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Author Topic: SWR problem  (Read 1464 times)
VE3TRU
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Posts: 27




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« on: May 17, 2013, 01:42:02 PM »

Not sure I'm in the right forum area but here goes.
I have a new vertical antenna, it seems as though it likes the 20m band the best, and that's fine by me.
Worked well until recently I can get a 1.1 or less (with a tuner)or (1.5 without one @ full power, that's the best I can get out of it). The problem is if I push up the watts beyond 50 watts I get a bounce on the forward reflected is fine. Its got to be something with the antenna, it worked fine until now, the only thing I can think of is that its been very dry and its in sand so the grounding has got to be really poor by now.
any Ideas would be appreciated
Thanks

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N4JTE
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Posts: 1158




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« Reply #1 on: May 17, 2013, 04:14:39 PM »

Need a lot more info, the problem could be a lot of things, check on dummy load,feedline connectors etc.
bob
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VE3TRU
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Posts: 27




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« Reply #2 on: May 17, 2013, 05:09:26 PM »

I checked all the convectors visibly, seems ok tight and all
The dummy load is built into my tuner works great, solid full power sits around 120 watts steady.
The antenna not so great after about 50 watts the forward jumps around like a ping pong ball, more power the worse it gets.
Seems like the tuner is also a little finicky, at times I can get it to work but way too unstable. Played with the tuning coil wish they had a better system then that stupid clip, but that's not getting me anywhere. Funny thing is this worked at 1st, but I didn't use it much at the time. The instructions say you can run 4 33' radials I only have 2 as I'm near building, I will fix that later.They sit 1/2 inch underground but they are suppose to be optional anyway. To me 33' seem too long but I'm going by the instructions. I can dig up a multimeter but that's it for testing equipment, cant see how that will help. My MFJ tuner has always been good to me, but maybe that's failing IDK could be anything where do you start.
P.S.
Thanks for the help
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WB6BYU
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Posts: 13341




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« Reply #3 on: May 17, 2013, 07:12:47 PM »

What type of antenna are you using that has a clip on a matching coil?

Do you have a lightning arrestor anywhere in the system?

Do you see the same problem when you bypass the antenna tuner
and feed the antenna directly?  Or only when you are using the tuner?

Did the tuner settings change at some point?  (You do record the settings
for each band to make it easy to retune, don't you?)


Most commonly such symptoms are caused by something arcing when the
voltage gets high enough:  at low power there isn't enough voltage and
the system operates normally.  There are a number of possible causes,
including:

1) fault in the antenna or coax.  Sometimes this is a bad connection to the
braid in the shell of the coax connector.  Sometimes it is due to corrosion
or other issues with the antenna.  If there is a poor connection somewhere
then the tuner might have much higher voltage across it than normal.

2) grass or other material too close to the base of the antenna (though
normally a blade of grass shouldn't be a problem at 50 watts.)

3) some other change to the antenna tuning.  For example, the clip on
the loading coil doesn't make good contact, or a cracked insulator
with some moisture trapped in it.


It sounds as though you have some sort of simple antenna fed against
ground (like the old HyGain 18V.)  Most such antennas NEED a good
ground system for reasonable performance, even though you can sometimes
get a low SWR otherwise due to high ground losses.
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VE3TRU
Member

Posts: 27




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« Reply #4 on: May 18, 2013, 03:56:27 AM »

thanks
I suspect arching in the feed line connectors.
The antenna is a Hy-gain AV-18VS 10-80 meter, the radio is a yaesu FT-840, the tuner is a MFJ Delux Versa Tuner II. I have the antenna and radio grounded using interdependent grounding plates.No I don't have a feed line lightning arrestor I need to get one put it in.
The thing is in abought 20 min or so the problem almost goes away.
I'm not running tubes so I cant see a warm up time like that and besides I still get the occasional problem.
Thanks for giving me some Ideas
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K1CJS
Member

Posts: 6045




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« Reply #5 on: May 18, 2013, 05:14:16 AM »

What are you using for a ground plane?  In the manual for that antenna on one of the illustrations, it says "radials, if required."  From your description here, it seems that is the problem--that radials are required at your installation. 

Try a simple experiment.  Take at 4 lengths of wire, 16 1/2 to 17 feet long.  It can be covered (insulated) or bare wire, for this purpose one is as good as the other.  Attach these wires to the ground point of the antenna at the antenna base, making sure the connections are good and tight, and stretch them out in opposite directions, 90 degrees apart.  Now, go back in and check your SWR and tuning.  If it has steadied and seems OK, you have a ground problem and need to lay out a radial field--because simply grounding the antenna isn't good enough.

