREEN
Well-Known Member
Ok Jon, now Chris and I are really confused.............
First we tried with Chris' SWR and got high readings simular to those of my SWR so we adjusted the aerial length with no benefit, we then tried using a length of earthing cable, one end to the mount bracket and the other to a bolt on the hinge which strangely sent the reading higher !! It was then that we noticed that the way to reduce the results was to hold onto the roof rails to ground them, by doing this we got them down to an average of around 1.5.
The next thing I tried was to insulate the connector to simulate a mag mount connection by using rubber washers on both sides of the mount where the connector passes through, again results in the red, so I made a solid earth connection from the mount bolts to the door hinge and still no good.
I then tried my small mag mount and took the results, in the red......... so is my rig that's dodgy ?
Paul
Well-Known Member
When i did this recently i was getting the same and never got a good result on roof rails.
I bought a mag mount and had the same issues again despite being told it would adjust by altering the length. In the end i had to start trimming the antenna which i did in 1/4 inch chops and ended up get just over an inch off. Then i was able to alter antenna length in the base up and down and got a very good SWR reading. It stayed in the red right up to the final cut.
I bought a mag mount and had the same issues again despite being told it would adjust by altering the length. In the end i had to start trimming the antenna which i did in 1/4 inch chops and ended up get just over an inch off. Then i was able to alter antenna length in the base up and down and got a very good SWR reading. It stayed in the red right up to the final cut.
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Have you tried another antenna, i.e. Chris'? Although I checked the SWR on your base before I returned it maybe it has developed a fault. You've pretty much eliminated the SWR meter, now eliminate the antenna, or not. Rule out the simple things first because they can cause strange results
BIG clean GREEN
Well-Known Member
We tried using Chris' brand new un-cut whip, with simular results !
When I fist installed the sirio I snipped a fair bit off it to get good readings, so not sure if or how much further I could go, also am I correct in thinking when you only do this when you can calibrate it in on
ch20 ?
The only difference with the base from when you sent it back to me Jon is that I ferked the upper grub screw up so now it has a small screw in bollt instead.
When I fist installed the sirio I snipped a fair bit off it to get good readings, so not sure if or how much further I could go, also am I correct in thinking when you only do this when you can calibrate it in on
ch20 ?
The only difference with the base from when you sent it back to me Jon is that I ferked the upper grub screw up so now it has a small screw in bollt instead.
mmm, an uncut Sirio shouldn't give you an infinite SWR (that's the reading at full scale deflection), more like 2.5-3 IIRC. So it's probably not the meter, probably not the antenna but if you swap the antenna to your mag mount it still doesn't behave, suggesting it's not the cable Definitely a bit of a conundrum to figure out remotely that one is!
Probably not a good idea to cut any more off your whip, it'll end up too short. As the results are not straight forward, can you try your antenna and your meter on Chris' car, so you hopefully get a good reading as a sanity check that they are ok.
Definitely a bit of a conundrum to figure out remotely that one is!Probably not a good idea to cut any more off your whip, it'll end up too short. As the results are not straight forward, can you try your antenna and your meter on Chris' car, so you hopefully get a good reading as a sanity check that they are ok.
BIG clean GREEN
Well-Known Member
Yes I'll try that when I'm next at Chris' It may be one of those that'll have to wait untill our next meet at Lincomb
ok, I do usually take my antenna analyzer to Lincomb in case someone has a problem
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