mobile problems (swr)

[crusader]

today i went out with my mobile station and some very strange swr problems occured. while static with engine off the swr started off very low but would fluctuate to 2:1 or 3:1 making the radio drop off and stop txing.
starting the engine stopped this problem completely the swr was low and stayed low and did not fluctuate at all,very strange,any ideas any one? station as follows;

car negative ground
radio lincoln running into
zetagi power reducer running into
reace power/swr meter running into
zetagi b300 amplifier running into
zetagi t1000 transmatch and finally out to the
1/4 wave steel 2 piece antenna mounted on an aluminium bracket bolted to the roof rack mounting position 8mm bolt.

many thanks crusader

 

[Switch Kit]

it's not real clear .Zetagi ? .....sounds like a grounding problem ,but also ,IM guessing your running an amp ? goood chance if the radio is tuned low ? many times SWR meters can't read or be calobrated without a 3 to 4 watt drive into them ,but as you said your fluctuating ? Hmmmm .....if this just started on you and you didn't have the problems before ? check your grounds and make sure everything is as should be ,make sure all your 259ers are tight ect. ect. sorry I couldn't help you any more then that. Let us know.

 

[crusader]

both swr meters are rated at 1Kw max so 200w from the amp should not upset them.the strange thing is why only have a problem when the engine is off? if it was bad grounding or dodgy 259's/ bad soldering, it would give bad swr readings with or without the engine running? thanks for the thoughts its usually the simple things we overlook!!

 

[nomadradio]

Hi Crusader,
You sure do have a whole lotta stuff in line between that radio and the antenna.


This leads me to wonder about the quality of the coax jumper cables you're using. We see a lot of them assembled without ANY solder on the coax braid (ground) in the connectors. Everybody knows to solder the center wire to the center pin of the plug. It's out in the open where everybody can see it.

Some folks will simply fold the braid over the cable, or over the adapter sleeve, screw the plug together and call that close enough. Trouble is, those thin strands are exposed to the oxygen in the air. Eventually the copper surface will oxidize, and the quality of the metal-to-metal connection will degrade. Once this happens, heat is released where the strands touch the inside of the plug body when any real RF power is fed into it. This accelerates the oxidation further. Just pulling on the coax cables or moving them about will cause those braid strands to "squirm" about inside the plug. The friction will pierce the oxide layer on the strands, and the SWR reading will improve. Until the cycle begins again.


Soldering the body of a PL-259 requires a LOT of heat, and it's common to see that step get skipped. Especially since you have to unscrew the outer ring of the plug back down the cable to even see if this has been done. At a glance, you can't tell by looking when the plug is assembled.

And then there are the "crimped" cables sold with a rubber/plastic "strain relief" at the rear of the plug. These will last for a while, but only at low power. High power will degrade them. A question of "when", not "if".

Any time an antenna system acts in an inconsistent or intermittent fashion, I start looking for unsoldered ground connections inside the coax connectors.

73

 

[crusader]

thanks nomadradio

going to have to concentrate on the coax and patch/jumper leads between equipment,even with a view to removing some from the line.the coax is from germany so should be good quality, but i agree,will have to go through everything with a fine toothcomb!!

 

[Switch Kit]

I've noticed that of late myself Nomad ....people feeling like it's no big deal to solder the braid through the 4 little holes ? (quicky sales) ....especially if power is involved !! .....I see it alot !! I was taught a long time ago that it was best to always solder the braid to the connectors ,as a matter of fact ,depending on the coax being used ? .....would even take the time to file down or even use a wheel grinder on the reducers when using mini 8 coax or 58 for a better grab of the solder and the braid ,also give the 4 little holes on the 259ers a slash with a file on both sides of the holes for a better solder grab as well .....good well used heat is always a plus with those as well ......