You simply cannot use a connection to a ground rod for an RF ground, in almost all cases, an RF ground has to be a radial field even if your 1/4 wave vertical antenna paperwork says you don't need one.  Also, even if the four radial wires seem to work OK, you'll be better off adding more radial wires, especially for the lower bends.
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WB6BYU
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Posts: 13341




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« Reply #6 on: May 18, 2013, 07:12:31 AM »

I think I found an important piece of information on re-reading your original post:


Quote from: VE3TRU

...The problem is if I push up the watts beyond 50 watts I get a bounce on the forward reflected is fine...




Most types of antenna or feedline faults will result in higher reflected
power when the forward power jumps around.  If the reflected power doesn't
change, then that limits the possible causes.

So the next question:  if you bypass the tuner so you have an SWR of 1.5 : 1,
does the reflected power change when this happens?

And does the forward power go up or down?

Does the rig have an SWR meter?  What does it say when this happens?  Does
the meter on the rig (output power, current, etc.) show anything different?

One possible explanation is that there is a poor connection between the rig
and the tuner that causes the RF to the tuner to drop out.  That would cause
both the forward and reflected power to drop to a low value.  This could be
due to a poor contact in the coax (either center conductor or shield, open
or short.)  In that case I would expect the metering in the rig to change, but
the SWR at the tuner won't read any higher because the antenna itself hasn't
changed.  (There is simply less power reaching the tuner.)

If the reflected power and the rig metering don't change when this happens,
then it would seem that the output power is OK, so the fault would be in the
forward power metering circuit.  Could be a dirty switch or a poor contact in
the wiper of one of the power calibration pots inside, the forward power
detector diode may be flakey, or it could just be a loose wire or poor solder
joint somewhere.

Hmmm...  but since you don't seen the problem when using the dummy load,
that would tend to rule out some of these problems.

In that case, a good start would be to put out a steady carrier and wiggle
all the connections to the rig and tuner and see if you see any shift, both
on the dummy load and on the antenna (both direct and through the tuner.)
Thumping on the tuner case might cause something to shift as well.

Otherwise, we need more details on the exact symptoms:  what all the
meters show in the various conditions.
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K1CJS
Member

Posts: 6045




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« Reply #7 on: May 18, 2013, 07:18:09 AM »

Quote
...you'll be better off adding more radial wires, especially for the lower bends.

Sorry, I meant for the lower bands.   Embarrassed
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K0ZN
Member

Posts: 1553




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« Reply #8 on: May 18, 2013, 09:11:11 AM »

 You need to start a sequential, methodical troubleshooting program. The previous posts have some very good info/suggestions.

Start with the radio. Absolutely confirm it and even possibly the power supply are OK. Use a dummy load.

Check the coax and connectors carefully and check them with an ohmmeter, wiggle and aggressively MOVE all cable and connectors, etc.
Could you have water in the coax or some part of the antenna or connector at the antenna?

Double check ALL mechanical connections, screws, nuts, bolts, EVERYWHERE, including grounds, etc. Don't overlook the ground connections in the shack.

At those power levels, the possibility of arcing is quite small, especially since with that type of antenna and coax, the
operating voltage on the system at that SWR is pretty low.

I had a somewhat similar problem with my 40M vertical.....problem turned out to be a poor, possibly corroded connection on the ground circuit at the
antenna.

Good luck.  73,  K0ZN
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KO3D
Member

Posts: 49




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« Reply #9 on: May 18, 2013, 09:40:16 AM »

Played with the tuning coil wish they had a better system then that stupid clip, but that's not getting me anywhere. Funny thing is this worked at 1st, but I didn't use it much at the time. The instructions say you can run 4 33' radials I only have 2 as I'm near building, I will fix that later.They sit 1/2 inch underground but they are suppose to be optional anyway. To me 33' seem too long but I'm going by the instructions.

I have this antenna and had nothing but high SWRs until I removed the tuning coil. It wasn't helping on 80/40 and isn't needed for the higher bands (I've worked 98 entities with 100W on it.) It's really useless with the small clip and deforms if you attach a stronger one. I have roughly 300 feet of wire under it now and the more I add the better it works.
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VE3TRU
Member

Posts: 27




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« Reply #10 on: May 19, 2013, 06:17:36 PM »

Thanks for all the wonderful input, the problem is I'm working now and wont get back to the rig for a couple weeks.
Removing the coil is not a bad Idea.
I suspect the feed line is the problem so Ill start there
I got to check so many things and just guessing at this point would be wasting our time.

I will post you what I find later
73s for now.
Tnx






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