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Author Topic: Odd antenna tweak?  (Read 1927 times)
W9KDX
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Posts: 771




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« on: January 21, 2013, 08:03:54 AM »

Quite often I notice that my antennas are deaf.  When I run a quick 5 watts into them, as in tuning, they come alive.

It is really not an issue, but I am curious as to what might be going on.  The antennas are dipoles, one a fan, with baluns, fed with coax.

Thanks
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Sam
W9KDX
M6GOM
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Posts: 987




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« Reply #1 on: January 21, 2013, 08:10:58 AM »

Sounds like corrosion in one of the connections.
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AC5UP
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Posts: 3927




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« Reply #2 on: January 21, 2013, 08:20:35 AM »

Ditto.
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Never change a password on a Friday                
K8AXW
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Posts: 3958




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« Reply #3 on: January 21, 2013, 08:31:29 AM »

Or antenna changeover relay contacts??
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WB6BYU
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Posts: 13458




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« Reply #4 on: January 21, 2013, 08:45:52 AM »

The most common cause is a thin layer of corrosion or other deposit that builds up on
a contact.  It acts as an insulator until  you run some current though it, after which it
works fine until it sits for a while longer.

Very often this is a relay contact, especially on the receive side.  Often just exercising
the relays a few times will cause enough physical wiping action in the contacts to clean
them off.  It's particularly a problem in the receive path because incoming signals aren't
strong enough to keep the contacts clean.  (Some radios are designed to run a small bit
of DC though the receive contacts to avoid this problem.)
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AC2EU
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Posts: 450


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« Reply #5 on: January 21, 2013, 09:13:51 AM »

Yes! Bad solder and/or corrosion.
My problem was traced to a bad voltage balun from W2AU.
http://www.eham.net/reviews/detail/7460

It worked for about a year, then had symptoms just like you describe.
I opened it up and found the connections form the balun were just pushed through the solder lug holes with no crimping then topped off with a very poor soldering job.  It was a apparently a cold joint from day one, but it took a year to oxidize .

Worse yet, I discovered that they used a a ferrite rod instead of a toroid!
If you have one of these, I'd go there first and replace it with a well made home brew or one of the better manufacturers.
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KA4POL
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Posts: 2084




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« Reply #6 on: January 21, 2013, 09:15:39 AM »

Moisture could also be involved.
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W9KDX
Member

Posts: 771




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« Reply #7 on: January 21, 2013, 10:38:30 AM »

Yes! Bad solder and/or corrosion.
My problem was traced to a bad voltage balun from W2AU.
http://www.eham.net/reviews/detail/7460

It worked for about a year, then had symptoms just like you describe.
I opened it up and found the connections form the balun were just pushed through the solder lug holes with no crimping then topped off with a very poor soldering job.  It was a apparently a cold joint from day one, but it took a year to oxidize .

Worse yet, I discovered that they used a a ferrite rod instead of a toroid!
If you have one of these, I'd go there first and replace it with a well made home brew or one of the better manufacturers.

This is exactly the balun I also have, just over a year old.  Looks like it is time to junk it.  I'll need to wait a few months until the temp gets above zero; do I just grab the caps with a channel lock and unscrew to check it out? 

I am pretty confident with the solder joints, after a few false starts I finally got the hang of it, and I will exercise the switches on my tuner a bit to see if that is the cause.

Any suggestions for a brand with better quality control?  I'm looking at a Hy Power GU 6-160-5KW as I have had very good luck with their 4:1.

Thanks guys.
« Last Edit: January 21, 2013, 11:04:00 AM by W9KDX » Logged

Sam
W9KDX
AC2EU
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« Reply #8 on: January 21, 2013, 12:55:19 PM »

Quote
Any suggestions for a brand with better quality control?  I'm looking at a Hy Power GU 6-160-5KW as I have had very good luck with their 4:1.

I went the home-brew route to ensure a quality ferrite and quality construction.
Other Hams do seem to like Hy power and DX engineering.
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KE3WD
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Posts: 5689




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« Reply #9 on: January 21, 2013, 03:17:11 PM »

Nevermind the use of ferrite rod and not toroid, if the doggone thing functioned just fine for that amount of time, simply lowering it and putting some attention to joint cleanup and good resolder would likely cure it for a long, long time.  And not cost $$$. 

Pay attention to weatherization of said joints too, while you have it down for the maintenance. 


73
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KC8VWM
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Posts: 3121




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« Reply #10 on: January 21, 2013, 09:04:02 PM »

If it "comes alive" when pushing RF through it, I am willing to bet you have moisture in your feed line.

Cut off the connector from the feed line and observe for any signs of discoloration in the center conductor or shielding in the feed line. Copper wire exhibiting colors like green or black is not usually a good thing.
 
 
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KA4POL
Member

Posts: 2084




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« Reply #11 on: January 21, 2013, 09:53:41 PM »

Moisture could also be involved.

My bad experience as well.
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G7MRV
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Posts: 481


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« Reply #12 on: January 22, 2013, 02:28:01 AM »

You stated your antennas, plural, seem deaf. If this is the case it is highly unlikely to be a fault with an antenna, but with something common to all. Do you use just one rig? Have your tried with another rig?

My bet is that you have all the antennas coming down seperately to an antenna switch of ports on an ATU with a switch, then a patch lead to the radio. Look at those items that are common.

I agree with the comments previously that it is probably an issue with the changeover relay in the rig.
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W9KDX
Member

Posts: 771




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« Reply #13 on: January 25, 2013, 02:23:33 PM »

I have to do some more monitoring to see entirely where the issues are.  I have two feed lines, one to a OCF dipole with balun and one to a fan dipole with the W2AU.  The feed line is about 6 months old and is sealed, as well, we had a drought up here for almost the entire time I have used it so moisture, while possible, is unlikely.
The inside line goes to a manual tuner with a switch, a linear, an SWR meter and a Yaesu about 9 months old.

I know the problem is on the fan dipole; I am uncertain about the OCF.

I do have temps well below zero unlike last year (different feed line).

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Sam
W9KDX
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