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Author Topic: New Cushcraft A3S install: Issues and questions.  (Read 2893 times)
NB8I
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« on: June 18, 2012, 06:44:31 AM »

Good morning:

I put up a Cushcraft A3S with 743 40 m add on kit over the weekend on a 50 ft tower.

My swr measuresmets:
40 m: 1.2: 1 to 1.5:1
20 m: 1.5: 1 to 2:1
15 m: 4:1
10m:  3:1

The measurement between the elements was set up for phone as per the instructions.

I'm assuming its an issue with the traps based on the readings above. So back down it will come in a week or so to recheck and remeasure.

Until then I can always use the tuner to get a better match on 15.

The question is: Can i safely run power (1 kw) through the traps (10 and 15) in their current state without fear of damage until then using the tuner to create a match?

Thanks as always for your assistance.





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AA4PB
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« Reply #1 on: June 18, 2012, 06:51:28 AM »

If it were me, I would not apply full power until I knew what was going on. Recheck all measurements and make sure traps are in the proper location and the correct direction.
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K3VAT
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« Reply #2 on: June 19, 2012, 05:45:26 AM »

Good morning:  I put up a Cushcraft A3S with 743 40 m add on kit over the weekend on a 50 ft tower.

My swr measuresmets:
40 m: 1.2: 1 to 1.5:1
20 m: 1.5: 1 to 2:1
15 m: 4:1
10m:  3:1

The measurement between the elements was set up for phone as per the instructions. I'm assuming its an issue with the traps based on the readings above. So back down it will come in a week or so to recheck and remeasure.  Until then I can always use the tuner to get a better match on 15. The question is: Can i safely run power (1 kw) through the traps (10 and 15) in their current state without fear of damage until then using the tuner to create a match? Thanks as always for your assistance. 

I agree with AA4PB  ... "don't run full power ... recheck all measurements" ...

I didn't see whether this A3S is a new antenna or an older one.  If an older one (say, greater than 5 or so years), then, depending on your particular environmental factors, you may need to refurbish certain components.  For example inspect each trap carefully, look for any compromises to their integrity; check out and see if there is signs of corrosion between aluminum sections.  How's the feed assembly - does the SO238 need to be wire brushed.  You get the idea.

GL, 73, Rich, K3VAT
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K3GM
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« Reply #3 on: June 19, 2012, 05:58:23 AM »

Insure that you have correctly positioned the 15m traps (TB &TC).  They physically look the same, but resonate at different frequencies. TB goes on the director.  It's a good idea to engrave the trap ID now, because I can't tell you haow many people take their A3 down for a reburb, and mix up the traps.  The paper stickers ID's don't last ver long.
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NB8I
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« Reply #4 on: June 19, 2012, 10:48:08 AM »

Ok,  thank you all for the advice!
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NB8I
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« Reply #5 on: June 19, 2012, 12:26:19 PM »

A new development:

I've discovered that both the "TB" 15 meter traps on the director "slide" back and forth along the tube they reside on.

The other traps appear to be "fixed" and not moving on all the other elements. I would assume that the tab inside the moving 15 m traps on the director is either broken or non existant.

Any opinions?

Thanks again.
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NB8I
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« Reply #6 on: July 03, 2012, 01:12:33 AM »

Good morning:

The solution to my problems was the following:

I replaced the two 15 meter traps on the director element and readjusted the antenna element lengths to reflect the "center" of the band.

When using the MFJ analyzer to check our work on with the antenna on sawhorses 30" above ground, the lowest swr was consistently lower than the band it was intended to work on:

40 meters: 6.195 mhz = 1.2:1
20 meters: 13.585 mhz = 1.2:1
15 meters: 20.166 mhz = 1.5:1
10 meters: 26.277 MHz = 1.2:1

This had occurred before but the feeling was the after raising the antenna that the proximity to ground would bring the antenna into correct readings.

Well it didn't. It was actually worse than before. LOL

We started to look at the balun (a Comtek 1:1 dual torrid) I had gotten and attached to the boom.


The leads from the balun to the driven element were 18" on each leg. We had added 3 feet of length to the driven element.
 Roll Eyes.


We repositioned the balun and left 5" on each leg of the balanced feedline wire to the driven element and the readings were correct and the antenna is exceeding my expectations. The center of the band element spacing is right on in relation to the q of the antenna.

Lessons learned:

Keep the balun to driven element leads as short as possible. They become part of the antenna system.

If the antenna is not even close to the band you wish to work when using your analyer, don't put it up thinking that your problems will go away. You should be in the ball park or close to a match at the band you wish to use it on.



« Last Edit: July 03, 2012, 01:34:27 AM by NB8I » Logged

K3GM
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« Reply #7 on: July 03, 2012, 05:46:12 AM »

......This had occurred before but the feeling was the after raising the antenna that the proximity to ground would bring the antenna into correct readings.....


I work alone or with the aid of my wife on the ground.  It's just not practical for me to tram the yagi up and down to adjust the traps.  This is how I tuned my A3.  Once on the tower, it was fairly close to what I saw using this method:
http://i9.photobucket.com/albums/a96/TwoSevenRight/DSCN1142.jpg

For years, I used a coil of feedline at the antenna before switching to a commercial balun.  I chose a DX Engineering balun, and mounted is like so:
http://i9.photobucket.com/albums/a96/TwoSevenRight/DSCN1143.jpg
http://i9.photobucket.com/albums/a96/TwoSevenRight/DSCN1144.jpg

Note that this was a very old A3 with some replaced tubing, so there might be some things in the picture that don't resemble what's on yours.
« Last Edit: July 03, 2012, 05:48:40 AM by K3GM » Logged
K5KNE
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« Reply #8 on: July 04, 2012, 02:00:44 PM »

I use an A3 and have recently refurbished it by cleaning and new trap caps.  It is a very good antenna and should serve you well.

I would be reluctant to run high power into antenna that was not pretty close to the operating frequencies I use. Antenna tuners make your transmitter think things are right, but if the antenna is not resonant - you are asking for problems with high power. Working on getting the antenna adjusted to as good as it is capabable of being would be my priority - not higher power.

Walter K5KNE
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KC4MOP
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« Reply #9 on: July 05, 2012, 03:58:25 AM »

......This had occurred before but the feeling was the after raising the antenna that the proximity to ground would bring the antenna into correct readings.....


I work alone or with the aid of my wife on the ground.  It's just not practical for me to tram the yagi up and down to adjust the traps.  This is how I tuned my A3.  Once on the tower, it was fairly close to what I saw using this method:
http://i9.photobucket.com/albums/a96/TwoSevenRight/DSCN1142.jpg

For years, I used a coil of feedline at the antenna before switching to a commercial balun.  I chose a DX Engineering balun, and mounted is like so:
http://i9.photobucket.com/albums/a96/TwoSevenRight/DSCN1143.jpg
http://i9.photobucket.com/albums/a96/TwoSevenRight/DSCN1144.jpg

Note that this was a very old A3 with some replaced tubing, so there might be some things in the picture that don't resemble what's on yours.

I really really wished I wudda remembered that trick for tuning when my A3S was on the ground. Your first photobucket picture. That is the accurate way to tune it.
And I am thinking now that the balun I built is the cause of most bands dead, except for 40M. I have the 40M option BTW.
Some days I put the analyzer on the feed line in the shack and the antenna is perfect 1.5:1 on the phone portions of all of the bands, then another day it is in left field with no resonance on any band except 40.......
For the DX hound the A3S is a great antenna. Patience with a rotor and you make many contacts. I am too casual of an operator and will be happy with the accidental DX with my other antennas I have built to work-around my A3s problem. I do not have $600 for a crane truck to remove my A3S from the pole and let me figure what is wrong.
Fred
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